A Rational Basis for Comparing Diesel-Engine Performances 350099
THE paper describes a procedure for analyzing the performance of an internal-combustion engine. It is first shown that the characteristics of ideal cycles can be conveniently represented with the help of a fictitious “fuel mean pressure” which is proportional to the useful heat input. The diagram so obtained is used to represent certain ideal Otto and Diesel cycles. It is pointed out that actual performance can be similarly expressed.
A simple correction for the variation of atmospheric conditions is then introduced. Examples from tests are used to show that this correction is in accordance with actual experience. The final form of the proposed diagram embodies the correction.
It is then shown that the performance of a cylinder as it appears in this diagram is a measure of the success of the designer in dealing with factors lying within his control, as distinguished from those arising from the conditions of operation. Therefore, a comparison of divergent designs, of whatever size and type, is possible by representing the indicated performance of each in the manner described.
The friction mean pressure is discussed briefly. The contention is that, while its variation with speed is large, its value at a given speed is practically independent of load.
The procedure of analysis is applied to a group of engines of varied type and size. A wide divergence among these performances is found, and some reasons for the variations are discussed.
In conclusion, a power-characteristic diagram is added, supplementing the preceding analysis which refers to the individual cycle.