Laser-induced multi-point ignition with a single-shot laser using two conical cavities for hydrogen/air mixture

A multi-point ignition technique with a single-shot laser is proposed and its feasibility has been tested experimentally in a constant volume chamber filled with premixed hydrogen/air mixture. Two conical cavities are installed on combustion chamber walls, which are aligned with laser. The first cavity has an opening near the apex. By directing unfocused laser beam into the first cavity, part of the incident laser energy passes through the opening and irradiates into the second cavity. Simultaneous two-point ignition is achieved at each cavity. A simultaneous three-point ignition technique is based on directing focused laser beam into the two-cavity arrangement, which produces additional ignition at the center of the chamber through laser-induced spark ignition. Advantages of the proposed techniques over single-point ignition techniques are demonstrated through significant reduction in total combustion time. Shadowgraphs of the early stage of combustion process show that hot gaseous jets are ejected from the cavities, resulting in rapid combustion. It is also found that increase in incident laser energy accelerates jet ejection from the cavities.