Flame Propagation in Natural Gas Fueled Direct Injection Engines

Injected natural gas requires some form of ignition assist in order to ignite in the time available in a diesel engine combustion chamber. A glow plug — a heated surface — is one form of ignition assist. Ignition by glow plug results in a single site of ignition from which the flame must propagate to other jets in the injection pattern. The goal of this work was to determine what factors affect how the flame propagates from this initial ignition site to the remaining unburned mixture site. The combustion of natural gas jets under diesel engine conditions was studied over a range to temperatures, pressures with and without a glow plug shield using a CFR engine as a rapid compression device. The results showed that of all the factors considered it is the geometry of the injection pattern, combustion chamber and glow plug shield that are most dominant in controlling combustion rates and fuel utilization.