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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.

This study describes the design and proof-of-concept testing of a system which has enabled sub-zero cold starting of a port-injected V6 engine fuelled with M100. At -30°C, the engine could reach running speed about 5s after the beginning of cranking. At a given temperature, starts were achieved using a fraction of the mixture enrichment normally required for the more volatile M85 fuels. During cold start cranking, firing is achieved using a high energy plasma jet ignition system. The achievement of stable idling following first fire is made possible through the use of an Exhaust Charged Cycle (ECC) camshaft design. The ECC camshaft promptly recirculates hot exhaust products, unburnt methanol and partial combustion products back into the cylinder to enhance combustion. The combined plasma jet/ECC system demonstrated exceptionally good combustion stability during fast idle following sub-zero cold starts.

Formation of pulsed plasma jets, or puffs, was examined using several visualization techniques. Self-light streak photography was first employed to record salient global features of the development and structure of the jet. This provided information on the motion of the luminous gas particles in its core, revealing that plasma jets can have two distinct modes, being either totally subsonic or embodying a supersonic efflux manifested by the recorded streaks of Mach discs. At a fixed power pulse of electrical energy discharge in the plenum chamber, the outcome depends on the constriction imposed by an orifice at its outlet. Whereas the difference between the two types of jets was quite small, penetration in the subsonic case was found to be definitely larger than in supersonic.

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.