Optimization of multiple fuel injection events in a common rail diesel engine for low temperature combustion

As one of the many strategies being researched in order to reduce NO x and particulate matter formation, low temperature combustion works without the need for excessive after-treatment equipment. This paper is divided into two main parts. First, a computational model that simulates the thermodynamic response of a 2.0 L multi-injection direct injection diesel engine was developed. The second part of the research involved optimization of each of the fuel injection events in order for the engine to operate in the low temperature combustion region.Two objective functions were identified to optimize the injection events. The first maximized the peak cylinder temperatures, and the second minimized the difference in work output between a single injection and multiple injections. A constraint on the first objective function was established with a temperature limit of 2000 K, which is the definition of low temperature combustion.The computational model, created in Matlab 7.0 (Mathworks, Inc.), was validated with data provided by a simulation of a 2.0 L diesel engine using commercially available software, Virtual 4-Stroke. The simulations were compared against identical engines with single-injection strategies and showed good agreement. For the multi-injection simulation, the heat release rates (HRR) of each injection were governed by an equation found by regression fitting HRR with gas temperatures, cylinder volume and air-fuel ratios. The equation showed good agreement when used as a single-injection HRR limiter therefore, it was also used for multi-injections. The final results provide an optimized injection strategy that achieves low temperature combustion.