Effects of Burn Rate Parameters on Nitric Oxide Emissions for a Spark Ignition Engine: Results from a Three-Zone, Thermodynamic Simulation

A thermodynamic engine cycle simulation which includes three zones for the combustion process was used to study the effects of burn rate parameters on nitric oxide (NO) emissions for an automotive, spark-ignition engine. For the combustion process, the engine cycle simulation includes unburned and burned zones. The burned zone is further divided into an adiabatic core zone surrounded by a boundary layer zone. The importance of the adiabatic zone gas temperature for computing nitric oxide emissions is noted. The combustion process was modeled using the well-known Wiebe function to express the mass fraction burned. The effects of varying the Wiebe function parameters on engine performance, and on instantaneous and net final nitric oxide emissions were determined. For the range of Wiebe function parameters investigated, nitric oxide concentrations increased by up to about 25%. The changes of the nitric oxide concentrations were explained in terms of adiabatic zone gas temperatures, and cylinder pressures. The implications of these results to actual engines are described.