Keeping Cool and Clean: Regulating Heat and Exhaust in Aircraft Engines

Operating an aircraft’s engine at excessively high temperatures is dangerous. Outside of the correct temperature range, an engine can lose power and suffer damage such as scoring on the cylinder walls and burning or warping in the valves. Therefore, maintaining optimal temperatures is a central part of ensuring healthy engine operations in an aircraft.

In an engine, internal cooling is handled by the engine’s oil system. Oil that is circulated through an engine for lubrication purposes will also act as a heat-dissipating agent, drawing heat from the cylinder heads in the engine as it passes over them. The hot oil is cooled as it pumps through the radiator, before repeating the process as it passes over the cylinder heads once more.

However, the external surface of an aircraft’s engine must be cooled as well. In civilian prop-driven aircraft, this is handled via air-cooling that flows into the engine compartment through openings in the front of the aircraft engine cowling. Baffles rout this air over fins attached to the engine’s cylinders, where the air absorbs the engine’s heat. The hot air is then expelled through openings in the lower aft portion of the engine cowling.

Air cooling does have its disadvantages, however. While air-cooling is effective in flight, where there is a reliable source of fast-moving air, the system is less effective while the aircraft is on the ground, while taxing, during take-offs, and other periods of high-power, low-speed operation. On the other hand, a high-speed descent can cause too much air to flow into the compartment, causing the engine to cool too quickly and causing cylinder heads to crack. In these situations, the oil-cooling system actually serves to warm and regulate cylinder temperature.

Engine exhaust systems vent combustion gases overboard, provide heat for the cabin, and defrost the windshield. The exhaust system consists of piping attached to the cylinder, and a muffler and muffler shroud. The gases are pushed out of the cylinder through the exhaust valve, and from the exhaust valve out into the atmosphere. Engine exhaust contains carbon monoxide, an odorless, colorless gas that is toxic for humans. To prevent exposure, an exhaust system has to be kept in good condition and free of cracks.

Some exhaust systems will also come with an exhaust gas temperature (EGT) probe. Situated at the exhaust manifold, the EGT gauge can determine the ratio of fuel and air entering the engine’s cylinders, based on how hot the exhaust is. This can in turn be used to regulate the fuel/air mixture and ensure a healthy fuel economy.