Working of four stroke engine

An automobile engine. This engine is a V6, which means it has six cylinders and a "V" shaped block.

A car engine uses internal combustion engine which is a mechanical device which burns a fuel to produce power rotation which moves a vehicle.

Who invented it?[edit]

Nicolaus Otto was the first person to successfully build the 4-stroke type of engine that would later become an car engine in 1876. In 1885 Karl Benz used an engine similar to Otto's engine to make a three-wheeled automobile move. In the same year, Benz began producing and selling automobiles.

The first commercial two-stroke engine involving in-cylinder compression is attributed to Scottish engineer Dugald Clerk, who patented his design in 1881

How does it get power?[edit]

The internal combustion engine gets its power from the heat generated from the burning of liquid fuels mixed with air (vaporized).

These are mostly 'fossil fuels' like gasoline, diesel, compressed natural gas (CNG) and liquefied petroleum gas (LPG) that are mined from the ground, and are becoming harder to find and extract, but some recent technologies use synthetic or renewable fuels such as hydrogen, which can be produced by electrolysis using renewable energy sources.

What does it do?[edit]

It is a mechanical device that converts chemical energy (the fuel) to heat energy, and then to mechanical energy. Reciprocating (back and forth) motion is converted to rotary (spinning) motion, and transmitted through a clutch, gear box etc. to move the wheels of the car.

How does it work?[edit]

Four-stroke cycle (or Otto cycle)
1. Intake
2. Compression
3. Power
4. Exhaust

An engine is properly called a motor because it makes things move! Engine really means ingenious devices, but we use the term because the process of burning a fuel and delivering power usually requires much more than a simple motor spinning an axle. (clever things like gears, levers and cables to get the power to where it is really needed).

A motor burns a mixture of fuel and air in one or more metal tubes called cylinders. The hot, expanding gas from the combustion drives a piston downwards, causing a crankshaft to rotate, and spin a flywheel, absorbs energy from the burned fuel and keeps things rotating until the next cycle. The power from the rotating crankshaft and flywheel is what ultimately drives the wheels.

There are lots of different types of motor, but only two common sorts: the cheap, noisy and rather limited 2-stroke usually only found on small motorcycles and garden machines, and the more sophisticated Otto or 4-stroke used for cars, trucks and buses, which motor (pictured here) has a fun mnemonic, starting with the piston at the 'top' (but note: this is not always actually at the top, but - as in the picture left - that is how most folks call the end of the cylinder with the spark-plug or igniter which is also furthest from the 'bottom-end' or crankshaft):

• SUCK (1) in a mixture of air and fuel vapor (actually called induction stroke as the piston starts at the 'top' of the cylinder near the spark plug or igniter and goes down to the 'bottom' near the crankshaft)
• SQUEEZE (2) the mixture (a compression stroke as the piston goes 'up' towards the spark plug or igniter)
• BANG! (3) the spark plug or igniter sets fire to the compressed fuel and air (a power stroke to force the piston 'down' towards the crankshaft) - When the piston is furthest from the crankshaft, it is said to be at 'top-dead-center' - the actual spark usually occurs when the flywheel inertia has moved the crankshaft a few degrees further, so the piston has actually already started its 'decent' before it gets a push from the expanding hot burning gasses!
• BLOW (4) out the exhausted (burned) gasses form the burnt fuel (the exhaust stroke - the piston returns to the 'top' of the cylinder ready to suck-in some fresh fuel and restart the cycle.

Two Stroke Motor[edit]

A Trabant 601 De Luxe Limousine.

These were used in only a few small cars in the mid 20th century, notably the mass-produced East German Trabant, but also more famous makers of 'super-compacts' or 'ultra-lights' such as DKW, Saab, Wartburg, Suzuki and Subaru produced small numbers of 2-stroke vehicles.

A special mixture of fuel and lubricating oil is needed, because the fuel-and-air mixture is drawn in through the crankcase, with the end of the combustion stroke and the beginning of the compression stroke happening at the same time so that it performs the intake and exhaust functions together!

Although they have a better power-to-weight ratio than 4-strokes, they are more prone to wear and very polluting. Many industrial machines or ship engines use large 2-stroke diesel motors.

Gasoline and diesel[edit]

The speed of gasoline (or petrol) engines is easier to control and usually lighter than an equivalent diesel, which work best at constant speed and really needs a turbo-charger to compensate for the diesel inertia.

Gasoline is a 'light' fuel, highly combustible and ignited with an electrical spark-plug. Diesel (sometimes called 'vaporising oil) is a thicker 'heavy' fuel which is much less inflammable, and is fired by very high compression within the cylinder. The diesel is 'injected' by a tube fitted about where a gasoline engine has its spark-plug. Diesel fuel is apt to become solid at low temperatures, and often has an 'anti-wax-agent' to prevent this.