Calculated Nitric Oxide Emissions of an Unthrottled Spark Ignited, Stratified Charge Internal Combustion Engine

This paper presents a theoretical study of nitric oxide emissions from an unthrottled stratified charge, spark ignition engine. This investigation was undertaken to determine the nitric oxide production when an ideal rich-lean stratification is present and to determine the effects of introducing an intermediate stoichiometric region. In order to study this problem a three-region (generally rich, stoichiometric, and lean) combustion model was used, and the effects of the following variables were studied:

1. 1.
   Excess air number of the rich mixture.
2. 2.
   Percentage of the total fuel in the rich-mixture region.
3. 3.
   Percentage of fuel burned stoichiometrically.
4. 4.
   Exhaust gas recirculation, percentage and distribution.

Comparisons are made to both experimental results from a throttled engine and calculated results for an unthrottled engine with a homogeneous mixture. For illustrative purposes, an application of the model to a particular geometrical form of charge distribution is analyzed.