Visualization Study On Constant Volume Combustion Of Gasoline In Nitrogen Free Environment

The contradiction between oil supply and demand has become increasingly prominent,at the same time,the pollution caused by vehicle emissions has become more and more serious,therefor,energy conservation and emission reduction and the enhancement of engine performance have become an important direction for the development of internal combustion engines.With the continuous advancement of internal combustion engine technology,more and more new technologies are being applied to internal combustion engines,while the application of turbocharging technology can save energy and reduce emissions and enhance engine performance,it also increases its cost;Oxygen-enriched combustion can enhance engine performance,but it will cause a sharp increase in NO_x content in the exhaust gas;Based on the idea of engine oxygen-enriched combustion and internal combustion Rankine cycle,this paper puts forward that nitrogen-free combustion of gasoline engine,that is,gasoline is burned in an atmosphere free of nitrogen（O₂/CO₂）.The combustion of gasoline in a nitrogen-free atmosphere can produce rough work and heat loads.In this paper,based on the constant volume combustion optical test platform,the combustion process control strategy and key technical problems of gasoline burning in nitrogen-free atmosphere are studied,this paper mainly studies the combustion characteristics,flame propagation characteristics and emission characteristics of gasoline burning in nitrogen-free atmosphere with boundary conditions such as initial oxygen concentration,cyclic fuel injection,and excess oxygen coefficient,also this paper studies the relationship between the combustion pressure rise rate and the knocking combustion,and how to control the combustion pressure increase rate by adjusting the boundary conditions,so as to effectively suppress the occurrence of knocking.The pressure rise rate can be obtained by derivative of cylinder pressure data which has been filtered by the b2b wavelet filter,according to the first law of thermodynamics,the combustion heat release rate can be obtained by the pressure rise rate,the ignition delay and the combustion duration can be obtained from the heat release rate;the flame propagation distance and the flame propagation speed can be obtained from the combustion flame image,combustion end flame image and combustion knock intensity are used to determine whether knocking occurs.The results are as follows:Gasoline burns in nitrogen-free atmosphere that can prevent NO_x production,at the same time the concentration of CO₂ in the tail gas after cooling is high,which can be easily collected and reused,so it is expected to achieve ultra-low emissions.When the initial oxygen concentration increases,the pressure increase rate and the combustion heat release rate increase significantly,the HC content in the exhaust gas decreases,the flame propagation speed increases,the flame brightness increases,and the combustion is intense,as the load increases,the initial oxygen pressure increases,the combustion becomes more intense,and knocking is more likely to occur.When the excess oxygen coefficient increases,the pressure rise rate and the combustion heat release rate gradually decrease,the HC content in the exhaust gas remains basically unchanged,the flame propagation speed decreases,the knock intensity decreases,and the knocking tendency decreases.The rate of pressure rise is closely related to the detonation combustion.The higher the rate of pressure rise,the higher the intensity of detonation,the higher the tendency of detonation,and the more likely the detonation occur,when the pressure increase rate is less than 1.7MPa/ms,the knock intensity is less than 1MPa,which can effectively suppress the occurrence of knock.Gasoline burning in nitrogen-free and oxygen-enriched conditions can achieve higher pressure rise rate and combustion heat release rate,under normal combustion conditions,the higher pressure rise rate and heat release rate can improve the engine dynamics and economy,and enhance engine performance,but it will not cause NO_x increase.At the same time,when the excess oxygen coefficient and initial oxygen pressure are fixed,by improving the intake oxygen concentration of the engine,it can also improve the engine cycle fuel injection volume,so as to improve the engine power per liter.