Simulation of combustion in direct-injection low swirl heavy-duty type diesel engines

摘要

A two phase, global combustion model has been developed for quiescent chamber, direct injection diesel engines. The first stage of the model is essentially a spark ignition engine flame spread model which has been adapted to account for fuel injection effects. During this stage of the combustion process, ignition and subsequent flame spread/heat release are confined to a mixing layer which has formed on the injected jet periphery during the ignition delay period. Fuel consumption rate is dictated by mixing layer dynamics, laminar flame speed, large scale turbulence intensity, and local jet penetration rate. The second stage of the model is also a time scale approach which is explicitly controlled by the global mixing rate. Fuel-air preparation occurs on a large-scale level throughout this phase of the combustion process with each mixed fuel parcel eventually burning at a characteristic time scale as dictated by the global mixing rate. Overall, many key engine parameters are explicitly and implicitly included in this two phase combustion model such as load, speed, injector characteristics, limited geometry, fuel properties, etc. Experimentally determined net heat release rate profiles have been generated for both a special single cylinder research engine and a production-type multi-cylinder engine over a multitude of operating conditions and compared to the proposed model. The initial results have demonstrated great promise in predicting both phasing and magnitude of the premixed and mixing controlled phases of the net heat release rate profile.