CFD Investigation on the Influence of In-Cylinder Mixture Distribution from Multiple Pilot Injections on Cold Idle Behaviour of a Light Duty Diesel Engine 2014-01-2708

Cold idle operation of a modern design light duty diesel engine and the effect of multiple pilot injections on stability were investigated. The investigation was initially carried out experimentally at 1000rpm and at −20°C. Benefits of mixture preparation were initially explored by a heat release analysis. Kiva 3v was then used to model the effect of multiple pilots on in-cylinder mixture distribution. A 60° sector of mesh was used taking advantage of rotational symmetry. The combustion system and injector arrangements mimic the HPCR diesel engine used in the experimental investigation. The CFD analysis covers evolutions from intake valve closing to start of combustion. The number of injections was varied from 1 to 4, but the total fuel injected was kept constant at 17mm³/stroke. Start of main injection timing was fixed at 7.5°BTDC. The experimental study shows that increasing the number of pilots improves stability and leads to fuel preparation resulting in higher initial peak rate of heat release. CFD results show that multiple pilot injections are capable of better fuel distribution; noticeable by injecting just one pilot compared to no pilot. A further pilot increases the surface area of the vapour cloud to a greater extent. Three pilots allow for fuel to be well distributed in the full bowl with no lean regions; a greater proportion of the fuel is exposed to the glow plug temperature. The glow plug is enclosed by a fuel cloud over a longer period of time as the number of pilot injections is increased.