Experimental and Numerical Study on Effects of Impingement Parameters on Fuel-Air Mixture Formation in the Near Wall Region for Diesel-DME Blended Fuels

Spray-wall impingement is an unavoidable physical process in homogeneous charge compression ignition (HCCI) diesel engines using early injection strategy which is the main source for the hydrogen carbon (HC) and monoxide (CO) emissions. Dimethyl ether (DME) is a potential fuel additive to decrease HC and CO emissions due to its higher oxygen content. However, issues relating to structural design and early injection timing mean spray-wall impingement still occurs when using the diesel-DME blended fuels, which directly affect the fuel-air mixture formation in the near wall region and further influence the emission characteristics. The better understanding for the effects of spray-wall impingement parameters on fuel-air mixture formation in near wall region for diesel-DME blended fuels is helpful for the improvement of HC and CO emissions for HCCI diesel engines.

This paper therefore experimentally and numerically investigates the effects of impingement parameters on fuel-air mixture formation in the near wall region for diesel-DME blended fuels. The impingement parameters including environmental pressure, environmental temperature, impingement distance and fuel blending ratio. The variations of fuel-air mixture morphology were obtained by the methods of high-speed photography. The variations of fuel-air mixture equivalence ratio distribution were studied by the numerical methods and a concept of a Mixture Homogenous Index (MHI) had been used to evaluate the homogeneity of fuel-air mixture.