Initial development of non-evaporating diesel sprays in common-rail injection systems

Abstract

Transient nature of common-rail diesel sprays was characterized at the initial stage of fuel injection, the effects of injection rate being taken into account. Direct photography and the shadowgraph technique were used to obtain macroscopic spray images at several different experimental conditions. Highly versatile image processing software was developed to analyse the spray images. In the analysis, spray penetration, dispersion and spray angles were defined and accurately measured by the software with consistency. The effects of rail pressure and ambient gas density upon spray behaviours were discussed in detail. Based on the measured injection rates, the asymptotic relations of spray penetration were found at early and late stages of injection. The changes in spray volume were correlated with the measured injection rates. It was found that the initial spray penetration correlates well with the amount of fuel injected. The increase in injection rate during the injection period was observed to induce a smaller spray angle.