Research On Combustion Process In Cylinder Of Large Bore Nature Gas Engine By Using Numerical Simulation

Facing increasingly severe environmental pollution and energy crisis, natural gas as an automotive alternative fuels have greater advantages, therefore, the research and development of natural gas engines are more and more attention. Study of the combustion process of the gas engine and combustion mechanism has an important theoretical significance to enhance the overall natural gas combustion theory.Experimental research and numerical simulation are two effective means of research on natural gas engines. The numerical simulation is short-time, low-cost, easy modification, and is able to provide more burning microscopic information. Numerical simulation of the combustion process of a gas engine is used in this article.By coupled the simplified kinetic reaction mechanism of methane to the CFD software, this paper simulates the combustion process of a large bore natural gas engine cylinder. The calculation and experimental results are consistent, showing the selected model suitable for this engine simulation analysis. By analysis the main combustion chamber temperature field, the velocity field, flame propagation and combustion intermediates, this paper gets that eight tubes which connected to the main combustion chamber and the pre-combustion chamber, can make the high-speed flame injected into the main combustion chamber. The flame injected from the tube quickly spread to the main combustion chamber along each direction, but at a low level due to the vortex flow, resulting in a small amount of natural gas lag burning.Based simplified the kinetics of the reaction mechanism, six different pre-combustion chamber structure are designed in this paper, the results show that: when the circumferentially arranged more connecting pipe, flame spray may interfere with each other, which is not conducive to the spread of flame in the main combustion chamber. Comparing to weeks to the different number of connecting pipe, the flame propagation are more sensitive to the connection pipe diameter. For larger diameter more fuel combustion at the same time. The smaller diameter tube may decrease the flame propagation. Selecting the appropriate connection tube angle, can effectively improve the speed of propagation of the flame in the main combustion chamber. Several different compression ratio, the ignition timing and the mixed gas concentration were designed and compared to the original model. The calculation results show that:Increasing the ignition advance angle appropriately can reduce fuel lag burning. Diluted mixed gas can reduce the amount of emissions, but too much, it will make flame propagation in the main combustion chamber slower. Over-rich mixture will make cylinder pressure increases rapidly, NOx emission will substantial increase.