Pressure trace and high speed schlieren video analyses were employed to investigate the effects of turbulence on spark-ignited flame growth in a closed vessel. Premixed methane-air mixtures of equivalence ratios between 1.0 and 0.6 were ignited at 300 K and 1 atm. Schlieren flame growth images were recorded at 2000 frames per second while the combustion chamber pressure was concurrently recorded. Pre-ignition turbulence was generated by pulling a perforated plate across the chamber. The ignition- time turbulence intensity was up to 2 m/s with integral scale of 1, 2, 4 or 8 mm. In the analysis, the turbulence parameters during flame propagation were adjusted for the effects of decay, compression and rapid distortion.

The schlieren video laminar flame growths agreed well with those calculated from the pressure traces. After the ignition phase, the laminar burning velocity remains quasi- steady until it is quenched by the chamber walls. The schlieren turbulent flame growths were somewhat faster than those deduced from the pressure traces, roughly by the amount of unburnt mixture embraced by the two-dimensional turbulent flame contour. Over the ranges of turbulence parameters studied, the turbulent burning velocity can be modelled by:​ S_t/S_l - 1 = C_L u'/S_l;​ where S_t is the turbulent burning velocity, S_l is the laminar burning velocity and u' is the root-mean-square turbulence intensity. The linear coefficient, C_L, designates the effectiveness of turbulence enhancement on the turbulent burning velocity. This linear coefficient increased continuously as the lame grew from ignition spark up to 55 mm radius limited by the size of the chamber. The linear coefficient decreased with the increase in the integral scale. In consequence, C_L = C_D г/√Λ + C_I;​ where C_D and C_I are constants, r is the flame radius and Λ is the integral scale. Alternatively, the turbulent burning velocity-turbulence intensity relation can be expressed as S_t/S_l - 1 = C_D(r√Λ)u'/S_l + C_I.

A semi-empirical, multi-zone thermodynamics equilibrium flame growth model has been proposed. The model simulations are in sound qualitative agreement and fair quantitative agreement with the experiments.