Optimization of Combustion Chamber Design for Spark Ignition Engines

A two-dimensional model of combustion in spark ignition engines was applied to ten chamber configurations of three types: wedge, hemispherical, and Heron. With a compression ratio of 11.5 and a swirl ratio of 3, a range of engine speeds loads and mixture ratios was explored. The objective was to compare indicated efficiencies. For a given cylinder displacement, the indicated efficiency is found to be insensitive to chamber geometry because those changes that lead to faster combustion also lead to larger wall heat losses. However, indicated efficiency does increase with increasing cylinder displacement and a linear correlation is found between indicated efficiency and chamber surface-to-volume ratio. The computed trends are in agreement with measured ones. The additional constraints of knock, cyclic variations, and emissions were not considered. For a given cylinder displacement, different chamber geometries may still be preferable if those additional constraints are included.