Impingement and Adhesion on Cylinder Liners with Post Diesel Fuel Injections 2016-01-2193
Diesel particulate filters (DPF) are widely used in diesel engines, and forced regeneration is necessary to remove particulate matter (PM) accumulating on the DPF. This may be achieved with fuel injected after the main combustion is complete, the socalled “post fuel injection”, and supplied to the diesel oxidation catalyst (DOC) upstream of the DPF. This increases the exhaust gas temperature in the DOC and the DPF is regenerated with the high temperature gas flow. In most cases, the post fuel injection takes place at 30-90CA ATDC, and fuel may impinge on and adhere to the cylinder liner wall in some cases. Buddie and Pischinger  have reported a lubricant oil dilution with the post fuel injection by engine tests and simulations, and adhering fuel is a cause of worsening fuel consumption.
In this paper, the impingement and adhesion of post diesel fuel injections on the cylinder liner was investigated by an optical method with a high pressure constant volume chamber (ϕ110mm, 883cm3). The pressure and temperature are increased by the combustion of a spark ignited ethylene-air mixture, and the diesel fuel is impinged on a sampling plate on the stage of a constant volume chamber when the pressure and temperature has reached the aimed conditions for the post fuel injection. The post fuel injection behavior in the chamber was recorded by the optical methods of shadowgraph and Mie scattering with a high speed video camera. Further, the fuel film thickness and area of adhering fuel on the plate were measured by the LIF (laser induced fluorescence) optical method, and the mass of the adhering fuel determined by a precision balance.
The cylinder temperatures and pressures at 30, 60, and 90 CA ATDC, commonly employed post fuel injection timings, were measured by an actual engine, and similar conditions were created in the constant volume chamber. Fuel masses of 0.6mg, 1.1mg, and 1.7mg were injected in each case. The fuel impingement and adhesion on a sampling plate (adhesion plate) were investigated. The liquid and vapor phases were investigated and were in good agreement with calculations by the equations suggested by the Hiroyasu model . At the 30 CA ATDC condition, the fuel penetration is short and liquid fuel did not reach the sampling plate, but the liquid fuel did impinge at 60 and 90 CAs ATDC. The fuel adhesion ratios decreased with increases in the post fuel injection quantities. The thickness of the fuel film was measured by LIF. At the 30 CA ATDC condition, a thin fuel film adhered on the sampling plate, and the fuel film was thicker at the delayed post fuel injection timings. Further, the effects of the boost pressure and load on the fuel adhesion were investigated, and the optimum operation conditions for low adherence of the injected post fuel were determined.