The effect of enhanced ignition on the burning characteristics of methane-air mixtures

Abstract

Recently there has been renewed interest in using natural gas (methane) as an automotive fuel. Some of the problems with using natural gas (NG) in spark ignited engines are its high minimum ignition energy, long ignition delay, and low flame speed relative to gasoline, which results in a significant power loss. This paper examines the possibility of solving some of these problems by using a more efficient ignition source to reduce ignition delay and to enhance the initial burning rate. The ignition sources considered are a multiple electrode spark plug, plasma jet igniter, and conventional spark plug. Each of these ignition sources was also supplemented with varying amounts of additional energy from a high voltage storage capacitor. The experiments are performed in a constant volume combustion chamber. The pressure in the bomb during combustion was measured, and from this the mass fraction burned was determined. The time to burn 10% of the mixture (which includes flame initiation and initial propagation) was compared for each ignition source. The multiple electrode spark plug, using only the energy of a conventional ignition system, reduced this time by 12% compared to a conventional spark plug. Larger reductions (up to 45%) were found for the multiple electrode spark plug and plasma jet igniter when additional energy (up to 4.5 J) was supplied to the discharge.