E85 is used to operate spark-ignited engines that have been modified to accept this fuel. Unlike E10, E85 cannot be used in spark-ignited engines that have not been modified. This has slowed the adoption of E85 because there is a supply and demand problem: consumers will not buy vehicles unless there is a readily available source of fuel, and fuel companies will not invest in the alternative fuels unless there is a large supply of vehicles that use the fuel. This has led to the development of a new type of vehicle, called a Flexible Fuel Vehicle, which can operate using various blends of alcohol.

Flexible Fuel Vehicles

Flexible Fuel Vehicles, or FFVs, can operate on ethanol-blends from 0% (gaso­line) up to 85% (E85) by volume. This eliminates the supply and demand problem as consumers can fuel with any combination of fuel, not worrying whether the correct fuel will be available. These vehicles are produced by most of the major automakers and represent the largest class of vehicles using E85. Most of these vehicles are sold without any cost penalty to the consumer. This is both an indication of the automakers’ desire to develop the market and the incremental costs required to produce these vehicles compared with their gasoline-fueled counterparts.

These vehicles are designed and manufactured using E85 compatible mate­rials. Further, due to the different fuel-air mixture requirements of gasoline and E85, the fuel delivery systems are sized to handle the increased volumes of fuel when using E85. Other changes are made to the control algorithms in order to optimize the vehicle for use with this fuel. Since E85 has a higher octane than gasoline, the spark timing can be advanced, improving engine performance. Further, the fuel injection pulsewidth or duration must be lengthened to increase the flowrate of E85 for given engine load and speed conditions.

Since consumers can fuel these vehicles with either E85 or gasoline (or any blend in between), these vehicles must determine the levels of ethanol present onboard the vehicle in order to ensure that the engine is operating at the best conditions for the given fuel blend. In order to accomplish this, current FFVs have a fuel sensor, which is located in the fuel delivery lines leading from the fuel tank to the engine. The fuel sensor measures the conductivity of the current fuel blend. Since ethanol and gasoline have vastly different levels of conductivity (ethanol is about 135,000 times more conductive than gasoline),8 this is a rela­tively easy task to accomplish with some precision. Older FFVs relied on the use of a feedback signal from an exhaust gas oxygen (EGO) sensor located in the exhaust stream. This sensor, already present on all spark-ignited vehicles, detects the presence of excess oxygen in the exhaust. Because of exhaust after-treatment requirements on-road vehicles generally operate using stoichiometric mixtures of fuel and air. Thus, the oxygen sensor is used to maintain stoichiometric combus­tion in an engine. This sensor can be used to determine fuel mixture as ethanol is an oxygenated fuel with a richer stoichiometric mixture; thus, the mixture used for gasoline will be too lean with E85 and lead to excess oxygen in the exhaust. Unfortunately, these sensors only function when warm, so they cannot be used to help during cold starts of the engine. Thus, going from gasoline to E85 results in a lean mixture until the EGO is functioning. This can lead to poorer quality cold starts and poor drivability under acceleration.9

Many environmental groups have been critical of using FFVs, since modify­ing gasoline-powered vehicles to operate using E85 puts E85 at an inherent disadvantage and it does not force the rapid buildup of an E85 fueling infrastruc­ture since consumers can continue to use gasoline.2 It is important to remember that the automakers need to produce vehicles that consumers will actually buy; most consumers will not buy a vehicle for which there are few fueling opportu­nities. This criticism is perhaps premature at this early stage of E85 development.