Air Injection: Description and Operation

Description

The Thermactor air injection system reduces the level of hydrocarbon, carbon monoxide and NOx emissions by oxidizing the hydrocarbon and carbon monoxide contaminants in the exhaust ports of the cylinder head. Air under pressure is injected into the exhaust ports near each exhaust valve. The oxygen in the air plus the heat of the exhaust gases induces further combustion of the exhaust gases.

Construction

Fig. 2 - Air Manifold Assembly:

The basic system incorporates an air pump, a check valve, and air injection nozzles, Fig. 2. 1972-74 models use an air bypass valve. All 1975-76 vehicles and 1977-82 California vehicles use an air control valve. 1979-82 vehicles (except California) use a reed valve (refer to "Secondary Air Injection"). 1977-82 California vehicles use a vacuum delay valve.

Operation

Air under pressure flows through a hose to the air manifold which distributes the air to the injection nozzles in each exhaust port. The air oxidizes the unburned portion of the exhaust gases, in turn reducing the level of harmful emissions. A relief valve, located on the air pump, relieves excess pressure in the pump, protecting the pump and reducing excessive power loss. A check valve, located in the inlet air side of the air manifold, prevents backflow of exhaust gases when the air pressure from the pump is lower than that of the exhaust gas. The difference in pressure opens the valve and air from the pump may flow into the air injection manifold. If the exhaust gas pressure exceeds the air pressure because of engine speed increases or air pressure decreases, the check valve will close immediately to prevent hot exhaust gas from entering into and damaging the air pump or the connecting rubber hoses.

Fig. 4 - Air Control Valve:

On 1977-82 models, an air control valve is installed between the air pump and check valve on California models. On the 1800cc engine and the 2300cc engine equipped with automatic transmission, the air control valve has one relief valve and is activated by intake manifold vacuum. On 2300cc engines equipped with manual transmission, the air control valve has two relief valves, No. 1 and No. 2. The No. 1 relief valve is activated by intake manifold vacuum. The No. 2 relief valve modulates the amount of secondary air to accelerate the oxidation of unburned exhaust gases according to vehicle operating conditions.

At low engine speeds, the No. 1 relief valve is closed on all California models and air from the pump is directed to the check valve and into the air injection nozzles. This prevents the exhaust system from overheating at low speeds. At higher speeds, the No. 1 relief valve opens, venting the air pump air to the atmosphere.

The No. 2 relief valve opens to reduce air flow to the injection manifold during low engine load when only a small volume of air for injection is necessary due to the decreased volume of exhaust gases. When engine load increases, the valve closes and increases air flow to the injection manifold.