Optimization Research Of The Low Speed Torque Performance Of An Automotive Diesel Engine That Meets China Stage V Emission Standards

With the energy problem and environment problem becoming increasingly serious, the development of the high-efficiency and clean diesel engine has became an important task in the engine research. Turbocharger is a basic part of modern diesel engine. The turbocharger can't supply enough fresh air at low speed because of the lack of exhaust energy which causes the low speed torque problem.The optimization research of the low speed torque performance was carried out on an automobile diesel engine that meets China stage V emission standards in this paper. The AVL-BOOST simulation model was built and the basic theory of the software was analyzed deeply. Three turbocharger solutions were proposed based on the boosting target requirements. Later, a BorgWarner turbocharger was selected according to the detailed simulation results based on the AVL-BOOST model. The test results showed poor intake ability of the engine at low speed that the excess air ratio at 1000r/min was only 1.09 so that the smoke exhaust was too high to meet the emission standards.The valve timing of the turbocharger engine was analyzed based on the simulation model. After studying the influence of the valve timing on performance,an optimization model was set up to obtain nice performance at both low and high speed.Then the maximum valve lift was also determined based on the simulation model.The intake and exhaust valve train model were established with AVL-EXCITE Timing Drive. New cam profiles were designed using high-order equations on the basis of the valve timing and maximum valve lift calculated by the thermodynamic model. Through kinematic and dynamic calculation, it was found that the valve train with new cam profiles performed both stability and reliability and it could meet all requirements.Camshafts with new designed cam profiles was trial-produced. Then the test results showed that the engine with the new camshaft performed better at low speed. The excess air ratio at 1000r/min increased to 1.2 and the smoke exhaust decreased considerably. The torque could reach 220N·m at 1000r/min under the condition of meeting emission standards, while the fuel consumption at high speed increased by about 10g/kW·h which was acceptable.