Optimization of Natural Gas Combustion in Spark-Ignited Engines Through Manipulation of Intake-Flow Configuration 2000-01-1948

An investigation was performed to try to quantify the relative importance of large-scale mixing and turbulence in a multi-valve spark-ignited automotive engine converted to use natural gas fuel. The role of mixing was examined by comparing single-point versus multi-point combustion performance at several operating conditions. The fuel-air mixture passed through a static mixer prior to entering the intake manifold in the single point case. This configuration was assumed to produce a well-mixed charge entering the combustion chamber. The fuel was delivered just upstream of the intake port in the multi-point configuration. The charge was assumed to be stratified in this case. The results showed a significant degradation in combustion stability and maximum power but little difference in ignition delay and fully-developed burn duration using multi-point injection.

The relative role of turbulence was examined by altering the intake-flow configuration to create three levels of inlet swirl. A thermodynamic model was used to characterize the effect of the altered flow on mean flow and turbulence. The engine was then tested using each intake-flow configuration. Inlet swirl typically improved combustion stability and decreased fully-developed burn duration, but consistently increased ignition delay. The differences were generally most dramatic at lower engine speeds.