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Research on ignition, flame growth and flame propagation in engine-like turbulence has produced widely varying correlations between turbulence parameters and flame speed. Some previous work has shown that the burning velocity observed in a given turbulence level depends on the flame size as well as the turbulence intensity and scale. This explains some of the previous experimental discrepancy and emphasizes the importance of measuring flame growth and turbulence effects over the range of interest for a given modelling requirement. This paper reports on an experimental study of flame growth from ignition sparks in spatially uniform, decaying turbulence similar to that found in engine combustion chambers. High speed schlieren video and pressure trace analyses were used to study 3-dimensional turbulent flame growth in a constant volume, cubical combustion chamber. Lean methane-air mixtures of 60%, 70%, 80%, 90% and 100% stoichiometric compositions were ignited at 1 atm and 300 K.

Preliminary test results are presented for an S.I. engine which used a focused laser beam and conventional spark ignition as ignition sources. The results show that for a steady running single-cylinder engine with MBT spark timing and fixed throttle position, engine performance and efficiency are improved, extension of the lean limit of operation by 5 air-fuel ratios is possible, and more NO is produced with laser ignition. The effects of EGR are also examined. The CO and HC emissions are essentially the same. With the laser, the spark location was found to have little effect on performance except when it was moved near the combustion chamber wall. The minimum laser pulse energy required for steady engine operation seems to be dictated by the minimum energy required to achieve breakdown of the laser pulse in air at the same pressure.