Ignition Quality Effects of Advanced Fuels at Reduced Temperatures

The impact of molecular structure on ignition properties were compared using an ignition quality tester constant volume combustion apparatus. All hydrocarbon fuels had approximately the same slope and shape when plotted on an Arrhenius plot. However, certain oxygenates (e.g., acetals) had a reduced slope relative to the hydrocarbon fuels. The temperature dependence of ignition delay was correlated with the C-H bond strength in the parent fuel molecule. The relative ranking of fuel ignition quality changed at lower temperature. This was presented in terms of an effective cetane boost at low temperatures for these oxygenates. Dipropylene glycol monomethyl ether had a cetane number of 42 under normal test conditions, but ignited faster than n-hexadecane at a charge temperature of 400°C. A fuel containing these oxygenates would ignite faster under cold-start conditions in a diesel engine than traditional hydrocarbon fuel, resulting in better performance and reduced unburned fuel emissions. This is an abstract of a paper presented at the 229th ACS National Meeting (San Diego, CA 3/13-17/2005).