Understanding the effect of inter-jet spacing on lift-off length and ignition delay

Abstract

[EN] In recent years, injectors with multiple outlet-holes and smaller diameters have been implemented to reduce pollutant emissions during the combustion development. Nevertheless, increasing the number of holes has also decreased the spacing between the jets, which could lead to interactions between sprays affecting their behavior, a phenomenon that has not been defined in detail. In this sense, this study analyzes the influence of inter-jet spacing on the ignition delay and lift-off length for a wide range of boundary conditions. To this end, two multi-hole diesel injectors were manufactured with different distributions of the outlet orifices, which allowed the study of the development of an isolated spray and a spray with an inter-jet spacing of 30 degrees during the same injection event. Additionally, the results were compared to the development of sprays under inter-jet spacing values of 36 degrees and 45 degrees. The results showed that the spray with smaller inter-jet spacing had a slightly larger ignition delay at low chamber temperature and density conditions. Regarding the lift-off length, reducing the inter-jet spacing decreased the lift-off length values, these reductions being more noticeable after a threshold of proximity between sprays was achieved. In particular, the spray with an inter-jet spacing value of 30 degrees had considerably lower lift-off length values than those with an inter-jet spacing of 36 degrees and 45 degrees, which in turn had closer lift-off length values than those obtained with the isolated spray. Finally, a novel empirical correlation was developed for the lift-off length considering the influence of inter-jet spacing, thus contributing to the understanding of the effect of the interaction between sprays in the combustion process.