THE tendency toward increasing the speeds of Diesel engines has caused them to become more sensitive to fuels and research on the latter has brought out the importance of ignition quality; however, some coordination has been needed for this research in order to develop a standard ignition-quality test. In order to escape the difficulties that were hampering the activities of a joint research committee of the S.A.E. and A.S.M.E., a Volunteer Group for C.I. Fuel Research took up the study of fuels in their own laboratories.
Two test methods had been proposed before the formation of this Volunteer Group, the critical-compression-ratio test and the ignition-delay test. The former gave considerable variation; however, the converted C.F.R. engine could not be used for the latter method because of unsteady operation, so a new cylinder was designed. Experiments with the new cylinder, using the delay-measuring method, are in progress. The ignition delay is indicated on the knockmeter, operated by the bouncing pin, a matching test being used similar to the octane-number test for gasoline. The result is expressed in the equivalent mixture of reference fuels, cetene and alpha methylnaphthalene, called the cetene number. The delay method appears to be less rapid than the critical-compression-ratio method, but more accurate.
The program of the Volunteer Group includes improvements in the test procedure and correlation with service engines. Other methods of test will be investigated along with the engine method.
About ten of the new engines are in operation, the laboratories mostly familiarizing themselves with the new equipment. The main difficulty is in obtaining steady injection, though no major difficulties appear to be in sight.