An experimental investigation of the ignition and combustion characteristics of two low cetane fuels in a spark assisted diesel engine at cold starting conditions is described. A three cylinder diesel engine was modified for single cylinder operation and fitted with a spark plug located in the periphery of the fuel injection spray plume. Optical observations of ignition and combustion were obtained with high speed photography. Optical access was provided by a quartz piston crown and extended head arrangement. The low cetane fuels, a light end low viscosity fuel and a heavy end high viscosity fuel, which were blended to bracket No. 2 diesel fuel on the distillation curve, demonstrated extended operation at low temperature starting conditions in the modified diesel engine. Qualitative and quantitative experimental observations of fuel spray characteristics, ignition delay, pressure rise, heat release, and white smoke formation were compared and evaluated against theoretical predictions. Results indicate that reducing the minimum ignition temperature and controlling combustion of extended fuel blends in a diesel engine may be possible without inlet air preconditioning.