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

摘要

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