RECENT tests conducted at the Langley Memorial Aeronautical Laboratory have shown that considerable improvement in the performance of the compression-ignition engine can be obtained by the use of a displacer piston.
To observe the effects of the displacer piston on the air flow, and the effects of the air flow on the fuel spray and flame formation, high-speed motion pictures have been taken at the rate of 2200 exposures per sec. of these phenomena in the combustion chamber of the N.A.C.A. combustion apparatus.
This apparatus consists of a single-cylinder test engine which is operated under its own power for a single cycle. A vertical-disc combustion-chamber was employed, the sides of which were formed by two 2½-in. glass windows. A single 0.020-in. fuel-injection nozzle was used so that the effects of the air flow on the spray distribution could be visualized easily. By using “Schlieren” photography the air flow, fuel injection, and flame formation were recorded simultaneously. When the motion pictures are projected, the phenomena can be observed at 1/150th of their actual speed.
The results show that, although the core of the fuel spray was not destroyed by the air movement, the direction of the spray was changed and the spray envelope was carried away by the moving air. The volume of the chamber reached by the combustion was increased considerably when the displacer piston was used. It was found that the air movement set up during the induction of air into the engine cylinder could be controlled so as to materially aid the air flow set up during the last of the compression stroke.