Development of global mixing, combustion, and ignition models for quiescent chamber direct-injection diesel engines

A large scale mixing and combustion model has been developed and studied through testing of two separate direct injection diesel engines. As a corollary, a shear layer ignition model was also developed for estimating the effects of key engine-related parameters on autoignition. Both models were developed for eventual inclusion into an engine cycle simulation for studying the effect of various key engine design parameters on overall power plant performance. The combustion model is comprised of two phases whose general behavior is characterized by a transient, representative time scale indicative of global mixing rate, mixing length scale, in-cylinder thermodynamic condition, and fuel properties. During the initial premixed phase, a mixing layer located on the injected fuel jet periphery is allowed to ignite and subsequently burn as controlled by the flame spread entrainment rate. After a determined delay, the second or mixing controlled phase is initiated and burns at a rate controlled by mixing, air utilization, impingement, and jet expansion. The shear layer ignition model is a transient, one-dimensional approach which accounts for fuel-air ratio stratification in the aforementioned mixing layer through assumed temperature and fuel specie profiles whose general shape is dictated by the conservation of energy.; The first engine employed in this study was a Cummins VTA903 while the second engine was a heavy duty, Detroit Diesel (DDC) Series 60. In-cylinder pressure data was acquired for each engine and further analyzed using a commercially available thermodynamic engine cycle analysis code for net heat release rate analysis. Each engine was also instrumented to provide key details about the injection event such that reasonable estimates for autoignition were available for comparison with the proposed shear layer ignition model. Over a broad range of operating conditions for both engines, the mixing and combustion model exhibited predictive capability compared to experimentally determined net heat release rate profiles. Similarly, the shear layer ignition performed in an acceptable manner demonstrating superior performance compared to published empirical ignition delay models for diesel engines.