A Statistical Approach to Determining the Effects of Speed, Load, Oil and Coolant Temperature on Diesel Engine Specific Fuel Consumption

Abstract

Experimental brake-specific fuel consumption (BSFC) data are presented for two diesel engines as a function of engine speed, load, outlet coolant temperature, and inlet oil temperature. Engines used in the study were the Cummins VT-903 (turbocharged) and the Caterpillar 3208, both being direct injection and four-cycle. Data were obtained for the Caterpillar engine using a fractional, factorial statistical method which reduced the total test matrix from 256 to 64 data points. A test tree approach was employed in collecting data for the Cummins engine. Neither engine had a vehicle exhaust system, and back pressure might be different in actual vehicle testing. Engine exhaust pressure was adjusted to ambient conditions for all experimental tests. A mathematical parameter for quantitatively expressing the change in BSFC per 10 degree F change in coolant and oil temperature was derived. Results based on using Mobile Delvac 1330 oil (Society of Automotive Engineers 30 type oil) and Amoco Premier Fuel (Diesel No. 2) revealed that an increase in coolant and/or oil temperatures had the effect of reducing BSFC in both engines. An increase in the outlet coolant temperature had a greater effect on reducing BSFC in the Caterpillar engine at any given speed and load condition, while an increase in the inlet oil temperature had a greater effect on reducing BSFC in the Cummins engine. It is believed that the statistical regression method for assessing BSFC is useful in developing engines and their performance maps.