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What is Car Exhaust System and How it Works?

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This shows the underhood of a car, exposing the car exhaust system.
Car exhaust system is a important part of our car – if you don’t like to get poisoned!

How would you feel if you have to wear a heavy-duty gas mask whenever you drive a car? Not a pleasant experience, I suppose. Luckily, we don’t need to do that but we owe it all to our car’s exhaust system.

Exhaust system collects, purify, and expels harmful substances away from the car’s occupants.

In the article below you will find more about…

Parts of a Car Exhaust System

Just like how a movie always introduces its cast, here are some of the main parts of a car exhaust system.

Part #1: Exhaust Manifold

Exhaust manifold is a single part that guides and delivers the exhaust fumes from our car engine cylinder into the exhaust pipe. It is usually made from cast-iron or stainless steel, although you can find custom exhaust manifold that are coated with ceramic or even polished chrome.

The exhaust manifold is attached to the engine. It's slightly red in color due to the fact that it is constantly exposed to high heat.
As you can see, exhaust manifolds are the red hot part. It converges the gas into a singular pipe.

Source

Image by smneale (CC BY 2.0)

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Part #2: Exhaust Pipe

Exhaust pipes is a vessel that takes the exhaust gases from the exhaust manifold, through the catalytic converter, then the muffler and finally out the exhaust pipe tips. The pipes are made from stainless steel. Depending on the design, the exhaust pipes can be either straight or bent.

The exhaust pipes is a cylindrical shaped aluminium tube that allows exhaust gases to flow in.
Exhaust pipes are just aluminium tubing that gas flows in. It’s like a sewer for gas.

Part #3: Catalytic Converter

Catalytic converter looks like a large metal box and you can see it if you jack your car up. It sole mission in life is to make the exhaust gas less harmful by converting unburned hydrocarbons, nitrogen and carbon monoxide into carbon dioxide and water. Its playing an increasingly significant role due to the increased regulation of air pollution in the car industry.

The catalytic converter looks like a "bulge" from the cylindrical aluminium tubing. Within it, is a honeycomb structure that is coated with catalysts.
Catalytic converters are expensive! Mostly because of the precious elements found within it.

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Image by Kim2480 (CC BY-SA 3.0)

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Part #4: Muffler

Muffler is created to quiet the noise that comes from the engine when it is running. The fiberglass insulation, stainless scrubble, or resonating chambers lessens the sound that comes from the engine. The negative side of some mufflers is the backpressure they create. Backpressure is well known to reduce the vehicles power and fuel efficiency.

The muffler looks like an oversized, oval-shaped can of soda. It's got a exhaust pipe as the input and another as the output.
“mh mh hmm hmhm”. Muffler quiet down the noise made by exhaust gas.

How Does a Car Exhaust System Works?

The journey of an exhaust gas starts from the car engine and eventually make its way to the tailpipe found at the rear of our vehicle.

In this part of the article, we have broken it down to 5 phases that tells you where it come from, what we do to it, and how we get rid of it. Enjoy!

Phase #1 Origin of Exhaust Gas

When we start our car, the engine combusts petrol to generate power. Most passenger car runs on 4 strokes engine, which is a cycle between intake, compression, power, and exhaust stroke in that particular order. It helps to understand how car engine works to get a full picture.

This is a 4-strokes engine. The piston moves up and down in a cyclic motion with the force of explosion within the piston chamber.
If you cut the car engine in half, this is how a 4-stroke engine will look like.

Source

Original animation by Zephyris (CC BY-SA 3.0), edited by D S AUTO.

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  1. Intake Stroke. The first stroke opens up the intake valve, which allows the air-fuel mixture to enter the cylinder.
  2. Compression Stroke. On the second stroke, both the intake valve and exhaust valve are closed. So, when the pistons move upward, it compresses the air-fuel mixture.
  3. Power Stroke. When the piston reaches the top, the spark plug ignites the air-fuel mixture, producing a downward thrust that is harvested as rotational power that moves our car.
  4. Exhaust Stroke. The forth stroke opens up the exhaust valve. As the piston moves upward again, it forces the exhaust gas out of our car engine, and into the exhaust manifold.

With that, the engine produces power. However, this process also produces exhaust gas as a by-product that we want to get rid of. It is a toxic fume that is hazardous to the car occupants and the environment. This is where the exhaust system steps in.

Phase #2 Collecting Exhaust Gas

Exhaust manifold is basically a funnel. It is designed in such a way that each “funnel” meets with one of the engine exhaust port and then converges into a single pipe that leads directly to the rest of the exhaust system.

Very much like many small roads leading into a single highway, the purpose of exhaust manifold is to guide and collect the exhaust gases from all the engine cylinders and converges them into one single opening, known as the front pipe.

From there, the exhaust gas goes through the catalytic converter.

Phase #3 Purifying Exhaust Gas

Catalytic converter are like filters, except for gases. It purifies the gases. At this stage, the exhaust gases are a mixture of six different gases, namely…

  • Nitrogen
  • Water Vapor
  • Carbon Dioxide
  • Carbon Monoxide
  • Nitrogen Oxides
  • Particulate Matters

The first three on the list are not toxic while the subsequent three are extremely toxic to the car occupants and the environment. With the increasing awareness of global warming and environmental concerns, we can’t just release them into the atmosphere!

Fun fact. The catalytic converter is capable of purifying (up to 90% of the harmful substances!).

The catalytic converter looks like a "bulge" from the cylindrical aluminium tubing. Within it, is a honeycomb structure that is coated with catalysts.
It’s quite magical. You shoot exhaust gas through the catalytic converter, and you get clean emission out the other end. All this owing to the honeycomb structure and catalysts.

Source

Image by OpenStax (CC BY 4.0).

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Inside the catalytic converter, you will find two things. A honeycomb structure that is covered with catalyst, usually made from platinum, palladium, or rhodium. The honeycomb structure increases the surface area, so more pollutants are in contact with the catalyst.

The catalyst induces a chemical reaction that converts the harmful elements found in exhaust gas (e.g: carbon monoxide and hydrogen monoxide) into harmless inert gases. It is achieved through either oxidation or reduction process. As the exhaust gas flows through the catalytic converter, it reacts the the catalyst and gets turned into less harmful substances.

At this stage, the exhaust gases are purified and is ready to be removed from the car.

Phase #4 Silencing Exhaust Gas

As the purified exhaust gases exits the catalytic converter at a very high speed, it creates unpleasantly loud noises, loud enough for you to hate driving altogether. Thankfully, we don’t hear that, owing to the silencer.

Befitting to the name it was given, silencer a.k.a muffler, reduces the noise level of exhaust gases. You don’t realise its importance because you don’t get to “hear” it. It’s something that you can only truly appreciate when the muffler is damaged.

Let’s take a step back and see how sound are produced. Sound waves are produced by an alternating pressure waves that looks like this.

Sound are produced by an alternating pressure wave. It goes up and down like a hill.
Sound waves go up and down like a hill.

This alternating pressure wave comes by as a nature of a cyclic motion, very much like a vibrating guitar string or a 4-stroke engines. In the case of a car exhaust system, here’s how it works.

When the engine exhaust port opens up, it sends a burst of high pressure exhaust gas through the exhaust system. Because the exhaust port opens and closes very rapidly, these “new” burst of exhaust gas meet up with the exhaust gas from the previous cycle, thus creating a high pressure area. But at the same time, it leaves behind a low pressure area. As a consequence of that, this creates an alternating high and low air pressure.

I know, it’s a bit tough to wrap your head around this. But here’s another example.

Imagine it like turning a water pipe on and off. In this metaphor, the water pipe switch is like the engine exhaust port (opening and closing), and the water coming out is the exhaust gas. You get a lot of water coming out, then very little, then a lot of water, so on and so forth.

If an alternating pressure wave produces noise, what happens if you take the inverse and put them together? Interestingly, it cancels each other out. Like this.

This is called destructive interference. In another words, if a + 5 sound meets with a – 5 sound, you get a 0. This is actually how noise cancelling headphone fundamentally works.

If you take a peak of a wave, and match it with the troughs of another wave, you get a flat line.
As you can see, if you match a “peak” of wave 1 with the “troughs” of wave 2 and vice versa, you will end up with a flat line.

Source

Original Image by Haade, Wjh31, and Quibik (CC BY-SA 3.0). Edited by D S AUTO.

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So if you open up the muffler, it is a simple set of tubes engineered to reflect sound waves. By reflecting them, the sound wave will meet with its counterpart, which becomes self cancelling.

Here’s a great video that may help.

This video did a great job explaining everything that you need to know about muffler. It even shows you the inside of a muffler.

Source

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Video by speedkar99 [/show_more}

As the noise level reduces, the harmless exhaust gas eventually reaches the tailpipe.

Phase #5 Removing Exhaust Gas

Finally, the exhaust gas exits from the tailpipe found at the rear of our vehicles, therefore channeling the gases away from the occupants of the car.

Hurray! Thanks to the exhaust system, the exhaust gas are:

  • channeled away from the engine and the car occupants.
  • less harmful to the environment.
  • not projecting loud noise that are uncalled for on the highway.

There we go! Catastrophe avoided and the world is a better place because of it.

The Bottom Line

Car exhaust system is like a trash management system, but for gas. It improves our driving comfort by reducing noise level, while keeping us safe from toxic fumes. It is one of the system that is often overlooked, undervalued, but yet so important.

Needless to say, we should never drive with a faulty exhaust gas system. If you’re wondering how to diagnose that, have a look at the Top 7 Symptoms of a Faulty Exhaust System.

Anyway, I hope you’ve thoroughly enjoyed the article and find it helpful. Are there any thing that you’d like to see added to the article? Let us know in the comment section below and we’ll do it!

Until then, drive safe and drive smart!

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