Diesel Fuel Ignition Quality as Determined in a Variable Compression Ratio, Direct-Injection Engine

A single-cylinder, variable-compression ratio, direct-injection diesel engine was designed and constructed to study the ignition quality of seventeen different test fuels, ranging from the primary reference fuels to a vegetable oil. The objective of the work was to compare the ignition quality rating of the fuels using the standard cetane rating technique to ratings obtained in the test engine.

The ignition delay times have been measured as functions of the engine speed, load, and compression ratio. As in the standard cetane rating technique, injection timing was adjusted so that combustion started at top dead center. This was accomplished by adjusting the injection timing as the speed, load, and compression ratio were varied. The resulting data is plotted as the ignition delay times versus compression ratio at the various speed-load conditions. For one of the test fuels, a very narrow-cut middle distillate, the compression ratio was varied in conjunction with variations in speed, load and injection timing. The resulting data indicated that the compression ratio is the dominant factor in controlling the ignition delay times. The data is discussed in terms of comparisons between the standard CFR engine rating technique and a proposed new technique based on the variable-compression, direct-injection engine.