On laminar flame speed correlations for H2/CO combustion in premixed spark ignition engines

The stringent regulations on the reduction of both pollutant emissions and dependence from crude oil have increased the interest toward alternative energy resources. Transport and energy production sectors are strongly involved in the pollutions net environmental balance and, at the same time, their primary energy requirements are significant. In this scenario, several efforts are carried out to identify new solutions. In the last two decades, in the automotive industry, the use of several alternative fuels for internal combustion engine applications has been investigated. Specifically, this work focuses on syngas and its use in spark ignition (SI) engines. First, a comprehensive analysis of the syngas combustion process has been carried out and accurate laminar flame speed correlations are proposed to characterize the fuel oxidation. Then, these correlations have been implemented in a CFD model to simulate a CFR engine combustion process. Different H2/CO–air mixtures (fuel molar ratio ranging from 50:50 to 100:0 of H2:CO) at different engine operating conditions (compression ratio from 6:1 to 10:1 and fuel equivalence ratio from 0.6 to 0.8) have been considered and the results have been compared with available experimental data. A good agreement has been observed in all conditions, in terms of pressure trace, heat release and other parameters that are useful to characterize the combustion process in SI engines, i.e. burn duration, ignition lag and rapid burn angle.