Simulation Study And Optimization Of Combustion Chamber In Large Bore Nature Gas Engine

Under the pressure of the energy of supply crisis and the serious pollution of the environment,seeking alternative fuels for internal combustion engine has become an urgent and important issue in the study of internal combustion engine.Due to its abundant resources,clean combustion and low CO2 emission level,natural gas has been widely used on internal combustion engine.In this paper,there is a problem of power shortage and poor economic performance for a certain engine to burn natural gas,this article emphasizes on the above problems by means of experiments and simulations with a large diameter natural gas engine to improve the economy and power.(1)In order to study the influence of compression ratio on the performance of large diameter gas engine and cylinder combustion process.To increase the compression ratio from 10.5 to 11,the top clearance has been decreased from 10.5mm to 9.3mm,taking advantage of GT-Power and AVL-Fire to establish simulation models of large diameter gas engine under the condition of compression ratio ? =11.Calculating the indicator diagram and heat release rate by in-cylinder combustion model,getting the MBT to lay the foundation for the GT-Power model.With the help of simulation models to research the influence of compression ratio on the performance of large diameter gas engine and cylinder combustion process.The whole performance simulation results show that: when the compression ratio increased from 10.5 to 11,under the condition of speed n=1000r/min,excess air a? =1.6,100% load,not only the power but also the fuel economy improved.The indicated thermal efficiency increased from 34.83% to 36.88%,increased by 5.89%.The maximum pressure in the cylinder rises 20.77% and the peak value is closer to the top dead center,the break specific fuel consumption is reduced from 224.07g/(kW·h)to 213.54 g/(kW·h),reduced by 4.70%.The in-cylinder combustion process simulation results show that,the higher compression ratio,the faster flame propagation,the higher maximum value of in-cylinder temperatures and NOx emissions and the earlier moment to appear NOx.When the combustion tends to end,temperature in the cylinder began to decrease,and the higher compression ratio,the faster temperature decrease.(2)To study the influence of combustion chamber shape on the performance of large diameter natural gas engine.Based on the compression ratio ? =11 as the target value,two kinds of combustion chamber shape named NO.2 and NO.3 are designed under the condition of the original engine combustion chamber.A simulation model has been established with AVL-Fire.The simulation results show that: under the condition of speed n=1000r/min,excess air a? =1.6,100% load,the ignition angle of NO.2 and NO.3 combustion chamber are 26 °CA BTDC,28°CA BTDC.Both the combustion process and flame propagation improved.Compared to NO.1 combustion chamber,maximum value of pressure in NO.2 and NO.3 increased by 10%,5.2%,NO.2 and NO.3 indicated power were increased by 3.16%,1.74%;NO.2 and NO.3 combustion chamber indicated specific fuel consumption were decreased by 2.2%,1.43%,so NO.2 combustion chamber for engine power and economy promotion effect is more obvious.To validate the simulation calculation of reasonable and feasibility under the condition of speed n = 1000 r/min,excess air a? = 1.6,full load.The big diameter using the NO.2 combustion chamber gas engine has been taking a test analysis,through experimental and simulation value comparison shows that: the relative error between the simulation result and the experimental value is within the reasonable range of 5% which indicate that the simulation calculation is reasonable and feasibility.