Turbocharger Matching And Performance Optimization Of A Turbocharged Natural Gas Vehicle Engine

As the increase of oil shortage and environmental problems, development of alternative fuel for vehicle engines has become very important. In this paper, turbocharging matching and performance optimization for a 1.5L vehicle CNG(compressed natural gas) engine was performed by using a numerical software GT-Power.Firstly, a 1.5L naturally aspirated compressed natural gas vehicle engine model was established in GT-Power through the GEM3 D discretization method. This method can improve the efficiency and accuracy of modeling effectively. The model was validated against experimental measurements and the maximal error is 3.64%, which meets the demands of engineering applications.Then, a turbocharged engine model was established based on the naturally aspirated engine model. There are six turbocharging schemes for combination of A, B turbines and C, D, E compressors. These six turbochanging schemes were calculated and compared respectively. Results show that the scheme 3 with A turbine and E compressor is the optimal scheme. The bench test results of scheme 3 indicate that the engine perfomance has achieved the scheduled target. The engine maximal torque reaches 190.8 N.m at 2800 r/min and the maximum power reaches 85.9 k W at 5200 r/min. For the chosen scheme, the difference between simulation and experimental results is within 5%, which is within the engineering application permissible error range.Finally, a DOE(design of experiment) approach was conducted to optimize the ignition advance angle. The maximal torque is increase by 9.3% after the ignition advance angle is optimized under the restrictions of peek cylinder pressure and exhaust temperature before the turbine. The ignition advanced angles were also optimized while analyzing different compression ratios at engine full-load and part-load at 2800 r/min. With the increased of the CR(compression ratio), at engine full-loads, the engine torque increased slightly and fuel efficiency decreased slightly. The peek cylinder pressure and exhaust temperature before the turbine changed obviously at low engine speeds which had not reached the limit values, while their changes were not evident at middle and high engine speeds which have reached the limit values. With the increased of the CR at engine part-loads of 2800 r/min, the engine torque and peek cylinder pressure increased, and the fuel efficiency and exhaust temperature before the turbine decreased. The optimal compression ratio is then determined as 12. The ignition advanced angles were also optimized while analyzing different engine excess air coefficients. With the increase of the coefficient under the optimized ignition advanced angle, fuel efficiency showed an increasing trend after decreasing firstly.The best fuel efficiency was obtained when the excess air coefficient was 1.1.