Fuel saving device

Fuel saving devices are sold on the aftermarket with claims to improve the fuel economy and/or the exhaust emissions of a vehicle. There are numerous different types of device; many purport to optimize ignition, air flow, or fuel flow in some way. An early example of such a device sold with difficult-to-justify claims is the 200 mpg carburetor designed by Canadian inventor Charles Nelson Pogue.

The US EPA is required by Section 511 of the Motor Vehicle Information and Cost Savings Act to test many of these devices and to provide public reports on their efficacy; the agency finds most devices do not improve fuel economy to any measurable degree. Tests by Popular Mechanics magazine also found these types of devices yield no measurable improvements in fuel consumption or power, and in some cases actually decrease both power and fuel economy.

Other organizations generally considered reputable, such as the American Automobile Association and Consumer Reports have performed studies with the same result.

One reason that ineffective fuel saving gadgets are popular is the difficulty of accurately measuring small changes in the fuel economy of a vehicle. This is because of the high level of variance in the fuel consumption of a vehicle under normal driving conditions. Due to selective perception and confirmation bias, the buyer of a device can perceive an improvement where none actually exists. For this reason, regulatory bodies have developed standardized drive cycles for consistent, accurate testing of of vehicle fuel consumption.

Types of devices

Fuel & oil additives

Compounds sold for addition to the vehicle's fuel may include tin, magnesium and platinum. The claimed purpose of these is generally to improve the energy density of the fuel. Additives for addition to the engine oil, sometimes marketed as "engine treatments", contain teflon, zinc, or chlorine compounds; none of these is appropriate or helpful when added to an engine's crankcase, and they can in fact damage the engine. The US Federal Trade Commission has aggressively pursued marketers of oil additives falsely claimed to improve fuel economy.

Magnets

Magnets attached to a vehicle's fuel line have been claimed to improve fuel economy by aligning fuel molecules, but because motor fuels are non-polar, no such alignment or other magnetic effect on the fuel is possible.

Vapor devices

Some devices claim to improve efficiency by changing the way that liquid fuel is converted to vapor. These include fuel heaters and devices to increase or decrease turbulence in the intake manifold. These do not work because the principle is already applied to the design of the engine, and because intake tract flow dynamics are highly specific to each engine design, no universal device could have any given effect on more than one kind of engine.

Electronic devices

Some electronic devices are marketed as fuel savers. The Fuel Doctor FD-47, for example, plugs into the vehicle's cigarette lighter and displays several LEDs. It is claimed to increase vehicle fuel economy by up to 25% through "power conditioning of the vehicles electrical systems", but Consumer Reports detected no difference in economy or power in tests on ten seperate vehicles, finding that the device did nothing but light up. Car and Driver magazine found that the device contains nothing but "a simple circuit board for the LED lights", and disassembly and circuit analysis reaches the same conclusion. The maker has been sued by a customer who experienced no increase in her vehicle's fuel economy with use of the device., and is being investigated over complaints from customers who purchased the FD-47 device on the basis of the company's advertising claims.

Thermodynamic Efficiency

The reason why most devices are not capable of producing the claimed improvements is based in thermodynamics. This formula expresses the theoretical efficiency of an engine:

$h=1-{1 \over rv^{g-1}}$

where h is efficiency, rv is the compression ratio, and g is the ratio of the specific heats of the gases before and after combustion.

Assuming an ideal engine with no friction, perfect insulation, perfect combustion, a compression ratio of 10:1, and a g of 1.27 (for gasoline-air combustion), the theoretical efficiency of the engine would be 46%.

For example, if an automobile typically gets 20 miles per gallon with a 20% efficient engine that has a 10:1 compression ratio, a carburetor claiming 100MPG would have to increase the efficiency by a factor of 5, to 100%. This is clearly beyond what is theoretically or practically possible. A similar claim of 300MPG for any vehicle would require the engine (in this particular case) that is 300% efficient, which violates the Second Law of Thermodynamics.

Extremely efficient vehicle designs capable of achieving 100MPG+ (such as the VW 1l) do not have substantially greater engine efficiency, but instead focus on better aerodynamics, reduced vehicle weight, and using energy that would otherwise be dissipated as heat during braking.

Urban legend

There is a debunked urban legend about an inventor who creates a 100 mpg (2.35 L/100 km) or even 200 mpg carburetor, but after demonstrating it for the major vehicle manufacturers, the inventor mysteriously disappears. In some versions of the story, he is claimed to have been killed by the government. This fiction is thought to have started after Canadian Charles Nelson Pogue filed in 1930 U.S. patent 1,750,354 for such a device (followed by others including U.S. patent 1,938,497 & U.S. patent 1,997,497).

MythBusters

The popular U.S. television show MythBusters investigated several fuel-saving devices using gasoline- and diesel-powered fuel-injected cars under controlled circumstances. Fuel line magnets, which supposedly align the fuel molecules so they burn better, were tested and found to make no difference in fuel consumption. The debunked notion that adding acetone to gasoline improves efficiency by making the gasoline burn more completely without damaging the plastic parts of the fuel system was tested, and although there was no apparent damage the fuel system, the efficiency of the fuel actually decreased.

The show tested the theory that a diesel-powered car can run on hydrogen gas alone, which surprisingly, was confirmed as viable, although hydrogen gas itself is very expensive. They also tested a device that supposedly produces sufficient hydrogen to power a car by hydrolysis (running an electric current through water to split its molecules into hydrogen and oxygen). Although some hydrogen was produced, the amount was minuscule compared to the quantity necessary to run a car for even a few seconds.

The show also tested a carburetor that, according to its manufacturer, could improve fuel efficiency to 300 miles per gallon. However, the device actually made the car less fuel efficient. They also determined that a diesel-powered car can run on used cooking oil though they did not check whether it damaged the engine.

The show noted that out of 104 fuel efficiency devices tested by the EPA, only seven showed any improvement in efficiency, and even then, the improvement was never more than six percent. The show also noted that if any of the devices they tested actually worked to the extent they were supposed to, the episode would have been one of the most legendary hours of television.

See also

• Telematics
• history of perpetual motion machines
• Corporate Average Fuel Economy
• Emission standard
• Jack Talbert (Vaporization)

External links

• Tony's Guide to Fuel Saving Gadgets including a case study on Vaporate
• FCIC warning on fuel saving devices
• Better Business Bureau list of ineffective retrofit devices and glossary of terms