Effect Of Combustion Chamber Shape On Performance Of Natural Gas Engine

As a kind of fuel for motor, the natural gas has the advantages of low pollutant emissions and high economic efficiency. It has prominent significance to improve the environment condition and solve the energy issues by developing CNG (Compressed Natural Gas) vehicle, however, there are two main problems on application of natural gas in the car. One is the performance of engine drops significantly, the other is the thermal efficiency is low and the economic performance is far from satisfactory condition. Therefor, the scholar in and abroad make a lot of research, and obtain much new technique. Such as the in-cylinder direct injection technology, the exhaust gas recirculation (EGR) technology, mixed the hydrogen to natural gas engine technology and so on. How to improve the performance of natural gas engine by ameliorating combustion is the purpose of this research. Research what effect dose the combustion chamber shape have on the performance and combustion process of the CNG engine. The former simulation result analyzed and predicted the changes of turbulence parameters, the concentration of mixture, the temperature distribution, cylinder pressure distribution and the concentration distribution of various products of combustion in intake stroke and combustion stroke. The result shows that combustion chamber shape has an great effect on the performance and combustion process of the CNG engine. Then, designed a crisscross combustion chamber after optimize many factor. How to checkout the simulation result by experiment will be detailed discussed in this thesis.Based on CA6SE1-21N heavy duty CNG engine with turbo charged and inter-cooled technique produced by FAW Group Corporation, the experiment is made to compare with the difference between the crisscross combustion chamber which is designed by former numerical simulation and original combustion chamber(column combustion chamber ). Then, study the law how combustion chamber shape affects CNG engine combustion and emissions through the experiment. The main data need to measure including: the wastage of natural gas and air, the temperature and press of the exhaust gas, the press in the cylinder and pollution emissions such as NOx,CO,HC etc. After analyze the data, the law how combustion chamber shape affects CNG engine combustion and emissions was found:1. The combustion efficiency in the crisscross combustion chamber is higher and the temperature of the exhaust gas is lower than that in column combustion chamber. The tiptop of the combustion press is higher in crisscross combustion chamber,and the position of the crank angle correspond to that tiptop , crisscross combustion chamber is at the behind of column combustion chamber. In the initial period of combustion,the average temperature in the cylinder have little difference in both combustion chamber, only some load the average temperature is lower in crisscross combustion chamber. The crisscross combustion chamber gets a remarkable higher the average temperature than the column combustion chamber in the main combustion period. The heat release rate in crisscross combustion chamber is lower than that in column combustion chamber in the initial combustion period, but in the main combustion period it's opposite. The tiptop of the heat release rate in crisscross combustion chamber is almost 13% higher than that in crisscross combustion chamber, and the heat releases more concentrated in crisscross combustion chamber.2. There are four ribs in crisscross combustion chamber, the combustible mixture flows towards to the rib and then along the cylinder wall. The impact between the flow and the cylinder wall strengthen the turbulent kinetic energy of the cylinder, although it's harmful to form a stable flame kernel, it can help accelerat flame propagation speed and enhance combustion speed when the flame is stable, and help burn the natural gas mixture completely. The combustion duration are shorter in crisscross combustion chamber. The timing of combustion in crisscross combustion chamber has little difference with column combustion chamber,but combustion termination and center of heat release rate in front.3. The quality of HC in the the exhaust gas is depend on the size of Cycle-to -cycle Combustion Variations which have slightly difference between the two combustion chamber,so The quality of HC in the the exhaust gas almost the same, but still, the quality of HC in crisscross combustion chamber is lower. Smaller fuel consumption rate results to a lower quality of CO and CO2 emission in crisscross combustion chamber. Combustion chamber shape have a remarkable influence on the NOx emission, a higher average combustion temperature , a advanced center of heat release rate determine a lager amount of NOx emission. The concentration of NOx in crisscross combustion chamber are about 40% more than that in column combustion chamber.The result shows combustion chamber shape have a remarkable influence on CNG engine performance. The combustion in crisscross combustion chamber is improved, the speed of combustion is accelerate and the combustion efficiency enhanced, also, EGR technology can eliminate the high concentration of NOx emission brought by improved combustion.