Dual fuel engines offer the potential for considerable reductions in emissions of carbon dioxide (CO2), as well as reducing emissions of particulate matter (PM). However, the combustion processes occurring inside a dual fuel engine are complex. This is due to the ignition of a homogeneous lean premixed charge by a pilot fuel spray, which combines elements of both conventional spark ignition and diesel combustion.
Combustion models provide an effective means of investigating the phenomena taking place inside the cylinder. This paper describes a phenomenological model used for performance and emissions predictions in a dual fuel engine. The pilot fuel spray is described using a packet model approach, which includes sub-models for spray development and mixing, swirl, spray wall impingement, ignition and combustion. Flame growth is coupled to the burning zones in the cylinder and is described using a turbulent entrainment model. Oxides of nitrogen (NOx) and PM are also evaluated.
Simulated in-cylinder pressures and rates of heat release are in good agreement with experimental data obtained from a naturally aspirated, in-line, four-cylinder, direct injection diesel engine operating with methane (CH4) as the gaseous fuel. Crank angle resolved emissions of NOx and PM are also presented. The model results give good confidence in the current approach for the description of premixed combustion following the ignition of the pilot.