| The energy crisis and environmental pollution become more and more serious.Automobile has a lot of energy consumption and carbon emissions.So its regulations of fuel consumption and emission are also more and more stringent,which puts forward higher requirements for energy saving and emission reduction of engines.It is the most effective method for engine to realize energy saving and emission reduction that improving the thermal efficiency of the engine by appropriately organizing the combustion in the cylinder.The combustion in the cylinder of a SI engine is premixed turbulent combustion.And the turbulence in the cylinder has an important influence on the formation,ignition and combustion of combustible mixture and the propagation of flame.For further study on the influence mechanism of turbulence on flame and combustion,and then appropriately organize the combustion in the cylinder by controlling the turbulence,this paper investigated the influence of turbulence intensity on flame propagation and flame micromorphology through the numerical simulation.An experimental platform of a rapid compression machine has been build.The experiment under different turbulence intensity conditions were carried out based on that platform.The influence of turbulence on ignition and flame propagation process were explored by analyzing cylinder pressure.First of all,the calculation model of the rapid compression machine combustion chamber was established.The combustion process from the beginning of the spark ignition in cylinder was calculated by large eddy simulation in Converge software.Four different turbulence fluctuation were set up by Passot Pouquet turbulent energy spectrum equations.The effect of different turbulence intensity on the combustion and flame were researched.The results show that with the increase of turbulence intensity,the interaction of turbulent eddies and combustion flame are strengthen,the effect of turbulence on the acceleration of flame is enhanced,the combustion phase in advance.With the increasing of the pressure,the accelerate effect of turbulence on flame propagation is more obvious.When the flame propagation to the turbulent flame from the layer flame,turbulent fluctuation around flame becomes more strong,the flame surface becomes more fold because of the effects of turbulence.Secondly,the experimental platform of a rapid compression machine was developed and debugged,in order to verification the influence of turbulence on the combustion from the experiment.The influences of system parameters on the movement of the piston are analyzed.For acquire an ideal piston motion characteristics,the driving pressure has been set up as 1.0 MPa,the number of exhaust port opened has been set up as 5 and the initial pressure is less than 1.4 bar.At the same time,the other functions of the platform had been optimized,the reliability of the platform and the efficiency of the experiment were strengthened.The experimental steps were put forward for standardization.Finally,the influence of the thermodynamic parameters,the equivalent ratio and the ignition time on the combustion were studied on the experimental platform of a rapid compression machine at first.Then the effect of turbulence intensity on the combustion process was studied by using the piston of different structures for achieve different internal flow in the cylinder after compression.The results show that with the increase of initial pressure,generated weakened in the process of piston movement,and the effect of turbulence on combustion under the low initial pressure is more obvious.As the equivalent ratio was 1.0,the enhancement of turbulence on combustion was higher than that of 0.5 and 2.Turbulence has inhibitory effect on the ignition process.When the ignition time arrange from 5 ms BTDC to 10 ms ATDC,the turbulence inhibiting effect on the ignition delay increases with delay of ignition time. |
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