Influence of Laminar Burning Velocity on Performance of Gasoline Engines

Laminar burning velocity is a fundamental combustion property of any fuel/air mixture. Formulating gasoline fuel blends having faster burning velocities can be an effective strategy for enhancing engine and vehicle performance. Formulation of faster burning fuels by changing the fuel composition has been explored in this work leading to a clear correlation between engine performance and fuel burning velocity. In principle a gasoline vehicle should be calibrated to give optimal ignition timing (also known as MBT - minimum spark advance for best torque) while at the same time avoiding any possible engine knock. However, modern downsized/boosted engines frequently tend to be limited by knock and the spark timing is retarded in respect of the optimum. In such scenarios, faster burning fuels can lead to a more optimum combustion phasing resulting in a more efficient energy transfer and hence a faster acceleration and better performance. Tests carried out using fuel blends with different burn velocity enhancing components on a single cylinder engine with retarded spark timing showed appreciable benefits (e.g. 1.5% performance benefit using a gasoline blend with 20% of a certain aromatic added). The trends observed in the engine were in good agreement with results of laminar burning velocity measurements published in literature.