Talk:Fuel economy in automobiles

Speed and fuel economy studies IS ALMOST ALL WRONG AND SHOULD BE COMPLETELY REWRITTEN

The writing makes little common sense, the numbers are wrong and do not correspond to the graph.

This site has data showing data where the most efficient speed is between about 50kmph and 80kmph, as we would all expect.

https://www.quora.com/By-how-much-does-driving-at-200-km-h-instead-of-100-km-h-increase-the-fuel-consumption/answer/Francois-Dovat?ch=10&share=2aea6204&srid=uehfj — Preceding unsigned comment added by 58.96.70.237 (talk) 23:49, 16 September 2022 (UTC)

This one shows best is at 80kmph or less:

https://www.greencarcongress.com/2006/05/fuel_consumptio.html

"Physics" section

currently, it says: "The power to overcome air resistance increases roughly with the cube of the speed, and thus the energy required per unit distance is roughly proportional to the square of speed" I can see that this is somewhat intuitive as exerting a force that goes like the cube of the speed for a fixed amount of time would mean that you covered more ground the faster you go, but the work done is actually F times X, so the energy required per unit distance is actually linear with the force, and goes like the cube of the speed, not the square! ~~

Speed and fuel economy studies

In this section, the numbers for the 1994 Oldsmobile Cutlass are incorrect. It states that it "gets 2 mpg better economy at 105 km/h (65 mph) than at 72 km/h (45 mph) (9.4 L/100 km (25 mpg-US) vs 5.53 L/100 km (42.5 mpg-US))". Clearly 42.5mpg and 25mpg are not a 2mpg difference.

This is likely just a typo; it might originally have been meant to read 20 (rounded). Anyway, mpg figures really shouldn't be compared by subtracting them, so the statement is quite misleading in the first place. Archon 2488 (talk) 13:23, 13 November 2014 (UTC)

Graph of mpg versus l/100 km is wrong

the conversion between mpg and l/100km is wrong. It should be linear. This graph should be deleted.

The graph looks fine to me. y(x)=235/x is not a linear function.

It's not y=235/x, the relationship is 1 mile per gallon = 235.2 l/100km. That's a linear relationship. You either multiply or divide by 235.2 depending on which way you're going. It's a straight line on a graph.

Think about that for a second. So if 1 mpg = 235.2 l/100km, then 2 mpg = 470.4 l/100km? 2 mpg is clearly going twice as far per one gallon of gas, but somehow when converting it to l/100km you're saying it converts to using twice the amount of fuel for the same distance traveled? Quite simply, mpg is a measure of "distance per quantity", while l/100km is "quantity consumed per distance". They're inverse units and will not have a linear relationship. Ayocee (talk) 17:12, 17 November 2007 (UTC)

I'm sorry. You guys are right. I using the google calculator and the results are quite nonlinear. Interestingly, if you type "mpg in l/100 km" into google you get a result that seems to imply the misconception of linearity I had.

The conversion is linear. (the graph looks curved because the vertical axis is 10 times the horizontal, which magnifies the rounding errors)
The function y(x)=235/x is linear by definition. For it to be non-linear, x would need to have an exponent other than one,    e.g. y(x)=235/x^2 or y(x)=235/(x*x).
Confusion arises because mpg is an inverse function of l/100km. So doubling mpg results in l/100km being halved.
Thus, the graph must be removed. It is inaccurate.
[It may be useful to eco-lobbyists but it is still wrong.] 69.159.26.193 (talk) 19:44, 17 June 2008 (UTC)

Nope. It's nonlinear. x has an exponent of −1. —Ben FrantzDale (talk) 19:53, 17 June 2008 (UTC)

Yup! I obviously should have been more clear, an exponent whose absolute value is not one. Negating the exponent doesn't make it non-linear, it just changes the slope from increasing to decreasing (a reflection in the y-axis) 69.159.26.193 (talk) 20:14, 17 June 2008 (UTC)

Still not quite right. Negating the coefficient just changes the sign of the slope: e.g., y=ax vs. y=−ax. Negating the exponent does make it nonlinear. In this case, y is linearly related to $x^{-1}$, but y is not linearly related to x. See linear.

That is neither here nor there, though. The graph looks right to me. I would expect "100km/L" to be linearly related to "MPG". As you say, MPG and L/100km are inversely related. Now that I double check, though the graph does look wrong: I compute 30MPG as being equivalent to 7.8L/100km and 70MPG as equivalent to 3.4L/100km. So yea, I agree, the graph needs to change, but it is the right shape overall and this has nothing to do with rounding error. —Ben FrantzDale (talk) 21:03, 17 June 2008 (UTC)

I partially take that back. The graph does say that it is in imperial gallons, which are 0.83 regular gallons. —Ben FrantzDale (talk) 21:04, 17 June 2008 (UTC)

Anyone who understands units knows that there is an inverse relationship between mpg and l/100km. Let me explain, mpg is distance (in miles) divided by volume (in gallons), ie, distance/volume. l/100km, on the other hand, is volume (in litres) divided by distance (in 100s of km), ie, volume/distance, hence the inverse relationship between the two, therefore the graph is correct. Derekjc (talk) 20:50, 13 June 2010 (UTC) Derek Chandler, MEng CEng MIET

The graph is OK, the right shape, and the red and blue are correctly labelled because an imperial gallon is larger, therefore it takes the car for more miles. A graph of y=x is linear (a straight line) with a slope of 1, but a graph of y=1/x has a slope of -1/x^2, so the slope changes from being steep when x is small to gradual when x is large, therefore it's a curve, not a line - in other words, it's nonlinear. That applies also to y=235/x and also any other number divided by x. —Preceding unsigned comment added by 83.143.85.214 (talk) 13:08, 18 March 2011 (UTC)

---

The graph should be expanded, not deleted. Right now its in imperial gallons not U.S. gallons and a second curve, with appropriate labels, with US gallons would be very appropriate. Casual users may not read all the graph labels and easily get the wrong conversions (imperial gallons are pretty rare in the U.S. and the rest of the non British world).

Incidentally, the EU standard of 120 g CO2/km translates to about 45.7 mpg [U.S.] or 5.2 L/100km. Which is going to be very tough for them to meet by 2012 since cars normally have a 4-5 year design to production cycle time and only the Prius and Civic hybrids and few small diesels meet that standard now.

Cheers, D'lin (talk) —Preceding undated comment was added at 06:29, 6 August 2008 (UTC)

Imperial gallons may be pretty rare in the U.S., but are what the word "gallon" generally means in the majority of the rest of the English-speaking world (Australia, Canada, India, Ireland, New Zealand, Pakistan, South Africa, UK, etc.) where imperial units were used. Now, as in the UK, the official measure for fuel may well be the litre (liter), but people brought-up in those countries prior to metrication will still relate to their old gallon - the imperial gallon. -- de Facto (talk). 08:36, 6 August 2008 (UTC)

Expanded is what I did. The graph is absolutely exact and now includes US and Imperial gallons. --85.176.76.85 (talk) 21:02, 25 July 2009 (UTC)

As far as I can see, the updated graph is mislabeled in that the red upper line should be tagged US MPG while the blue lower line should be Imperial MPG. The US gallon is smaller but the mile is the same (since the 1959 adoption of the international mile anyway) so you burn more US gallons to do the same distance. Chook, Pt Pirie, S. Australia 220.235.117.188 (talk) 14:05, 25 August 2009 (UTC)

Don't think so. 4l/100km=60mpUSg=66mpImpg Greglocock (talk) 03:56, 26 August 2009 (UTC)

Drag

In Drag, is the scaling in consumption per time or consumption per kilometer? Any figure for scaling of consumption per kilometer with speed?

The way of expressing fuel consumption in metric countries is to use litres per 100 km. I would write this as L/(100 km) but I have seen L/100 km and L/100km. L/100 km is wrong according to the precedence rules of algebra and L/100km is wrong because it leaves out the space, which is mandatory (see ISO 1000 or ISO 31). In addtion, use of 100 km is poor use of the metric system, which is specifically designed to avoid the need for arbitary constants. A better solution, in my view is to express fuel consumption in centilitres per kilometre (cL/km). This is numerically equal to litres per 100 km, but can be written tidily. The problem can be seen in the paragraph about motorcycles, where the litres per 100 km figures are in brackets, which makes them look even more clumsy.Blaise 09:18, 14 March 2006 (UTC)

I thought the use of centi was frowned upon in SI. (In at least engineering applications, I see mostly meters and millimeters.) Why not use liters per kilometer and expect a small coefficient, or else liters per megameter and expect a number ten times larger than what we currently see? To see 80 L/Mm is not confusing when compared with 70 L/Mm. The only reason I can think of for using these units is identical with the reason we don't use m/s for travel times: because the number you're seeing should be relevant to length and time of travel. 1000 km is vastly longer than many trips; and 33 m/s is simply not as meaningful as 120 km/h. And this reason--sadly--is also why there is little push to use metric in the U.S. D. F. Schmidt (talk) 23:49, 19 March 2011 (UTC)

Relation among energy spent in manufacturing and in operation

This article will make many people think about substituting their current vehicle. It would be good if a representative figure could be offered for how much energy is wasted in the manufacturing process vs. the lifecycle, so that we don't end up with an increased total energy consumption. —The preceding unsigned comment was added by Alv (talk • contribs) 07:28, 30 January 2007 (UTC).

Energy Content

The energy content for Gasoline is listed in the first chart as 29 MJ/L, whereas in the Diesel article, it is listed as 34.9. Which is right, if either? NcLean 5th July 2006

Diesel is denser, a litre of diesel is heavier than a litre of gasoline, so a litre of diesel has more carbon and hydrogen atoms in it than a litre of gasoline, that's why its energy content is higher. —Preceding unsigned comment added by 83.143.85.214 (talk) 13:14, 18 March 2011 (UTC)

29 MJ/L for the energy content of gasoline is inconsistent with the values given in Btu/IGal and Btu/USgal.

Also, the statement made later on in the article about the relative energy content of diesel and gaoline does not agree with this chart. 69.107.90.97 00:25, 1 October 2006 (UTC)

I have redone the values in this table using data from the Bosch Automotive Handbook, 4th edition. The MJ/kg figures are straight from the reference. Petrol, LPG and diesel densities are typical values only, so MJ/L values can vary with density value used and this obviously affects derived numbers. The octane ratings of fuels other than petrol (gasoline) are not taken from this reference. --Athol Mullen 04:57, 25 November 2006 (UTC)

I would have liked to have put the ref to the right of the table, at the bottom corner. The closest I can seem to get is underneath. If anyone knows how to fix this, please do. --Athol Mullen 05:02, 26 November 2006 (UTC)

Introduction example

I don't think the tone of the example with a Frenchman and an Englishman is really appropriate. It looks a bit like a school book. Should I change it ? Arsine 21:44, 29 March 2006 (UTC)

If you think you can improve the tone please do so. Be bold! Blaise 22:06, 31 August 2006 (UTC)

Is that example needed at all? Who compares the average consumptions of groups of cars (and very unappropriately grouped by the way - a car that does 3L/100km and one that does 12L/100km. I know it's merely illustrative yet it's not a valid way to judge)? The problem here stems from the arithmetic mean function itself and not the way we express the consumption figures of cars. It may mislead some people to think that they can't compare the consumption figures of two different cars expressed in different units. Again, the fictive comparison of French and English cars is flawed and would be so even without using different units of consumption. Think about a car that consumes 3L and another that consumes 12L. Now on average each one of the cars consume 7,5L, right? Actually neither car consumes that! Let's not forget the shortcomings of mathematical/statistical tools and be careful when interpreting the outcomes.. One must be careful trying to squeeze a lot of information into one or two numbers. ozkaplan 07:21, 21 October 2006 (UTC)

Is it me or is this table inaccurate? For example, Methanol,Etanol etc are shown has having a lower accessible energy content than Gasoline. This is surely upside down in all 4 of the MJ and BTU columns.

"accelerate as gradually as possible"

Slow acceleration's effect on fuel consumption is greatly overemphasized in North America. Ever since side valve engines disappeared, most engines have had their greatest efficiency at a large fraction of their maximum horsepower. Starting slowly helps much less than stopping slowly, if at all. David R. Ingham 21:33, 23 April 2006 (UTC)

This popular idea may be left over from the age of side valve engines, when more people worried about fuel consumption than now do (Remember gas rationing.), and advocated by people who think that slow acceleration contributes to safety, or it may be a result of the simplified view that the energy is lost when the fuel is burned, rather than when the kinetic energy is converted to heat by the brakes. I suppose it might also be encouraged by the car companies who don't want people to know that it is buying the engine, carrying its weight and size around and keeping it going, not using its full power, that is expensive. The engine uses more fuel when producing more power, but that does not imply that limiting it to a small fraction of its full power achieves an overall reduction in fuel consumption. See "Your Mileage May Differ", Road and Track, May 2006, pp. 105–111. David R. Ingham 05:06, 24 April 2006 (UTC)

Gradual accelaration is not the same as slow accelaration! NcLean 5th July 2006

The most important factor on a modern fuel injection car is keeping the emsisions control in closed loop. As you apply more throttle the ecu will go into open loop (not longer reading the 02 sensor voltage). In open loop control a stock ECU will add extra fuel as a safety margin. In other words the car runs rich at high throttle, this hurts your fuel efficency. Thegreatms; 1st Aug 2006

"Gradual accelaration is not the same as slow accelaration" Do you mean moving the throttle gently?

Mixture vs. pumping losses: At least since mid century car engine fuel systems have increased the mixture at full throttle, so maximum efficiency is typically around 3/4 throttle. (With low octane fuel, detonation or retarded timing also contributes.) Only with variable valve timing can a spark ignition engine be efficient at less than half throttle, and probably still not as efficient as at more throttle. This is the difference between adiabatic expansion and free expansion. Free expansion is fundamentally wasteful. This is usually referred to as "pumping losses". Now that they are using neural networks to control the mixture, which loop you are in is not a large factor. David R. Ingham 04:33, 30 September 2006 (UTC)

Difference for automatic vs manual transmission?

Does automatic vs manual transmission make much difference to the importance of low acceleration for fuel efficiency?

I get the impression that the fluid coupling is less efficient at high loads (steep hill, high acceleration, etc.). (I'm not very confident about this.)

Also, I've found that automatic transmissions sometimes change to a lower gear in response to throttle even if doing so actually reduces speed: a lower gear has greater engine speed & friction for a given vehicle speed, which can reduce overall efficiency (or even speed, in extreme cases). Pjrm 07:59, 21 August 2006 (UTC)

A fluid coupling such as a torque converter does wast power by slipping, but modern transmitions lock them out some of the time. (I think this was introduced by Peugeot.) A skillful driver may still be able to do better with a manual, but the difference is decreasing. David R. Ingham 04:41, 30 September 2006 (UTC)

Economical driving: Slow acceleration, low engine speeds?

Has anyone had a thought about the history of automobiling, in the technological sense? What is considered as economical now, differs from the idea of economical of the past: Nowadays Engines, fuel and lubrication oil have evolved a lot from what they were in the beginning of the 20th century. By todays standarts, it is economical to drive wasting as little fuel as possible, because (in addition to the enviromental issues) fuel costs a lot. However back in the days of old fuel was cheap, but because engine and lubricating technology was in its birth, building, maintaining and rebuilding engines were heavy for the wallet. Old sidevalve engines, in addition to their poor breathing ability which lowered top end power (~75% at low speeds, ~55% at high speeds, compared to the overheadvalve-engines ~90% and ~75% respectively, if I remember correctly) the engines of old used heavy parts (for example iron pistons were commonplace) and thus the wear and tear was fast when running at high revolutions. This problem was made worse by the combination of long stroke structure and poor lubrication due to oil and engines own lubricating system. However shortstrokers were even worse with their (piston)overheating and predetonation habits, wich made them very unfavorable to the engine manufacturer. This is why the slow acceleration, especially accelerating at low engine speeds, was economical: In those days it was more affordable to use more gasolene, than to cause the engine wear out prematurely. Also large longstrokers were able to pull well at low engine speeds, and as the engines were far less muflled than now, unnecessary noise was avoided.

'Back in the days of old, fuel was cheap'? . . . it still is, why else are the roads clogged by millions of cars? it's so cheap no-one has to think. Our obsession with fundamentally inefficient heat-engines is the real problem. —Preceding unsigned comment added by 82.34.45.137 (talk) 09:15, 27 March 2011 (UTC)

As I see it, the old way of economical driving comes from those days and has seemingly stayed alive as an urban legend, which are, frankly, seemingly common in the USA. —Preceding unsigned comment added by 84.248.56.90 (talk) 12:36, 11 January 2008 (UTC)

get a diesel and the only significant difference is braking loss Wdl1961 (talk) 19:54, 13 August 2009 (UTC)

Thanks, but I already have had a diesel a long time. Besides this was written as an answer to the earlier pondering about gradual/slow acceleration above. People sometimes tend to forget to take into account the advancements taken in the technology and its effects to the case. In other words, with the modern knowledge, technology and lubricants the old engines, for example the sidevalve units, last much longer and produce more power than they ever could when they were new, and the difference is even greater when these engines are hot rodded. The issues have changed a lot during the years and also has the consept of expensiveness: what was cheap then might be expensive nowadays or vice versa. During those days the averige milage a car could last was much lower than it is today, and the cost of fuel in comparison to the monthly wages has, at least as far as I know, changed a lot. However so has the whole culture, roads, driving habbits and averige vehicle speeds in general. —Preceding unsigned comment added by 80.223.93.188 (talk) 23:26, 16 October 2009 (UTC)

Mexican overdrive

"Temporarily shifting to neutral on a sufficiently lengthy downhill grade will dramatically increase mileage for carburetor cars, while cars with fuel injection - or carburetor cars with a fuel cut-off solenoid - will benefit more from the fuel cutoff when the car is left in gear."

This is misleading. The friction and compression drag of the engine (its negative efficiency) is much more important that any fuel that is burned while the throttle is closed. How effective this is depends on how much the engine slows the car in highest gear.

(Also, note that it is illegal in some US States.) David R. Ingham 21:41, 23 April 2006 (UTC)

note about the fuel cutoff feature of fuel injection systems: Taking the 25+ year old Bosch Motronic system as an example, the way it works is that the fuel injectors stay closed whenever the throttle is closed and the engine speed is above a certain value (usually in the 1000-2000RPM range depending on the particular model vehicle). It's as simple as that.

This will not save fuel on the highway (except in the case where you would otherwise be using the brakes to stay within a legal speed limit). Depending on the speed one is traveling (and associated drag) and the grade of a hill that one is descending, there are a couple different situations. In the case that shifting into neutral will result in the vehicle losing speed due to drag that the driver will regain by accelerating again shortly after, it is more efficient to leave the car in gear and simply reduce the throttle opening to maintain speed. If shifting into neutral results in the vehicle gaining speed due to gravity, then allowing the vehicle to build speed on the hill and using it to coast some distance after reaching the bottom of the hill before shifting back into gear is the most efficient method.

The fuel cutoff feature is beneficial when the driver intends to reduce speed (ie. coming up to a stop sign) and when the engine is spinning down between upshifts.69.205.237.124 20:42, 22 September 2007 (UTC)

In addition to the negative efficiency of compression drag, modern fuel-injected engines appear to consume much more fuel when coasting in gear than when idling (although the difference seems to be smaller for engines featuring variable valve timing). At least that is what a fuel consumption meter (such as ScanGauge) which derives data from the Onboard Diagnostic Port indicates. Ad hoc fuel economy measurements over medium length trips also indicate that shifting into neutral on modern fuel-injected cars save noticeable amounts of fuel.

I disagree. What is the source for this "testing"? Modern, computer-controlled engines base the amount of fuel fed to the engine on the load requested, either from the driver or the computer. An idling engine still needs enough fuel to keep itself running and to drive the accessories (alternator, water pump, power steering pump, etc). When the transmission is in gear and the vehicle is decelerating, the transmission can backdrive the engine, reducing (but not eliminating) the amount of fuel required to keep the engine running. R.Yo 21:19, 11 November 2006 (UTC)

'An example familiar to many fuel economy enthusiasts is the "fuel cut" feature. It's common for fuel-injected engines to stop injecting fuel when the accelerator is released above a certain engine RPM. The problem is that manufacturers don't follow a standard method of describing when this mode is active. The result is that some cars continue to report active fuel injection to the ScanGauge, even when it's not actually happening.' http://www.metrompg.com/posts/scangauge-interview.htm ~kps 64.235.97.125 (talk) 16:28, 2 March 2007 (UTC).

I (the source of the ad hoc measurements mentioned above) regularly drive a couple of specific freeway routes 70-80 miles long where I fill up right before and right after the trip. Of course, I make sure the engine is warm before I fill up the first time, I pay particular attention to my speed (I do drive at different speeds sometimes, but those results go in separate bins), and if I run into significant traffic I obviously ignore the results. I have done this at least ~10 times in a 2004 Civic about 5 times in a 2006 Camry. Usually I put it in neutral at every opportunity, but I have tried not using neutral at least once each car. I feel my results have been pretty consistent. The Civic gets ~50MPG with neutral and ~40 without. The Camry gets ~40MPG with neutral and ~36 without. I believe the difference is bigger for the Civic for 2 reasons: (1) the Civic's tallest gear - 2500RPM @60MPH - is more inefficient than the Camrys 2000RPM @60MPH; (2) the Civic was a manual, so the engine/car speed ratio was locked, whereas the Camry is an automatic, and I've noticed (by looking at the tachometer) its torque converter tends to release a little (lets the engine speed drop about 10%) if you coast in gear for more than a few seconds. But anyway, I've done these experiments enough times to be convinced that neutral saves measurable amounts of gas for my cars. This is not wishful thinking - I would rather have this *not* be the case. I would rather just stay in gear, since messing with neutral worries me in terms of how much life I am taking off of the transmission. 67.170.72.55 22:58, 18 February 2007 (UTC)

(to be clear, I am not disputing the claim that the engine consumes less fuel when coasting in gear than when idling; I am, however, quite convinced based on my experience that coasting in neutral saves fuel overall. I suppose that could be entirely due to engine drag when coasting in gear) 67.170.72.55 22:58, 18 February 2007 (UTC)

I believe the main effect here is engine braking, the work required to pump air through the engine. Downhill, the engine rotates faster in gear and more air is pumped than if it were at idle.

The automatic version of this was called freewheeling, and Saabs had it around 1960. It supposedly increased fuel economy about 15%. It was outlawed because of fears it would lead to runaway cars if it failed to cut out at the same time that brakes failed while descending a long pass, just when engine braking is needed. But decades ago I saw an article (since lost) by an automotive engineer claiming this was wrong: with several independent automatic cutouts -- upon braking, on shifting, manual etc. -- the chance of failure would be astronomically low. Its return would seem to offer an easy way to improve economy and I wish the main article could discuss it.Alan Mole 00:56, 27 February 2007 (UTC)

Measurement cycles

Government-mandated fuel efficiency measurements generally have two regimens or driving cycle patterns: a city or urban cycle, and an highway or extra-urban cycle. In Europe, the two standard measuring cycles for "L/100 km" value are motorway travel at 90 km/h and rush hour city traffic. A reasonably modern European supermini may manage motorway travel at 5 L/100 km (47 mpg US) or 6.5 L/100 km in city traffic (36 mpg US), with carbon dioxide emissions of around 140 g/km.

Well, the "European driving cycle pattern" is not 90 km/h (56 mph) on Motorways, but 120 km/h (75 mph), which is quite worse on economy-aspects (wind drag is much higher). See also NEDC (or for german speaking people a much more extensive description: VDA.de - Unterschiede der Messmethoden) 129.247.247.238 08:13, 1 June 2006 (UTC)

Which condition does the 140 g/km apply to? 5 L/100 km or 6.5 L/100 km? in fact 5 L/100 km is 115 gm CO2/L, while 6.5 is L/100 km is nearer 150 gm/L CO2. In the UK only one mandatory fuel-consumption figure is used to generate a gm/L figure, which is used in the car tax regime. —Preceding unsigned comment added by 82.45.83.254 (talk) 18:38, 18 March 2011 (UTC)

The note about European driving cycles yielding higher fuel consumption levels than the U.S. cycle needs correction, and the comparison cited, for the Honda CRZ, appears to be comparing the European test results to the U.S. adjusted (for onroad) values, not the actual test results....the U.S. test results will tend to give LOWER fuel consumption levels than the European cycle in most cases. A 2007 ICCT report on fuel economy standards worldwide gave a 1.12 average adjustment factor (multiply European fuel economy test results by 1.12 to get U.S. test results (in mpg or km/L). However, the report also said that the adjustment factors tended to shrink for higher efficiency vehicles.....today, the Honda CRZ has a U.S. test result of about 5.8/4.5 L/100km (city/highway); versus the cited 6.1/4.4 European results...virtually the same. Steve PlotkinSteveneplotkin (talk) 17:23, 27 March 2013 (UTC)

US Consumer Information on Highway Fuel Economy is Misleading

This effect is largely due to aerodynamic drag. In highway driving over 80-90 km/h (50-55 mph) the aerodynamic drag will rise sharply, thus increasing fuel consumption.

When highway speed limits and driving behaviors in the United States regularly exceed 50-55mph, the EPA provided information on highway fuel economy is therefore almost useless. The energy required to overcome aerodynamic drag alone over a given distance is 1.4x greater at 65mph and 1.9x greater at 75mph.

The actual fuel economy achieved on highways may therefore actually be worse than those specifications given for "city" driving.

Although your assessment of EPA mileage ratings is correct (the stated MPG a car gets is rarely accurate), I have yet to drive a car that got worse gas mileage on a highway than in a city. - Runch 18:13, 14 August 2006 (UTC)

The only one I know of that actually gets better gas mile in the city compared to the highway is the Toyota Prius; and that's only if you exclude the first few minutes or so of driving while it warms up the emissions equipment. Jon 18:03, 30 March 2007 (UTC)

It depends upon how one actually drives in both places. Skyemoor 02:17, 25 August 2006 (UTC)

It depends on the characteristics of the engine. Typical engines in developed countries are big and tuned for power, so they are not efficient at low speeds. I saw data somewhere that a typical car got best economey around 60 or 70 mph. David R. Ingham 04:05, 30 September 2006 (UTC)

from article: ...as people in developed countries tend to buy bigger and heavier cars. Then why don't US tend to build and use more fuel efficient vehicles? --217.72.64.8 07:21, 20 January 2007 (UTC)

Because fuel is so cheap and no-one is interested in economy? 82.34.45.137 (talk) 10:10, 20 March 2011 (UTC)

I saw data somewhere that a typical car got best economey around 60 or 70 mph. Please provide a reliable source for this claim. Skyemoor 18:59, 22 January 2007 (UTC)

I don't know if you count me as reliable, but MY car gets its best fuel economy at exactly 70mph, as tested (extensively) by me. I do know this isn't any good as a source for Wikipedia, however... Midlandstoday 22:14, 18 October 2007 (UTC)

The EPA's fuel economy pages says it's currently 60 MPH and then it starts to make a 5% drop every 5 MPH thereafter. Personally, I found on a 2003 Ford Taurus I didn't notice a significant fuel consumption difference until past 65 MPH. Now on a 2005 Toyota Prius, the difference between 60 MPH and 65 MPH is apprent; and (less so) between 55 MPH and 60, but this is in large part because the Prius tells you exactly what MPH your getting at every instant. Jon 18:03, 30 March 2007 (UTC)

Merg of Fuel efficient driving into this article.

My expectation is that this article will grow too long for a single article as petroleum becomes scarcer and the US comes to its senses about global warming. So if it is merged in now, it might have to be split off again later. David R. Ingham 03:27, 30 September 2006 (UTC)

Fuel efficient driving redirect to this article , but Fuel efficient driving is also in the See Also of this article, just letting you know --shodan

I just removed the link in the See Also section --JVersteeg 17:30, 21 November 2006 (UTC)

The type of engine paragraph

This needs a lot of work. There are various considerations such as idle consumption. Displacement is really not a primary consideration, it is more weight volume and cost. David R. Ingham 03:36, 30 September 2006 (UTC)

"Under certain circumstances, minor long-term engine damage may be sustained."

I have wondered about this, but the expert that I consulted on this matter did not think this would happen. Turning the key off while moving and in gear will damage engines and catalytic converters of cars that do not shut off the fuel. David R. Ingham 04:12, 30 September 2006 (UTC)

Gas Guzzler Tax

I added a section on this, and an external link to a more detailed discussion of the legislation. KonaScout 00:04, 11 October 2006 (UTC)

Are SUVs and other cars masquerading as trucks exempted?

It would seem simpler and more straightforward to tax fuel. It is always easy to find some other tax to reduce. David R. Ingham 04:30, 15 October 2006 (UTC)

But a fuel tax would produce much less revenue. In the UK the vehicle duty (tax) rises by £235 per year for cars producing 255 g/km CO2, over and above that for cars producing 185 g/km. Therefore the additional 70 g/km costs £235, which for a yearly distance of 20,000 km means 1.4 tons of additional CO2. This marginal rate of £167 per ton is way in excess of the government's target price on the carbon market (£20/ton). It's a type of fuel tax that does not cause riots; the motorists remain ignorant basically because Jeremy Clarkson (famous motoring journalist of the 'vroom-vroom' variety) doesn't do sums :) —Preceding unsigned comment added by 82.34.45.137 (talk) 11:03, 27 March 2011 (UTC)

In Turkey there's a %200 tax on fuel, i.e. if oil is 1 USD/liter without tax, it becomes 3 USD/liter with tax. Also annual taxes for cars are based on engine volume and car age, nothing more. i.e. 2 year old car with 1.6 lt engine is taxed at 400 USD / year whereas a 2 year old car with 4.0+ lt engine is taxed at 10,000 USD/year. These two measures greatly discourage the use of large engines, which corresponds to an overall fuel consumption decrease for the country. —Preceding unsigned comment added by 81.213.159.132 (talk) 08:35, 21 August 2009 (UTC)

Fuel economy-boosting technologies

This section needs lots of clean-up! Is it a list of devices consumers can install on a car to achieve greater fuel efficiency, or is it technologies that automakers can employ to provide more efficient cars?

Some of these items are scams or hoaxes (magnets, vaporizers, intake air cyclones), which have their own wikipedia page (http://en.wikipedia.org/wiki/Aftermarket_fuel_economy_device).

The "Quasiturbine" is a type of engine, like the Wankel Rotary engine or the reciprocating four-stroke engine. That in and of itself is not enough to be considered a fuel-saving technology, as one could easily design a Quasiturbine to have greater fuel consumption than an equally powerful conventional engine.

Torque converters "lock" or "lock up", they don't get "locked out."

"Variable Oxygen Sensor Dial"? This needs to be described. Today's oxygen sensors are variable, in that they return a range of voltages corresponding to the amount of oxygen in a car's exhaust.

"EPROM Fuel Computer Chips for leaner burn"? "Lean-burn" is a combustion strategy that can yield higher fuel economy (usually at a high NOx emissions penalty), but EPROM Fuel Computer Chips is gibberish. "EPROM" is a type of computer memory, "Computer Chips" is a generic way to describe computer components, usually processor-related, and sticking the word "Fuel" in the middle is meaningless.

I'm going to make these changes, but I feel more work will need to be done before this section is good to go.

R.Yo 21:19, 11 November 2006 (UTC)

Also, this section is accompanied by a photo of someone riding in a bus powered by charcoal gas. This has nothing to do with fuel economy; this photo should be deleted or moved to an article on alternative fuels. R.Yo 22:06, 11 November 2006 (UTC)

New EPA methods / CAFE

I just did a partial rewrite of the section covering the EPA test methods, as those have been revised as of December 2006 for use on MY2008 vehicles. Additionally, the CAFE standard does not use (and as far as I know, never has used) the EPA fuel economy ratings - so changes in the EPA methods have zero effect on CAFE. Ayocee 14:09, 2 January 2007 (UTC)

Fatter U.S. drivers guzzle more gas, spend extra $2.8 billion annually

Fatter U.S. drivers guzzle more gas, spend extra $2.8 billion annually. --217.72.64.8 06:51, 20 January 2007 (UTC)

Title

The title of this article is very childish. How about Automotive fuel economy? X570 06:30, 30 January 2007 (UTC)

poorly written

Excuse me, but wtf does "MJ/L" "MJ/kg" "BTU/imp" and "BTU/US" mean?!? Was this written by some acronym geek for other acronym geeks? JayKeaton 15:59, 8 February 2007 (UTC)

Megajoules per liter, megajoules per kilogram - both measures of energy density though I am not sure which would be preferred / more appropriate. The BTU/imp and BTU/US are incomplete, as the full headings should be read as BTUs per Imperial gallon, and BTUs per US Gallon, as the two are different measures of volume. Curious that you would use 'wtf' in a post complaining about acronyms. Ayocee 18:01, 19 February 2007 (UTC)

excuse to tail gate?

"While following large transportation vehicles such as trucks or buses can be tedious, on motorways or highways they assist in reducing drag, pushing through the air and leaving your vehicle a large pocket of turbulence to drive behind." Isn't this highly dangerous considering your probably going to have to tail gate that other vechicle so closely to noticeablly reduce drag there's no way you could stop if they hit their breaks sudenly? Jon 18:08, 30 March 2007 (UTC)

Following at an unsafe distance would indeed incur risks. However, large trucks have a deep 'shadow' of turbulence, and can provide some drag reduction benefits even at a safe distance. --Skyemoor 14:25, 3 May 2007 (UTC)

Not likely. A safe distance is defined as three seconds, which is way outside of drafting distance. 199.125.109.31 22:33, 13 July 2007 (UTC)

Defined by who as 3 seconds? Round here (UK) the recommended distance is 2 seconds, with a sometimes-quoted minimum of 0.5 sec. Midlandstoday (talk) 20:44, 26 November 2007 (UTC)

That's an outdated standard. The recommended safe following distance has continued to increase, beginning in the 1950s with one car length for every 10 mph (about 1 second) to two car lengths for every 10 mph, also given as 2 seconds, but now the recommendation for those in the know is 3 seconds (4 for trucks) plus an additional second for each combination of adverse conditions (including driver distractions such as kids, conversation, looking at a map, etc.). Obviously the greater the distance the less the likelihood there is of an accident. One recommendation calls for four seconds in city driving and six seconds on the highway, plus additional time in adverse conditions.[1] Bottom line though, is I don't think you'd save even a tenth of a percent even at a one second following distance. Race cars and bicycle racers use drafting distances of less than a tenth of a second - and they regularly pile into each other. Not exactly acceptable for the morning commute. 199.125.109.105 (talk) 18:22, 30 July 2008 (UTC)

Actually, Mythbusters got an 11% increase in fuel efficiency while driving at 55 mph with a distance of 100 feet. Now, 55 mph equals 80 feet per second, so that's a distance of 1.25 seconds. While 2 seconds is generally considered to be a safe distance, 1.25 is in no way "highly dangerous". It's probably more close to what most people's actual distance is than 2 seconds. Also, if you set your cruise control to 55 mph, put your foot over the brakes, turn off the radio, and aren't tired or 70 years old, your reaction time will be under 0.5 seconds, compared to the average 1 second under standard conditions. Trucks on highways will also pretty much never use their brakes at all, let alone do a full brake, and your car will probably come to a stop quicker than a heavy truck. So maybe if you drove at a distance of 50 feet, the worst that could happen would be that you ram the truck at 10 or 20 mph, which would cause you some trouble but isn't exactly life-threatening.

But I reckon if you save 11% at 100 ft, you will probably save at least 1% at 160 ft (2 sec distance), which is still considerable.

Also, I don't know where you got those figures. In driving school they teach a 2 second distance in normal conditions or 3 seconds during rain. 6 seconds is just completely insane, if it takes you six seconds to react to something, please, take the bus. –Kloth (talk) 18:01, 13 August 2009 (UTC)

Energy Tax Act accuracy question

Energy Tax Act says the law was passed in 1979, not 1978. Which article is correct? -- Beland 21:04, 16 May 2007 (UTC)

That article says it was enacted in 79, not that it passed in 78. There's a decent chance that both are correct, although it certainly warrants verification. MrZaius^talk 16:48, 28 May 2007 (UTC)

Merger discussion

Nempimania & Hypermiler contain about two-three sentences each about the terms in their title. Everything else in both articles is so general that it overlaps considerably with this article. Both should be merged into here. Hypermiler in particular spends more than 3/4 of its length discussing techniques to increase fuel economy, which are mainly dealt with here in a short bulletted list. This article, too, would benefit from the merge. Any objections? MrZaius^talk 16:48, 28 May 2007 (UTC)

Well I for one object. I think Fuel Economy is a design, Hypermiling is a behavior. I definately agree that the articles should be linked to fuel economy, but feel that they should be seperated from the fuel economy page since they are behavioral. I feel this applies to Ecodriving, Nempimania & Hypermiler. DKBryant^talk 12:50, 01 June 2007 (UTC)

Does it? Fuel_economy_in_automobiles#Fuel_economy-boosting_actions_and_technologies exists, and seems to be covering exactly the same ground. There's so little difference between the three terms you linked, and so much overlap between their articles and the section I just mentioned that they could easily be merged into a single section here with an opening sentence reading:

Governments and environmental organizations urge drivers to adopt driving patterns that minimize their use of fuel, calling them Ecodrivers in Europe, Hypermilers in America, or urging them to obsess to the point of Nepimania in Japan.

Also keep in mind that all three are such rarely used neologisms that, stripped of the content that plainly belongs here, they'd be left with only a sentence or two each in their leads, defining the three concepts in almost identical terms. MrZaius^talk 12:33, 1 June 2007 (UTC)

I've got to agree with MrZaius here, those are methods / behaviors that are a subset of the fuel economy idea. Ayocee 15:12, 1 June 2007 (UTC)

Still disagree, although probably on more personal reasons than impartial ones. Taking the Ecodriving and Nempimania articles out of the equation, as those are really stub articles, I see little more than bullets on behavior in the fuel economy entry. There are no mentions of Pulse & Glide which is far and away the most efficient use of commonly tuned internal combustion engines. Behavior is the single largest component of fuel efficiency, much more so than engine design or even displacement. The term "fuel economy" in no way eludes to a behavior, but rather an empirically tested value. I see it in the same vain as merging Conservation movement into Greenhouse gas, conservation reduces greenhouse gases, just as Hypermiling increases Fuel Efficiency. Still only one vote, but I vote against merging.DKBryant^talk 22:28, 01 June 2007 (UTC)

Support : Neipmanica is all of one paragraph. Hypermiling appears to be a subset of this article. Jon 17:44, 1 June 2007 (UTC)

Merge completed to Fuel economy maximizing behaviors to prevent it from dominating this article, given the length of the content found in Ecodriving. MrZaius^talk 10:03, 3 June 2007 (UTC)

Factors in fuel economy

Why is idling not included in this section?--John of Paris 08:40, 3 June 2007 (UTC)

It should be. In Germany the law requires shutting off the engine at railroad crossings. 199.125.109.31 22:35, 13 July 2007 (UTC)

Km/h at what speed

The article points out that the speed is highly significant for the mileage. But at what speed is an average mileage measured? 90 km/h? --17:54, 16 July 2007 (UTC)

The short answer is over the total distance travelled. The long answer is that fuel economy is measured on a dynamometer over a specified driving cycle. The cycle used is different in the US than it is in the EU. See article for references. 199.125.109.31 02:54, 30 July 2007 (UTC)

Rename article to Fuel economy

Right now Fuel economy does not exist, it is simply a redirect to Fuel economy in automobiles, this article. There is a separate article Fuel efficiency, which covers the generic issues of fuel economy. 199.125.109.135 06:35, 18 August 2007 (UTC)

charging system

"Headlights, media systems, and other electronics do not increase fuel consumption, as the energy to power these devices comes from the charging system; either the alternator or battery."

This is wrong. Putting a higher electrical load on an alternator causes it to take more mechanical energy from the engine via its drive belt. There's no free energy.69.205.237.124 20:56, 22 September 2007 (UTC)

Agreed. I updated the text accordingly - although it should definitely be noted that the effect from the electrical system is rarely more than minimal, and is one of the smallest factors in determining the fuel economy of a given driver / vehicle. A worst-case scenario for most cars would be a total draw of 60-80A; at 12V that's 720-960W. Figuring for an alternator's efficiency and the sake of easier to work with numbers, if we peg the alternator's additional load at 1000W over its 'normal' running condition, that's a drag of a bit over 1.3 horsepower. Considering that not many people would be loading their electrical systems to that extent on a constant basis, the fuel economy hit presented by it would be minimal compared to that of air conditioning, underinflated tires, or a heavy right foot. Still very much present, though. Ayocee 17:10, 24 September 2007 (UTC)

This would be true if the lights were directly connected to the alternator and not through the battery. Can anybody confirm which is true? I can't seem to find this. — Preceding unsigned comment added by 62.131.207.221 (talk) 14:02, 28 December 2013 (UTC)

More statistics needed

I started assembling a chart showing actual and required fuel efficiency in various countries, since this information is somewhat scattered about in prose. But we need more numbers for more countries. -- Beland (talk) 21:41, 4 February 2008 (UTC)

That's a great idea. Are you using US gallons or imperial (etc)??? Perhaps a chart would be better, although I suppose it would be more work to create it and keep it live. And it might even count as OR. I'll look out figures for Oz. Remember to give references.Greg Locock (talk) 23:06, 4 February 2008 (UTC)

Possible source for this article

I was reading some news and stumbled upon this article that might provide some useful information for this article. Quite a few facts are presented in this article that might be useful for citations.

"The Good News and Bad News On U.S. Fuel-Economy Trends" by Joseph B. White October 1, 2007 Wall Street Journal
URL: http://online.wsj.com/article/SB119099903267842827.html?mod=hpp_us_personal_journal
Archive URL: http://www.webcitation.org/5WLHShMhd

Formatted for inline citation:

--Smiller933 (talk) 17:19, 15 March 2008 (UTC)

References

Social Issues Section is Incorrect

"Social issues - In Sweden statistical analysis has shown that men do buy less energy efficient cars. The average CO2 emissions for men in Sweden is 184.1 g/km and for women 169.2 g/km (-8.1%).[8]"

Although emissions and fuel mileage are often correlated, they are in no way a function of one another. In other words, higher CO2 doesn't necessarily mean that someone is driving a less energy efficient vehicle. —Preceding unsigned comment added by Daveclark35 (talk • contribs) 15:37, 5 April 2008 (UTC)

Try plotting claimed fuel economy vs CO2 emissions for petrol or diesel engines. There is a very good reason why they are almost 100% correlated. On what do you base your argument? Greg Locock (talk) 01:55, 6 April 2008 (UTC)

The consequent may be true, but it does not follow from the antecedent: if men and women bought exactly the same kind of car, but women drove them faster, we would expect women to use more fuel, and hence emit more CO2. mdf (talk) 16:47, 28 April 2008 (UTC)

"Although emissions and fuel mileage are often correlated, they are in no way a function of one another." is just plain wrong. Greg Locock (talk) 01:05, 29 April 2008 (UTC)

No it's not. "In other words, higher CO2 doesn't necessarily mean that someone is driving a less energy efficient vehicle." If you buy a massive, piggy SUV with the fuel economy of a battle tank ... but leave it parked in your driveway, except on nights of a full moon, your emissions are going to be smaller than a Prius that is driven 100km every day. If, as you aver, emissions are functions of fuel mileage, how do you explain this result? If you have to introduce another variable into the discussion to do so, then the article proper should receive the same treatment.

Which is the core of Daveclark35's argument. mdf (talk) 12:25, 29 April 2008 (UTC)

OK, I forgot we are arguing in greeny world. You win, by your logic. Meanwhile, I suggest you look up figures for CO2 emissions in g/km, and fuel consumption, in say litres/100km, and plot them against each other. Greg Locock (talk) 12:57, 29 April 2008 (UTC)

"If you buy a massive, piggy SUV with the fuel economy of a battle tank ... but leave it parked in your driveway" This doesn't change the fact that the line quoted in the opening post of this topic specifies CO2 emissions in g/km - the average is based on grams per kilometer driven, not grams released total. Yes, a Prius that is never parked will have higher total carbon emissions than a Suburban that gets driven once a month - but per kilometer driven, there's no comparison. Ayocee (talk) 14:00, 29 April 2008 (UTC)

Once again, this is not true in general. Suppose both parties purchase a Prius and drive it exactly the same distance every day. However, the woman has a type-A personality and drives it faster than the man. Who has the higher emissions? mdf (talk) 14:53, 29 April 2008 (UTC)

Your logic is flawed here. The spreadsheet used as the source is based on data from car manufacturers - this is g/km driven that is determined on a standardized test that eliminates driving style as a variable. According to that study, it shows that men in Sweden on average buy cars that, according to that test, release more CO2.

All that said, I don't think that section needs to be in the article - it's a one-line stub that doesn't seem to add anything of any real value to the article. Ayocee (talk) 16:16, 29 April 2008 (UTC)

Flawed? The logic appears to be fine. Maybe irrelevant is the word you wanted to use? If so, I'll note what the article says: "The average CO2 emissions for men in Sweden is 184.1 g/km and for women 169.2 g/km (-8.1%)." If it was corrected to read "The CO2 emissions, per distance driven while under standard test conditions, for cars that men buy in Sweden [...]" (or a better written equivalent), the issue is indeed resolved to a large extent.

But even that version of the statement has a tinge of "those filthy, piggish, Swedish men are laying waste to the planet!" to it. This is why that though the fact may be true, I don't think we can not completely divorce ourselves from end-use to which the vehicle is put. Maybe it is indeed better to just remove the statement, until someone publishes a more formal analysis on the subject. Mind you, the source itself should somehow remain. mdf (talk) 17:19, 29 April 2008 (UTC)

Fuel Economy infobox

In a related matter, does anyone think that fuel economy should be kept out of the automobile infoboxes? Please voice your opinion at http://en.wikipedia.org/wiki/Template_talk:Infobox_Automobile#Vote_on_Fuel_Economy_in_the_Infobox 198.151.13.8 (talk) 18:28, 7 May 2008 (UTC)

Diminishing Returns or Diminishing Math Skill

It is this kind of numerical nonsense that is used by lobbyists and politicians to justify irrational policies.
"switching from a 10 mpg vehicle to a 15 mpg vehicle" allows you to travel 5 miles further on that gallon, a 50% increase.
"switching from a 50 mpg vehicle to a 100 mpg vehicle" gets you 50 miles farther, a 100% increase.
So, the savings in the first case is half that of the second, not 3 times!
Only a deeply entrenched auto executive would try to argue that doubling fuel efficiency (vs half again as much) is a diminishment. 69.159.26.193 (talk) 20:48, 17 June 2008 (UTC)

Not too sure where you are coming. JoeTruck drives 100 miles in his 10 mpg truck, and uses 10 gallons. We persuade him to buy a more efficient truck that gets 15 mpg. He would now use 6 gallons (roughly), saving about 4 gallons. Menawhile we get NancyPrius to move from a 50 mpg Prius to some unspecified device that gets 100 mpg. For 100 miles travelled the saving in gas is 1 gallon. So, how's that math going for you? The point is that it is far more important (from a fuel usage viewpoint) to get the worst vehicles to improve by 50% than it is to get the best ones to improve by 100%. Greg Locock (talk) 00:09, 18 June 2008 (UTC)

Obviously it important to improve (or remove) the worst vehicles. And if you fix the distance (your 100 miles), the improved truck nets you more ounces of saved fuel than the car but you're comparing apples and oranges.
My problem with the "Diminishing return" was the implication that upon achieving a certain level of efficiency, it was pointless to go further. This may be a sound business/investment theory but it doesn't apply to a model whose cost (price of fuel) is ever increasing and supply is finite. I wonder what the price of a gallon of gas was when this entry was first made. —Preceding unsigned comment added by 69.159.8.176 (talk) 20:49, 18 June 2008 (UTC)

All Things Considered tonight had an article suggesting that people should be getting the most-efficient cars off the road, which is most logical if you measure in gallons per mile. —Ben FrantzDale (talk) 00:19, 20 June 2008 (UTC)

km/l usage in the wrong places

I can understand people wanting to use the more familiar (to them) km/l designation. But it is absolutely ridiculous to use km/l in the EPA section of the article. The EPA is an American agency which deals in m.p.g. Hell, you'd be hard pressed to find anyone in the US who has any conception of what km/l really means. —Preceding unsigned comment added by 137.28.228.112 (talk) 18:19, 5 September 2008 (UTC)

I disagree - people from all over the world are reading that section, and it helps a lot to translate it into units that they understand. It's l/100km (liters per 100 kilometers) though, not to be picky. 199.125.109.33 (talk) 04:06, 11 September 2008 (UTC)

Actually I don't understand the usage of Imperial units. Do all the world other than the Americans and Brits (which is 95% btw) have to search for "what is the corresponding SI unit for this gallon, is it US or imperial gallon..." Correct usage should be lt/100km imo. 81.213.159.132 (talk) 09:18, 21 August 2009 (UTC)

carbon dioxide production

A petrol (gasoline) engine will produce around 2.32 kg of carbon dioxide for each litre of petrol consumed. Can anyone explain to me how this is possible if a litre of petrol does not even weigh 1 kg??? Shouldn't this be 2.32 grams per litre? (my chemistry knowledge is poor, I admit) Lexw (talk) 20:59, 17 April 2009 (UTC)

The engine runs on fuel PLUS air. The oxygen taken in from the air is where the extra weight comes from. —Preceding unsigned comment added by 83.143.85.214 (talk) 13:23, 18 March 2011 (UTC)

The article is correct. The oxygen in the CO2 weighs far more than the carbon. Greglocock (talk) 02:02, 18 April 2009 (UTC)

This is true. Petroleum is composed of hydrocarbons pentane to octane. Octane has the chemical formula C8H18, which has an atomic mass of (8*12 + 18 =) 114 g/mol (assuming Carbon is 12 and Hydrogen is 1). CO2 has an atomic weight of (12 + 2*16 =) 44 g/mol (assuming Oxygen is 16). Therefore, assuming the combustion of all 8 carbon atoms, 8 molecules of CO2 has a mass of (8*44 =) 352, which is over three times the mass of the original hydrocarbon. The same is true of all hydrocarbons in petrol; pentane (at the other end of the scale) is C5H12, which has an atomic mass of (5*12 + 12 =) 72 g/mol, but the CO2 produced is (5*44 =) 220. Obviously the mass increase is due to the addition of oxygen, despite the oxidation of hydrogen to water, since hydrogen is the least massive atom, whereas oxygen is 16 times its weight and two atoms of oxygen are joined to each atom of carbon in carbon dioxide. Derekjc (talk) 21:30, 13 June 2010 (UTC)

Fuel economy standards

27 mpg for the US market? Pretty sure there are a lot of cars with worse mileage than that out there… like, most of the cars on this list. Maybe the average of the whole fleet of an automaker? But what about Ferrari or Hummer, they don't have a single car with such a mileage… or are they counted as Fiat and GM, respectively? The 43 mpg number for China sounds even crazier… Basically there needs to be a lot more sources and explanations for this table, otherwise it's pretty useless. –Kloth (talk) 18:08, 13 August 2009 (UTC)

The data for the UK fuel economy (or more correct CO2) ratings are incorrect. The correct values follow.

Band	CO2 emission (g/km)
A	Up to 100
B	101-110
C	111-120
D	121-130
E	131-140
F	141-150
G	151-165
H	166-175
I	176-185
J	186-200
K*	201-225
L	226-255
M	Over 255

• Band K includes cars that have a CO2 figure over 225g/km but were registered before 23 March 2006

These bands are used by the DVLA to determine Vehicle Excuse Duty (aka Road Tax) for cars registered after 1 March 2001; found on the Direct Gov website (http://www.direct.gov.uk/en/Motoring/OwningAVehicle/HowToTaxYourVehicle/DG_10012524). Derekjc (talk) 21:53, 13 June 2010 (UTC)

Change title to "Fuel usage in automobiles"?

"Fuel economy" is a particular quantity defined by "distance/volume". This general article is about, and should be titled, "Automotive fuel usage" with redirects from "fuel consumption in automobiles and " and "fuel economy in automobiles" —Preceding unsigned comment added by 138.194.37.80 (talk) 03:09, 21 August 2009 (UTC)

Requested move

The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the move request was not moved. Fuel consumption in automobiles has already been redirected here. Jafeluv (talk) 13:06, 15 September 2009 (UTC)

---

Fuel economy in automobiles → Fuel_usage_in automobiles — The article is about fuel usage, as measured by the reciprocal quantities "fuel economy" (mpg) and "fuel consumption" (L/100 km). There should be a redirect from "Fuel_economy_in_automobiles" and "Fuel_consumption_in_automobiles" Adamtester (talk) 06:11, 4 September 2009 (UTC)

• In other words, it's about both topics, they being mathematical transformations of one another. Why is this a case to move? Septentrionalis PMAnderson 22:22, 4 September 2009 (UTC)

• Just for neutrality. It would suffice to have a redirect from "fuel_consumption_in_automobiles", I guess. Adamtester (talk) 06:19, 5 September 2009 (UTC)

I can't really see a strong case for a move, what's wrong with a redirect from fuel consumption? Fuel usage is not really a phrase I hear much, in context. Greglocock (talk) 09:07, 5 September 2009 (UTC)

Redirect will do .Wdl1961 (talk) 12:37, 5 September 2009 (UTC)

The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Merge in Miles per gallon

The article Miles per gallon needs to be merged into this one. That article is mostly

• Restatements of some of this article's content
• Statements of the obvious (miles per gallon is a reciprocal concept to liters per km)
• Tables of conversions

To the extent that the tables are noteworthy (not sure they are) these can be merged into this article or put in a list article. The rest of it can obviously be merged here. There is no evidence that there is enough that is unique about "miles per gallon" that could be stated to merit a separate article. And regardless, certainly that unique content is not there now.

Dissenting opinions?

--Mcorazao (talk) 20:52, 23 May 2010 (UTC)

Good idea Greglocock (talk) 02:20, 24 May 2010 (UTC)

• Support - The tables should probably be eliminated per WP:NOTGUIDE (maybe Wikibooks or something else would be a better place for those), and once that stuff is gone there really isn't much to justify a stand-alone article at this time. --Sable232 (talk) 02:43, 25 May 2010 (UTC)

Do American drivers actually beat EPA MPG numbers?

I'm sort of curious of the sticker pic that say "25 MPG average, expect 21 to 29 in real-world driving".

I'm more used to the fact that numbers quoted by European automakers are hopelessly inflated. That is, converted to US MPGs, my car should make 50 MPG highway, 34 MPG city (European manufacturers' data FWIW). In fact it makes a warm season's average of 29, that's all off-peak city driving. The EPA data for the same engine/transmission/grossweight in a different body style are 40 highway, 29 city - spot on.

Is this a regular pattern (that EPA is closer to real life than Euro-specs) or it is just a random sample?

East of Borschov (talk) 11:41, 10 June 2010 (UTC)

According to the EPA [2], my car should get 34 mpg on the highway. On the freeway, when my speedometer reads 80 (which means I'm going 76 mph or so), according to my onboard computer, I get 40 mpg. I believe the results are similar along a non-freeway highway. When my speedometer says 60 (on the Natchez Trace, a two-lane expressway with no lights), I get about 60 mpg. I haven't bothered with local driving, but I think I usually get about 25 to 30 mpg around town. D. F. Schmidt (talk) 23:24, 19 March 2011 (UTC)

Specially with a look at the German Website "spritmonitor.de" (where people are submitting their mileage) I tend to "European values are best possible; EPA is average". --TheK (talk) 05:03, 13 April 2012 (UTC)

Formula for percentages of consumption vs milage?

Hi, I'm too mathematecally stupid to derive this on my own. Could anyone give me a formula to convert the percentage of fuel savings into the percentage of the corresponding mileage gain? Like in, if a new model uses x per cent less fuel than the previous model, by how many per cent does the milage increase?--Cancun771 (talk) 06:57, 5 November 2010 (UTC)

A car that has a 10% higher miles/gallon rating, or a 10% lower litres/100 km rating, will use 10% less fuel in a year (hypothetically, and with dozens of real-world factors ignored). If your arithmetic is that weak, why would this information be any use to you? --Wtshymanski (talk) 13:16, 5 November 2010 (UTC)

You are right, your info is useless. It wasn't what I asked for though. Here's my explanation - wikipedia is about widening horizons, after all:

I needed the formular for a translation, because there are plenty of countries where fuel consumption is used rather than mileage. Now in translating a text about a new version of a car where a certain percentage of mileage gain is mentioned, you need to convert that into fuel savings percentage. If you want to do it properly, that is.--Cancun771 (talk) 09:01, 15 December 2010 (UTC)

There are people who understand algebra, and people who ask "What's the formula for...?" for every single problem they are given. I have never succeeded in transforming one of the latter type into one of the former type. You will have to consult an algebra teacher. If the car has a 10% milage gain, it will use 10% less fuel in a year. --Wtshymanski (talk) 14:35, 15 December 2010 (UTC)

Wtshymanski, I think you are mistaken. If a car gets 10% higher miles/gallon rating than some reference car, that means it gets 1.1 times the miles per gallon. Let d be the distance traveled and v is the volume of fuel consumed, and if we say the reference car goes d₀ consuming v₀, then we have:

${\frac {d}{v}}=(1+0.1){\frac {d_{0}}{v_{0}}}=1.1{\frac {d_{0}}{v_{0}}}$

and so

${\frac {v}{d}}={\frac {v_{0}}{1.1d_{0}}}=0.90909\dots {\frac {v_{0}}{d_{0}}}=(1-0.0909\dots ){\frac {v_{0}}{d_{0}}}$

which is to say that 10% more miles per gallon translates to about 9.1% fewer gallons per mile. That discrepancy gets bigger the more the efficiency change. (Try the above algebra for the case that the car gets twice the miles per gallon and see what you get.)

Also, there is the issue of what efficiency does to the number of miles driven. If you assume the same number of miles driven, then you get

${\frac {v}{d_{0}}}=(1-0.0909\dots ){\frac {v_{0}}{d_{0}}}$

$v=(1-0.0909\dots )v_{0}$

i.e., that you burn 9.091% fewer gallons. On the other extreme, if you have a fixed gas budget, you will drive 10% more miles. Again, this is important because if you have fixed distance needs, miles per gallon is difficult to reason about. If you replace a 20 MPG car with a 40 MPG car and drive the same distance, you use half as much fuel, say 50 gallons instead of 100 gallons (i.e., d = 2,000 mi). If you then switch to a car that gets 80 MPG, you won't burn zero gallons, you'll burn half again the gallons, or 25 gallons. That is, the benefit of swapping out a very-respectable 40 MPG for an almost unheard of 80 MPG is the same in absolute terms as swapping out a thirsty 20-MPG car for a middle-of-the-pack 26.6-MPG car which would do the same 2,000 miles with 75 gallons of gas. —Ben FrantzDale (talk) 13:53, 16 December 2010 (UTC)

But which base? 20,000 miles, two cars 22 MPG and 20 MPG (10% worse milage). 22 MPG car uses 909 gallons, 20 MPG car with 10% worse milage uses 1000 gallons - 10% more. Pick the base you like, get the numbers you like. People don't have a clue what their actual milage is within 30%, so for small differences they'll never worry about which base is used for milage, and those who own calculators can runthe numbers for themselves. --Wtshymanski (talk) 14:14, 16 December 2010 (UTC)

I'm not quite sure what you mean by "base". I was just trying to emphasize that 10% more miles per gallon does not mean 10% less gallons per mile. Similarly, 20 MPG is not 10% worse mileage than 22 MPG (although 22 MPG is 10% better than 20 MPG). The decimals make things confusing. You are right if you mean "about 10%" in the above, but that is an approximation that doesn't hold.

Restating your example, if we wand to drive 20,000 miles with two cars, one gets 40 MPG and one gets 20 MPG (50% worse mileage), the 40 MPG car uses 500 gallons whereas the 20 MPG car with 50% worse mileage uses 1000 gallons—100% more. —Ben FrantzDale (talk) 15:16, 16 December 2010 (UTC)

But 40 is 100% of 20 larger than 20. So the percentage improvement in MPG is reciprocal with the percentage improvement in gallons per mile, right? I suppose it's how you look at it. Anyone using actual numbers will have no trouble with it. --Wtshymanski (talk) 15:23, 16 December 2010 (UTC)

Yes, that sounds right. The other part of the confusion is that percent differences are multiplicative, so 50% less than 50% more than x is not equal to x, because that's really $0.5\cdot 1.5\cdot x=0.75x$. —Ben FrantzDale (talk) 15:54, 16 December 2010 (UTC)

This whole section is a lesson on grade-school arithmetic that has lost its way and stumbled into a comment on fuel usage. —Preceding unsigned comment added by 82.34.42.39 (talk) 20:13, 6 April 2011 (UTC)

Misconversions

Here's a quote from the Gallons per mile section as it currently reads (with a minor typo fixed, the reference removed and the {{convert}} call written out explicitely).

For example, replacing a car that gets 14 mpg_-US (17 mpg_-imp; 17 L/100 km) with a car that gets 25 mpg_-US (30 mpg_-imp; 9.4 L/100 km) saves 3 US gallons (2.5 imp gal; 11 L) of fuel every 100 miles (160 km). Because 1 US gallon (0.83 imp gal; 3.8 L) of fuel emits 20 pounds (9.1 kg) of carbon dioxide, saving 3 US gallons (11 L) of fuel every 100 miles (160 km) saves 3 short tons (2.7 t) of carbon dioxide every 10,000 miles (16,000 km) of driving.

Let's look at these conversions. I believe that we would generally agree that conversions should provide readers with a clear and accurate picture of what the original text attempts to illustrate. In order to judge whether this example lives up to this let's filter this text.

Let's first apply an imperial filter. Here's what we'll get.

For example, replacing a car that gets 17 mpg_-imp with a car that gets 30 mpg_-imp saves 2.5 imp gal of fuel every 100 miles. Because 0.83 imp gal of fuel emits 20 pounds of carbon dioxide, saving 2.5 imperial gallons of fuel every 100 miles saves ??? of carbon dioxide every 10,000 miles of driving.

Now, we should note a potential for rounding error here.

• 17 mpg_-imp and 30 mpg_-imp are conversions from the miles per US gallon orginals which were rounded to the nearest mile per imperial gallon. If we instead round to the nearest 0.001 mpg_-imp, we get 16.813 mpg_-imp and 30.024 mpg_-imp giving us a difference of 13.211 mpg_-imp as opposed to 13 mpg_-imp. This is approximately a 1.6% error.
• 3 US gallons is also a rounded figure.
    100 mi ÷ 14 mpg_-US = 7+1⁄7 US gal
    100 mi ÷ 25 mpg_-US = 4 US gal
  So the actual difference is 3+1⁄7 US gal which is about 2.617 imp gal. This is about 4.5% greater than the 2.5 imp gal claimed.

So going from US to imperial the difference in miles per gallon was rounded down but the difference in gallons used per 100 miles was also rounded down. Thus the first of these two rounding errors partially cancells the second such that the total error is about 2.9%. So replacing a car that gets 17 mpg_-imp with a car that gets 30 mpg_-imp actually does save 2.5 imp gal of fuel every 100 miles.
  100 mi ÷ 17 mpg_-imp = 5+15⁄17 imp gal
  100 mi ÷ 30 mpg_-imp = 3+1⁄3 imp gal
This gives a difference of 2+28⁄51 imp gal, which is approximately 2.5 imp gal. Thus, all's well so far when we look through our imperial filter.

But now we come across this. "0.83 imp gal of fuel emits 20 pounds of carbon dioxide". Why in the world would we be considering how much CO
₂ is emitted when 0.83 imp gal of fuel is burnt? What kind of number is 0.83? This is what I'm calling a "misconversion". The original ratio was "20 lb/US gal" and we converted the wrong part. "20 lb/0.83 imp gal" is pure nonsense imparting very little understanding to our imperial-minded readers. The sensible conversion is, of course, "24 lb/imp gal".

How much does this amount to in tons of CO
₂ per 10,000 miles, then? 3 short tons ... short tons ... ? Wait a minute ... 2.7 tonnes ... what happened to the conversion to imperial? If we're going to bother with imperial gallons, we ought to bother with imperial tons i.e. long tons. So we should convert these 3 short tons into long tons ... but wait.

Compare these:
  1. "Replacing car 1 with car 2 saves 3 US gal/100 mi. Saving 3 US gal/100 mi saves 3 short tons per 10,000 mi."
  2. "Replacing car 1 with car 2 saves 3 US gal/100 mi, this entails a saving of 3 short tons per 10,000 mi."
Number 2 is more concise but there is a more subtle difference. Number 1 says "Saving 3 US gal/100 mi saves 3 short tons per 10,000 mi." whereas number 2 implies "Replacing car 1 with car 2 saves 3 short tons per 10,000 mi."

Saving 3 US gal/100 mi does indeed save 3 short tons per 10,000 miles which is equal to a saving of 2.7 long tons per 10,000 miles. However, remember that the 3 US gal/100 mi figure was an approximation in the first place. How many long tons are we saving by replacing car 1 with car 2? Well, replacing the 14 mpg_-US with the 25 mpg_-US car actually saved us 3+1⁄7 US gal/100 mi which saves us 3+1⁄7 short tons per 10,000 miles which is actually 2.806 long tons per 10,000 miles (to four sig figs) rather than 2.7. But what about the (slightly different) 17 mpg_-imp vs 30 mpg_-imp cars? As with the previous calculation, the errors partially cancel leaving no difference when rounded to two significant figures.

• (10,000 mi ÷ (1⁄17 mpg_-imp − 1⁄30 mpg_-imp)) × (4.54609⁄3.785411784 US gal/imp gal) × (20 lb/US gal) ÷ (2240 lb/long ton) ≈ 2.7 long tons

Thus it's still accurate to say the following.

For example, replacing a car that gets 17 mpg_-imp with a car that gets 30 mpg_-imp saves 2.5 imperial gallons of fuel every 100 miles. Because the combustion of 1 imperial gallon of fuel emits 24 pounds of carbon dioxide, this will save 2.7 long tons of carbon dioxide every 10,000 miles of driving.

I think therefore, we could justify the following.

For example, replacing a car that gets 14 mpg_-US (17 mpg_-imp) with a car that gets 25 mpg_-US (30 mpg_-imp) saves 3 US gallons (2.5 imp gal) of fuel every 100 miles. Because the combustion of 1 US gallon of fuel emits 20 pounds of carbon dioxide (1 imp gal emits 24 lb), this saves 3 short tons (2.7 long tons) of carbon dioxide every 10,000 miles of driving.

But now let's apply our metric filter. This is where the fun really begins.

For example, replacing a car that uses 17 L/100 km with a car that uses 9.4 L/100 km saves 11 L of fuel every 160 km. Because 3.8 L of fuel emits 9.1 kg of carbon dioxide, saving 11 L of fuel every 160 km saves 2.7 t of carbon dioxide every 16,000 km of driving.

Not really, replacing a car that uses 17 L/100 km with a car that uses 9.4 L/100 km saves 7.6 L/100 km which is 12.16 L/160 km not 11 L/160 km. So, it's not accurate at all, there an approximate 11% error here. But wait ... why ... oh, why are we talking litres per 160 km? What's the significance of this number 160? None. In the metric world, none at all. Here again is what I'm calling misconversion. A conversion from US gallons per hundred miles to litres per hundred miles is as useful as windscreen wipers on a submarine. This is not a conversion to metric, it's a conversion to mongrel. Further, what kind of example is this? Replacing a car that uses 17 L/100 km with a car that uses 9.4 L/100 km? Why choose such a number as 9.4 for an example? Why not a nice round number like 9 or 10?

Next, "3.8 L of fuel emits 9.1 kg of carbon dioxide" ... how many litres? Is there anything special about 3.8? Here's another misconversion. 20 pounds per US gallon is 2.4 kilograms per litre. "9.1 kilograms per 3.8 litres" is rubbish. More rubbish follows with 2.7 tonnes per 16,000 kilometres. What's the sense in a conversion to tonnes per 16,000 km? We want tonnes per 10,000 km.

How can we rescue this example? We might like to round 9.4 down to 9. The we're saving 8 L/100 km. This saves us 1.917 t of CO
₂ per 10,000 kilometres. But 3 short tons per 10,000 miles is 1.691 t/10,000 km. Rounding up to 10 would give 1.678 t/10,000 km so we could accurately say "3 short tons per 10,000 miles (1.7 t/10,000 km)" but "25 mpg_-US (10 L/100 km)" would not be valid. Perhaps the best thing would be to split the example up like this.

For example, replacing a car that gets 14 mpg_-US (17 mpg_-imp) with a car that gets 25 mpg_-US (30 mpg_-imp) saves 3 US gallons (2.5 imp gal) of fuel every 100 miles. Because 1 US gallon of fuel emits 20 pounds of carbon dioxide (1 imp gal emits 24 lb and 1 L emits 2.4 kg), this saves 3 short tons (2.7 long tons) of carbon dioxide every 10,000 miles of driving. Similarly, replacing a car that uses 17 L/100 km with a car that uses 10 L/100 km saves 7 L of fuel every 100 km. This represents a saving of 1.7 t of carbon dioxide every 10,000 km of driving.

But was there anything special about 14 mpg_-US and 25 mpg_-US in the first place? What about choosing different numbers? How about 16 mpg_-US and 30 mpg_-US? 16 mpg_-US is about 19.215 mpg_-imp or 14.701 L/100 km. 30 mpg_-US is about 36.028 mpg_-imp or 7.840 L/100 km. Now for a little rounding off and we're replacing a car that gets 16 mpg_-US (19 mpg_-imp or 15 L/100 km) with a car that gets 30 mpg_-US (36 mpg_-imp or 8 L/100 km).

• 100 mi × (1⁄16 mpg_-US − 1⁄30 mpg_-US) ≈ 2.917 US gal
• 100 mi × (1⁄19 mpg_-imp − 1⁄36 mpg_-imp) ≈ 2.485 imp gal
• 15 L/100 km − 8 L/100 km = 7 L/100 km

So 16 mpg_-US → 30 mpg_-US still saves about 3 US gal per 100 mi, 19 mpg_-imp → 36 mpg_-imp still saves about 2.5 im gal per 100 mi and we've now got a nice round 7 L/100 km. So we could reword the whole thing like this.

For example, replacing a car that gets 16 mpg_-US (19 mpg_-imp or 15 L/100 km) with a car that gets 30 mpg_-US (36 mpg_-imp or 8 L/100 km) saves 3 US gallons (2.5 imp gal) of fuel every 100 miles (7 L/100 km). Because the combustion of 1 US gallon of fuel emits 20 pounds of carbon dioxide (burning 1 imp gal emits 24 lb and burning 1 L emits 2.4 kg), this saves 3 short tons (2.7 long tons) of carbon dioxide every 10,000 miles (1.7 t every 10,000 km) of driving.

JIMp _talk·cont 08:22, 7 August 2011 (UTC)

Units of confusion

It seems to me the entire "Units of measure" section is needlessly complicated and laden with so much alphabet soup that it does more to confuse the issue than explain it.

This may spring from my ignorance of the field, but, describing fuel consumption and fuel economy as two different things ("fuel per distance" and "input per output") seems absurd. Both measure exactly the same thing - the relationship of fuel consumed to distance traveled. It's just a question of which unit is in the numerator. Why not state this as "fuel per unit distance" and "distance per unit fuel"? This would make the inverse proportionality more intuitively clear to the reader.

Likewise, much of this section is bogged down in unit conversions - would it work better if the table at the end of the "Gallons per mile" section was higher up, and the discussion of the math stuck to a single unit?

Finally, the "Inverse or reciprocal scale" section seems to make the argument that one measurement is better than the other for comparing the fuel efficiency of automobiles. Again, they both measure the same thing, and the mathematical operation to compare them (dividing one by the other) will give the same result.

10 MPG = 0.1 GPM

20 MPG = 0.05 GPM

20 MPG / 10 MPG = 2, an improvement by a factor of 2.

0.1 GPM / 0.05 GPM = 2, an improvement by a factor of 2.

You have to flip the division order, because you've flipped the units; however, even if you don't, you're going to get the proportionality constant (or its reciprocal) out. It's the same number because by finding the factor of improvement, you cancel out the units. The consumer confusion mentioned in this section seems not to be due to the inverse relationship (as it claims), but because consumers are comparing the numbers by looking at the difference in values, rather than the factor between them.

I didn't want to make any changes (I know a lot more about manipulating units than I do about cars), but hopefully this will draw more informed editors' attention to the confusing nature of the section. I came across this page today, and spent a good 10-15 minutes trying to decipher what it was trying to convey, and I teach general chemistry - I fiddle with these types of unit conversions every day. I can't imagine how confusing it would be to the average consumer.

Of course, if my thinking is way off base here (entirely a possibility) please feel free to correct me. Thanks! StellarFury (talk) 00:02, 10 December 2011 (UTC)

Be bold. Go ahead and change things. —Ben FrantzDale (talk) 03:09, 11 December 2011 (UTC)

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Use of Imperial Gallons

The article correctly says that L/100km is the measure of fuel economy used in Australia, New Zealand and South Africa. However, the diagram says "MPG to l/100km conversion chart: blue: US gal, red: imp gal (UK and British commonwealth)"

This is wrong in several ways:

• The term is British Commonwealth, not British commonwealth.
• The term "British Commonwealth" has now been superseded by "Commonwealth of Nations"
• The usage is inaccurate, as large parts of the Commonwealth use l/100km.

To remedy this inaccuracy, I suggest the following change:

• "MPG to L/100km conversion chart: blue: US gallon, red: imperial gallon

I also suggest spelling out the words for greater ease of reading. Michael Glass (talk) 13:50, 10 February 2013 (UTC)

Diagram label changed as proposed. Michael Glass (talk) 21:51, 11 February 2013 (UTC)

Proposal: L instead of l for litre.

I have noticed that the article frequently uses a lower case l as a symbol for litre. The BIPM allows both the lower case l and the upper case, but it notes that the lower case l is liable to be confused with the numeral 1 See the BIPM brochure (PDF), page 38. I therefore propose that the the upper case L be used consistently throughout the article.

Are there any comments or concerns? Michael Glass (talk) 21:48, 11 February 2013 (UTC)

HCCI

I have moved HCCI from the section Engine combustion strategies to the section Future technologies. No-one is in production with HCCI as of Jan 2014, and I'm not sure it will happen as soon as proposed by some OEMs either.Mike163 (talk) 17:02, 17 January 2014 (UTC)

Fuel efficiency statistics

Following text (taken from the old Low-energy vehicle page) can be added to the fuel efficiency statistics page;

Higher efficiency can be achieved by changing the vehicle's design, and/or by modifying its powertrain. Energy consumption as low as 5-12.5 kWh/100 km (180-450 kJ/km) is achieved directly by battery electric microcars. When comparing the efficiency of electric cars with IC cars the efficiency of the power generation has to be considered, for example the distribution efficiency for Europe is about 40%, so the overall energy consumption of electric cars lies in the range 0.45 to 1.1 MJ/km. (Average energy efficiency of US plants 33% US DOE (ref to follow) US grid transmission loss 9.5%, UK grid transmission loss 7.4 (ref Wikipedia national grid entry) - transmission losses not included in electric car efficiency figure.) By the year 2050, consumption levels of 1.6 l/100 km (0.64 MJ/km) in diesel-fuelled cars and 2 l/100 km (0.7 MJ/km) in petrol-fuelled cars are deemed feasible. The energy consumption figures for petrol and diesel cars also need to be increased by 18% to represent the oil used in processing and distributing oil-based fuel, to 0.75 MJ/km for diesel, and 0.82 MJ/km for petrol.

To put these consumption figures into perspective a consumption of 1000 km/litre (2350 mpg US) is 0.0344 MJ/km, excluding distribution energy. At 20 km/h it would take 50 hours to travel 1000 km, so with a 20% efficient internal combustion engine it would need to attain and keep this speed using just 38.2 watts.

LEV Twike

Even one of the most fuel efficient two seater on the market - the Smart MHD- consumes two or three times more energy per km than a cabin based ultralight two seater would - proven by the 1l prototype by VW. Pilot vehicles have proven that a feasible target may lie in the range of 1-2 l/100 km, or lower, or 10 kWh/100 km electricity. Available electric LEVs already use substantially less energy than available cars, e.g. 4–8 kW·h/100 km for the Twike,. Here the challenges are increasing range and lifetime of batteries, crash worthiness, passenger comfort, performance and reducing the price (which is currently about twice that of a cheap conventional four seater).

Energy Efficiency in MJ per km or kWh per 100 km: It is more straightforward to express energy efficiency in MJ (Mega-Joule) per km because terms like MPG (Miles Per Gallon) and litres per 100 km do not take into account what type of fuel is used and thus the numbers will be distorted for different fuel types. Diesel contains 38.7MJ per litre, Gasoline 34.6MJ per litre and Bio-Diesel 30.5MJ per litre, whereas LPG contains only 22.2MJ per liter which is why the number of litres consumed go up drastically when converting a gasoline car to LPG. This does not mean that the energy consumption goes up; it only means that there is less energy in a litre of LPG. Ethanol also contains much less energy per litre than gasoline. To compare electricity and gasoline its easier to use kWh/100 km since 1l gasoline holds around 10kWh.

Physical background

Energy demand may be kept low by:

• lower parasitic masses (compared to the average load) causing low energy demand in transitional operation (stop and go operation in the cities) ${P_{accel}=m_{vehicle}\cdot a\cdot v}$ where P stands for power, $m_{vehicle}$ for the total vehicle mass, a for the vehicle's acceleration and v for the vehicle's velocity. Extreme masses will go down to 300 kg from today's 1100 kg to 1600 kg. Five seaters of the sixties had 625 kg. Japanese sub-compact cars have 500–600 kg. Further mass reduction is possible by adapting the maximum number of passengers to the average occupancy rate and having removable seats. Two-seater microcars have less than 400 kg, single-seaters less than 300 kg. Further reductions are possible with very light construction, e.g. Twike. The crash protection is certainly a problem in current traffic conditions, but the low energy vehicles are driven mainly at low velocities in cities.

• low cross-sectional area and mirrors replaced by cameras causing very low drag losses especially when driven at higher speed ${F_{drag}=A_{cross}\cdot C_{d}\cdot {\frac {v_{air}^{2}\rho _{air}}{2}}}$ where F stands for the force, ${A_{cross}}$ for the cross-sectional area of the vehicle, ${\rho _{air}}$ for the density of the air and ${v_{air}}$ for the relative velocity of the air (incl. wind). Two seating places in a tandem (back-to-back or forward-facing in line) arrangement drastically reduce the cross-sectional area down to 1 m². The drag coefficient C_d of the vehicle may be as low as 0.15 for very good vehicles.
• low rolling resistance due to smaller and high pressure tires with optimised tread and low vehicle mass driving the rolling resistance ${F_{roll}=\mu _{roll}\cdot m_{vehicle}\cdot g}$ where ${\mu _{roll}}$ stands for the rolling resistance coefficient, g for acceleration due to gravity and ${m_{vehicle}}$ for the vehicle mass. Advanced driver assistance and ABS could prevent safety problems caused by the small tires, but current light weight vehicles do not possess these systems. Values of ${\mu _{roll}}$ down to 0.0025 are possible but are more usually 0.005 to 0.008 for cycle-type tires and 0.010 to 0.015 for car tires.

Technological support for low energy operation may also come from driver assistance systems since driving style can be adapted to achieve lower energy consumption. Energy management becomes possible with hybrid vehicles with the possibility to recuperate braking energy and to operate the internal combustion engine (ICE) at higher efficiency on average. Hybrid power trains may also reduce the ICE-engine size thus increasing the average load factor and minimising the part load losses. Purely electric vehicles use up to 10 x less energy (0,3 to 0,5MJ/km) than those with combustion engines (3 to 5MJ/km and up to 10MJ/km for SUVs) because of the much higher motor and battery efficiencies.

Size and performance of various vehicles

Average data for vehicle types sold in the U.S.A.:

Type	Width	Height	Curb weight	Combined fuel economy	Percent	Occupancy rate 2005 Florida
SUVs	73.5 in 187 cm	70.7 in 180 cm	4242 lb 1924 kg	19.19 mpg 12.25 l/100 km	328%
Minivans	75.9 in 193 cm	70.2 in 178 cm	4275 lb 1939 kg	20.36 mpg 11.55 l/100 km	309%	1.67
Family sedans	70.3 in 179 cm	57.3 in 146 cm	3144 lb 1426 kg	26.94 mpg 8.73 l/100 km	234%	1.35
Toyota Prius	66.7 in 169 cm	57.6 in 146 cm	2765 lb 1254 kg	56 mpg 4.2 l/100 km	112%	n.a
GM Volt	70.8 in 180 cm	56.3 in 143 cm	3790 lb 1720 kg	60 mpg 4.0 l/100 km	105%	n.a.
Honda Insight	66.7 in 169 cm	53.3 in 135 cm	1850 lb 839 kg	63 mpg 3.73 l/100 km	100%	n.a.
Audi A2	65.9 in 167 cm	61.1 in 155 cm	1973 lb 895 kg	71 mpg 3.0 l/100 km	81%	n.a.

The drag resistance for an SUV, compared with a family sedan with the same drag coefficient, is approximately 30% higher, and its increased mass means that the acceleration forces has to be 35% bigger for a given acceleration. This gives a 40% increase in fuel consumption. The last column in the table demonstrates that with the exception of the Prius and the pick-ups all the alternatives have roughly the same potential fuel usage per passenger IF they were fully occupied. However the fuel usage per passenger really depends on the occupancy rate of each type. In 2000 the occupancy rate was only 1.6 in practice, decreasing each year, averaged across all vehicle types and journey types, and 1.2 for commuting.

The fuel consumption of an engine is depicted as a 3dimensional map where the consumption is shown against RPM and torque. Normally the smallest consumption is seen in the upper middle part of the diagram. For diesel engines this region is bigger to lower torque and extends to higher RPM. The choice of engine power for a given vehicle should consider the typical application - for non transient low velocity operation this leads to lower power requirements, at the cost of reduced acceleration and top speed. A hybrid electric concept allows an even lower power internal combustion engine, but the added weight pays only off if operating in stop and go conditions frequently or generally at low power, if using a series hybrid electric concept.

Fleet Management and Low Energy Consumption

The EU- sponsored RECODRIVE project has set up a quality circle to manage low energy consumption in fleets. This starts with energy aware procurement, and includes fuel management, driver information and training and incentives for all staff involved in the fleet management and maintenance process. Vehicle equipped with gear shift indicators, tire pressure monitoring systems and downsized internal combustion engines and for stop'n go operation also hybrid electric power trains will help to save fuel.

KVDP (talk) 12:20, 11 February 2014 (UTC)

Referneces

References

Reorganizing the article

I'd like to propose some changes to this article, mostly regarding restructuring for better readability and flow:

1. "Energy considerations" should be moved to directly follow "Units of measure". It presents more general information and is easier to follow, and seems to be more directly related to the topic at hand than the regulation of fuel economy and its measurement as described in "Fuel economy statistics". Additionally, I think the information presented in the lists under "Fuel economy-boosting technologies" and "Future technologies" would be better expressed as a table like this.
2. "Fuel Economy Statistics" should be nested as a subsection within the "Fuel economy standards and testing procedures" section. As such, it would follow the "Fuel economy data reliability" and "Concerns over EPA estimates" subsections (which I think should be combined under a header "Concerns and criticism") of "Energy considerations". After being informed about the problems that can arise with all these standards, the reader then gets to read about each instance more specifically.
3. "Unit conversions" should be removed entirely. Not only does it strike me as superfluous to include the conversions, they certainly don't warrant their own section of the article, nor do we necessitate an entire table of arbitrary values and calculations of these units.
4. "EPA" should be clarified, or a link to another page added. My best guess (after 5 minutes of googling) is that it stands for the "Environmental Protection Act/Administration/Agency/Authority" (depending on the country). For more options see: http://acronyms.thefreedictionary.com/EPA

I've got a version of my proposed edits in my sandbox here, and given my COI, I'm happy to collaborate and discuss any concerns or the merits of these suggestions and make changes accordingly before submitting an edit request. FacultiesIntact (talk) 23:30, 23 March 2015 (UTC)

@FacultiesIntact, I've briefly reviewed the article and also took a look at what you have in your sandbox. I saw some much needed improvements in your revision, which if implemented, will probably catch the attention of other editors. I think you might want to implement your changes and see what others have to say. (Regushee (talk) 00:55, 14 June 2015 (UTC))

@Regushee Thanks for your input. Could you clarify your suggestion regarding "much needed improvements"? Are you suggesting my sandbox needs improving, or that it (my sandbox) improves the article itself? As I have a Conflict of Interest on this article, I'm aware that directly editing this article is prohibited. If there's anything you would endorse as beneficial, would you like to collaborate and aid me in implementing it? For example, does presenting the Fuel economy-boosting technologies section as a table like this rather than as a list improve the article?--FacultiesIntact (talk) 22:37, 15 June 2015 (UTC)

@FacultiesIntact, your article is much better; the improvements needed are in the article posted, which your work will improve. I could look at your recomendations and see what I come up with, and would be happy to work with you where possible and time permits. (Regushee (talk) 22:43, 15 June 2015 (UTC))

Thanks so much for your time and your help! If you think the table improves the article, do you think you have the time to implement it? Since the other changes are structural, why don't we take those a step at a time?--FacultiesIntact (talk) 23:06, 15 June 2015 (UTC)

Thanks again Regushee for getting those changes implemented. How do you feel about collaborating on an organizational overhaul of the article?--FacultiesIntact (talk) 22:46, 25 June 2015 (UTC)

THS nonsense

THS was based on a vehicle built at TRW by Dr. Baruch Berman, Dr. George H. Gelb and Dr. Neal A. Richardson in 1971 so Toyota is NOT the inventor of series/parallel hybrids. Greglocock (talk) 12:37, 18 July 2015 (UTC)

"Experimental car"

Hi. FYI the "experimental car" from 1916 pictured is a production car, see this article

Rolling Phantom (talk) 21:00, 23 June 2016 (UTC)

Fuel cell vehicle econmy.

I reverted this edit by @Minisatoshi because it made a claim that fuel cell vehicles don't have fuel economy. But we have sources like:

• Rajesh K Ahluwalia, X Wang, A Rousseau, R Kumar, "Fuel economy of hydrogen fuel cell vehicles", Journal of Power Sources, Volume 130, Issues 1–2, 2004, Pages 192-201, ISSN 0378-7753, https://doi.org/10.1016/j.jpowsour.2003.12.061.

As well as discussions in

• M. Muthukumar, N. Rengarajan, B. Velliyangiri, M.A. Omprakas, C.B. Rohit, U. Kartheek Raja, The development of fuel cell electric vehicles – A review, Materials Today: Proceedings, Volume 45, Part 2, 2021, Pages 1181-1187, ISSN 2214-7853, https://doi.org/10.1016/j.matpr.2020.03.679.

In addition, this material should be added to the body of the article, and if sufficiently notable, summarized in the lead. Johnjbarton (talk) 03:04, 23 July 2024 (UTC)