Fundamental Study Of Flame Acceleration Generating Pressure Wave And Flame-Pressure Wave Interaction In Confined Space

Knock is a prominent constraint on the efficiency of downsized spark ignition engines,which will induce intense pressure oscillations and make damage to engine.There are two main theories about the mechanism of detonation in combustion: the end gas autoignition theory and the detonation theory.Both theories suggest that detonation is related to the flame-pressure wave interaction,and pressure wave is generated by the flame acceleration.The present work is conducted in a newly designed constant volume combustion bomb using optical methods and theoretical analysis.The objective is to investigate the flame acceleration generating pressure wave and the flame-pressure wave interaction,providing a reference for the detonation mechanism.The process of laminar flame converting into turbulent flame accompanied by pressure waves was investigated in a newly designed constant volume combustion bomb by using different perforated plates.It is found that the process of flame acceleration through the perforated plate can be divided into three stages: laminar flame,jet flame and turbulent flame.The formation mechanism of pressure wave is analyzed in the view of gas dynamics: the flame propagation in combustion chamber is an acceleration process after orifice plate and thus generates several compression waves ahead of the accelerated flame front.Gradually,the compression waves coalesce with other and thus forms a clear pressure wave.Then the author studied the lame acceleration generating pressure wave in confined space by changing initial conditions.It is found that the flame acceleration intensity with different fuels declines in the sequence of hydrogen/acetylene/methane/propane.There are there perforated plate locations according to the distance between the spark plug and the perforated plate.It is found that the flame acceleration is the most obvious in the middle perforated plate location,accompanied by the pressure wave.Note that no pressure wave can be seen in another two locations.The flame propagation speed and the in-cylinder pressure fluctuation intensity increase with the initial pressure.In addition,the numerical simulation was carried out to investigate the flame acceleration through the perforated plate in confined space,further verifying the experimental results.According to the experimental results of flame acceleration,hydrogen was selected as the fuel and the perforated plate was installed in the middle position to investigate the turbulent flame-pressure wave interaction in confined space.The experimental results show that the reflected pressure wave will interact with the turbulent flame causing the flame front to stop or even reverse.The flame-pressure wave interaction will increase the surface area of the flame and accelerate the flame propagation again.Then the author studied the effect of different initial conditions on the flame-pressure wave interaction.It is found that the velocity of turbulent flame propagation,the pressure wave intensity and the amplitude of pressure oscillation all increase with the increase of initial pressure.The dilution of inert gas can constrain flame propagation,pressure wave generation and pressure oscillation in cylinder,with the inhibiting effect declining in the sequence of carbon dioxide/nitrogen/argon.In summary,the constant volume combustion bomb with perforated plate was designed.The processes of flame acceleration,pressure wave generation and flame-pressure wave interaction were studied in detail.The effect of different initial conditions on these combustion phenomena was also analyzed based on the experimental results.Thus the present work attempts to provided theoretical support for the prediction and suppression of engine knock in the view of flame-pressure interaction.