An optical investigation on macro spray characteristics of convergent-divergent ducted fuel injection under high ambient pressures

Abstract

The fuel-air mixing process can be improved via straight (ST) ducted fuel injection along with the risk of greater heat transfer loss due to prolonged spray tip penetration (STP) and spray impingement. We proposed the convergent-divergent (CD) duct spray in this study to produce acceptable STP and wider spray cone angle (SCA) for improving engine efficiency. STP and SCA are closely related to ambient pressure. This paper aims to explore the influence of ambient pressure on the macro spray characteristics of CD duct spray for better fuel-air mixing with the analysis of spray air entrainment (SAE). The Schlieren system was used to record the spray morphology of different duct sprays under ambient pressures of 20, 30, 40, and 50 bar. The results showed that compared with free spray, with the increase of ambient pressure, the application of CD duct can more effectively improve the SCA increase rate of free spray. With the ambient pressure changes from 20 to 50 bar, the SCA increase rate is up to 20.17% for free spray, and the SCA increase rate increased more than three times to 76.96% with ST3 duct and more than eight times to 173.06% with CD 4.5 duct compared with free spray respectively. The SAE of CD3 and ST3 duct sprays is higher than that of other sprays. CD4.5 and CD6 duct sprays reduce the probability of spray-wall impingement but along with a certain reduced amount of SAE.