First tests of laser ignition in Wankel engine

Laser ignition has been studied in powerful four-stroke engines, not only because of the fast payback, but also because of the more convenient diagnostics in a large scale setup. High-performance compact engines have not been studied, even though advantages of laser ignition could be much more pronounced for those because of harmful emission reduction and multi-fuel abilities. Compact piston engines are considered as an alternative for fuel elements and batteries for portable, automotive and unmanned aerial vehicles. These are characterized by a small combustion chamber comparable to the spark plug inter-electrode gap in axial direction, and its low ratio to bore size. However, for Wankel engines this problem exists at any scale. Laser ignition of lean fuel mixtures in such engines could significantly improve performance by reduced fuel consumption, thermal loads, and a cleaner exhaust. We have investigated the possibility of laser ignition in rotary-piston (Wankel) sub-kW scale model engine using different kinds of fuel mixtures: hydrogen, methane, propane, butane, gasoline, and ethanol based. A custom built compact diode-pumped solid state laser has been used to substitute the original glow plug, respectively. Laser ignition has been found possible and quite beneficial for both types of engines and different fuel mixtures; in terms of NO_x emission reduction especially. (paper)