Optimization of supercharger and injection parameters for diesel engine at plateau

Abstract: Supercharge and fuel injection are direct factors to improve the performance of diesel engines at plateau. When diesel engines are used at higher altitudes, especially in the Qinghai-Tibet plateau region with the altitude ranging from 3000 to 5000 m, the decreasing ambient pressure and temperature reduce the air inflow resulting in deteriorating combustion, reducing power output, increasing fuel consumption, worsening emissions, exceeding cylinder pressure, cylinder pressure, thermal load and turbocharger speed limits. The optimization of injection parameters can improve the plateau combustion process of diesel engine to some extent, however, optimization of injection parameters alone cannot fundamentally solve the problem of insufficient intake and power decline of diesel engines at plateau. Two-stage variable geometry turbocharge (VGT) system is an effective way to increase the intake pressure effectively. However, only optimizing the control parameters of the supercharging system without adjusting the injection parameters will lead to the problem of "improper oil and gas coordination" at high altitude, and the plateau application potential of the two-stage variable geometry turbocharge system cannot be fully play. Recent researches mainly focused on optimizing injection parameters or two-stage variable geometry turbocharge system, there was few about the comprehensive optimization of supercharger and injection parameters, therefore, the paper focused on optimizing the compositive control strategy of supercharge and injection parameters. In the paper, a GT-Power model of a two-stage variable geometry turbocharged (VGT) diesel engine was built and verified by experiment on engine plateau environment simulating testing bed. The simulation performance date of the engine was obtained from the model. What's more, the neural network was established and then trained with these simulation values to improve the power performance of the engine, and finally the optimization rules and comprehensive control strategy of supercharge and injection parameters were obtained. The results showed that: The optimized circulating fuel injection quantity had similar variation trend with the original parameters. What was different was that the circulating fuel injection quantity increased after optimizing, the increment came to its maximum at lower speed and its minimum at speed of maximum torque, and it showed a trend that the increment quantity gradually increased from the speed point of the maximum torque to both sides. With the increase of altitude, the optimal cycle fuel injection quantity of the engine decreased gradually, and the decreasing trend increased gradually with altitude increasing. The circulating fuel injection quantity decreased by 10.96% on average from 0 to 3500 m, and by 16.99% on average from 3500 to 5500 m. At a certain altitude, the optimal injection advance angle of the engine decreased first and then increased with the increase of speed, and the average value of the optimal injection advance angle increased with altitude increasing. Compared with the original parameters, the optimum injection advance angle increased by 1 and 1.5℃A, respectively, at low speed conditions of 2500 and 5500 m, however, when it came to higher speed, the optimum injection advance angle decreased by 25.2% and 17.5%, respectively. The optimum VGT opening increased large gradually with the increase of the speed at 0 m, while when it came to 5500 m, it kept invariable at lower speed, and increased firstly and then decreased at higher speed. After comprehensive optimizing of supercharge and fuel injection, the VGT opening and circulating fuel injection quantity increased and the injection advance angle decreased at 0 m. When it came to low speed of 5500 m, the VGT opening kept invariable, the circulating fuel injection quantity and injection advance angle increased, however, the VGT opening and circulating fuel injection quantity increased, the injection advance angle decreased at high speed.