The effects of a glow plug on the gas temperature distribution prior to ignition in HCCI combustion are investigated. Two custom sleeve adapters-were constructed to allow the glow plug access to the gasoline engine in two different locations. The results show that increasing the glow plug voltage causes combustion to advance, which presents a method for controlling the combustion phasing in HCCI. Furthermore, the glow plug is able to broaden the temperature distribution prior to ignition by unevenly heating the charge. This broadening of the temperature distribution decreases the heat release rate in HCCI. Therefore, an actively controlled glow plug could be used for control over the rate of heat release in HCCI, within certain limits. The effect of the glow plug on the temperature distribution is larger when the glow plug is centrally mounted with a longer penetration into the chamber. Additionally, it was found that swirl causes the uneven heating effect of the glow plug to diminish due to enhanced mixing, resulting in a slightly narrower temperature distribution. The combustion efficiency when using the glow plug was slightly improved by reducing the unburned hydrocarbon emissions. The NOx emissions were also reduced somewhat due to the elongation of the heat release causing slightly lower peak temperatures. While much of the results are encouraging, the glow plug has the specific disadvantage of requiring electrical energy, and when counted against the work produced by the engine, the efficiency decreased by 1.4-2.5 percentage points at relatively low loads.