L52071 Literature Review Fuel-Air Mixing in Large Bore Natural Gas Engines

Abstract

Mixing is viewed as being problematic in many internal combustion engines, particularly large bore natural gas engines. In reviewing the literature an attempt is made to distinguish between the influences of mixing and turbulence, although for much of the published research the distinction is not made. Mixing is determined to have a major impact on engine efficiency, overall emissions, flame propagation, and cycle-to-cycle variations. The improvement of engine efficiency and overall emissions is concluded to be primarily due to the extension of the lean limit, a direct consequence of improved mixing. Test results from a study on propane combustion in a constant volume combustion chamber indicate that there is an optimum level of mixing for maximizing the flame propagation speed. In other words, the fastest flame speed occurs when there is some level of mixture heterogeneity, as opposed to a completely uniform mixture. A detailed literature review is carried out on air-fuel mixing in internal combustion engines, emphasizing application to direct injection large bore natural gas engines. The literature is separated into three broad categories, (1) the effects of mixing on engine performance, emissions, and combustion characteristics, (2) factors affecting mixing, and (3) mixing characterization.