Engineers at Ricardo have produced a more efficient flex-fuel engine that doesn’t pay the usual 30-percent efficiency penalty for using E85, because it isn’t optimized strictly for gasoline:
Ricardo’s new Ethanol Boosted Direct Injection (EBDI) engine is designed to take full advantage of the favorable properties of ethanol to improve performance and reduce consumption. “[Ethanol] has a very high octane rating compared to other fuels, and a higher heat of vaporization,” says Luke Cruff, chief engineer for the EBDI program at Ricardo.A higher octane rating means that a fuel is less prone to unwanted detonation, or “knocking.” A higher latent heat of vaporization means that ethanol can help control gas conditions in the combustion chamber by lowering temperatures. By modifyingthe pressure and temperature, fuel injected into the engine will burn more efficiently and reduce the formation of nitrous-oxide gases.
Regular flex-fuel engines are unable to exploit these properties because they are optimized for gasoline and run at lower cylinder pressures, says Cruff. The EBDI engine continually monitors the fuel blend using sensors. It then modifies cylinder pressure, fuel injection, valve timing, and other factors to ensure that the conditions get the most out of the fuel mix. One way that the engine modifies cylinder pressure is by using turbocharging.