THE 2-cyl “compound” engine on which the data reported in this paper were obtained is provided with a high-pressure cylinder, and a low-pressure cylinder which serves as a compressor as well as a working cylinder.
The primary consideration in this work was the extracting of additional work from the already partially expanded gases from the high-pressure cylinder; a secondary consideration was the use of the same low-pressure cylinder as a second-stage compressor to aid in supercharging the high-pressure cylinder.
In reporting test results covering the development and testing program on the 2-cyl test unit, indicator diagrams showing the power developed in both high-pressure and low-pressure cylinders are presented. The method of summarizing the test results is by tabulating the representative runs and plotting the final runs. Some results and conclusions follow:
An indicated mep of 705 psi was recorded in the high-pressure cylinder, but the corresponding imep in the low-pressure cylinder was only 63 psi.
Fuels are available which make possible mean effective pressures in the high-pressure cylinder heretofore considered fantastic, resulting in release pressures to the low-pressure cylinder of 350 to 400 psi.
Two-stage expansion to a final ratio of 15:1 or more is feasible.
Modern internally cooled valves are satisfactory even under the unusual temperatures and pressure conditions encountered by the high-pressure exhaust valve.
Compounding the expansion results in a definite increase in thermal efficiency.
Although the results of the test are not as good as desired, Mr. Prescott concludes, it is considered that the project is worthy of further development and research.