Optimization of piston cavity in a DME engine

초록

A DME fuel has a strong potential as an alternative fuel for compression ignition engine in term of emissions and diversification of energy sources. In order to improve combustion efficiency the conventional piston cavity, re-entrant type, which is suitable for light oil engine, needs to be optimized to reduce the piston surface and enhance the mixing between gaseous DME fuel and air. In this work, the experimental and analytical studies were carried out, which reveals the optimized piston cavity to replace the conventional re-entrant type piston for DME fuelled engines. Two piston cavities, re-entrant and bathtub, were are installed in a constant volume combustion chamber in order to investigate the flow and mixing characteristics inside cavities when DME in injected. A bathtub piston cavity has smaller surface area that corresponds to 90.3% of that of re-entrant type, while maintaining the same cavity volume. At high pressure(30bar) and temperature(200oC), a DME fuel was injected and flow was observed with the back light method. An auto correlation method was used to investigate the flow and mixing characteristics between air and fuel. Mild turbulent flow was observed with the bathtub type cavity, while maintaining the smaller surface area, compared to the re-entrant type cavity.