Hello steemians! It is another beautiful and cozy morning here today. The weekend is here and i'm sure we are all glad that few days rest is near.
Today, I am here again with another automobile article, but this time, I will not be discussing the automobile solely. You will find out what I mean soon enough. Let's good ahead.
By now, almost everyone should be aware of the adverse effect of our activities on the ecosystem. Human activities result in pollution of the environment and this leaves no region untouched. From the non-degradable plastic bottle of water, to the dumping of harmful waste in water bodies and emission of harmful gases into the atmosphere, we are killing mother earth.
It is well established that one source of harm to our atmosphere is from the burning of fossils, with the automotive industry being a chief contributor. Burning produces products which includes carbon monoxide, carbon dioxide, oxides of nitrogen (NOx), Sulphur oxide (SO2), and unburnt hydrocarbons (HC).
Let’s see how bad these chemicals can be.
Hydrocarbons react with oxides of nitrogen on the ground level to form ozone. This ozone differs from the Ozone present in the earth’s stratosphere (the ozone layer). Ground level ozone is a harmful substance which if inhaled could cause pain in the chest, irritation of the throat, congestion. It can even worsen health issues such as asthma and repeated exposure can cause scar in the lungs.
Another point to note is that Oxides of nitrogen are responsible for smog formation in the atmosphere which limits visibility.
It doesn’t stop there.
Vegetation is not left out, as it is estimated that crop production in the US is reduced by about $500 million worth by the ground-level ozone. You can read up more here.
I’m not done with these bad guys yet.
Carbon monoxide another culprit. It is an unstable substance and would combine with oxygen spontaneously to achieve stability. This is why it is advised that the exhaust of Portable generators should be directed away from the house (a case in my country). Otherwise, Carbon monoxide a product of incomplete combustion could be inhaled and will compete with the brain for oxygen of course will win. This particular case have caused the death of many. At least, I have read many of such case in the news.
Sulphur dioxide is another air pollutant and similar to the ground level Ozone, it causes irritation of the throat, airway (which results in coughing), nose; chest problem and breath shortness. Asthmatic patient and people with similar conditions are prone to more adverse effects in the presence of this chemical.
Carbon dioxide is well known. Its emission is inevitable as it is one main product of combustion. CO2 is a very popular greenhouse gas which causes the greenhouse effect. In fact, carbon dioxide is ranked as the number one greenhouse gas.
I think we have seen how bad this guys can be. Now let’s see the good guys.
Automobile Emission Standards
Generally, developed countries have risen and come up with a means to curb the emission of these harmful products into the atmosphere. This control is not limited to the automobile industry only but covers various other sectors responsible for the release of pollutants into the atmosphere such as power plants. However, more focus and stringent control have been established towards the automotive industry.
These emission standards are quantitative restrictions or limits set by a statutory body in which every automobile manufacturer must meet for specific pollutants. This emission standards are implemented to achieve a better atmospheric condition in other to improve the quality of the ecosystem.
In the United States, the Environmental Protection Agency (EPA), through the Clean Air Act is responsible. Other regions in the world including Canada, Germany, UK, China, Japan, South Africa and India have their own emission standard. These emission standards are reviewed periodically to ensure adequate control.
The good news is that with each review, the emission tolerance is reduced, forcing Automotive engineers to come up with various technologies in other to meet the emission requirement.
Each technology cannot tackle all these emissions at once, but instead has specific type(s) of emission it can control. The improvement in the quality of fuel has made sulphur emission minute, therefore, we shall not discuss sulphur emission in this article.
We will be looking at the following systems, viz:
- Evaporative Emission Control system
- Exhaust Gas recirculation system
- Catalytic converters
- Positive Crankcase ventilation
The emission of CO2 is inevitable as long as we are utilizing an internal combustion engine. However, we can limit the quantity by tightening the fuel efficiency of the vehicle. We shall look more into this in the next episode of this article.
Evaporative emission control system (EVAP)
Remember I talked about hydrocarbons being one of the harmful emissions from automobile, one source of this is the vapour of gasoline. Imagine the concentrated odour you perceive whenever you open a container of gasoline. It even gets more concentrated when you agitate the container.
Well, this is due to the fact that evaporation occurs at all temperatures. Even water which is not volatile will evaporate and will be lost if you store it in an open tank over time. Now think of gasoline which is well known to be volatile in nature. Events such as refilling of your fuel tank or when you drive on a road with a lot of pot holes and dishes resulting in the slushing of the fuel in different directions even enhances this evaporation.
Now, how do we get rid of this volatile matters?
If care is not taken, they could easily find their way out of the tank resulting in what we are trying to tackle and even a waste of fuel. The latter I’m sure you care much more about.
Consequently, the evaporation emission control system is put in place. This is a system put in place to trap and hold gasoline vapour from the fuel tank which would later be burnt in the engine and as mentioned in addition to preventing pollution, it prevents the waste of fuel (i.e. it improves fuel economy) – A win win situation.
Now what do we do with this fuel trapped? I think I already mentioned - we route it back into the engine cylinder and then have it burn.
Now let’s look at what makes of the EVAP system. I will combine two things here – the components of the EVAP system and the operation of the system. Don’t worry, you wouldn’t miss out on anything.
Schematic of an EVAP system (Image created by me - 
)
)Operation of the EVAP system
The EVAP system consists of these major components – the Fuel Tank, Charcoal Canister, and Valves. Surely we are familiar with fuel tank and there’s no point in dwelling much on it. It is of course the reservoir for the fuel used by your car.
But one interesting fact you should know is that your fuel tank consists of an expansion chamber which is usually 10 – 20% of the total volume of the tank - this is no waste of space my friend. It is actually put in place to cater for expansion of the fuel during hot conditions and to allow gasoline vapour to be collected.
Once collected, there is need to route this vapour to a storage place, otherwise, too much pressure will build up in your tank and theirs is risk of explosion. The charcoal canister is this storage. It basically contains some activated carbon, which is a good adsorbent – please read that again its adsorbent not absorbent.
Wait a minute!
Remember the explosion thing I mentioned? I wasn’t kidding. Perhaps I should tell you there’s risk of implosion as well - Hmm, relax. The good news is that all EVAP fuel tanks have their caps having a pressure and vacuum relief mechanism. They are able to vent excess pressure or vacuum (in case of implosion).
Now let’s go back to Adsorption which I mention before the last paragraph.
Activated carbon are one very popular adsorbent and a few grammes of such has a surface area equivalent to an average football pitch – Isn’t that a lot of space. Imagine that we could make gasoline vapour adhere to the whole surface of a football pitch, think of the quantity that could be stored. But instead of a football pitch, we have a small container positioned in a suitable place in your vehicle and it is able to allow a tremendous quantity of gasoline vapour to adhere to its large surface area.
You could visit here to read my article on adsorption. You will find it a good read.
At this point, let me draw your attention also to the fact that the vapour is transported into the canister via a hose – you could have been wondering how we channeled the vapour out of the expansion chamber.
Now let’s talk about the valves, there is majorly one valve, although there could be more, depending on the level of sophistication of the vehicle, but this one is the fundamental. This valve is called the purge valve.
The purge valve is used to draw vapour from the charcoal canister into the engine cylinder. So you can see it as a gate between the canister and the engine cylinder. The purge valve is always in the closed position and it is control by a solenoid mechanism. Remember a solenoid is simply a device that behaves like a magnet when electric current passes through it.
Therefore at the appropriate time, current (from the Engine control unit) is supplied to this solenoid and it pulls the purge valve disk (the valve element responsible for opening and closing the valve).
For a clearer picture on the operation of the EVAP system, please refer to the simply schematic below.
Now let’s take the next ride!
Exhaust Gas Recirculation (EGR) System
This guy here sounds clear, init? – like my cousin in the UK.
Perhaps the term still looks vague to you? However, it’s quite simple. Here we will be reusing the exhaust gas. Maybe you are beginning to wonder - Of what use will waste be to us? Or where are we going to use it?
)I will feed your curiosity soon, but allow me sip some Zobo.
Now here is what you need to know.
The formation of NOx (I hope you have not forgotten them) gases is favoured by high combustion temperature and pressure in the combustion chamber. These agents split Nitrogen gas (N2) and Oxygen gas (O2) gas into their individual atoms which then combines to form NOx gases which are then emitted into the atmosphere through the exhaust tailpipe.
Now how does exhaust gases help out?
The exhaust gas recirculation system reduces the production NOx gases by routing a small quantity (about 6% - 10%) of the exhaust gas into the intake charge (air-fuel mixture). The presence of the exhaust gases result in the reduction of the amount of intake charge admitted into the combustion chamber thereby reducing the peak combustion temperature.
At this point, we have successfully deprived the engine the ability to produce Nox since its agent have been taken care of. Also, note that the exhaust gas is inert and does not take part in the combustion.
That’s not all. There is a promo - “buy one, get one free”.
In addition to reducing NOx formation, EGR system reduces Detonation. Detonation also called spark knock or ping is a phenomenon whereby high pressure and heat causes fuel to be ignited unevenly which can cause the damage of the Engine.
Another point to note is that the EGR system is not required at idle (when your engine is running but your car isn’t), when the engine is cold, or at wide-open-throttle (WOT) – when you have the gas pedal depress to a large extent. Although, the NOx formation is high during wide-open-throttle but the overall effect of not using the EGR system is minor.
The major component of an EGR system is the EGR valve which controls the flow of the recirculated Exhaust gas based on input from the ECU, to the engine intake. There are various designs of EGR valves. Some are vacuum-operated, electronically operated or a combination of both. A back pressure EGR valve is a typical example of an EGR valve.
Note: The introduction of variable valve timing (VVT) technology in most new cars, eliminate the use of EGR system. This is due to the fact that the Engine control unit can control the time in which the exhaust valve closes, such that some exhaust gases remain and mix with the fresh charges. Thus performing the Job of an EGR system.
Conclusion
In this episode, remember we have discussed two things – The EVAP system which helps to tackle the issue of Hydrocarbon emission as well as the Exhaust gas recirculation system which deals with Nox emissions.
More is to come in the next episode.
In the meantime, remember that these technologies wouldn’t have existed without the intervention of the right bodies. The emission standards of various regions in the world has made automotive engineers devise various technologies to combat harmful emissions.
It doesn’t end there.
These bodies have inspection programme to ensure that automotive industries comply with this regulation and any violation will not go unpunished. Perhaps it would interest you to find out what happened with Volk wagon in 2015, when it tried to pull a smart one with in the US. The summary is that all those involved paid dearly for it and even the company had to pay a huge fine. You should read more on it here.
Having said these, allow me stop here for now. I will come again with the completion of this article. Then we will look at the catalytic converter and the Positive crankcase ventilation. Some technologies which have helped to curb the quantity of CO2 emission will also be explored.
Thanks for being here again.
References
- Halderman, J. D. Automotive Technology - Principles, Diagnosis and Services. (Fourth Edition)
- EPA - History of Reducing Air Pollution from Transportation in the United States
- EPA: Mobile Sources Compliance Monitoring Program
- mnn - Ozone: Health and environmental effects
- Wikipedia - Emission standard
- Autohowstuffsworks - How much air pollution comes from cars?
