Comparison of Pfi and Di Superbike Engines

Gasoline Direct Injection (DI) is a technique that was successful in motor sports several decades ago and is now relatively popular in passenger car applications only. DI gasoline fuel injectors have been recently improved considerably, with much higher fuel flow rates and much finer atomization enabled by the advances in fuel pressure and needle actuation. These improved injector performance and the general interest in reducing fuel consumption also in motor sports have made this option interesting again. This paper compares Port Fuel Injection (PFI) and DI of gasoline fuel in a high performance, four cylinder spark ignition engine for super bike racing. Computations are performed with a code for gas exchange, heat transfer and combustion, simulating turbulent combustion and knock. Results obtained at full and part loads show the DI solution does not improve wide open throttle power output, but significantly helps reducing values of brake specific fuel consumption especially at low loads. Considering the increased complexity, the DI option may therefore become a necessity in super bike applications when sporting rules are developed to prescribe much lower fuel consumption per race and engine speed limiters.