Experimental and Theoretical Investigation of Turbulent Burning Model for Internal Combustion Engines

A model for describing turbulent flame propagation in internal combustion engines is presented. The model is based upon the assumption that eddies having a characteristic radius ℓ_e are entrained by the flame front at a turbulent entrainment velocity u_e and subsequently burn in a characteristic time τ = ℓ_e/u_ℓ, where u_ℓ is the laminar flame speed for the fuel-air mixture. An approximate analytic method for determining the equilibrium state of the burned gases is also presented. To verify the predictions of the model, experiments were carried out in a single-cylinder research engine at speeds from 1000-3200 rpm, spark advances from 30-110 deg btc and fuel-air equivalence ratios from 0.7-1.5. Simultaneous measurements of the cylinder pressure and the position of the flame front as a function of crank angle were made, and good agreement with the predictions of the model was obtained for all operating conditions. Correlations were developed that permit both the entrainment speed u_e and the eddy radius ℓ_e to be calculated from a knowledge of the engine geometry, fuel type, and operating conditions. It is anticipated that the model will be useful for design studies directed toward improving the efficiency and pollution characteristics of internal combustion engines.