How a Car Engine Works – Investigating What’s Under the Hood

Every day millions of people around the world jump into their cars, turn on the ignition, and off they go. Whether it’s to work, taking the kids to school or going to the local mall to do shopping, they trust the car to get them there. But have you ever stopped and wondered how the engine actually works in a vehicle? There are many different types of internal combustion engine available, but for simplicity, we will look at how the engine in an average family car works its magic in order to get you from A to B.

Many people have been credited with the invention of the internal combustion engine but in reality, it was a long series of inventions, incremental advances, adaptations and enhancements that lead to the early internal combustion engines.

Karl Benz was issued the first patent for a gas-fuelled car in January 1886. Note that this was for a car, not the engine itself. This came about after the pioneering work of many engineers and inventors dating as far back as 1680.

Irrespective of who the actual inventor was, the inner workings of a car engine is something that every man is expected to know. Perhaps not surprisingly, very few actually do understand it well enough to explain to someone else. These days, an increasing number of woman also want to understand the workings of engines.

In this article, we will explain the various components of the internal combustion engine, what each one is, what it does and how they work together to make the vehicle drive. While this is interesting and good to know, modern cars have such advanced technology that computers control most of the functions and activity within the engine. Popping the hood on many modern vehicles and you will be hard-pressed to find any of the things we talk about here. Walk around a modern workshop, particularly those of the more high-end cars, and you are likely to see more smartly dressed people with computers attached to the vehicles than mechanics in overalls with greasy hands.

The internal combustion engine (ICE)

Car internal combustion engine

It is named the internal combustion engine because fuel and air are mixed together and combust inside the engine to create energy to move the pistons, which in turn move the car. The internal combustion engine used as an example will be a standard four-stroke engine.

To put it in very simple terms, which we will expand on later, the internal combustion engine works by means of the explosive power caused by the combustion of fuel. This force pushes the pistons or pistons down the cylinder. The powerful movement of the pistons turns the crankshaft which then turns the drive shaft or drive chain to make the wheels turn.

This all sounds very simple and if you break it down, it actually is quite basic. Obviously, there is a lot more to the modern car than just the engine, especially on the more upmarket cars.

Components of an internal combustion engine

The engine block

Internal combustion engine body

The engine block is the base of the four-stroke engine. Usually, the engine blocks are cast from an alloy, but cast iron engine blocks are still used by some car manufacturers. The engine block can also be referred to as the cylinder block because of the cylinders cast in the block. The cylinders are where the pistons move up and down when the engine is running. Generally, more cylinders mean more powerful engines. There are other ducts and passages cast into the engine block that allows for the all-important lubricant and coolant to move to all the various parts of the engine.

The combustion chamber

The combustion chamber is where the fuel-air mixture, pressure, and an electrical spark occur under the right conditions to produce a mini explosion that causes the pistons in the engine to move up and down. This creates the power to move the car. The combustion chamber is comprised of the following; a cylinder, a piston and cylinder head. The cylinders are the walls of the combustion chamber, while the top of the piston is the floor of the combustion chamber, the cylinder head is the ceiling of the combustion chamber.

The cylinder head

The cylinder head sits on top of the engine’s cylinders. There are rounded compartments cast into the cylinder head in order to give enough space at the top of the chamber for the combustion of the fuel-air mixture. The join in between the engines cylinder head and the cylinder block is sealed using a head gasket. Intake and outtake valves are mounted in the cylinder head as well as the spark plugs and fuel injectors.

Internal combustion engine cylinder head and valve rockers

The pistons

The pistons move up and down the cylinder. When the fuel and air mixture ignites in the combustion chamber, the forces created push the piston downward, which in turn moves the crankshaft. The pistons are attached to the crankshaft via a connecting rod. At the top of each piston are three or four grooves cast into the piston where the piston rings are placed.

Internal combustion engine pistons cross section

The piston rings press against the walls of the cylinder. There are two types of piston ring, compression and oil rings respectively. The compression rings are placed in the top grooves and these rings provide a strong seal for the combustion chamber. The oil ring is placed in the bottom groove and is used to prevent oil from the crankcase entering into the combustion chamber. The oil ring also wipes excess oil off the cylinder walls and back into the crankcase.

The crankshaft

After the spark plug causes the combustion of the fuel and air mixture, the piston is pushed down with great force. The crankshaft converts the upwards and downwards motion into rotational motion that allows the vehicle to move forward. The crankshaft fits lengthways near the bottom of the engine block, extending from one end of the block to the other. At the front of the car’s engine, the crankshaft is connected to various rubber belts which connect to the camshaft and delivers power to other parts of the car. At the rear, the camshaft connects to the drivetrain which then transfers power to the wheels. Each end of the crankshaft is sealed with o-rings which prevent oil from leaking out of the engine.

Internal combustion engine crank shaft

The crankshaft rests in the crankcase of the engine which is located beneath the cylinder block. The crankcase protects the crankshaft and the pistons connecting rods. At the bottom of the crankcase is the sump, this is where the all-important lubricating oil is stored. Inside the sump or oil pan is the engines oil pump which pumps the oil through a filter before squirting the oil onto the crankshaft, connecting rods and cylinder walls providing lubrication for the pistons and moving parts. The oil drips back down into the sump where the process will begin again. At certain points along the crankshaft, there are balancing lobes which act as counterweights to balance the crankshaft, these are important to prevent potential engine damage due to any wobbling that may occur when the crankshaft is spinning. Without the lubrication provided by the oil, the part moving repeatedly at high speeds for long durations would soon wear out and either cease or perish.

The camshaft

One of the most important parts of the engine, the camshaft works together with the crankshaft via a timing belt in order to ensure that the intake and outtake valves open and close at precisely the right time during the four-stroke cycle. The camshaft has lobes along its length that control the opening and closing of the valves. The camshaft is situated above the crankshaft along the top of the engine block.

The rocker arms

The rocker arms are small levers that touch the cams on the camshaft. When the lobe lifts one end of the rocker, the other end of the rocker presses down on the stem opening the valve in order to let fuel-air mixture into the combustion chamber, or alternatively to allow the release of the exhaust gases.

The Timing System

The camshaft and crankshaft movement is coordinated by the timing belt or chain. The timing belt or chain keeps the camshaft and crankshaft in the same position relative to each other during the operation of the engine. If by some chance the camshaft and crankshaft are out of sync for any reason, the engine will no longer function. As you can imagine, all of the various stages in the process need to take place at exactly the right time in order for the engine to run effectively and efficiently.

Car engine timing belt

The Valvetrain

This is a mechanical system that is mounted to the cylinder head which controls the operation of the valves. The valve train consists of the valves, the rocker arms, the pushrods and the lifters.

The Valves

A typical engine has two types of valves, the intake valves, and the outtake valves. The intake valves allow a mixture of fuel and air into the combustion chamber where under the pressure of the piston produces the power of the engine. The outtake valves open to allow the combusted fuel-air gases to escape via the exhaust pipe. Most cars have one intake and one outtake valve although there are exceptions.

The fuel injectors

All modern cars use one of several different types of fuel injection systems, these can be either a direct fuel injection system, a ported fuel injection system or a throttle body fuel injection system.

Direct fuel injection means that each cylinder gets its own fuel injector, the fuel is sprayed directly into the combustion chamber at the exact time required for the combustion process.

With a ported fuel injection system, instead of the fuel being sprayed directly into the combustion chamber it is instead sprayed into the intake manifold just outside of the valves when the intake valves open, the fuel-air mixture then enters the combustion chamber.

Internal combustion engine fuel injector

Throttle body injection systems work similarly to the old carburetor system whereby, instead of each cylinder getting its own fuel injector, there is only one fuel injector that goes to the throttle body. The fuel mixes with the air in the throttle body and the fuel-air mixture is dispersed to the combustion chamber via the intake valves.

The sparkplugs

Critical to the combustion process is the spark plug. The spark plug is situated at the top of each cylinder and when the fuel-air mixture is compressed, the spark plug sparks, igniting the mixture causing the gases to rapidly expand pushing the piston down powering the engine.

Internal combustion engine spark plugs

So those are the critical components which make the engine work, let’s take a look at how they all come together to make the four-stroke internal combustion engine perform its magic.

How many cylinders does an internal combustion engine need?

One issue with the four-stroke design, although highly efficient, is that the crankshaft is being powered by the piston for only one stage out of the four to be discussed. Because of this, most cars have at least four cylinders arranged so that they fire out of sequence with each other. At any given moment, one cylinder is always going through one of the four stages in the cycle so that one cylinder is always powering the crankshaft ensuring no loss of power at any time the engine is running.

The four strokes of the internal combustion engine are, intake, compression, power, and exhaust. The piston travels down on the intake stroke, up on the compression stroke, down on the power stroke and up on the exhaust stroke, when all these processes are combined they provide the rotational movement of the crankshaft to move the vehicle.

Intake stroke

When the piston moves down the cylinder on the intake stroke, the intake valve opens to allow the fuel-air mixture into the combustion chamber. When the piston reaches the end of the intake stroke, the intake valve closes sealing off the cylinder with the mixture inside, which then leads us into the compression phase of the cycle.Four stroke cycle intake and compression

Compression stroke

During this stroke, the piston moves up the cylinder and begins to compress the fuel-air mixture within the sealed cylinder. The amount that the fuel-air mixture is compressed during this stroke is determined by the compression ratio of the engine, this is usually specified by the manufacturer. The compression ratio on the average four-stroke engine is between 8 and 10 to 1. What this means is that the fuel-air mixture is compressed to about one-tenth of its original volume.

Power stroke

Once the fuel is compressed, the spark plug sparks igniting the compressed fuel-air mixture which then starts to rapidly expand. The power stroke or combustion process pushes the piston down the cylinder with great force, in turn causing the crankshaft to rotate providing the power to move the vehicle. Each of the individual pistons in the engine fire at different times determined by the engines firing order. When the crankshaft has completed two full revolutions, each cylinder in the engine would have gone through one power stroke. This then leads us into the final phase of the cycle, which is the exhaust phase.

Four stroke cycle power and exhaust

Exhaust stroke

When the piston reaches the bottom of the cylinder after the power stroke, the exhaust valve opens in order to allow the burned fuel-air gases to be expelled from the cylinder via the exhaust system. At this stage, the cylinder contains a lot of pressure so that when the exhaust valve opens the gas is expelled with great force, the piston completes the exhaust stroke when it reaches the top of the cylinder pushing out all the burnt gases before the exhaust valve once again closes and the whole four-stroke process starts again.

All the moving parts and the combustion process cause a lot of heat and friction during the operation of the engine. In order to keep the engine well lubricated and cool to aid the dispersion of heat, there are systems in place which are critical for the engine to run smoothly and avoid engine damage. If any of these were to fail, catastrophic engine failure can occur.


Oil is quite literally the lifeblood of the internal combustion engine, without it the engine will not function correctly and will fail very quickly. The oil is pumped under pressure to all the moving parts of the engine via the oil pump mentioned in the critical components section. The oil pump is mounted in the sump or oil pan at the bottom of the engine and is connected to the crankshaft or camshaft by a gear. So when the engine is running, the oil pump is pumping oil to the moving parts. Every car has an oil pressure sensor mounted near the oil pump that monitors the internal oil pressure and sends this information to the oil pressure warning light or gauge in the car’s dashboard.

When the ignition key is turned on, the oil light comes on. As soon as you start the engine the oil light should go out indicating sufficient oil pressure for optimal efficiency. If the oil light does not go out, there could be too little oil in the sump or alternatively, the pump may be faulty requiring specialist attention.

Engine cooling system

As explained, the internal combustion engine generates a lot of heat and in order for the engine to maintain a stable operating temperature, the cooling system is of great importance. Without proper cooling, the engine may overheat causing engine failure due to engine parts warping causing oil and water leaks and raising the temperature of the oil too high to be effective rendering it useless. There are air cooled engines available, but the vast majority of internal combustion engines are liquid cooled. There is a water pump that circulates coolant through the engine past the hot areas around the cylinders and cylinder head and back through the radiator to be cooled off and the cycle continues.

Other components used to ensure the smooth operation of the engine

A flywheel

In order to keep the combustion pulses from generating any vibrations, a flywheel is attached to the back of the crankshaft. The flywheel is a disk that is approximately 12 to 15 inches in diameter and also doubles as part of the vehicles clutch system. The flywheel uses inertial forces to smooth out the combustion pulses of the engine.

A balance shaft

Some engines have a rocking motion that can produce an annoying vibration whilst the engine is running. In order to combat this, some engines use one or more balance shafts. The balance shaft is a heavy shaft which runs through the engine parallel to the crankshaft. The balance shaft has large weights on it that while it is spinning offsets any rocking motion eliminating the vibration.

Types of internal combustion engines in modern cars

There are two types of internal combustion engine used in most vehicles. The spark ignition type using petrol or gasoline which was the basis for this article and the compression ignition type or diesel engine.

In the spark ignition engine, the fuel burns when a spark is introduced during the compression stroke.

In the compression ignition engine, usually diesel, the fuel self-ignites under the extreme pressure exerted on the fuel-air mixture.

In the diagram below we can compare the two types of internal combustion engines, seeing how they operate, while using past information we learned about to better understand each of them.

Diesel engine versus gasoline engine

In conclusion

Having discussed the main components of an internal combustion engine and how the four-stroke system works, I hope it gives you a better understanding of how the science and technology of this world-changing invention has and will continue to impact the lives of millions of people across the world.

Every year car manufacturers and engineers strive to make engines more reliable and less costly. They also go to great lengths to make them more economical and environmentally friendly by reducing the toxic emissions which are released by the burning of fossil fuels. Over the last three decades, the development and fine tuning of the internal combustion engine have seen the engines getting smaller in capacity, yet delivering more power while using less energy.

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