Simulation And Optimization Of Working Process For Miller Cycle Natural Gas Engine

As new energy Engines Natural Gas Engine has developed very rapidly in recent years, but there exist some problem such as the combustion knock and the low thermal efficiency, in that way, there is an urgent need to study the more efficient Natural Gas Engine. The use of Miller Cycle technology in Natural Gas Engine can not only improves the compression ratio without combustion knock and improves the thermal efficiency of the engine, but also can reduce the NOx emissions significantly to meet the increasingly stringent emission regulations. In this paper, on account of the current research status of domestic heavy-duty Natural Gas Engine, using simulation technology to simulate the working process of Miller Cycle Natural Gas Engine, and verified the working process by experiment. Some work has been done on these problems as follows:(1) A one-dimensional simulation model of Natural Gas Engine was established based on GT- Power software, we analysis the performance of engine and thermodynamic parameters under different rotating speed, and the cylinder pressure of each cylinder and the heat release rate, the results show that the simulation model can fit with the experimental results well.(2) Based on the simulation research on geometry compression ratio and intake phase of Natural Gas Engine,found the law that the effects of two parameters on the performance of Natural Gas Engine. Studied the effects of expansion ratio on engine thermal efficiency and gas consumption rate with a fixed effective compression ratio, and found out the optimum expansion ratio for Miller Cycle.(3)As for the problem of the decline of the power performance of Miller Cycle, studied the air intake system of engine and the influence of different EGR rate on the engine performance, and optimized the reasonable basic parameters for the Natural Gas Engine used Miller Cycle. Analyzed the design, dynamic performance and the performance differences of Miller Cycles which taken the plan of intake valve shut early or late, and the bench test validated Miller Cycle and compared it with the different performance of the Otto Cycle.(4) Simulated and analyzed the performance of the Miller-cycle Gas Engine based on one-dimensional model, and the experimental verification of prototype engine was conducted. The study found that the coupled of Miller cycle and EGR could broaden the knocking boundary effectively, improve engine thermal efficiency 1-2% at low or middle speed and reduce the machine heat load significantly, it can also reduce NOx emission effectively. Therefore, the application of Miller Cycle has great significance on improving the Gas Engine’s economic performance, reliability, and reducing emission.