Experimental investigation on spray-wall impingement characteristics of n-butanol/diesel blended fuels

Abstract

n-Butanol is one of the most promising conventional fuel alternatives for diesel engines using advanced combustion modes such as homogeneous charge ignition and premixed charge compression ignition. However, effects associated with the structural design of these engines as well as early injection strategies still result unavoidable spray–wall impingement when using n-butanol/diesel blended fuels, which directly affects the combustion and emission characteristics of the diesel engines. The present work therefore investigated the spray–wall impingement characteristics of n-butanol/diesel blended fuels under various environmental conditions and when applying different injection strategies. The parameters that were varied included fuel temperature, environmental temperature and pressure, impingement distance, blending ratio, and the presence or absence of an oil film. The impingement spray radius (Rw) and height (Hw) were obtained experimentally so as to evaluate the impingement characteristics, and the effects of each parameter on Rw and Hw were assessed. In addition, based on the momentum transition of the impinged spray, the variations in Rw and Hw were attributed to four factors: the mass and momentum of the impinged spray; the spreading or splashing resistance of the spray, and the strength of air entrainment. The relative effects of each of these factors on Rw and Hw were examined, and results showed that the spray impingement momentum had the greatest effect on Rw, followed by air entrainment, while the impact of the fuel viscosity and surface tension (or spreading resistance) were limited. However, the effects of spray impingement momentum and air entrainment on Hw were less pronounced, while the viscosity and surface tension had a greater impact.