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

Abstract

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 17mm 3 /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.

CFD-Guided Evaluation of Spark-Assisted Gasoline Compression Ignition for Cold Idle Operation

“…Our analysis revealed that the spark assistance with appropriate injector spray pattern and fuel injection strategy enhanced GCI combustion at cold idle conditions. The effectiveness of spark-assisted cold starting strategy has been also reported by other researchers [32][33][34][35].…”

Numerical Optimization of Spray-Guided Spark Assistance for Cold Idle Operation in a Heavy-Duty Gasoline Compression Ignition Engine

“…Generally, when a spark plug was used, an early ignition occurred near the spark plug, and the combustion efficiency of the case with spark plug assistance was found to increase by 11% compared to the case without it. Other studies [40][41][42] have also demonstrated the effectiveness of spark assistance in enhancing engine combustion performance under cold-starting conditions.…”

Heat and mass transfer effects in the nozzle of a fuel injector from the start of needle lift to after the end of injection in the presence of fuel dribble and air entrainment

“…Nevertheless, they still cover a quite wide range of engine operation, including typical pilot and main injection events, and are also representative of novel injection strategies targeted at partially premixed charge compression ignition operation with quite advanced injection timings. For example, typical pilot injections start well in advance of the main injection, about 20-40° crank angle before top dead centre [82][83][84], or even 90° crank angle before top dead centre for highly premixed charge operation, e.g. [85], hence in-cylinder pressures in such cases can be significantly lower than the main injection event.…”