<div class="htmlview paragraph">A method of cooling piston engines by direct injection of a fluid into the combustion chamber is described. Significant changes in power performance, fuel octane or cetane number requirements, exhaust emission quality, engine life, and engine configuration can be expected from injection cooling.</div> <div class="htmlview paragraph">This paper includes a theoretical discussion of the process and then presents a description of the laboratory apparatus and procedures and an evaluation of experimental data.</div>