Description
Ethanol Race Fuel
The benefits of ethanol relative to race fuel and/or methanol are multifold, but let’s start with the one many of you already have guessed-power. A typical (R+M)/2 octane rating of E85 is around 100. The naturally high octane allows for greater compression and expansion ratios-the power and efficiency benefits to the racer of higher octane are well known and widely published.
Second, ethanol has a higher heat of vaporization relative to gasoline-a significantly higher value. A typical heat of vaporization for gasoline may be on the order of 59 kilojoules per kilogram of fuel. For ethanol, it’s approximately 130 kilojoules per kilogram, which is more than twice that value for gasoline.
Why is this important? Before a fuel combusts, it must exist as vapor mixed with air, using oxygen in the atmosphere as the source of its oxidant. Therefore, as liquid fuel is introduced into the manifold either by carburetion or fuel injection, it must first change from the liquid to vapor phase and sufficiently mix with the air before it will combust.
The energy required to vaporize the fuel comes mostly from the air, but a portion actually comes from engine intake surfaces as the fuel vapor contacts it. However, it is most ideal to use as much of the air for vaporization to maximize volumetric efficiency. If a fuel has a higher heat of vaporization, the intake air temperature will be reduced, resulting in better volumetric efficiencies as the inlet charge has a higher density. From this, one would expect significant gains in torque performance with ethanol relative to gasoline, and this will be shown to indeed be the case.
In published research work conducted by General Motors, full-load data of a four-cylinder, naturally aspirated spark-ignition direct-injection flex-fuel engine running on E85 demonstrated a near 15 percent increase in specific output relative to production gasoline counterparts, while showing an improvement in part load operation of 3-6 percent. These gains were associated with reduced heat rejection, increased volumetric efficiency, and increased dilution (EGR) tolerance.
