Experimental Study of Glow Plug Assisted Methanol Compression Ignition

Methanol can be produced renewably and used in compression ignition (CI) engines as a replacement for fossil diesel. However, methanol is a low cetane fuel, creating challenges in achieving stable operation, particularly at low load. One potential solution is through surface ignition via a glow plug. In this work, experiments were conducted on a methanol-fueled 2.1 L single cylinder engine instrumented with a glow plug. The engine was designed for alcohol combustion with an elevated compression ratio (26:1) and a narrow injector umbrella angle (120 degrees) compared to standard diesel compression ignition hardware. As such, no plume was directly intercepted by the glow plug. A representative low load case of two conventional mixing controlled compression ignition (MCCI) strategies (single injection and pilot-main) and three kinetically controlled advanced CI strategies (homogenous charge compression ignition, split injection, partially premixed combustion) were tested with and without the glow plug active. It was found that the glow plug had no significant impact on either MCCI strategy because no plume was directly intercepted by the glow plug. In the advanced combustion strategies, the glow plug advanced combustion phasing by several degrees, due to an apparent combination of charge heating and small amounts of exothermic reactions from fuel located near the glow plug during the compression stroke. When the charge was heavily stratified, it was hypothesized that flames could propagate from the glow plug and the start of combustion could advance substantially. However, this significantly decreased low load stability as cyclic variability in the local conditions near the glow plug resulted in high cyclic variability in flame propagation and subsequent autoignition of the charge. This work highlights the potential incompatibility between narrow angled injectors designed for alcohol CI and glow plugs, as well as the ineffectiveness of glow plugs in alcohol fueled advanced combustion strategies.