Air injection reactor
Encyclopedia
Secondary air injection is a vehicle emissions control strategy introduced in 1966, wherein fresh air is injected into the exhaust stream to allow for a fuller combustion of exhaust gases
.
The first systems injected air very close to the engine, either in the cylinder head's exhaust ports or in the exhaust manifold
. These systems provided oxygen to oxidize (burn) unburned and partially-burned fuel in the exhaust before its ejection from the tailpipe. There was significant unburned and partially-burned fuel in the exhaust of 1960s and early 1970s vehicles, and so secondary air injection significantly reduced tailpipe emissions. However, the extra heat of recombustion, particularly with an excessively rich exhaust caused by misfiring or a maladjusted
carburetor
, tended to damage exhaust valves and could even be seen to cause the exhaust manifold
to incandesce
.
As emission control strategies grew more sophisticated and effective, the amount of unburned and partially-burned fuel in the exhaust stream shrank, and particularly when the catalytic converter
was introduced, the function of secondary air injection shifted. Rather than being a primary emission control device, the secondary air injection system was adapted to support the efficient function of the catalytic converter. The original air injection point became known as the upstream injection point. When the engine is cold, air injected at this point cleans up the extra-rich exhaust and raises the temperature of the exhaust so as to bring the catalytic converter to operating temperature
quickly. Once the engine is warm, air is injected to the downstream location — the catalytic converter itself — to assist with catalysis of unburned hydrocarbons and carbon monoxide.
prevents exhaust forcing its way back through the air injection system, which would damage the pump and other components.
Carbureted
engines' exhaust raw fuel content tends to spike when the driver suddenly releases the throttle
. To prevent the startling and potentially damaging effects of the explosive combustion of this raw fuel, a diverter valve is used. This valve senses the sharp increase in intake manifold vacuum resulting from the sudden closure of the throttle, and diverts the air pump's outlet to atmosphere. Usually this diverted air is routed to the engine air cleaner or to a separate silencer to muffle objectionable pump noise.
assembly called the aspirator valve is placed in the air injection plumbing, which draws its air directly from the clean side of the air filter
. During engine idle, brief but periodic negative pressure pulses in the exhaust system draw air through the aspirator valve and into the exhaust stream at the catalytic converter. This system, marketed as Pulse Air, was used by American Motors
, Chrysler
, and other manufacturers beginning in the 1970s. The aspirator provided advantages in cost, weight, packaging, and simplicity compared to the pump, but the aspirator functions only at idle and so admits significantly less air within a significantly narrower range of engine speeds compared to a pump. This system is still used on modern motorcycle engines, e.g. the Yamaha AIS (Air Injection System).
Motor vehicle emissions
Motor vehicle emissions are composed of the by-products that comes out of the exhaust systems or other emissions such as gasoline evaporation...
.
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 has varied during the course of the development of the technology.The first systems injected air very close to the engine, either in the cylinder head's exhaust ports or in the exhaust manifold
Exhaust manifold
In automotive engineering, an exhaust manifold collects the exhaust gases from multiple cylinders into one pipe. The word manifold comes from the Old English word manigfeald and refers to the folding together of multiple inputs and outputs.In contrast, an inlet manifold is the part of an engine...
. These systems provided oxygen to oxidize (burn) unburned and partially-burned fuel in the exhaust before its ejection from the tailpipe. There was significant unburned and partially-burned fuel in the exhaust of 1960s and early 1970s vehicles, and so secondary air injection significantly reduced tailpipe emissions. However, the extra heat of recombustion, particularly with an excessively rich exhaust caused by misfiring or a maladjusted
Stoichiometry
Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...
carburetor
Carburetor
A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....
, tended to damage exhaust valves and could even be seen to cause the exhaust manifold
Exhaust manifold
In automotive engineering, an exhaust manifold collects the exhaust gases from multiple cylinders into one pipe. The word manifold comes from the Old English word manigfeald and refers to the folding together of multiple inputs and outputs.In contrast, an inlet manifold is the part of an engine...
to incandesce
Incandescence
Incandescence is the emission of light from a hot body as a result of its temperature. The term derives from the Latin verb incandescere, to glow white....
.
As emission control strategies grew more sophisticated and effective, the amount of unburned and partially-burned fuel in the exhaust stream shrank, and particularly when the catalytic converter
Catalytic converter
A catalytic converter is a device used to convert toxic exhaust emissions from an internal combustion engine into non-toxic substances. Inside a catalytic converter, a catalyst stimulates a chemical reaction in which noxious byproducts of combustion are converted to less toxic substances by dint...
was introduced, the function of secondary air injection shifted. Rather than being a primary emission control device, the secondary air injection system was adapted to support the efficient function of the catalytic converter. The original air injection point became known as the upstream injection point. When the engine is cold, air injected at this point cleans up the extra-rich exhaust and raises the temperature of the exhaust so as to bring the catalytic converter to operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
quickly. Once the engine is warm, air is injected to the downstream location — the catalytic converter itself — to assist with catalysis of unburned hydrocarbons and carbon monoxide.
Pumped air injection
Pumped air injection systems use a vane pump turned by the engine via a belt. The pump's air intake is centrifugally filtered by a rotating screen to exclude dirt particles large enough to damage the system. Air is delivered under pressure to the injection point(s). A check valveCheck valve
A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid to flow through it in only one direction....
prevents exhaust forcing its way back through the air injection system, which would damage the pump and other components.
Carbureted
Carburetor
A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....
engines' exhaust raw fuel content tends to spike when the driver suddenly releases the throttle
Throttle
A throttle is the mechanism by which the flow of a fluid is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases , but usually decreased. The term throttle has come to refer, informally and incorrectly, to any mechanism by which...
. To prevent the startling and potentially damaging effects of the explosive combustion of this raw fuel, a diverter valve is used. This valve senses the sharp increase in intake manifold vacuum resulting from the sudden closure of the throttle, and diverts the air pump's outlet to atmosphere. Usually this diverted air is routed to the engine air cleaner or to a separate silencer to muffle objectionable pump noise.
Aspirated air injection
Air injection can also be achieved by taking advantage of the negative pressure pulses in the exhaust system at engine idle. A sensitive reed valveReed valve
Reed valves are a type of check valve which restrict the flow of fluids to a single direction, opening and closing under changing pressure on each face...
assembly called the aspirator valve is placed in the air injection plumbing, which draws its air directly from the clean side of the air filter
Air filter
A particulate air filter is a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. A chemical air filter consists of an absorbent or catalyst for the removal of airborne molecular contaminants such as volatile organic compounds...
. During engine idle, brief but periodic negative pressure pulses in the exhaust system draw air through the aspirator valve and into the exhaust stream at the catalytic converter. This system, marketed as Pulse Air, was used by American Motors
American Motors
American Motors Corporation was an American automobile company formed by the 1954 merger of Nash-Kelvinator Corporation and Hudson Motor Car Company. At the time, it was the largest corporate merger in U.S. history.George W...
, Chrysler
Chrysler
Chrysler Group LLC is a multinational automaker headquartered in Auburn Hills, Michigan, USA. Chrysler was first organized as the Chrysler Corporation in 1925....
, and other manufacturers beginning in the 1970s. The aspirator provided advantages in cost, weight, packaging, and simplicity compared to the pump, but the aspirator functions only at idle and so admits significantly less air within a significantly narrower range of engine speeds compared to a pump. This system is still used on modern motorcycle engines, e.g. the Yamaha AIS (Air Injection System).
External links
- Jeep Adventures Under the Hood A detailed guide on the CEC system and how to tune it
- Details with diagrams of the Chevrolet CamaroChevrolet CamaroThe Chevrolet Camaro is an automobile manufactured by General Motors under the Chevrolet brand, classified as a pony car and some versions also as a muscle car. It went on sale on September 29, 1966, for the 1967 model year and was designed as a competing model to the Ford Mustang...
AIR system www.camaros.org