Simultaneous Laser Measurements of Local Values of Turbulence and Burning Velocity of Flames Propagating in Fuel-air Mixtures in Closed Combustion Chambers.

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The research for clarifying the interaction between turbulence of fuel-air mixture and burning velocity is one of the most important subjects for the study on premixed combustion, and many research papers have been published. In the previous experimental research works, however, the relation between the local values of turbulence and the average values of burning velocity in total flames have been discussed. For the profound understanding of turbulent premixed combustion, it is necessary to measure simultaneously the local values of the burning velocity and the turbulence. The purpose of this study is the development of such a measurement method.In this study, nonintrusive methods for determining the local values of burning velocity of flames, turbulence characteristics and temperatures of unburned mixture in closed combustion chambers, were developed. The velocity of unburned mixture ahead of a flame front was measured with a laser Doppler velocimeter, and the flame propagation speed was simultaneously determined by measuring the time of flame travel over a fixed distance. The flame front was detected by the refraction of a laser beam due to the rapid change in the refractive index at the flame front. The burning velocity can be determined as the difference between the flame propagation speed and the unburned mixture velocity. The velocity data of unburned mixture were separated to the mean velocity and the turbulence intensity by using digital filter method. Further, the temperature change in unburned mixture with the compression due to combustion was measured by a laser interferometry. The experiments were carried out under several kinds of conditions of the turbulence characteristics and the equivalence ratio of propane-air homogeneous mixture in closed combustion chambers.