Methanol Combustion in Low Compression Ratio D.I. Engines Enabled by Sonex Piston Design

Using methanol as a fuel, this study examines the chemical-kinetics mechanism responsible for the enhancement of combustion in I.C. engines due to intermediate and radical chemical species produced in micro-chambers of Sonex Combustion System (SCS) pistons. This homogeneous combustion enhancement was first shown experimentally (in 1991) to be capable of enabling an IC engine to operate stably and smoke free on methanol over an entire engine map while using a compression ratio of only 17:1 and without a spark or other assists. The distinction is made between thermally induced variants of homogeneous combustion: HCCI and ATAC; and intermediate species/radical induced homogeneous combustion: LAG and SCRl (Stratified Charge Radical Ignition). In order to determine the kinetic mechanisms responsible for the intermediate and radical species enhanced combustion of methanol and of similar enhancements with other fuels, the present study explores the effects of several important species on the numerically simulated methanol combustion. A detailed chemical kinetics approach is adopted using CHEMKIN-II and integrated with axi-symmetric turbulent combustion KIVA-II flow-field calculations. Results point conclusively to the importance of the dominant effects of two intermediate species formed and retained in frozen equilibrium (inactive at lower pressures and temperatures) in the SCS micro-chamber along with the importance of one “frozen” radical specie. These dominant species are shown to enhance ignition by changing the oxidative chain initiation paths, thus reducing the ignition delay time. The end outcome is a faster, more complete and lower temperature combustion process that results in “ultra-clean” exhaust gases.