The adverse effects of charge dilution on combustion of spark ignition engines are well known; as a tool for reduction of nitrogen oxide emission, it becomes important.
Some methods of analyzing combustion phenomena in a single-cylinder engine (27.1 CID) with charge dilution were tried. Multiple ionization probes roughly indicate the pattern of flame propagation, but details of the flame, especially charge dilution, cannot be measured by this method. Flame photographs, on the other hand, showed clearly the effects of combustion chamber design on flame propagation and its cyclic dispersion. The effects of combustion chamber configuration, ignition energy and spark duration, ignition timing, composition of diluent gas, air-fuel ratio, and mixture homogeneity were examined. Mass burnt fraction was calculated from both flame photographs and pressure indicator diagrams.
A combustion chamber having high turbulence and a rich air-fuel ratio promoted the initial flame propagation and flame speed and improved cyclic dispersion.
For high turbulence design, the combustion chamber of the commercial 97.5 CID, 4-cyl engine was modified. Fluctuation of output torque was measured and analyzed by correlation and probability analyses. This analysis indicated that high turbulence design was effective for improvement of car surge caused by EGR, and this was confirmed by actual driving on the road.