Abstract
The compression-ignition (C. I.) engine differs from other types of internal-combustion (I. C.) engine in that the fuel supply is entirely independent from the air supply and, further, that at all times a large excess of air is present. It is to be expected therefore that although the weight of air received will be influenced by atmospheric changes, the effect of these changes will be much less than in the case of an engine in which the fuel supply is dependent upon the air flow. Basically the effect is a change in air utilization, that is, air/fuel ratio. This is not universally realized as is shown by the fact that, quite frequently, a formula developed for correcting petrol-engine test results for atmospheric changes is applied to C. I. engine figures.
The experiments described were designed to show the absurdity of this procedure and, if possible, to provide information from which a method of correcting C. I. engine results could be derived. The first objective is very definitely achieved; for the second, it is shown that a change in air utilization has precisely the same effect upon the indicated horsepower no matter whether the change is caused by the fuel delivery being varied while the air supply remains the same or the fuel supply is kept constant and the air supply varied by a change in temperature or in pressure.
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