Combustion and the thermodynamic performance of spark ignition engines

Some overall considerations for the optimization of the energy chain for th e spark ignition engine are briefly discussed and figures given for the rel ative inhaled energies with different fuels. There follows a description of the nature of turbulent flame propagation in engines, showing the computed characteristics of the burning rate for stoichiometric and lean mixtures a t different engine speeds. These reveal the factors influencing partial que nching and misfire. Flame instabilities are shown theoretically to become m ore important with increasing pressure. The associated flame wrinkling and cellularity increase the burning rate of both laminar and turbulent gaseous flames. Fundamental aspects of the present trend towards the direct inject ion of gasoline are discussed and the unique instabilities in aerosol combu stion are shown to increase the burning velocity above that of the correspo nding gaseous mixture. The degree to which evaporative cooling of droplets can enhance the volumetric efficiency is discussed. The onset of autoigniti on in an engine is calculated with recent shock tube data, which are also u sed to show that evaporative cooling can increase the knock resistance by a bout four octane numbers.