Development and Application of Gasoline/EtOH Combustion Mechanism: Modeling of Direct Injection Ethanol Boosted Gasoline Engine

Ethanol could play an important role to reduce the use of fossil fuels in the automotive industry together with asubstantial increase in the efficiency of direct injection gasoline engines. As suggested by Cohn, Bromberg, andHeywood, the concept of ethanol DI boosted gasoline engine can facilitate the high compression ratio engine operationby reducing the knock constraint. In this concept, the direct injection of ethanol was proposed as an effective knocksuppressant. As described, a small amount of ethanol could be used to reach the engine efficiency corresponding toinjection of larger (by 30 %) amount of gasoline. Gasoline consumption and out emissions would be reduced by 25%.The concept has been validated for the small bore model engine using the KIVA3V code supplemented by the detailed chemistry approach. The chemical mechanism for gasoline surrogate/ethanol blend was constructed consisting of 129 species participating in 700 reactions. The gasoline surrogate model was constructed using sub-mechanisms for constituent components (iso-octane, toluene, and n-heptane in a selected proportion) from classes of hydrocarbons typical for gasoline. The mechanism was validated using shock-tube auto-ignition data taken from Sakai (University of Tokyo) and Gauthier (Stanford University) data compilations. The sub-mechanism of ethanol combustion is described by the reduced mechanism of Marinov (LLNL). The KIVA3V code was modified to treat the chemical mechanism developed and allowing injections of different fuels. The numerical results illustrate the possible efficiency gain for the model DI gasoline engine with conventional compression ratio within the range of 10-20% by ethanol injection in 10-20% of the total amount of fuel.