Performance and NO_x Emissions of Spark Ignited Combustion Engines Using Alternative Fuels—Quasi One-Dimensional Modeling I. Hydrogen Fueled Engines

Abstract

Hydrogen and methanol have been suggested as potential non-petroleum derived substitutes for current reciprocating engine fuels. The present paper reports the results of a computer simulation of the performance and NO_x emissions of hydrogen fueled spark ignition engines. The engine combustion process is modeled by employing a semi-empirical turbulent flame speed expression. The NO_x emissions are determined by integrating the chemical rate equations resulting from the extended Zeldovich mechanism over the boundary conditions determined by the cycle analysis.

Hydrogen exhibits very rapid burning rates and the resulting high pressures and temperatures lead to fast NO formation and destruction rates. Maximum NO emissions are predicted for lean mixtures near φ = 0.8 in agreement with experimental observations. For richer mixtures rapid decomposition of NO during the expansion stroke lowers exhaust emissions. NO_x control by exhaust gas recirculation is much more effective in lean mixtures than in stoichiometric mixtures. While lean hydrogen-air mixtures are attractive from an efficiency standpoint, the near stoichiometric mixtures required for full power operation lead to excessively high pressure rise rates. Exhaust gas recirculation moderates the burning rate and reduces the power output at little or no loss in efficiency.