Fuel spray impingement and liquid film formation in a gasoline direct-injection spark-ignition engine

It is important to improve the thermal efficiency and reduce the harmful exhaust emissions of the direct-injection spark-ignition engine. However, this engine has problems such as the emission of particulate matter, including soot, from pool fire with luminous flames. Pool fire is caused by the thermal decomposition of a liquid film, which is created by fuel spray impinging on a piston surface. An understanding of liquid film formation process is important to reduce particulate matter. The purpose of this investigation was to evaluate the effects of injection pressure on fuel spray impingement and liquid film formation process, under engine motoring conditions, using the laser-induced fluorescence method. The fuel consisted of isooctane, 1-octanol and rhodamine B. 1-Octanol was the solvent for rhodamine B, which was illuminated with a neodymium-doped yttrium aluminum garnet laser, causing it to emit red fluorescence at a wavelength of 580 nm; the second harmonic of the laser is at 532 nm. Liquid film images were captured using a high-speed camera. Using image processing, the liquid film area, thickness and mass were estimated. It was found that increasing injection pressure increased the liquid film area, thinned the film and decreased the mass of fuel that remained. In total, 35.6% and 32.5% of the injection mass remained on the piston surface at an injection pressure of 5 and 13 MPa, respectively. In addition, the in-cylinder flow affected the liquid film formation process, stretching the film in the direction of the flow. [GRAPHICS]