Methanol, in common with other alternative fuels including natural gas and LPG, has autoignition characteristics which are poorly suited for use in compression ignition engines. Some sort of ignition assist has proven to be necessary. Considerable work has been carried out with hot surface (glow plug) ignition. The geometric relationship between the fuel injection nozzle and the glow plug is critical to achieving high efficiency and low emissions. Moreover, it is difficult to establish a single geometry which provides reliable ignition and stable operation over the entire range of engine speeds and loads.
The work described in this paper investigated extending the range of operation of a particular glow plug/fuel injection nozzle geometry by placing the glow plug in the wake of a bluff body. Bluff-body flame stabilization is a well-known technique in continuous combustors. Experiments were carried out in a single-cylinder CFR cetane rating engine fueled with methanol. Four different glow plug/fuel injection nozzle geometries were investigated, with and without a bluff-body stabilizer. Tests were carried out at a 22:1 compression ratio at engine speeds of 1200 RPM and 1500 RPM for three different loads. Additional tests with a 17:1 compression ratio were carried out at 1500 RPM. Ignition delay values were derived from cylinder pressure data. Engine performance and efficiency were measured, as well as exhaust emissions of carbon monoxide, unburned hydrocarbons, oxides of nitrogen and opacity. The results indicate the benefits and disadvantages of using a bluff-body with the glow plug.
The main overall conclusion is that addition of the bluff body does reduce the NOx emissions of the methanol fueled engine at a small penalty in fuel consumption and increased CO and unburned hydrocarbon emissions. Since NOx is the most difficult exhaust emission to control, this is a promising result.