In 2023, there is a technical topic related to plug-in hybrid vehicles, which revolves around the "carbon canister", and now it is time to reinterpret and summarize this topic.
Gasoline-powered vehicles and plug-in hybrids and plug-in range extender vehicles that still use engines both have carbon canister systems, which refer to devices with activated carbon inside, which are connected to the car's fuel tank and engine air intake system. Because the volatile performance of gasoline is very strong, even in a low temperature environment of tens of degrees below zero, and liquid gasoline volatilizes into gasoline vapor and the volume will expand, so it is necessary to set up a "fuel vapor exhaust pipe" for the fuel tank to avoid the fuel tank being broken.
The oil and gas exhaust pipe is connected to the carbon canister, the fuel vapor can be burned to do work, and the liquid gasoline to the engine also needs to be compressed and evaporated before it can be burned with higher efficiencyTherefore, it is a waste of fuel to exhaust the fuel vapor directly out of the car, and it will also pollute the air, so the carbon canister will be designed, which is used to adsorb the fuel in the gasoline vapor and exhaust the air.
The volatile gasoline vapor is adsorbed after reaching the canister, and then the filtered air is discharged through the canister vent, so that the constant pressure of the fuel tank can be achieved.
It's just that how does the gasoline adsorbed by activated carbon participate in the combustion?
The solution is simple, the other end of the canister is connected to the engine's intake manifold, which generates airflow after starting the engineThe airflow creates a negative pressure, which to put it bluntly creates a suction force on the pipes connected to the canister. At this time, the vent of the carbon canister becomes an "air intake hole", and the air flow generated by the intake air realizes the desorption of activated carbon adsorption fuel, and then enters the intake manifold with the air flow, and finally reaches the engine combustion chamber to participate in the work.
The size of the canister is very small, and the capacity of activated carbon is very limited.
As long as the vehicle is parked for too long, the capacity limit of the carbon canister will be exceeded, and then the air will be discharged from the vehicle instead of filtered airTherefore, the fuel vehicle will still be parked for a long time and the "vehicle evaporative evaporation emission" will exceed the standard, but as long as the fuel vehicle is used normally, it will often not be parked for a long time, and a few cases cannot be avoided.
However, the usage of plug-in hybrid vehicles (including plug-in range extended hybrid vehicles) is completely different, this type of car supports charging and pure electric driving, statistics show that more than 80% of plug-in hybrid car users do not start the engine in daily car use scenarios, and use the vehicle as an electric vehicle. As a result, the engines of these cars are likely to not be started once a month or two, and the evaporative emissions are bound to be large, so how to control the evaporative emissions of these cars has become a problem.
Plug-in hybrid cars will not use the engine for a long time, although the car may be driven every day, but the engine is like those gasoline vehicles that stop for dozens of days;Therefore, the adsorption capacity of the canister must be large enough, but the canister canister can't be too large, so the solution can only be explored from the direction of the fuel tank.
At present, the reasonable solution is to use high-pressure fuel tanks, and fuel vehicles use ordinary pressure fuel tanksThis kind of fuel tank is basically made of engineering plastic, and the strength is relatively low, even if it is a metal fuel tank, it will not have a high standard.
The high-pressure fuel tank has a high strength, mostly made of metal, and this kind of fuel tank can withstand higher pressures;That is, gasoline can be volatilized in the tank without being discharged into the canister system, and the tank can lock the gasoline vapor in the tank and wait for the next time when the hybrid mode is used for one-time consumption.
This seems to be the most reasonable solution at the moment, firstly, locking in the fuel vapor can minimize evaporative emissions and waste, and secondly, it will not be refueled when the oil is not used, so there will be no excessive gasoline vapor emissions when refuelingTherefore, whether it is from the perspective of safe use of the car or from the perspective of saving, the high-pressure fuel tank is indeed the only choice.
In 2023, one car company was reported by another car company that some of its vehicles were involved in "suspected excessive emission of pollutants from the whole vehicle", and the brand's plug-in hybrid vehicles used atmospheric fuel tanks instead of high-pressure fuel tanks, which could not lock gasoline vaporsSo there is a high chance that these cars will have excessive gasoline vapor emissions, but they have adopted a very peculiar alternative.
The solution is that the engine starts automatically at regular intervals, i.e. when the canister reaches a threshold.
After the engine starts, the fuel car adsorbed by the carbon canister will be desorbed and participate in the combustion, which can indeed avoid excessive evaporative emissions, but it allows the vehicle to burn oil for no reason - the result is more waste and emissions, and it is equivalent to "stealing" the owner's oil to ensure that the evaporative emissions of the vehicle meet the standard, whether such a scheme is reasonable is still controversial, this case has not yet been conclusively determined.
However, prospective users who are ready to choose plug-in hybrid and extended-range hybrid vehicles are not worried, after this case, all the brand's vehicles will be replaced with high-pressure fuel tanks, and other brands will of course use high-pressure fuel tanks.
Editor: Tianhe auto-auto science island, welcome to retweet the comments.
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