Glow plugs are currently the most employed solution to promote ignition in light-duty diesel engines during low temperature cold start. Improved knowledge about the mechanisms that control ignition and flame development under such conditions is necessary for design purposes, especially with current trends to reduce engine compression ratio. This paper aims to analyze the influence of the glow plug configuration (location and temperature) on cold start combustion. Experimental tests carried out in an optical engine with high speed visualization have confirmed that spray-glow plug configuration influences the whole combustion process through pilot ignition. Ignition of pilot injection is controlled by glow plug to spray distance, by glow plug temperature and by fuel and air motion after the end of injection. Nevertheless, glow plug temperature effect starts to be negligible above a certain value, since chemical ignition delay cannot be further reduced. (C) 2011 Elsevier Ltd. All rights reserved.