Effect Of Injection Strategy On Combustion Characteristics Of Compound Injection Natural Gas Engine

At a time when oil resources are running out and emissions regulations are tightening,the search for clean alternatives is urgent.Natural gas,as a better alternative fuel of petroleum resource,can effectively alleviate the energy crisis,reduce the pollution and destruction of atmospheric environment,and become a variety of marine engine fuel.The mixture characteristics in the cylinder of natural gas engine have a very important impact on ignition and combustion,but the high pressure direct injection in the cylinder has a high cost,and the traditional inlet injection has a weak ability to control the state of the mixture,which cannot increase the stability of fuel combustion.Now,a compound injection system combining single point and multiple point injection is studied,using the simulation software CONVERGE.The effects of injection strategy and ignition time on engine performance are compared and analyzed,and the optimization scheme is obtained.Firstly,the influence of injection strategy on the combustion characteristic of the compound injection natural gas engine is studied from the perspective of injection ratio and injection time.The combustion phase,in-cylinder pressure,average in-cylinder temperature and NO generation are analyzed in the two-dimensional curve.In the 3D simulation results,the longitudinal section through the spark plug is selected and the appropriate parameter range is set to analyze the concentration field of mixture in the inlet,the concentration field of mixture in the cylinder,the change of flame propagation,the change of OH radical distribution and the concentration field of NO.It is found that the proportional mode with single point ratio of 30%and multi-point ratio of 70% can form a suitable concentration gradient layered mixture,which increases the pressure in the cylinder,optimizes combustion and improves the engine dynamic performance.Based on this ratio,the combustion can be optimized when the injection time is-320°CA,but the generation of NO increases due to the increase of the temperature in the cylinder.Based on the above injection strategy,the influence of ignition time on the combustion characteristic of the compound injection natural gas engine is studied,and the two-dimensional and three-dimensional simulation results are analyzed.The results show that when the ignition time is-48°CA,the combustion can be effectively optimized and the engine dynamic performance can be improved.However,the generation of NO is increased at the same time.The degree of engine optimization is reduced.To sum up,in the scheme of injection strategy coordination ignition time explored,the proportion mode of 30% single point ratio,70% multi-point ratio,-320°CA injection time and-48°CA ignition time can increase the pressure in the cylinder,improve the average temperature in the cylinder,accelerate the combustion rate,effectively optimize the combustion in the cylinder,and improve the dynamic performance of the composite injection natural gas engine.At the same time,the increase of NO generation is also acceptable.