Characteristics of the combustion of a lean mixture and a nitrogen-diluted mixture in a spark-ignition engine were investigated under the conditions that the fluctuations of mixture strength and charge quantity were very small. The rate of heat release and the combustion duration were determined by a one-zone model from pressure data, and the effects of turbulence characteristics and laminar burning velocity on the combustion duration were discussed. Consequently, it was found that 1% combustion duration varied linearly with the parameter (L/u')3/3SL-2/3ν1/3, where L is the integral length scale of turbulence, u' turbulence intensity, SQL laminar burning velocity, and ν kinetic viscosity. The 1% combustion duration was a dominant factor for determining 100% combustion duration.
