Direct Measurement of the Turbulent Burning Velocity in a Homogeneous-Charge Engine

An experiment is described for the direct measurement of the turbulent burning velocity during premixed combustion in a spark ignition engine. The gas velocity is measured using a high data rate laser Doppler velocimeter system that resolves the unburned gas motion on an individual cycle basis. The ensemble-averaged flame speed is determined from ionization probe measurements of the time of flame arrival at discrete positions along the path of flame propagation. The difference between the cycle-resolved unburned gas velocity and the ensemble-averaged flame speed gives a direct measurement of the turbulent burning velocity that is unbiased by cyclic variations in the combustion rate. The value of burning velocity obtained is shown to be in close agreement with an empirical model previously determined.