Measurements of fuel adhesion on cylinder walls and fuel wall-flow behavior with post diesel fuel injections

• Published in: International journal of engine research 2020-02, Vol.21 (2), p.352-366
• Main Authors: Shibata, Gen, Nishiuchi, Shogo, Xie, Puqing, Takai, Shuntaro, Ogawa, Hideyuki, Kobashi, Yoshimitsu
• Format: Article
• Language: English
• Subjects: Adhesion tests; Combustion chambers; Cylinder liners; Diesel engines; Diesel fuels; Dilution; Fluid filters; Fuel injection; Fuel sprays; High speed; Laser induced fluorescence; Liquid fuels; Low temperature; Lubricants; Measurement methods; Mie scattering; Penetration; Pressure effects; Regeneration; Temperature; Thickness measurement; Vapor phases; Wall flow; Walls
• ISSN: 1468-0874; 2041-3149
• DOI: 10.1177/1468087419855200

Post fuel injection in the expansion stroke is used for diesel particulate filter regeneration; however, fuel spray impinges on the cylinder liner due to the low temperature and pressure conditions. Fuel adhesion and fuel flowing down across the cylinder liner, the so-called “wall-flow,” was observed by high-speed video images, and this adhesion is a cause of diesel engine lubricant oil dilution and the deterioration of fuel consumption in diesel engines. In this article, the fuel adhesion and the wall-flow of post diesel fuel injections were investigated with a high pressure-temperature constant volume optical chamber. The in-cylinder temperatures and pressures at 30, 60, and 90 °CA ATDCs, conditions commonly employed in post fuel injection timings, were measured by an actual engine, and similar conditions were created in the constant volume chamber by the combustion of a pre-mixed gas of ethylene, oxygen, and nitrogen. Fuel masses of 0.6, 1.1, and 1.7 mg per hole were injected at each ATDC setting. The weight of the adhered fuel on the wall and the fuel in the piston-cylinder crevice were measured by precision balance, and the liquid–vapor phases in the spray were observed by Mie scattering and shadowgraph methods. To measure the thickness of the adhered fuel on the cylinder wall, the laser-induced fluorescence method was employed. The results show that the fuel spray penetration and adhesion on the cylinder wall were different in the test conditions investigated here. With the early post injection, most of the injected fuel vaporizes without penetrating to the cylinder liner and gaseous diesel fuel is condensed on the cylinder wall. A thin and widely spread out fuel film is formed on the cylinder wall; however, no wall-flow could be confirmed by the high-speed video images. With late post fuel injections, the strong penetration of liquid fuel reaches the cylinder wall, and a thick and widely spread out fuel film was formed on the cylinder wall and the wall-flow phenomenon was observed here. However, the quantity of fuel involved in the wall-flow was smaller than that of the fuel adhering to the cylinder wall. The effects of in-cylinder pressure and temperature on the fuel adhesion on the cylinder wall were investigated. With the increase in pressure and temperature, the quantity of adhering fuel was reduced, suggesting that the boost pressure increase by turbo charging and a higher engine load is effective to reduce fuel adhesion. Furthermore, the effec