Car Exhaust System Explained - Parts, Design, Construction, Working & more

Many of you may know how a four-stroke engine works, it consists of four different steps namely- intake, compression, power and exhaust. The intake stroke allows fresh and cool air to enter inside the cylinder, and this depends on how hard you are pushing the throttle pedal. If the accelerator pedal is pressed fully, it will open the entire throttle valve, and the airflow from outside is unrestricted. This is generally done by many drivers while doing overtakes or drag races, where you need quick acceleration.

The more air gets inside the cylinder, the more fuel will be injected into the cylinder, and the engine will make more power. The compression stroke compresses the air or the mixture of air and fuel so that the air and fuel and thoroughly mixed together. This process is required for complete and efficient combustion inside the cylinder. If the mixture of fuel and air is not thorough, then there will be a lot of toxins or unburnt hydrocarbons inside the exhaust. This will also increase the emission level of the vehicle. The power stroke occurs when the air-fuel mixture is burnt and releases energy. On the other hand, in diesel engines, the compressions ration is so high that the air-fuel mixture is burnt autonomously. 

The final process of the combustion process is exhaust stroke, which is responsible for throwing out exhaust gases, which are left after the whole combustion process. The exhaust gases are a mixture of NOx, CO and unburnt particles. Many of you may not know that internal combustion is not that efficient as exhaust gases consist of almost 60 to 70 per cent of energy, which is otherwise wasted. To make this energy useful, automakers have been developing a lot of techniques for decades. One of the most famous techniques is turbocharging. In this process, a mass flow of exhaust gases is used to rotate a turbine, which is positioned on the same shaft as the compressor. This allows the compressor to provide more air inside the cylinder by compressing it. Therefore, more fuel can be injected into the cylinder to produce more power. 

Different components of the exhaust system

1) O2 Sensor

The O2 sensor is known as the oxygen sensor, which is positioned just after the exhaust manifold. The main aim of this sensor is to calculate the content of oxygen in the exhaust because this will inform you whether the air-fuel mixture is rich or lean. 

2) Catalytic Converter

The second most important component of an exhaust system is the catalytic converter. The main function of a catalytic converter is to get rid of all toxic gases from the engine. It converts exhaust gases into CO2 and Nitrogen, which are less harmful to the environment.

3) Resonator

In an exhaust system, a resonator is employed to control the engine from getting to loud. For example, if you are driving a loud car on the highway for hours, it can get quite irritating. To avoid this unwanted noise, a resonator is installed specifically to tackle particular engine RPMs. 

4) Muffler

A muffler is the topic of an exhaust pipe, which helps in reducing the noise levels. This simply means that throughout the engine RPM range, the engine noise is controlled by the muffler. 

These are all the main components of an exhaust system. Now let’s talk about the smart technologies introduced to make maximum use of exhaust gases. After turbocharging, the most important of them all is exhaust gas scavenging. Talking about gas scavenging, the toxic exhaust gases are pushed out of the cylinder by piston via valves. It creates a vacuum inside the exhaust manifold. Depending on the width of the exhaust manifold along with the pace of exhaust gases, the vacuum created behind the gases is determined. There should be an ideal manifold length and diameter to maintain a balance between backpressure and velocity created by outside conditions. For example, if the outside pressure is high, then the toxic exhaust gases will not be able to move outside and this will result in inefficient combustion for the next cycle. This is not good for powertrains, and it can also damage the engine components due to excess heat. The positive effect of exhaust scavenging is that it can be used in combination with direct injection technology, variable valve timing and turbocharging. The will result in perfect control of all the variables to attain the best results across the RPM range.