Four-stroke Otto engine

This animation demonstrates the type of engine most commonly used in cars.

Physics

Keywords

Otto engine, engine, four-stroke, automobile, radial engine, crankshaft, valve, cylinder, piston, spark plug, combustion, spark, intake, compression, explosion, power stroke, work, cycle, petrol engine, internal combustion engine, petrol, carburettor, mechanical energy, combustion product, environmental pollution, air pollution, car, automobile factory, car manufacturing, thermodynamics, heat engine, heat energy, physical

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Scenes

Engine

engine block - The metal block containing the moving parts of the engine
gearbox - It adjusts the ratio of transmission from the engine to the drive shaft. It changes the number of rotations of the driven wheels during one turn of the crankshaft. In low gear the output of the engine is high but the speed is low, in high gear the car is faster and uses less fuel but it accelerates slower.
air filter - Air flows into the combustion chamber of the engine, containing oxygen necessary for the combustion process to take place. The air is cleaned by this filter.
intake manifold - The air, necessary for combustion to take place, flows into the cylinder through this opening.
exhaust manifold - Exhaust gases are expelled through this pipe.
timing belt - It transmits the rotation of the crankshaft to the camshafts.
ignition distributor - It ensures the coordinated operation of spark plugs.

Operation

intake port - Air flows into the combustion chamber - the part of the cylinder above the piston - through this opening.
spark plug - It ignites the mixture of air and petrol. The ignited mixture pushes back the piston.
exhaust port - Exhaust gases are expelled through this pipe.
intake valve - Its opening and closing is coordinated with the movement of the piston. It opens in the 1st stroke, when the piston moving downwards creates a decrease in pressure inside the cylinder, sucking in the mixture.
exhaust valve - Its opening and closing is coordinated with the movement of the piston. It opens in the 4th stroke, when the piston moving upwards expels the exhaust gases.
piston - Its alternating motion rotates the crankshaft. The explosion of the fuel forces it to move downwards. Then the inertia of the rotated crankshaft causes it to move upwards, downwards then upwards again. Then follows another ignition.
cylinder - The combustion forces the piston to move downwards inside it.
connecting rod
crankshaft - The alternating motion of the piston causes the crankshaft to rotate.

Stroke 1

intake port - Air flows into the combustion chamber - the part of the cylinder above the piston - through this opening.
spark plug - It ignites the mixture of air and petrol. The ignited mixture pushes back the piston.
exhaust port - Exhaust gases are expelled through this pipe.
intake valve - Its opening and closing is coordinated with the movement of the piston. It opens in the 1st stroke, when the piston moving downwards creates a decrease in pressure inside the cylinder, sucking in the mixture.
exhaust valve - Its opening and closing is coordinated with the movement of the piston. It opens in the 4th stroke, when the piston moving upwards expels the exhaust gases.
piston - Its alternating motion rotates the crankshaft. The explosion of the fuel forces it to move downwards. Then the inertia of the rotated crankshaft causes it to move upwards, downwards then upwards again. Then follows another ignition.
cylinder - The combustion forces the piston to move downwards inside it.
connecting rod
crankshaft - The alternating motion of the piston causes the crankshaft to rotate.

Stroke 2

intake port - Air flows into the combustion chamber - the part of the cylinder above the piston - through this opening.
spark plug - It ignites the mixture of air and petrol. The ignited mixture pushes back the piston.
exhaust port - Exhaust gases are expelled through this pipe.
intake valve - Its opening and closing is coordinated with the movement of the piston. It opens in the 1st stroke, when the piston moving downwards creates a decrease in pressure inside the cylinder, sucking in the mixture.
exhaust valve - Its opening and closing is coordinated with the movement of the piston. It opens in the 4th stroke, when the piston moving upwards expels the exhaust gases.
piston - Its alternating motion rotates the crankshaft. The explosion of the fuel forces it to move downwards. Then the inertia of the rotated crankshaft causes it to move upwards, downwards then upwards again. Then follows another ignition.
cylinder - The combustion forces the piston to move downwards inside it.
connecting rod
crankshaft - The alternating motion of the piston causes the crankshaft to rotate.

Stroke 3

intake port - Air flows into the combustion chamber - the part of the cylinder above the piston - through this opening.
spark plug - It ignites the mixture of air and petrol. The ignited mixture pushes back the piston.
exhaust port - Exhaust gases are expelled through this pipe.
intake valve - Its opening and closing is coordinated with the movement of the piston. It opens in the 1st stroke, when the piston moving downwards creates a decrease in pressure inside the cylinder, sucking in the mixture.
exhaust valve - Its opening and closing is coordinated with the movement of the piston. It opens in the 4th stroke, when the piston moving upwards expels the exhaust gases.
piston - Its alternating motion rotates the crankshaft. The explosion of the fuel forces it to move downwards. Then the inertia of the rotated crankshaft causes it to move upwards, downwards then upwards again. Then follows another ignition.
cylinder - The combustion forces the piston to move downwards inside it.
connecting rod
crankshaft - The alternating motion of the piston causes the crankshaft to rotate.

Stroke 4

intake port - Air flows into the combustion chamber - the part of the cylinder above the piston - through this opening.
spark plug - It ignites the mixture of air and petrol. The ignited mixture pushes back the piston.
exhaust port - Exhaust gases are expelled through this pipe.
intake valve - Its opening and closing is coordinated with the movement of the piston. It opens in the 1st stroke, when the piston moving downwards creates a decrease in pressure inside the cylinder, sucking in the mixture.
exhaust valve - Its opening and closing is coordinated with the movement of the piston. It opens in the 4th stroke, when the piston moving upwards expels the exhaust gases.
piston - Its alternating motion rotates the crankshaft. The explosion of the fuel forces it to move downwards. Then the inertia of the rotated crankshaft causes it to move upwards, downwards then upwards again. Then follows another ignition.
cylinder - The combustion forces the piston to move downwards inside it.
connecting rod
crankshaft - The alternating motion of the piston causes the crankshaft to rotate.

Construction

radiator - During the operation of the engine the cooling water heats up then releases the heat into the environment.
engine
gearbox - It adjusts the ratio of transmission from the engine to the drive shaft. It changes the number of rotations of the driven wheels during one turn of the crankshaft. In low gear the output of the engine is high but the speed is low, in high gear the car is faster and uses less fuel but it accelerates slower.
drive shaft - It transmits the rotating motion of the crankshaft to the wheels.
petrol tank - The fuel used in the four-stroke Otto engine is petrol. An important attribute of petrol is the octane number. The higher it is, the higher its boiling point, therefore it can be compressed more, resulting in greater efficiency.
differential gear - During turning it allows the driven wheels to roll at different speed.
driven shaft - The rotation of the crankshaft is transmitted to the driven shaft by the drive shaft.
exhaust pipe - Exhaust gases are expelled through this pipe.

Cylinders

crankshaft - It is driven by the pistons. Its rotation is transmitted to the driven shaft by the drive shaft, and to the camshaft by the timing belt, which operate the valves.
camshaft - Its rotation ensures the rhythmical operation of the valves, and it is controlled by the crankshaft through the timing belt.
piston - Its alternating motion rotates the crankshaft.
valves - They coordinate the intake of the mixture of air and petrol, and the exhaustion of exhaust gases. They are operated by the crankshaft through the timing belt.

Animation

gearbox - It adjusts the ratio of transmission from the engine to the drive shaft. It changes the number of rotations of the driven wheels during one turn of the crankshaft. In low gear the output of the engine is high but the speed is low, in high gear the car is faster and uses less fuel but it accelerates slower.
drive shaft - It transmits the rotating motion of the crankshaft to the wheels.
crankshaft - It is driven by the pistons. Its rotation is transmitted to the driven shaft by the drive shaft, and to the camshaft by the timing belt, which operate the valves.
camshaft - Its rotation ensures the rhythmical operation of the valves, and it is controlled by the crankshaft through the timing belt.
piston - Its alternating motion rotates the crankshaft.
intake valve - Its opening and closing is coordinated with the movement of the piston. It opens in the 1st stroke, when the piston moving downwards creates a decrease in pressure inside the cylinder, sucking in the mixture.
exhaust valve - Its opening and closing is coordinated with the movement of the piston. It opens in the 4th stroke, when the piston moving upwards expels the exhaust gases.
piston - Its alternating motion rotates the crankshaft. The explosion of the fuel forces it to move downwards. Then the inertia of the rotated crankshaft causes it to move upwards, downwards then upwards again. Then follows another ignition.
cylinder - The combustion forces the piston to move downwards inside it.
crankshaft - The alternating motion of the piston causes the crankshaft to rotate.

Narration

We know that cars are powered by engines, but how do they do this? The rotating motion of an engine´s crankshaft is transmitted to the wheels by the drive shaft. The gearbox changes the number of rotations of the driven wheels during one turn of the crankshaft. In low gear the output of the engine is high but the speed is low, in high gear the car is faster and uses less fuel but accelerates more slowly.

The most common type of engine used in cars is the four-stroke Otto engine.

It converts the alternating vertical motion of the pistons into the rotation of the crankshaft. The crankshaft drives the drive shaft and the camshaft through the timing belt. The camshaft operates the valves, which ensure fuel intake and the expulsion of exhaust gases through a coordinated, rhythmic opening and closing.

The first stroke is intake. The piston moves downwards, decreasing the pressure in the cylinder. The intake valve opens, and a mixture of air and fuel flows from the carburettor into the cylinder.

The second stroke is compression: both the intake and the exhaust valves are closed then. The momentum of the crankshaft and the counterweight causes the piston to move upwards, compressing the mixture of air and fuel and thereby increasing its temperature.

The third stroke is the power stroke. The spark plug ignites the compressed, heated mixture of fuel and air. The explosion pushes the piston down.

The fourth stroke is the exhaust stroke. The piston moves upwards, the exhaust valve opens and the exhaust gases are expelled.

As you can see, the linear motion of the piston is converted into the rotating motion of the crankshaft in the engine. The energy necessary to move the piston is provided by the combustion of fuel. The fuel used in the four-stroke Otto engine is petrol. An important attribute of petrol is the octane number. The higher it is, the higher its boiling point. Therefore it can be compressed more, resulting in greater efficiency.

Four-stroke Otto engine