Catalytic charge activation in a lean-burn internal combustion engine

Catalytic surface ignition commonly begins at temperatures several hundred degrees Celsius lower than the gas phase ignition temperature for the same combustible mixture. Heterogeneous catalysis therefore can be used to midify homogeneous chemical activity under otherwise non-reacting conditions. Theoretical analysis of flame propagation through catalytically activated mixtures and fundamental experiments with a catalytic plug-flow reactor have shown that catalytic prereaction can increase flame velocity and can reduce minimum ignition energy requirements. These effects result from thermal activation of the gas phase. Furthermore, if catalytic conversion is extensive enough it is possible to bring about self-ignition of the gas phase. For these reasons catalytic charge activation offers exciting engineering potential as a tool for supporting lean combustion of homogeneous mixtures.;These principles have been successfully applied in a catalytic prechamber for a lean-burn internal combustion engine. Unlike other catalytic engine concepts, catalytic prechamber technology serves to regulate catalytic surface temperature as well as contact between the catalyst and gas phase reactants. Catalytic effects are thus properly timed and are confined to a small volume where substantial thermal activation is possible. The prechamber also intensifies combustion gas dynamics which are necessary for rapid and complete consumption of the non-activated portions of the charge. Catalytic charge activation was found to decrease cycle-to-cycle pressure variation and to increase cycle efficiency near the lean-burn limit. These effects were found to be more pronounced as the prechamber was made more adiabatic. When surface prereaction was more extensive the catalytic prechamber proved to be a knock-free compression-ignition source.;In conjunction with these fundamental studies and parametric engine tests a physical model of in-cylinder activation has been formulated. Key assumptions have been investigated with a numerical model of catalytically assisted compression-ignition. This model has proved to be a valuable asset in understanding catalytic prechamber performance and in optimizing catalytic prechamber design.