Diesel Fuel Ignition Quality as Determined in a Constant Volume Combustion Bomb 870586
The ignition delay times of forty-two different fuels were measured in a constant volume combustion bomb. The measurements were performed at three different initial air temperatures using fuels ranging from the primary reference fuels for cetane rating to complex mixtures of coal-derived liquids.
The ignition delay times were examined in terms of the classical definitions of the physical and chemical delay times. The previously used definitions were found to be inadequate, and new definitions have been proposed.
The total ignition delay times were studied in the context of providing a means for rating the ignition quality of the fuels. Fuel ignition quality rating schemes are discussed, including one based on the current cetane number scale as well as one based on a new scale which includes a measure of the sensitivity of the various fuels to the air temperature.
The current cetane rating scale is discussed in terms of the extremely nonlinear nature of the scale and the inability of the ASTM technique to either distinguish the good ignition quality fuels or even rate the poor ignition quality fuels. The bomb technique does provide a measure of the ignition quality over the entire range of the current cetane scale. The correlations of the bomb technique and the cetane scale are good for the straight-run petroleum-derived fuels. In agreement with field experiences, the correlations break down for several of the highly processed and alternative fuels.