Secondary air injection

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Secondary air injections (commonly known as air injection ) is a vehicle emissions control strategy introduced in 1966, where fresh air is injected into the discharge stream to enable fuller combustion of exhaust gases.

Video Secondary air injection

Development

The mechanism by which exhaust emissions are controlled depends on the method of injection and the point at which air enters the exhaust system, and varies during technological development.

The first system injects very close air to the engine, either in the cylinder head exhaust port or in the exhaust manifold. This system provides oxygen for oxidizing (burning) unburned fuel and partially burning in the exhaust before being ejected from the exhaust. There is unburned fuel and mostly burns in the exhausts of the 1960s and early 1970s vehicles, and secondary air injection significantly reduces exhaust emissions. However, the extra heat of recombination, especially with a very rich exhaust caused by misfiring or damaged carburetors, tends to damage the exhaust valve and may even be seen causing the exhaust manifold to become incandescent.

As emissions control strategies become more sophisticated and effective, the amount of unburned and partially burned fuel in the discharge stream shrinks, and in particular when the catalytic converter is introduced, the secondary air injection function shifts. Instead of being a primary emission control device, a secondary air injection system is adapted to support the efficient function of a catalytic converter. The original air injection point is known as an upstream injection point. When the catalytic converter cools, the air being injected at the point of burning up with a richly deliberate exhaust brings the catalyst to the operating temperature rapidly. After the catalyst is warm, air is injected to the downstream location - the catalytic converter itself - to help the catalysis of unburned hydrocarbons.

Maps Secondary air injection

Implementation method

Pumped air circulation

The pumped air injection system uses a vane pump called an air pump, air pump, or daily "smoke pump" that is rotated by the engine through a belt or electric motor. The pump air intake is filtered by a rotating screen to remove large amounts of dirt particles to damage the system. Air is sent under light pressure to the injection points. A check valve prevents the exhaust from forcing its way back through an air injection system, which will damage the pump and other components.

Carburetor engine fuel exhaust fuel contents tend to jump when the driver suddenly releases the throttle. To prevent the surprising and potentially destructive effects of explosive combustion of these raw fuels, the flow valve is used. This valve feels a sharp decline in the vacuum intake manifold resulting from a sudden throttle closure, and diverts the air pump outlet into the atmosphere. Usually this transferred air is flowed to the engine air cleaner or to a separate silencer to muffle the unpleasant pump noise.

Aspirative air circulation

Air injection can also be achieved by taking advantage of negative pressure on the exhaust system in the idle machine. A sensitive reed valve assembly called the aspirator valve is placed in an air injection pump, which draws air directly from the clean side of the air filter. During the idle engine, a short but periodic negative pressure pulse in the exhaust system draws air through the aspirator valve and into the exhaust stream on the catalytic converter. This system, marketed as Air Pulse, is used by American Motors, Chrysler, and other manufacturers that began in the 1970s. Aspirators provide advantages in cost, weight, packaging, and simplicity compared to pumps, but aspirators only function when idle and therefore recognize significantly less air in a significantly narrower engine speed range compared to pumps. This system is still used on modern motorcycle engines, eg. Yamaha AIS (Air Injection System).

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See also

• Catalytic converter

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External links

• Secondary Air Systems Principle on YouTube
• Faiz, Asif; Weaver, Christopher S.; Walsh, Michael P. (January 1, 1996), "Thermal Oxidation", Air Pollution from Motor Vehicles: Standards and Technologies to Control Emissions , World Bank Publications, p. 96