Air Injection: Description and Operation

System Description:

The Thermactor (air injection) Exhaust Emission Control System reduces the hydrocarbon and carbon monoxide content of the gases by continuing the combustion of unburned gases after they leave the combustion chamber by injecting fresh air into the hot exhaust stream leaving the exhaust ports. At this point, the fresh air mixes with hot exhaust gases to promote further oxidation of both the hydrocarbons and carbon monoxide, thereby reducing their concentration and converting some of them into harmless carbon dioxide and water. During different engine operations, such as cruise and WOT, the thermactor air is dumped to atmosphere to prevent overheating in the exhaust system. A typical air injection system may contain the following components:
Air supply pump
Air bypass valve - TAB
Check valve
Air manifold
Air hoses
Air control valve - TAD

Typical Managed Air Thermactor System:

The Managed Air Thermactor System is utilized in electronic control systems to divert thermactor air either upstream to the exhaust manifold check valve or downstream to the rear section check valve and dual bed catalyst. The system will also dump thermactor air to atmosphere during some operating modes. An air control valve is used to direct the air either upstream or downstream. An air bypass valve is used to dump air to atmosphere. This system is used with a three-way catalyst and can be electronically or non-electronically controlled. The operation of air is as follows:
1. The air is dumped or bypassed to atmosphere when the exhaust is rich. This prevents backfire and catalyst damage along with removing the pump load from the engine.
2. The air is sent upstream (to exhaust manifold) when the engine is first started and the catalyst is still cold.
3. The air is sent downstream (to catalyst) after the engine and catalyst are warmed up.