Investigation On Parameters Adjustment Of Fuel-supplying And Air-intaking Systems For Diesel Engines Working At Plateau Environment

In China, the plateau terrain covers considerable areas. At the plateau area, the usage of diesel engines is limited by the low density of atmospheric, which leads to the deterioration of power, economics, reliability and emission. Based on experiments and simulation results, several schemes of fuel-supplying parameters adjustment and improvement of supercharging system were proposed in this paper. Advantages and disadvantages of the above schemes were analyzed, and meanwhile the feasibility evaluation and key points of each solution were indicated.Conducting the diesel engine bench-test at simulated plateau environment, the procedures of such tests were summed up. Besides, experience of experiments were presented such as: surge prevention, inject timing determination and data verification. After that, the influences of plateau environment and operating parameters on engine performance were analyzed.By combining the predicting ability of neural network and the efficient computing of zero-dimension combustion model, a combustion model called “Predictable 0-D Combustion Model based on Neural Network” was proposed. During the RoHR(Rate of Heat Release) fitting process, several constraints were put forward to solve the multi-solution proble m, based on the physical perspective of each parameter. Through deriving the error transfer process in calculating RoHR, the theoretical feasibility of the modeling method was verified. Compared to test results, the predicting accuracy of this model and the modeling method were validated. Sub models of the diesel engine were validated by experiment data, where the model with the ability to predict the engine performance at plateau was established based on GT-SUITE.The influences of fuel-supply parameters on engine performance were analyzed. After that, the optimization scheme of fuel-supply parameters based on GA(Genetic Algorithm) and performance-simulating was carried out. Considering the adaptability of diesel engine at plateau, a parameter to quantify the margin of compressor surging was proposed. Then, the fitness function for GA was put forward, which brought a method of determining penalty parameters, called “Fitness equal to Zero at the Worst Point”. Based on the GT-SUITE and MATLAB joint simulating platform, the optimization model of GA and performancesimulating coupled was established. The optimized rated power and BSFC at plateau of 4500 m are 14.7% higher and 9.6% lower than the values of the original respectively.According to several typical adjustable supercharger systems, relevant simula tio n projects were carried out, and main conclusions are as follow:l Applying VGT(Variable Geometry Turbocharger) alone will not do much for thediesel engine with limited turbocharger-matching allowance.l The matching method of Sequential Two Stage Turbocharging system was proposed,which is characterized by considering both plain and plateau conditions. The ratedpower and the max torque at 4500 m altitude are 13.4% and 19.8% higher than thevalues of the original respectively. However, the torque is 27.9% lower than thevalue of the original @1000r/min. The capacity of power recovery at plateau mainlycomes from LP(Low Press) compressor. The HP(High Press) compressor mainlytakes the tasks to enhance the intake pressure and to prevent surge at maximumtorque point.l The application of supercharger-turbocharger compound system on plateau wasexplored. Scheme B(a series system with a turbocharger at first stage and asupercharger at second stage) was proved to be efficient on power recovery atplateau. The rated power and the max torque at plateau of 4500 m are 11.75% and12% higher than the values of the original respectively. Moreover, the torque is 33.5%higher than the value of the original @1000r/min.Finally, based on the advantages of supercharging systems, the SAC(Speed Adjustable Compound supercharging system) was proposed, which employs a series system with a speed-adjustable supercharger at first stage and a turbocharger at second stage. The most prominent feature of SAC is the ability to adjust the supercharger speed according to working conditions. With SAC, the rated power and the max torque at plateau of 4500 m rise by 10% and 12% than original values respectively. Meanwhile, the torque increases 32% @1000r/min. And significantly, the time of the start process is shortened by 20%.