Relationship between Eddy Scales and Fuel Vapor-Cloud Scale in Diffusion Phenomena for Establishment of Controlling High Speed Turbulent Mixing

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For reducing carbon dioxide emissions and realizing societies with minimum disturbance on environments, one of the important technologies to be developed is combustion control , particularly diffusion combustion because of its wide use in variety of systems. This study aims to identify conditions of controlling turbulent mixing, which is important for emission reduction and efficiency. This study focuses on scales of eddies relative to fluid scales, and tries to clarify the major parameter controlling diffusion intensity.The experiments were conducted with a constant volume combustion vessel equipped with a jet-generating cell, from where a small amount of fuel is injected during the combustion of the main spray. The jet from the cell impinges the main flame, causing changes in the mixing of fuel and air. Observation was made for a variety combinations of distances between spray nozzle and jet orifice and for different directions of impingement.It was shown that spray flames with jet impingement have significantly decreased soot emission characteristics compared to the no-jet flames. The research showed conditions of jet impingement for the effective soot reduction. In engine experiment a parameter which strongly relates to soot emission was identified: the parameter is a function of jet momentum, jet timing, engine speed, and amount of spray fuel. Theoretical and experimental analysis showed that the major factor which control diffusion intensity was a product of turbulent scale and a square root of turbulent energy of eddies with scales smaller than the fluid cloud. A method was also developed which enables to evaluate diffusion degrees based on Entropy concept.