Numerical Investigation On The Combustion System Development For Direct Injection Of Heavy Fuel In A SI Aviation Piston Engine

With the increasing demand for single-fuel application strategy,the use of heavy fuel in aviation piston engines has become an inevitable trend in future engine combustion system design and development.Heavy fuel features high cetane number and high viscosity,results in challenges in fuel atomization,and high knocking propensity in ignition type aviation engines.The use of direct injection technology can improve the atomization quality of heavy fuel,and effectively suppress knocking by introduce strong mixture stratification,leads to improvements in both combustion efficiency and power output of aviation heavy fuel engines.In addition,the loss of fuelair mixture caused by scavenging short circuit can be reduced by the controlling of injection timing.Therefore,the current focuses on the design and development of a direct injection heavy fuel piston aviation engine combustion system based on a light fuel spark-ignited two-stroke piston aviation engine through numerical simulations.First,a heavy fuel direct injection combustion system was designed based on the base engine,and the effects of fuel injection timing and ignition strategy on combustion and knock of a two-stroke direct injection spark-ignition(DISI)engine fueled with heavy fuel were evaluated.The results show that the direct injection combustion system can increase the airflow velocity,thereby accelerating fuel diffusion and flame propagation.The knock intensity(KI)and indicated mean effective pressure(IMEP)all decrease with the retardation of the injection timing and spark timing.With the retardation of the injection timing,a much richer mixture gradually gathers towards the center of the cylinder,the low combustion efficiency due to the reduced time for fuels to evaporates and mixtures and the power recovery rate can only reach 73%.By using asynchronous ignition,the power recovery rate can reach 83.5%,which can meet the basic power requirements of the engine.Then,the strategy of increasing power output was explored.It was found that the effect of injection timing on IMEP is greater than that of spark timing by using the coordinated control strategy of ignition and fuel injection.Adopting the strategy of advancing injection timing and retarding spark timing can make the power recovery rate reach 88.57% and the indicating thermal efficiency(ITE)increased 5.72%compared to the baseline engine.Increasing the intake pressure can increase the quality of fresh air,make the combustion more sufficient and improve the combustion efficiency.Meanwhile,under the same heat release conditions,the maximum incylinder temperature decreases due to the in-cylinder charge density is increased,which can suppress knocking.Without considering the influence of supercharging technology on the power-to-weight ratio,the power recovery rate can be improved to 111.5% at the intake pressure of 1.4bar.In addition,although the power output is improved by increasing the compression ratio,the knock tendency of the engine is improved more obviously.Therefore,it has limited potential to improve the power recovery rate of heavy fuel direct injection engine.In summary,through the design and optimization of combustion system based on offset combustion chamber and in-cylinder heavy fuel direct injection system,the combustion optimization and power recovery control strategy of fuel injection and ignition coordination is proposed in this paper.The power recovery rate of heavy fuel engine can reach 88.57%,and the ITE increased 5.72% compared to the baseline engine.The results have high engineering guidance value for the development of efficient aviation heavy fuel piston engine.