Simulated Study On Effect Of In-cylinder Flow Field Structure On Natural Gas Engine

In this paper,we research the impact on the mixture formation, combustion and emissions of the natural gas engine taking by combustion chamber structure and swirl ratio when the engine speed is 1500r/min, 100% load, the ignition advance angle is 30 o CA before TDC.We design four kinds of combustion chamber, the squish ratio are 29%,48%,50% and 54%.We study the impact of different combustion chamber shape on the combustion of the natural gas engine. The results show that at the beginning of the compression stroke, combustion chamber shape has almost no impact on the distribution of the velocity field. With the piston moving up, squish and turbulent flame become main factors on the effect of the flow field. In the four kinds of combustion chamber shape,the squish area of the necking shape is the largest. Stronger squish is conducive to generate more turbulent kinetic energy, and it has more room at the same crank angle. Therefore, the burning velocity is the fastest. While the pit of the shallow dish-shaped combustion chamber is shallow, As the piston moving close to the TDC, The flame can only develop in a small space, so the burning velocity is the slowest. The performance natural gas engine by using deep pit-shaped and straightω-shaped combustion chamber performance is between the neck-shaped and shallow dish-shaped combustion chamber.We study the impact of different swirl ratio on the performance of the natural gas engine. The results show that the velocity field and turbulence field have a similar distribution when the swirl ratio is different. But with the swirl ratio increasing, velocity of gas in the cylinder increases, the best swirl ratio is different because squese and turbulence play different roles at different crank angleThe maximum turbulent kinetic energy appears in the swirl ratio of 1.5 when the crank angle is 330oCA while The maximum turbulent kinetic energy appears in the swirl ratio of 3 when the crank angle is 360oCA. This shows that we can get more turbulent kinetic energy by using a large swirl ratio with the increasing in squish.But hige swirl ratio can lead to increasing in heat loss, it is not conducive to generate fast-burning for natural gas engine. It can improve combustion of the natural gas engine which chamber is neck-shaped.However,It leads to NO emission increasing.