A thermodynamic cycle simulation was developed for spark-ignition engines which included a formulation using multiple zones for the combustion process and the capability to compute the net nitric oxide (NO) change due to the “thermal” formation mechanism. This simulation was used to complete analyses for a commercial, 5.7 l spark-ignition V-8 engine operating at a part load operating condition at 1400 rpm with an equivalence ratio of 1.0. The engine possessed a compression ratio of 8.1:1, and had a bore and stroke of 101.6 and 88.4 mm, respectively. At the base case conditions, the nitric oxide emissions were 15.7 g/bhp-hr (2903 ppm). The effects of equivalence ratio, combustion duration, spark timing, exhaust gas recirculation, compression ratio, speed and load on nitric oxide changes were examined. Results for instantaneous nitric oxide as a function of crank angle are presented. The use of an adiabatic zone was shown to dramatically increase the nitric oxide levels relative to using the burned gas temperature. For the base case, almost 50% more nitric oxide was computed using the adiabatic temperature relative to the burned gas temperature. The importance of gas temperature, cylinder gas pressure, and composition is illustrated.

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