Comparison of Analytically and Experimentally Obtained Residual Fractions and NOX Emissions in Spark-Ignited Engines

Using a fast-sampling valve, residual-fraction levels were determined in a 2.0L spark-ignited production engine, over varying engine operating conditions. Individual samples for each operating condition were analyzed by gas-chromatography which allowed for the determination of in-cylinder CO and CO₂ levels. Through a comparison of in-cylinder measurement and exhaust data measurements, residual molar fraction (RMF) levels were determined and compared to analytical results. Analytical calculations were performed using the General Engine SIMulation (GESIM) which is a steady state quasi-dimensional engine combustion cycle simulation. Analytical RMF levels, for identical engine operating conditions, were compared to the experimental results as well as a sensitivity study on wave-dynamics and heat transfer on the analytically predicted RMF. Similarly, theoretical and experimental NO_x emissions were compared and production sensitivity on RMF levels explored. A new heat transfer algorithm is developed which produced favorable agreement between the experimental and analytical RMF measurements. Improved NO_x predictions were similarly observed over varying operating conditions using the super-extended Zel'dovich mechanism (SEZM) in conjunction with the new heat transfer algorithms. The SEZM produces NO_x emissions within 10-15% of experimental data, while errors by more than 40% are obtained using the extended Zel'dovich mechanism (EZM).