Laser, Spark, and Self Ignition of Natural Gas In A Rapid Compression Machine

A rapid compression machine was designed and built to simulate in-cylinder conditions of a modern stationary natural gas fried reciprocating engine. Ignition properties of methane-air mixtures with initial pressures between 1 bar to 3 ber, and equivalence rations, Φ, between 0.45 and 1.0 were established. tests were performed to determine the ignition biundaries using a laser, a conventional Capacitance Discharge Ignition (CDI), and no ignition source (i.e.,self-ignition) as well as pressure rise, ignition delay, and minimuum required laser energy to ignite a miwture. It was observed that CDI is unable to ignite mixtures leaner than Φ≈0.5 regardless of pressure. Such exitensions are very desirable since it allows an engine to be operated with lower NOx emissions. Scans of minimum required energies for successful ignition (MRE) were also performed. Though the trends determined are in agreement with those previously reported in literature, the values measured were quite high. It is speculated that high velocities resulting from vortices generated from rapid piston movement result in quenching of the plasma kernel thereby resulting in an unsuccessful ignition. Ignition delay and pressure rise were also investigated for an initial pressure of 1.5 Bar. It was observed that faster combustion rates and smaller ignition delays occur for laser ignition as compared to a CDI (spark) ignition for 0.6 ≤Φ≤ 0.8 and also for Φ-1.0. However, for 0.6 ≤Φ≤ 0.9 a reversal of the aforementioned trends was observed.