Investigations on the transient coupling mechanism between heat transfer and key component transport of double diesel injections in confined spaces under near-ignition-limit temperature conditions

Abstract

Double injection strategy is an important solution to the difficulty of ignition and the long ignition delay time (IDT) of diesel sprays in cold environments, especially coupled with high altitudes. Under such extreme conditions, the pre-injected fuel does not ignite during the dwell time (DT) but instead facilitates the ignition process of the main injected fuel. To investigate this facilitation mechanism, the ignition process of five double injection strategies with different DTs was simulated using CFD coupled with chemical reaction kinetics. It was found that pre-injection has two simultaneous effects on the main injection: (1) The atomization and evaporation process of the pre-injection reduce the in-cylinder temperature, which subsequently hinders the ignition of the main injection. (2) The early reaction of the pre-injection accumulates part of the active substance for the following ignition of the main injection stage, resulting a shorter IDT of the main injection. (3) As the increase of dwell time (DT), the cooling and hindrance effects of the fuel evaporation increase, and the accumulation time of pre-reaction increased as well. The competition between these two effects in an optimal DT for the shortest ignition delay time of the main injection.