How does a petrol car engine and a diesel car engine work?

Answer 1

This is actually 2 questions but there is only one main difference in the two types of engine, namely the method of ignition of the fuel.

We are talking in both cases about internal combustion engines.

This means something (fuel) burns inside a chamber.

For something to burn you need oxygen and a means of ignition (setting fire to the fuel).

Let's talk about a standard petrol engine:

A mixture of air and petrol is blown into a cylindrical chamber. A piston moves to compress the mixture. A spark from a spark plug is set off at the moment the mixture is most compressed. The mixture ignites and explodes ( the amount of gas produced by the almost instantaneous burning of the fuel is much greater than the amount of gas that was there before ignition. Only some fuels are therefore suitable.)

So the piston is forced back. This motion is converted to rotational motion in much the same way as the downward force of a cyclist's foot is converted into rotational motion. There is more than one cylinder, and they are arranged to ignite in a sequence. On a bicycle we have two pedals directly opposite each other. In a petrol engine we have something called a camshaft. If we have four cylinders we might imagine 4 pedals at 90 degrees. We will have to leave more detail on camshafts for another answer.

( Let's assume the engine is oriented in the standard way, with the spark plugs on top of the cylinders.)

Almost all car engines are 4 stroke engines. This means there are 4 stages in the process taking place in each cylinder. In the first stage, the piston is moving down, which sucks the petrol-air mixture into the expanding chamber.

When the cylinder reaches the maximum size, the hole through which the fuel entered is closed by a valve; the cylinder is now closed off.

In the second stage, the piston comes back up, compressing the petrol-air mixture.

In the third stage a spark plug ignites the fuel, and the explosion forces the piston down. This is when the force of explosion pushes against the "pedal" and makes the cam shaft turn (keep turning).

In the fourth stage a valve opens so that the burnt gases will exit through the exhaust pipe. As the piston moves up these waste gases are expelled into the atmosphere (causing environmental problems).

Then we are back to the first stage and the cycle continues.

This all happens extremely quickly.

The tricky part in the design is organizing things so that the valves open and close at exactly the right times. Likewise the spark has to be set off at the right moment.

Now with diesel engines, there is no spark plug. If you put your finger over the outlet of a bicycle pump and quickly push the handle in, your finger will get very hot; you might even burn yourself. Whenever a gas is compressed it heats up. Diesel fuel heats up so much that it ignites without the need for a spark. Otherwise diesel engines are much the same as petrol engines.

It is worth noting that the design of the car engine has not changed significantly since it was first invented.

Other topics that help in understanding internal combustion engines include:

carburetors, distributors, electronic ignition, fuel injection, explosion, camshaft.

I forgot to log in when I first posted this- johnfingers

Diesel engines ignite by means of compression, unlike spark pulgs in gasoline engines which ignite the fuel, the diesel is compressed to a much much higher degree which causes a lot of heat and thus creates and ingnition of the fuel producing the movement of the piston.

Some diesel engines use preheaters which are glowpulgs that heat the diesel on a prechamber before it enters the combustion chamber that way its easier for diesel cars to start specially on winter.

Hope that clears it u :)

Konrad.