Investigation of the Effect of Glow Plugs on Low Load Gasoline PPC

Low temperature combustion (LTC), is a promising alternative for combustion engines, because it combines the positive aspects of both CI and SI engines, high efficiency and low emissions. Another positive aspect of LTC is that it can operate with gasoline of different octane ratings. Still, higher octane gasolines prove to be difficult to operate at low load conditions leading to high combustion instability (COV) that leads also to high emissions. This drawback can be reduced by increasing the intake air temperature or increasing compression ratio, but it is not a viable strategy in conventional applications. For a diesel engine running under LTC conditions, a possibility is to use the existing hardware, glow plugs in this case, to increase the in-cylinder temperature at low loads and facilitate an improved combustion event. Here, an experimental investigation is performed, to investigate how glow plug operation can affect the combustion stability of an engine at steady state operation at low load, with different intake temperatures, as well the effect of them at higher loads. Results show that glow plugs are effective at reducing the required inlet air temperature for keeping stable combustion, with minimal effect on efficiency. The load limit that glow plugs are useful is around 7 bar IMEPg, or about 30 % of the maximum load. After that, the intake conditions can sustain combustion without the use of glow plugs.