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Owing to the small size of engines and high injection pressures, it is difficult to avoid the fuel spray impingement on the combustion cylinder wall and piston head in Direct Injection Spark Ignition (DISI) engine, which is a possible source of hydrocarbons and soot emission. As a result, the droplets size and distribution are significantly important to evaluate the atomization and predict the impingement behaviors, such as stick, spread or splash. However, the microscopic behaviors of droplets are seldom reported due to the high density of small droplets, especially under high pressure conditions. In order to solve this problem, a “spray slicer” was designed to cut the spray before impingement as a sheet one to observe the droplets clearly. The experiment was performed in a constant volume chamber under non-evaporation condition, and a mini-sac injector with single hole was used.

In the present study, a challenge has been made to quantitatively determine the vapor phase concentration distributions in an evaporating multicomponent fuel spray using the LAS imaging technique. The theoretical considerations were particularly given when applying the LAS imaging technique to the multicomponent fuel spray and reconstructing the vapor concentration distributions from the spray images.

Among the alternative fuels, dimethyl ether (DME), one of the oxygenated fuels, attracts attention as an alternative fuel for the Diesel engine since the properties of the DME are fitted to the Diesel engine combustion and the know-how development has been made of the mass production of the DME from a natural gas. In this study, experiments were performed of ignition characteristics of the DME and Diesel fuel sprays injected by a D.I. Diesel injector into a high-pressure, high-temperature vessel. The fuel injection was made by a Bosch type injection system. A schlieren optical system was adopted for visualizing the ignition process as well as the vaporization process of the DME and Diesel fuel sprays. The ignition delay was measured by using a photo-sensor which had a sensitivity in the wavelength range from visible to ultraviolet. Pressure and temperature of the ambient air and the oxygen concentration of the ambient air were changed as experimental parameters.

Owing to the short impingement distance and high injection pressure, it is difficult to avoid the fuel spray impingement on the combustion cylinder wall and piston head in Direct Injection Spark Ignition (DISI) engine, which is a possible source of hydrocarbons and soot emission. For better understanding of the mechanisms behind the spray-wall impingement, the fuel spray and adhesion on a flat wall using a mini-sac injector with a single-hole was examined. The microscopic characteristics of impinging spray were investigated through Particle Image Analysis (PIA). The droplet size and velocity were compared before impingement. The adhered fuel on the wall was measured by Refractive Index Matching (RIM). The fuel adhesion mass and area were discussed. Moreover, the relationships between droplets behaviors and fuel adhesion on the wall were discussed.

The rapid compression expansion machine (RCEM) was used to investigate the temporal variations of the spray flame and wall heat flux in the diesel engine combustion process by using 120 MPa and 180 MPa common rail pressure. A stepped cavity was applied to investigate spray and flame behavior under the pilot, pre and main multiple injection strategy. Wall heat flux sensors were installed in the piston cavity and the cylinder side. The injector has 3 holes with the neighboring angle in the left direction and another 3 holes in the right direction to simulate the spray interaction in the 10-hole injector combustion system in the actual diesel engine. The spray and flame behavior were taken by a high-speed video camera with direct photograph. A two-color analysis was applied to investigate gas temperature and KL factor distribution. The effect of locations and common rail pressure on heat transfer was investigated.

Heat loss is more critical for the thermal efficiency improvement in small size diesel engines than large-size diesel engines. More than half of total heat energy in the internal-combustion engine is lost by cooling through the cylinder walls to the atmosphere and the exhaust gas. Therefore, the new combustion concept is needed to reduce losses in the cylinder wall. In a Direct Injection (DI) diesel engine, the spray behavior, including spray-wall impingement has an important role in the combustion development to reduce heat loss. The aim of this study is to understand the mechanism of the heat transfer from the spray and flame to the impinging wall. Experiments were performed in a constant volume vessel (CVV) at high pressures and high temperatures. Fuel was injected using a single-hole injector with a 0.133 mm diameter nozzle. Under these conditions, spray evaporates, then burns near the wall. Spray/flame behavior was investigated with a high-speed video camera.