16.6 and 16.7 Induction, exhaust and cooling; supercharging and turbocharging

Scope

Both A level 1, B1/B3 level 2.

• 16.6: construction and operation of induction systems including alternate air; exhaust systems; engine cooling — air and liquid.
• 16.7: principles and purpose of supercharging and its effect on engine parameters; construction and operation of supercharging/turbocharging systems; terminology; control systems; protection.

Induction system

Typical path: ram-air intake → air filter (paper, foam or gauze) → air box (with carburettor heat or alternate air valve) → carburettor or fuel-injection servo → induction manifold → cylinders.

• Alternate air: if the filter becomes blocked (ice, debris), air is drawn from an alternate source — a spring-loaded door that is sucked open automatically, or a manually selected valve. Alternate air is usually warm, unfiltered engine-compartment air, so power drops slightly.
• Carburettor heat (carburettor engines): air heated by an exhaust muff (see 16.4).
• Induction leaks downstream of the throttle → lean mixture in affected cylinders, rough idle, high CHT.
• Inspect hoses, clamps, filter condition and seals; replace filters per schedule.

Exhaust systems

• Short stacks (individual pipes) or collector systems joining to one or two tailpipes with a muffler (silencer).
• Heat exchanger (shroud) around the muffler supplies cabin heat and carburettor heat — a cracked muffler or exhaust leak inside the shroud can put carbon monoxide into the cabin, the most serious exhaust hazard. CO detectors are recommended.
• Exhaust leaks also cause burnt cowlings, wiring and fuel/oil lines, and fire risk.
• Materials: stainless steel or Inconel; slip joints and flexible couplings allow thermal expansion; ball joints on some.
• Augmentor tubes: exhaust gas flowing through a larger tube draws additional cooling air over the engine (FAA).
• Inspection: cracks near welds and clamps, bulging/thinning (internal baffles of mufflers can fail and block flow), pressure test of the heat exchanger, never use lead pencils or galvanised hardware on exhaust parts (carbon/zinc causes cracking at high temperature).