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The laser-induced exciplex fluorescence (LIEF) technique, currently used to observe mixture formation in a diesel engine, has been applied to a spark ignition (SI) engine and a new equivalence ratio calibration technique has been developed in order that two-dimensional measurements of the equivalence ratio may be made in an operating engine. Spectrally separated fluorescent images of liquid and vapor phase fuel distributions were obtained by adding new exciplex-forming dopants to the gasoline fuel. Dual light sheets from an excimer laser were introduced into one of the cylinders of a 4-valve lean-burn engine, and 2-D images of the mixture formation were recorded at pre-set crank angles during the induction and compression strokes by an image-intensified camera equipped with the appropriate filter.

In enhancing the performance of automotive internal combustion engines, increasing the compression ratio offers an effective means of improving engine thermal efficiency. If the compression ratio is increased, however, the problem of knock occurs in exchange for improvement in engine thermal efficiency. In other words, an increase in compression ratio causes in-cylinder compressive end gas temperature to rise, resulting in the occurrence of knock. This in turn requires ignition timing retard to combat the knock. This trade-off makes it difficult to achieve the theoretical maximum combustion efficiency. In this paper, we clarify the feasibility of suppressing the occurrence of knock by increasing the burn rate. Specifically, we increase the burn rate by injecting high-pressure air directly into the combustion chamber, causing highly turbulent in-cylinder flow.