Spray-Wall Interaction of Diesel Sprays

Doktorsavhandling, 2009

A promising combustion concept that aims at reducing emissions from DI Diesel engines is HCCI (Homogeneous Charge Compression Ignition). To achieve a combustible air/fuel mixture in such an engine one possible strategy is early fuel injection during the compression stroke, even though the in-cylinder conditions are different from those in conventional DI diesel engines. There are problems related to this strategy, however, such as if the fuel is injected shortly after intake valve closing when the in-cylinder air density is low and the fuel can penetrate a long distance, or if the fuel is injected somewhat later during the compression stroke when the air density is higher and the air temperature is increased, with a shortened liquid penetration as a consequence. Wall wetting might occur in both cases and influence the air/fuel mixing and thereby the combustion process. It has been found that a mixture of n-decane and 1-methylnaphthalene can be used as a two-component model fuel for combustion studies. With this fuel, called the IDEA fuel, relevant physical properties can be realized, such as fuel densities, boiling ranges, aromatic content and cetane numbers. Due to the different boiling points of the two components, the effect of the evaporation can be analyzed and used in simulations of sprays and, from an experimental point of view, it corresponds sufficiently to commercial diesel fuels. The objective of this work is to investigate the behavior of Diesel fuel sprays at conditions corresponding to those in a Diesel engine early during the compression stroke in order to increase knowledge about its characteristics before and after impinging a temperature controlled wall, making it possible to improve measurement and numerical methods. Another objective of this work is to clarify whether the two-component model fuel, IDEA, is suitable for studies of early injected sprays. This work has demonstrated that the two different fuels used in the experiments have characteristics that differ to a certain extent for a relatively wide range of air temperatures and air pressures.