Low End Performance Improvement by Effective Use of Multiple Injection Strategy in Common Rail Diesel Engine

Abstract

Main advantages of diesel engine are low fuel consumption coupled with high specific power output. However, benchmark Noise, Vibration and Harshness (NVH) of its counterpart (Gasoline), future stringent emission norms and overall system cost poses tough challenges. In a growing market like India, these benefits of diesel attract the buyer over its counterpart. Diesel engines are known for its heavy visible black smoke. The black smoke formation is more prominent in lower engine speed. This is due to lower injection pressure and the system limitation in conventional injection system and less air availability. Introduction of the common rail injection technology overcomes this difficulty by allowing the injection pressure to build irrespective of the engine speed. However, improving the air flow is a challenge. Generally waste gate turbo chargers are optimized for higher engine speed to match the rated engine performance, but compromising the lower engine speed performance. The use of Variable Geometry turbo charging (VGT), increase in number of valves per cylinder, two stage turbo charging are some of the solutions to this problem but it involves additional cost and fundamental design changes. Hence, it was a challenge to come up with a strategy to overcome this problem without any cost impact. Multiple injection strategy is one of the tools which improve the engine torque without the penalty of smoke. In this paper, a Multi Utility Vehicle (MUV) powered by a 2.5Ldiesel common rail engine, low end performance was effectively improved by this strategy. Current engine has BOSCH 2nd generation common rail system with waste gate Turbocharger. Torque at full load in lower engine speed was improved by introducing the early pilot with relatively higher quantity. However, in the part load, this pilot quantity was split into two successive pilot injections. Selection of pilot separation was optimized in such a way that Noise and Smoke levels are maintained or improved. In part load, improvement in smoke and BSFC was achieved without sacrificing noise level. Engine level trials were conducted with cylinder pressure and Noise Measurement with AVL Indicom. The Concept of Design of experiment (DOE) was used to minimize the number of iteration and for analysis of results. The vehicle performance, pass by noise were found to be improved.