Have you ever wondered how fascinating a car is? It is a device where you pour in some liquid, sit on a chair and use simple movements from your hand and feet to get to places faster. About 200 years ago, nobody would have even thought you’d have 4-wheeled enclosed metal carriages in the future, capable of moving above 27 metres in a single second. But it has happened and going at the current rate things are only going to get better. Today we’ll take a look at the working of the component in the car that allows it to move at such speeds, the engine. We will take a look at its intricate components and their individual functions. So let’s commence with this article and understand how a car engine works.
In broad terms, the engine can be segregated into three key parts, the head, the block and the oil sump.
1. The cylinder head is the channel through which the fuel enters the engine chamber and exhaust gases exit. Its key components are the camshafts, valves and spark plug.
2. The cylinder block is where all the combustion action takes place. The key components here are the combustion chamber, piston, and the crankshaft.
3. The oil sump constitutes the lowermost part of the engine. Its key components are the oil pan and the oil filter.
The modern day car engine is a 4-stroke engine which means it creates usable power in 4 strokes. Each stroke is defined as the movement of the piston from the bottom most position (Bottom Dead Centre) to the topmost position (top dead centre) and vice-versa. The 4-strokes are as follows: Intake Stroke, Compression Stroke, Power Stroke, Exhaust Stroke. Here is a flowchart overview of the processes taking place from the start of the power cycle to the end:
The combustion process begins at the engine head, precisely at the intake manifold. The intake manifold is the channel through which the air-fuel mixture flows into the combustion chamber. The air is directly sucked into the manifold from the throttle body. The fuel, on the other hand, is injected into the end of the manifold through a nozzle called the fuel injector.
Next, we move on to the tap controlling the fuel release, the valve. The valve in simple terms is the device that seals the chamber shut during combustion and opens the gate when fuel has to enter the chamber or gases have to exit. The valves open and close based on which stroke is taking place. The opening and closing of the valves are done by an actuator rod known as the camshaft.
The camshaft is a cylindrical rod with drop shaped protrusions known as cams. When the sharp end of the cam is rotating against the valve, it pushes the valve downwards and opens up the port. Once the sharp end transitions back to the round end, the valve springs push back the valve to its original position and shut the port. The rotation of the camshaft is connected to the rotation of the crankshaft via belts and pulleys. The rotation is timed with a very delicate and precise timing mechanism that can be adjusted manually.
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Now let’s get started with the serious business, i.e. the combustion process. The combustion process takes place inside the combustion chamber present in the head. Here the most important part is the piston. The rotational force that is generated on the wheels starts with the movement of the piston. The piston generates usable power through a total of 4 strokes or 4 movements of the piston from end to end. Let’s have a look at these 4 strokes in detail:
1. Intake Stroke: The combustion starts with the piston at the top dead centre or TDC position. The piston now starts to move down. Just before the piston begins its downward motion, the intake valve opens up. As the piston moves down, it sucks in the fresh air-fuel mixture from the manifold. As the piston reaches bottom dead centre or BDC, the chamber fills up with air-fuel mixture.
2. Compression Stroke: Once the piston has reached BDC, the compression stroke begins. Just before the piston reaches the lowermost position, the intake valve closes. Now the piston moves upwards. As it moves up, it compresses the air-fuel mixture as it has no place to escape with the closed valves.
3. Power Stroke: Just before the piston reaches the topmost position in the compression stroke, the spark plug mounted on the cylinder head lets off a very tiny spark. When this spark comes into contact with the compressed air-fuel mixture, it ignites the mixture. Once ignited, the flame rapidly expands. Since the valves are still closed, the flame has no place to escape and pushes the piston downwards. This is the power stroke where usable power is generated by the motion of the piston.
*Note– Diesel Engines don’t have spark plugs. Instead, the fuel injector sits in that position. On diesel engines, the combustion mechanism is slightly different. Only hot air is sent to the combustion chamber during the intake stroke. This air is then compressed which causes it to heat up even more. During the power stroke, the injector sprays the fuel which on coming into contact with the hot air catches fire and starts the combustion. The remaining cycle is the same as a petrol engine.
4. Exhaust Stroke: Last comes the exhaust stroke. The piston with the momentum gained from the previous stroke starts to move back upwards. As it begins to move, the exhaust valve opens up. The leftover gases from the combustion process are pushed out. With this one 4-stroke cycle is completed. After this, the piston again moves from TDC to BDC and the cycle restarts.
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*Note- You may be wondering that when you start the car from off position, how does the piston get the force to move downward. This is taken care of by the starter motor. When you turn the car on with your key, the starter motor provides the initial force to move the piston downwards which commences the combustion cycle. After that, the momentum created in each power cycle provides the necessary force to move the piston.
The piston is connected to a rotating shaft called the crankshaft through a connecting rod. The piston is connected on offset projections on the rod called crankpins. So it effectively converts the up and down motion of the piston into rotational motion. The crankshaft’s rotation is what reaches the wheel passing through various parts and components on the way. We’ll take a look at how the power reaches the wheels in detail in another article.
The Oil Sump is the lowermost part of the engine. The function of the oil sump is to store and circulate the lubricant oil to the different moving parts of the engine. Two primary parts are located in the oil sump, the oil pan, and the oil pump. The oil pan is the reservoir where all the lubricant is stored. Submerged in this oil pan is the oil pump which sucks in oil and transfers it to the lubricant channel.
The oil pump has a small strainer at its opening which is used to filter out large debris. Once the oil is sucked in by the pump, it passes the oil to a primary oil filter which removes all the smaller debris and metal bits as well. This oil is then passed into the lubricant channel and sprayed around the various engine parts. This oil falls back through a separate channel and is sent back to the sump where the process restarts.
*Note- Oil is sprayed directly on the combustion chamber to allow smooth up-and-down motion of the piston. But the mixture of oil and fuel will lead to improper combustion. So how is the piston sleeve lubricated? The piston has a set of rings that runs around its circumference. Every time the piston reaches BDC during the 4-stroke cycle, the oil sprayed on the walls of the combustion chamber. As the piston starts to move down, the oil spray is stopped and the rings scrape down the excess oil from the walls. Thus the oil and fuel are never allowed to mix.
So that sums our explanation of how a car engine works. For the next chapter, we will continue from where we left here, from the crankshaft. There we will see how the power moves from the engine and the various components it encounters in the path. Do leave a comment below in case you have any doubts or suggestions pertaining to this article and keep visiting our blog for more such interesting reads.