Modeling of NOx Emissions with Comparison to Exhaust Measurements for a Gas Fuel Converted Heavy-Duty Diesel Engine

In previous work the KIVA-II code has been modified to model modem DI diesel engines and their emissions of particulate soot and oxides of nitrogen (NOx). This work presents results from a program to further validate the NOx emissions models against engine experiments with a well characterized modern engine. To facilitate a simplified comparison with experiments, a single cylinder research version of the Caterpillar 3406 heavy duty DI diesel engine was retrofitted to run as a naturally-aspirated, propane-fueled, spark-ignited engine. The retrofit includes installing a low compression ratio piston with bowl, adding a gas mixer, replacing the fuel injector assembly with a spark plug assembly and adding spark and fuel stoichiometry control hardware. Cylinder pressure and engine-out NOx emissions were measured for a range of speeds, exhaust gas residual (EGR) fractions, and spark timing settings.

Cylinder pressure and engine-out NOx emissions results predicted with the modified version of KIVA were found to compare favorably with the engine measurements. Good agreement was found for both cylinder pressure and NOx emissions for the range of speeds, spark timings and EGR fractions of the engine experiments. Furthermore, the Extended Zel'dovich NO Mechanism was found to satisfactorily model the measured engine-out NOx emissions over the full range of conditions. The present results demonstrate that multidimensional modeling is useful for NOx emissions predictions in large bore spark ignition engines.