Squish Research In The Combustion Chamber Of Compression Ignition Engine

Diesel engine is widely used in auto industry, which has better thermal and economical efficiency. The"oil-air-chamber"matching-up is a fundamental condition of better mixed air, and how to utilize squish in the compression stroke is one of the key problems in diesel research. Combustion inside the chamber is complicate, with intense physical and chemistry exchange, and too rapid to easily detect. Although this subject had been researched for many years, a lot of questions are still not answered. In the circumenstence of lack of oil resources, it is meaningful to research diesel combustion prcedure and optimize chamber design. In this dissertation, a simple chamber shape is researched. On that basis, Ichange some key measurement and get two modified shapes. Then I use CATIA to build three-D models for these chambers. Three-D moving grids are generated by FIRE, a professional CFD software. After setting up the boundary conditions and initianl conditions, choosing appropriate combustion model, I run the simulation and get the result. At last, I discuss the generation of squish flow, the influnce for combustion by different shape of chambers and compare the chambers.The conclusion shows, the squish begins when the crank angle is 30°BTDC and reaches the maxium when the crank angle is 12°BTDC, then weakens till TDC. To spray at the maxium time point is the best choice, it could accelerate diesel-air mix-up speed and promote inflammation effect. By comparison, straight wall chamber(type A) is easy to be manufactured, has the lowest thermal stress and has obvious squish. Type A is the best combustion room choice. Smaller squish lip chamber(type B) has better squish effect and better engine performance, but it has higher temperature surround lips, it may conduce heat crack and harder to manufacture. Smaller squish lip could reduce the NOx emission, but could extend soot emission. It is recommended that choosing smaller squish lip when asking for higher engine performence, but it is necessary to improve piston intensity.