Study On Excellent Anti-knock Fuel Blending And Knock Prediction For Turbocharged Gasoline Engine

Turbocharged engine combined with direct injection in cylinder improves the thermal efficiency,but knock combustion inhibits its development.At the same time,in order to reduce the emission of pollutants,gasoline is required to be cleaner.The aromatic and olefin in gasoline have higher octane values,but they may increase harmful pollution such as soot.Therefore,this paper studies the optimization of the composition ratio of the high-strength engine under the new gasoline standard.Therefore,within the range of gasoline standard,the reactivity of gasoline components was studied based on gasoline PONA analysis results,and various knock evaluation indexes were compared in a turbocharged direct injection gasoline engine model to study the influence of each component on engine knock combustion.In this paper,PONA analysis is carried out on finished gasoline with different octane values in different periods.It is found that with the further strict requirements of gasoline standard,the content of aromatic and olefin in gasoline decreased significantly.On this basis,the octane numbers of the fuels with different molecular structures of the same group were compared,and the reactivity of the components with more content,the characterized components and the mixed fuels were qualitatively studied.The results show that in order to improve RON,isopentane and other isopentane should be increased in fuel;low RON fuel,high reactivity under high pressure conditions.However,the fuel with the same RON has a great difference in reactivity.Therefore,RON cannot be used as the only criterion to judge the antiknock property of fuel.By comparing CFR engine and modern SI engine,it is found that the pressure in the cylinder is greatly different under the same working condition,so the fuel anti-knock property needs to be re-evaluated in modern engine.A three-dimensional model of turbocharged direct injection gasoline engine was established.Three knock evaluation indexes based on pressure shock were compared and verified from heat release rate,temperature field,velocity field,free radical concentration and other aspects according to the rule of knock intensity increase by decreasing rotational speed.Results show that high frequency pressure oscillations can accurately characterize and quantify the knock combustion situation(knock point and knock severity),on the other hand,put a sudden high heat,hot result in higher temperature,cylinder wall in cylinder wall and the fluid flow rate increases,HCO radicals at the end of the mixture of appears as a symbol of knock occurs.In order to blend the fuel with excellent knock resistance,the influence of each component in the gasoline on the knock combustion of modern gasoline engine was analyzed,and BP neural network was established based on a large number of data,with the correlation coefficient of 0.9967,to predict the in-cylinder combustion of the fuel with different component ratio(the peak pressure and the maximum amplitude of pressure oscillation).The results show that within the range of component proportion required by the national gasoline standard specification,when the mass fraction of isooctane is 47%,n-heptane is 0,toluene is 35%,diisobutylene is18%,the maximum pressure in the cylinder is the smallest,and the MAPO value is the smallest,that is,the anti-knock property of the fuel is the best.