Combustion studies have been made in a prechamber diesel engine, with one cylinder instrumented for pressure histograms using a processing digital oscilloscope. Hydrocarbon, carbon monoxide, NOx, and smoke emissions for the complete engine exhaust also were measured. Fuels with natural and chemically derived cetane numbers spanning a range from 35 CN to 54 CN were investigated.This paper discusses the effects of cetane number on combustion characteristics, such as ignition delay and rates of pressure rise. Engine emission data also are reviewed. Data include operation at fully warmed-up and partially warmed-up conditions.