Preheating of intake air (Opel Vectra B)

The air sucked into the combustible mixture must not be too cold or too hot. Therefore, in 8-valve 1.6 l engines with central injection, under certain conditions, the air enters the intake channels preheated:

At low outside temperatures, the combustible mixture burns better (emissions of harmful substances are lower), if the air required for combustion is heated.

Preheated air prevents central injection icing, which can occur at temperatures from +3°C to +8°C and high air humidity. When the engine is running, some of the fuel evaporates; the resulting cold of evaporation at the appropriate air humidity can lead to the formation of a layer of ice and prevent the preparation of a perfect fuel-air mixture.

At higher outside temperatures, cooler intake air is better. Air expands when heated. Since the engine can only suck in a certain amount of air, it gets less when it is hot. This leads to a richer fuel-air mixture and increased fuel consumption.

Automatic control of intake air preheating

Preheating of the air is carried out depending on the load and temperature: cold air enters the air filter housing at the front through the intake pipe. Heated air from the exhaust manifold can enter through the second channel. In the air filter housing there is a control valve that regulates the flow of heated air. The so-called thermal valve determines from which channel the air is sucked. When the throttle valve is closed or only slightly open, there is high negative pressure in the intake manifold underneath it. This negative pressure acts on the membrane of the control valve, as a result of which it opens the flow of warm air and simultaneously reduces the flow of cold air. When gas is supplied, the negative pressure in the intake manifold decreases, and now the air valve closes the flow of warm air.



As soon as the intake air reaches a certain temperature, the thermal valve in the vacuum line closes the passage, the damper closes the supply of warm air, now only cold air can be sucked in.



(Article posted on an online resource: opelbook)