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Air Injection System

Air Injection Systems | What Is It?

An air injection system forces fresh air into the exhaust ports of the engine to reduce HC and CO emissions. The exhaust gases leaving an engine can contain unburned and partially burned fuel. Oxygen from the air injection system causes this fuel to continue to burn. The major parts of the system are the air pump, the diverter valve, the air distribution manifold, and the air check valve.

During the early days of emis­sion control, it was an easy task to meet the required emission standards through air injection. Air injec­tion, also known as the air pump system (Fig. 17.28), was one of the first add-on devices to oxidise HC and CO in the exhaust. By 1966 Chrysler, the only domes­tic manufacturer, was not using an air pump system on at least some cars. Early air injection systems used many hoses and tubes placed across the engine so that it became inconvenient to work on the engine, and hose failure due to engine heat also became common.

Parts of the System

  • The AIR PUMP is belt-driven and forces air at low pressure into the system. A hose is connected to the output of the diverter valve.
  • The DIVERTER VALVE keeps air from entering the exhaust system during deceleration. This prevents backfiring in the exhaust system. Also, the diverter valve limits maximum system air pressure when needed, releasing excessive pressure through a silencer or a muffler.
  • AIR DISTRIBUTION MANIFOLD directs a stream of fresh air toward each engine exhaust valve. Fittings on the air distribution manifold screw into a threaded hole in the exhaust manifold or cylinder head.
  • AIR CHECK VALVE is usually located in the line between the diverter valve and the air distribution manifold. It keeps exhaust gases from entering the air injection system.

How It Works

When the engine is running, the spinning vanes of the air pump force air into the diverter valve. If not decelerating, the air is forced through the diverter valve, the check valve, the air injection manifold, and into the engine. The fresh air blows on the exhaust valves.

During periods of deceleration, the diverter valve blocks airflow into the engine exhaust manifold. This prevents a possible backfire that could damage the exhaust system of the vehicle. When needed, the diverter valve will release excess pressure in the system.

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