An Extensive Comparison of Laser-Induced Plasma Ignition and Conventional Spark Plug Ignition of Lean Methane-Air Mixtures under Engine-Like Conditions

An extensive comparison of laser-induced ignition and spark plug ignition of lean methane-air mixtures was performed. Experiments were carried out under engine-like conditions in a high pressure, constant volume chamber (up to 25 MPa peak pressure) at an initial temperature of 473 K. To yield statistically relevant results, a total number of over 1800 ignitions was made in order to point out the advantages of the laser ignition scheme over the conventional spark plug ignition. It turned out that, especially at low initial pressures, laser ignition could expand the lean limit from an air/fuel equivalence ratio of λ = 1.65 for electrical to λ = 2.0 for laser ignition. The ignition delay was also significantly shorter when ignition was initiated by a laser. At the lean limit, the phenomenon of incomplete combustion was observed for both ignition sources. These findings were supported by exhaust gas measurements.