We can able to see this Secondary Air Induction system or SAI system almost in every BS IV motorbikes. Either the motorbike comes with Canister system or this SAI system. You can think about this. If this is called as secondary air induction, which one is called as primary air induction? Exactly..... It's the carburetor. It sucks air during the suction stroke and it is necessary for the vehicle to move. So it is called as primary air induction. This SAI system is designed and developed to control the pollution. As we know, from April 2017, BS IV has been implemented and manufacturers were looking for a way to reduce emissions. Manufacturers like Hero Motocorp implemented this SAI system in their motorbikes. Here in this post, let's see about SAI system and how it works...
Overview
What this SAI system does is, introducing fresh air from air filter to the exhaust manifold to convert carbon monoxide to carbon dioxide thereby reducing the release of harmful emissions. This system mainly consist of two components in it. First one is known as the one way valve or reed valve and the second one is known as diaphragm. In the SAI unit, three tubes will be connected. First hose will be connected near the carburetor or inlet flange. Second hose will be straightly connected to the air box. Third hose will be straightly connected to the exhaust's header pipe. The other two tube will be a normal rubber hose. Where this third hose is designed in such a way to withstand more heat because, it is in direct contact with the exhaust's header.
Working
During suction stroke of the combustion cycle, air and fuel mixture gets sucked into the combustion chamber due to the downward moment of piston. As we know, a hose is connected near the inlet flange which is straightly connected to the SAI unit. Because of the hose connected near the inlet flange, the suction pressure will act on that hose also. This suction pressure will activate the diaphragm present inside the SAI system. When the moment this diaphragm valve gets sucked, it allows the fresh air from air filter to enter to the SAI system. The entered air further travels to the exhaust's header passing the reed valve or one way valve. What this reed valve does is, it allows only the fresh air to enter into the header pipe. If the exhaust gas escape and travels through that hose, this reed valve blocks the way and thus prevents exhaust gas entering into the SAI system. Thus pure air is introduced to the exhaust gases thereby reducing the emissions.
I know you'll be in confusion. Without any work done, how this fresh air enters into the SAI unit and travels to the exhaust's header pipe? Right? The suction pressure from the cylinder only allows the diaphragm valve to open making way for the fresh air to enter the SAI system and allows it to travel to the header pipe. Then how this fresh air travels from the air filter to the header pipe?... It's much simple. The same principle used in the carburetor is also used here. Near the header pipe, hot burnt fuel air mixture will be travelling from the combustion chamber to the exhaust pipe. When velocity in that spot increases, then automatically the pressure will decrease. We know that the air will always travel from high pressure side to low pressure side. Then automatically, the fresh air from the air filter travels to the exhaust's header pipe via the SAI module. I hope you have understood the concept.
Things that you have to look after
As i said, a hose will be connected near the inlet flange for creating the suction pressure. If that hose is disconnected or if that hose have any holes or damages, the bike wouldn't start. Because, if that hose is disconnected or damaged, the suction needed for the combustion to happen will be disturbed. So, if you are facing starting trouble in your motorbike, make sure whether this hose is correctly fixed and not damaged. Make sure whether the hose from the air filter is correctly plugged into the SAI module. If not, the intake sound differs and filtered air will not be introduced into the exhaust's header pipe. If this happens, the pollution will not be controlled.
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| SAI module |
Overview
What this SAI system does is, introducing fresh air from air filter to the exhaust manifold to convert carbon monoxide to carbon dioxide thereby reducing the release of harmful emissions. This system mainly consist of two components in it. First one is known as the one way valve or reed valve and the second one is known as diaphragm. In the SAI unit, three tubes will be connected. First hose will be connected near the carburetor or inlet flange. Second hose will be straightly connected to the air box. Third hose will be straightly connected to the exhaust's header pipe. The other two tube will be a normal rubber hose. Where this third hose is designed in such a way to withstand more heat because, it is in direct contact with the exhaust's header.
Working
During suction stroke of the combustion cycle, air and fuel mixture gets sucked into the combustion chamber due to the downward moment of piston. As we know, a hose is connected near the inlet flange which is straightly connected to the SAI unit. Because of the hose connected near the inlet flange, the suction pressure will act on that hose also. This suction pressure will activate the diaphragm present inside the SAI system. When the moment this diaphragm valve gets sucked, it allows the fresh air from air filter to enter to the SAI system. The entered air further travels to the exhaust's header passing the reed valve or one way valve. What this reed valve does is, it allows only the fresh air to enter into the header pipe. If the exhaust gas escape and travels through that hose, this reed valve blocks the way and thus prevents exhaust gas entering into the SAI system. Thus pure air is introduced to the exhaust gases thereby reducing the emissions.
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| Layout diagram |
I know you'll be in confusion. Without any work done, how this fresh air enters into the SAI unit and travels to the exhaust's header pipe? Right? The suction pressure from the cylinder only allows the diaphragm valve to open making way for the fresh air to enter the SAI system and allows it to travel to the header pipe. Then how this fresh air travels from the air filter to the header pipe?... It's much simple. The same principle used in the carburetor is also used here. Near the header pipe, hot burnt fuel air mixture will be travelling from the combustion chamber to the exhaust pipe. When velocity in that spot increases, then automatically the pressure will decrease. We know that the air will always travel from high pressure side to low pressure side. Then automatically, the fresh air from the air filter travels to the exhaust's header pipe via the SAI module. I hope you have understood the concept.
Things that you have to look after
As i said, a hose will be connected near the inlet flange for creating the suction pressure. If that hose is disconnected or if that hose have any holes or damages, the bike wouldn't start. Because, if that hose is disconnected or damaged, the suction needed for the combustion to happen will be disturbed. So, if you are facing starting trouble in your motorbike, make sure whether this hose is correctly fixed and not damaged. Make sure whether the hose from the air filter is correctly plugged into the SAI module. If not, the intake sound differs and filtered air will not be introduced into the exhaust's header pipe. If this happens, the pollution will not be controlled.
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