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E85

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For the road, see European route E85
File:E85 logo.png
Logo used in the United States for E85 fuel

E85 is an alcohol fuel mixture of 85% ethanol (ethyl alcohol, i.e., grain alcohol) and 15% gasoline (petrol) (proportioned by volume rather than mass) that can be used in flexible-fuel vehicles.

Availability

The fuel is widely used in Sweden and is becoming increasingly common in the United States, mainly in the Midwest where corn is a major crop and is the primary source material for ethanol fuel production. Minnesota has the largest number of E85 fuel pumps of any U.S. state, with almost 150 of the 400+ pumps in the country. As of July 2005, Illinois has the second-greatest number of E85 pumps (about 60); most other states have fewer than two dozen. Even in Minnesota, the ethanol pumps represent a tiny fraction of the fuel outlets—there are about 4,000 gas stations in the state, each with several individual pumps (however, all stations there are required to carry E10, a 10% mixture of ethanol and gasoline). However, concerns about rising gasoline prices and energy dependence has led to a resurgence of interest in E85 fuel; for example, Nebraska mandated the use of E85 in state vehicles whenever possible in May 2005.

Cost

As of mid-2005, E85 is frequently sold for a 0 to 35% lower cost than gasoline. Much of this discount can be attributed to various government subsidies, and, at least in the United States, the elimination of state taxes that typically apply to gasoline and can amount to 47 cents, or more, per gallon of fuel. In the aftermath of Hurricane Katrina, the price of E85 has risen to nearly on par with the cost of 87 octane gasoline in many states in the United States, and is often the only fuel available when gasoline is sold out.

Unfortunately, because ethanol contains less energy per gallon of fuel than gasoline, fuel economy is normally negatively impacted for most FFVs (flexible-fuel vehicles) that are currently on the road by about 30% when operated on pure E85. (Newer vehicles can sometimes lessen this impact to only 5-15% through using higher compression ratio engines, or turbocharged engines.) Still, for all FFVs, more E85 is needed to do the same work as can be achieved with a lesser volume of gasoline. This difference is usually partially or totally offset by the lower cost of the E85 fuel, depending on E85's current price discount relative to the current price of gasoline.

For example, an existing FFV vehicle that normally achieves, say, 30 MPG on pure gasoline will typically achieve about 20 MPG, or slightly better, on E85. To achieve any short-term operational fuel cost savings, the price of E85 should therefore be 30% or more below the price of gasoline to equalize short term fuel costs for most existing FFVs. Life-cycle costs over the life of the FFV engine are theoretically lower for E85, as ethanol is a cooler and cleaner burning fuel than gasoline. Provided that one takes a longterm life-cycle operating cost view, a continuous price discount of only 20% to 25% below the cost of gasoline is probably about the break-even point in terms of vehicle life-cycle operating costs for operating an FFV on E85 continuously.

Fuel economy in fuel-injected non-FFVs operating on a mix of E85 and gasoline varies greatly depending on the engine and fuel mix. For a 60:40 blend of gasoline to E85, a typical fuel economy reduction of around 23.7% resulted in one controlled experiment with a 1998 Chevrolet S10 pickup with a 2.2L 4-cylinder engine, relative to the fuel economy achieved on pure gasoline. Similarly, for a 50:50 blend of gasoline to E85, a typical fuel economy reduction of around 25% resulted for the same vehicle. (Fuel economy performance numbers were measured on a fixed commute of approximately 110 miles roundtrip per day, on a predominately freeway commute, running at a fixed speed (62 mph), with cruise control activated, at sea level, with flat terrain, traveling to/from Kennedy Space Center, FL.)

Use in Flexible-fuel engines

E85 is best used in engines modified to accept higher concentrations of ethanol. Such flexible-fuel engines are designed to run on any mixture of gasoline or ethanol.

So far, most flexible-fuel vehicles that built in the United States have been sport-utility vehicles and other members of the "light truck" vehicle class, with smaller numbers of sedans, station wagons, and the like.

Swedish automobile maker Saab has developed a turbocharged flexible-fuel engine called the BioPower which takes advantage of the high-octane fuel. The engine allows the vehicle to accelerate faster and attain higher speeds when running on E85 than when running on straight gasoline.

General Motors subsidiary GM do Brazil adopted GM's Family II and Family 1 straight-4 engines with FlexPower technology that enables the use of ethanol, gasoline, or their mixture. The vehicles with FlexPower include the Chevrolet Corsa and the Chevrolet Astra.

Use in standard engines

E85 has a considerably higher octane rating than gasoline —about 110— a difference significant enough that it doesn't burn as efficiently in traditionally-manufactured internal-combustion engines.

Use of E85 in non-FFV vechicles is generally experimental, with some users recommending light blends as low as 20%, while others have successfully run 100% E85.

Modern cars (i.e., most cars built after 1988) have fuel-injection engines with oxygen sensors that will attempt to adjust the air-fuel mixture for the extra oxygenation of E85, with variable effects on performance.

Operation of fuel-injected non-FFVs on more than 50% E85 will generally cause the check engine light (CEL) to illuminate, indicating that the ECU can no longer maintain closed-loop control of the internal combustion process due to the presence of more oxygen in E85 than in gasoline. Beyond this point, adding more E85 to the fuel tank becomes rather inefficient. For example, running 90% E85 in a non-FFV will typically reduce fuel economy by 33% or more relative to what would be achieved running 100% gasoline. (This example is again for the same 1998 Chevy S10 pickup for which the fuel economy was studied in the controlled experiment mentioned previously.)

Prolonged exposure to high concentrations of ethanol may corrode metal and rubber parts in older engines (pre-1988) designed primarily for gasoline. For post-1988 fuel-injected engines, all the components are already designed to accommodate E10 (10% ethanol) blends, and there is a greater degree of flexibility in just how much more may be added without causing ethanol-induced damage, varying by automobile manufacturer. Though there is no appreciable difference in the corrosive properties between E10 and a 50:50 blend of gasoline and E85 (47.5% ethanol), operation with more than 10% ethanol has never been recommended by car manufacturers in non-FFVs. Still, starting in 2010, at least one US state (Minnesota) already has legislatively mandated and planned to force E20 (20% ethanol) into their general gasoline fuel-distribution network. Details of how this will work for individual vehicle owners while maintaining automobile manufacturer warranties, despite exceeding the manufacturer's maximum warranted operation percentage of 10% of ethanol in fuel, are still being worked as of late-2005.

E85 gives particularly good results in turbocharged cars due to its high octane [1]. It allows the ECU to run more favorable ignition timing and leaner fuel mixtures than are possible on normal premium gasoline. Users who have experimented with converting OBDII (i.e., On-Board Diagnostic System 2, that is for 1996 model year and later) turbocharged cars to run on E85 have had very good results. Experiments indicate that most OBDII-specification turbocharged cars can run up to approximately 39% E85 (33% ethanol) with no CEL's or other problems. (In contrast, most OBDII specification fuel-injected non-turbocharged cars and light trucks are more foregiving and can usually operate well with in excess of 50% E85 (42% ethanol) prior to having CEL's occur.) Fuel system compatibility issues have not been reported for any OBDII cars or light trucks running on high ethanol mixes of E85 and gasoline for periods of time exceeding two years. (This is likely to be the outcome justifiably expected of the normal conservative automotive engineer's predisposition not to design a fuel system merely resistant to ethanol in E10, or 10% percentages, but instead to select materials for the fuel system that are nearly impervious to ethanol.)

Fuel economy does not drop as much as might be expected in turbocharged engines based on the specific energy content of E85 compared to gasoline, in contrast to the previously-reported reduction of 23.7% reduction in a 60:40 blend of gasoline to E85 for one non-turbocharged, fuel-injected, non-FFV. Although E85 contains only 72% of the energy on a gallon for gallon basis compared to gasoline, experimenters have seen much better fuel mileage than this difference in energy content implies. Many commentators suggest that due to the lower energy content you should expect an equivalent 39% increase in fuel usage. This has not been the case in practice when running gasoline and ethanol blends. Some of the newest model FFV's get only about 7% less mileage per gallon of fuel of E85 compared to their gasoline fuel mileage.

The reason for this non-intuitive difference is that the turbocharged engine seems especially well-suited for operation on E85, for it in effect has a variable compression ratio capability, which is exactly what is needed to accomodate varying ethanol and gasoline ratios that occur in practice in an FFV. At light load cruise, the turbocharged engine operates as a low compression engine. Under high load and high manifold boost pressures, such as accelerating to pass or merge onto a highway, it makes full use of the higher octane of E85. It appears that due to the better ignition timing and better engine performance on a fuel of 100 octane, the driver spends less time at high throttle openings, and can cruise in a higher gear and at lower throttle openings than is possible on 100% premium gasoline. In daily commute driving, mostly highway, 100% E85 in a turbocharged car can hit fuel mileages of over 90% of the normal gasoline fuel economy. Tests indicate approximately a 5% increase in engine performance is possible by switching to E85 fuel in high performance cars.

Experimenters who have made conversions to 100% E85, find that cold start problems at very cold temperatures can easily be avoided through adding 1 - 2 gallons of gasoline to the E85 in the tank, prior to the arrival of the cold weather.

No significant ignition timing changes are required for a gasoline engine running on E85.

E85 fuel requires a richer air fuel mixture than gasoline for best results. For successful conversions, it generally requires 27% - 30% more fuel flow than when the engine burns 100% gasoline. 


Fuel                        AFRst      FARst      Equivalence   Lambda
----                        -----      -----        Ratio       -----
=========================================================================
Gasoline stoich             14.7       0.068        1           1
Gasoline Max power rich     12.5       0.08         1.176       0.8503
Gasoline Max power lean     13.23      0.0755       1.111       0.900

=========================================================================
E85 stoich                   9.765    0.10235       1           1
E85 Max power rich           6.975    0.1434        1.40        0.7143
E85 Max power lean           8.4687   0.118         1.153       0.8673  

=========================================================================
E100 stoich                  9.0      0.111         1           1
E100 Max power rich          6.429    0.155         1.4         0.714
E100 Max power lean          7.8      0.128         1.15        0.870
=======================--================================================


The term AFRst refers to the Air Fuel Ratio under stoichiometric, or ideal air fuel ratio mixture conditions. (See stoichiometry.) The "stoich" (common shorthand way to indicate stoichiometric) mixture typically burns too hot for any situation other than light load cruise. This is the target mixture that the ECU attempts to achieve in closed-loop fueling to get the best possible emissions and fuel mileage at light load cruise conditions. This mixture typically can give approximately 95% of the engine's best power, provided the fuel has sufficient octane to prevent damaging detonation ( knock ).

The "Max Power Rich" condition is the richest air fuel mixture (more fuel than best power) that gives both good drivability and power levels, within approximately 1% of the absolute best power on that fuel.

The "Max Power Lean" condition is the leanest air fuel mixture (less fuel than best power) that gives good drivability, acceptable exhaust gas temperatures to prevent engine damage, and power levels within approximately 1% of the absolute best power on that fuel.

Lambda, typically used for referring to lean versus rich air fuel mixtures, is normally measured by the so-called lambda sensor (also known as an oxygen sensor.)

After-market Conversion Kits

After-market conversion kits, for converting standard engines to operate on E85, are generally not legal in U.S. states subject to emissions controls, despite the fact that the exhaust emissions from such converted cars are improved by utilizing higher percentages of ethanol in the gasoline blend. Likewise, U.S. Federal law prohibits the manufacture of such conversion kits in the U.S., by a ban that dates to when conversion kits for converting vehicles to use compressed natural gas was enacted to prevent the sale of such conversion kits due to concern about the safety of such conversion kits being released among the general public. Still, there is one Brazilian after-market kit available legally in U.S. states not subject to emission controls that will nonetheless permit the conversion of 4, 6, or 8 cylinder engines to operate from fuels ranging from pure gasoline to a mix of gasoline and ethanol to pure ethanol, including E85. It operates by modifying the fuel-injection pulses sent to the fuel injectors, thereby extending the control range over which the ECU can adjust the air-fuel ratio to achieve an oxygen sensor reading measured before the catalytic converter that falls within nominal gasoline-burning limits.

See also

External links

References

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