A Study On Rapid Quasi-Homogeneous Diesel Fuel-Air Mixture Forming Process In A New Conceptual (Bump)Combustion Chamber

A new HCCI combustion system for diesel engine based on the technologies of multi-pulse fuel injection and the BUMP combustion chamber was developed by professor Su Wan-hua in NECL of Tianjin University. The premixed homogenous combustion is realized by the technology of multi-pulse fuel injection. The start of pulse injection, injection-pulse numbers, injection period of each pulse and the dwell time between injection pulses are controlled by a FIRCRI injector system. The last or main injection pulse is set around TDC. When the diesel spray impinging on the combustion wall, the BUMP around the combustion chamber wall can strip off the wall jet and form a secondary spray in combustion chamber, so the fuel and air can mix well and homogenous.Planar Laser Induced Fluorescence (PLIF) was used to study the spray/wall impinging in constant volume vessel. The experimental result show that when fuel spray impinging on the plane wall, wall jet was formed while fuel impinging on a plane wall with a BUMP, when the wall jet meet the BUMP, a secondary jet can be formed. Some parameters affecting the secondary spray were studied, including BUMP height, the secondary impinging distance, impinging distance and injector parameters. The experimental result show that when BUMP height is increased, the secondary angle is increased, when the secondary impinging distance is increased, the secondary angle is decreased, so the BUMP height and impinging distance and secondary impinging distance should be optimized to control the secondary spray and control the fuel-air mixing.Planar Laser Induced Fluorescence (PLIF) and multi-dimensional CFD software was used to study the fuel- air mixing process in traditional combustion chamber and BUMP combustion chamber, the experimental and simulated result agree well in room condition. The fuel-air mixing process in high pressure and temperature in traditional and BUMP combustion chamber were compared. The result show that fuel and air can mix more quickly in BUMP combustion chamber than in traditional combustion chamber, fuel-air mixture in BUMP combustion chamber is more homogenous than in traditional chamber.