After implementing BS-IV in the year of 2017, manufacturers used several ways to reduce emissions. Different methods have been implemented for example Secondary Air Induction or SAI system. Some of the manufactures used this Evaporative Emission Control System or simply called as EVAP. Generally what this system does is, when the petrol vapor is emitted from fuel tank, it is captured by a canister where coal is present inside it. Using inlet suction pressure, those vapor from the charcoal canister is sent to the carburetor again for combustion process. This petrol vapor consists of benzene, toluene and others which is harmful and when it is released into atmosphere, it pollutes the atmospheric air. To minimize this, EVAP system is introduced in motorbikes. And also, this is the reason why showroom people tells us not to full our fuel tank. Here in this post, let's see how this EVAP system works.
Firstly, let's see how i got to know about this EVAP. I have a 200NS BS-IV which is a carbureted one and non ABS. While cleaning, under the rider seat, i've seen a small black box with some tubes connected in it. Firstly i thought it as a CDI unit which is responsible for ignition. After that, i came to know that the CDI unit is present under the pillion seat. So i started to research about this mysterious black box in my motorbike. In a YouTube video, i came to know about this charcoal canister and its function.
We know that the atmospheric air have to enter into the fuel tank, if fuel wants to flow. In BS-III motorbikes and in old motorbikes, fuel cap itself acts as a fuel tank breather. I believe that you have heard a word of air lock in fuel tank. Its nothing but, the air gets blocked so that the fuel won't flow from the tank which results in starting trouble. By opening the fuel cap, the block will be cleared and you can again start your motorbike. In BS-IV motorbikes, this system is totally eliminated. Instead of that, two tubes will be present below or above the fuel tank. One tube is for draining out the water entered into the fuel tank. Here, this second tube plays an important role. It does the job of helping the fuel tank to breathe and carrying petrol vapor to the charcoal canister. This EVAP hose further splits into two, forming a Y shaped arrangement. One end is connected to the No Return Valve or NRV or one way valve. As we know, fuel tank needs to breathe. What this NRV does is, it allows the air to get in whenever needed. This valve acts only in one direction. The petrol vapor from the tank will not pass through this NRV and gets out.
Another end is connected to the roll over valve. It also plays a important role here. What it does is, during accidents, when our vehicle is flat, it prevents the petrol to flow via breather hose and entering to the charcoal canister. To understand it simply, imagine your vehicle is in straight position. When you full the tank, there are chances for the petrol to flow via this roll over valve and entering into the charcoal canister. But when your vehicle is in flat condition during accidents or in any other cases, this roll over valve prevents the petrol from entering to the charcoal canister. Inside this canister, charcoal will be present. It absorbs and store the vapor in it and sends it to the carb whenever there is a suction pressure. If petrol enters into the canister, the charcoal will lose its effectiveness. I hope that you've got the basic idea of this roll over valve.
After roll over valve, the hose straightly travels to the canister. Here, the petrol vapor is stored. Another tube coming out from the canister directly connected to carburetor via purge valve. When suction stroke happens, air and fuel mixture gets sucked into the combustion chamber. What this purge valve does is, when suction stroke happens, this purge valve sucks the petrol vapor from the canister and sends it to the carburetor for combustion process. Thus petrol vapor is also burned with the normal air fuel mixture thereby preventing this harmful gas getting released into the atmosphere. You may wonder why another two tubes is present in the canister on other side. If petrol vapor exits the canister during suction, those space need to be filled with atmospheric air. So one hose takes care of that. What other hose does is, when you full your tank, there are chances for petrol getting into this breather hose present inside the tank and travels to the canister via roll over valve. If this happens and if the petrol stays inside the canister, it won't work. So if the petrol enters to the canister, it'll drain via drain hose in the canister.
Working
Imagine you have parked your motorbike in a hot sun. Surely, some amount of petrol will be vaporized. Those petrol vapor travels through this EVAP hose and enters the canister via roll over valve. For breathing of the fuel tank, another hose is connected to it. In charcoal canister, those petrol vapor will be stored. When you try to start your motorbike, during suction stroke, those petrol vapor in the canister gets sucked and travels to the carburetor via purge valve. This purge valve is responsible for the petrol vapor entering the carburetor. Thus petrol vapor gets burned with the fresh charge thereby reducing emissions. During suction, fresh air enters into the canister via a separate hose. Roll over valve prevents the fuel entering into canister incase of any accidents. Unfortunately, if fuel enters enters into the canister, it'll drain via another hose.
Advantages
• Eliminate the release of vaporized HC into the atmosphere.
• Increase in fuel economy but not much. If you calculate total savings from this EVAP for a year, it'll worth it.
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| Canister |
Firstly, let's see how i got to know about this EVAP. I have a 200NS BS-IV which is a carbureted one and non ABS. While cleaning, under the rider seat, i've seen a small black box with some tubes connected in it. Firstly i thought it as a CDI unit which is responsible for ignition. After that, i came to know that the CDI unit is present under the pillion seat. So i started to research about this mysterious black box in my motorbike. In a YouTube video, i came to know about this charcoal canister and its function.
We know that the atmospheric air have to enter into the fuel tank, if fuel wants to flow. In BS-III motorbikes and in old motorbikes, fuel cap itself acts as a fuel tank breather. I believe that you have heard a word of air lock in fuel tank. Its nothing but, the air gets blocked so that the fuel won't flow from the tank which results in starting trouble. By opening the fuel cap, the block will be cleared and you can again start your motorbike. In BS-IV motorbikes, this system is totally eliminated. Instead of that, two tubes will be present below or above the fuel tank. One tube is for draining out the water entered into the fuel tank. Here, this second tube plays an important role. It does the job of helping the fuel tank to breathe and carrying petrol vapor to the charcoal canister. This EVAP hose further splits into two, forming a Y shaped arrangement. One end is connected to the No Return Valve or NRV or one way valve. As we know, fuel tank needs to breathe. What this NRV does is, it allows the air to get in whenever needed. This valve acts only in one direction. The petrol vapor from the tank will not pass through this NRV and gets out.
Another end is connected to the roll over valve. It also plays a important role here. What it does is, during accidents, when our vehicle is flat, it prevents the petrol to flow via breather hose and entering to the charcoal canister. To understand it simply, imagine your vehicle is in straight position. When you full the tank, there are chances for the petrol to flow via this roll over valve and entering into the charcoal canister. But when your vehicle is in flat condition during accidents or in any other cases, this roll over valve prevents the petrol from entering to the charcoal canister. Inside this canister, charcoal will be present. It absorbs and store the vapor in it and sends it to the carb whenever there is a suction pressure. If petrol enters into the canister, the charcoal will lose its effectiveness. I hope that you've got the basic idea of this roll over valve.
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| Purge valve |
After roll over valve, the hose straightly travels to the canister. Here, the petrol vapor is stored. Another tube coming out from the canister directly connected to carburetor via purge valve. When suction stroke happens, air and fuel mixture gets sucked into the combustion chamber. What this purge valve does is, when suction stroke happens, this purge valve sucks the petrol vapor from the canister and sends it to the carburetor for combustion process. Thus petrol vapor is also burned with the normal air fuel mixture thereby preventing this harmful gas getting released into the atmosphere. You may wonder why another two tubes is present in the canister on other side. If petrol vapor exits the canister during suction, those space need to be filled with atmospheric air. So one hose takes care of that. What other hose does is, when you full your tank, there are chances for petrol getting into this breather hose present inside the tank and travels to the canister via roll over valve. If this happens and if the petrol stays inside the canister, it won't work. So if the petrol enters to the canister, it'll drain via drain hose in the canister.
Working
Imagine you have parked your motorbike in a hot sun. Surely, some amount of petrol will be vaporized. Those petrol vapor travels through this EVAP hose and enters the canister via roll over valve. For breathing of the fuel tank, another hose is connected to it. In charcoal canister, those petrol vapor will be stored. When you try to start your motorbike, during suction stroke, those petrol vapor in the canister gets sucked and travels to the carburetor via purge valve. This purge valve is responsible for the petrol vapor entering the carburetor. Thus petrol vapor gets burned with the fresh charge thereby reducing emissions. During suction, fresh air enters into the canister via a separate hose. Roll over valve prevents the fuel entering into canister incase of any accidents. Unfortunately, if fuel enters enters into the canister, it'll drain via another hose.
Advantages
• Eliminate the release of vaporized HC into the atmosphere.
• Increase in fuel economy but not much. If you calculate total savings from this EVAP for a year, it'll worth it.
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