ARMY TM 9-6115-670-14&P
1-15
Section III. PRINCIPLES OF OPERATION
1.16. ENGINE OPERATION.
1.16.1. Combustion System. The engine operates on the typical diesel combustion cycle (Figure 1-3).
To improve efficiency in the APU's small engine, the combustion chamber of each cylinder has a three-
lobe throat in the air inlet. This produces three streams of air in the chamber, creating an ideal mixture of
air and fuel. The top of each piston has a fan-shaped indentation, allowing smooth ejection of exhaust
gas. The cross-flow intake/exhaust ports in this engine have their openings at both sides of the cylinder
head. Because overlaps of the intake/exhaust ports are comparatively small, the suction air is protected
from being heated and expanded by the heated exhaust air. Therefore, the cool, high density suction air
has high volume efficiency and raises the power of the engine. Throttle type injection nozzles and rapid
heating sheathed type glow plugs are installed in each cylinder combustion chamber. In addition, a
preheating glow plug is installed in the intake manifold. The engine will start easily at 5°F (-14°C).
Figure 1-3. Combustion System
