Here’s a quick overview of what you need to know about the differences between petrol (aka gasoline) and diesel engines. For the most part, petrol and diesel power units are quite similar as they are both internal combustion engines operating on the same four-stroke cycle, and they are designed to convert the chemical energy available in fuel into mechanical energy.
This mechanical energy is what moves the pistons, which are attached to a crankshaft, up and down inside cylinders. This up-and-down movement of the pistons creates the rotary motion needed to turn the wheels on your vehicle.
Both types of engines convert their respective fuels into energy through a series of small explosions called combustions, but the major difference is the way that this combustion happens.
The main difference is spark plugs – which are absent in a diesel motor. In a diesel, the air is compressed first and then the fuel is injected. The injected air heats up when it’s compressed, causing the fuel to ignite. This is called direct injection because the fuel is injected directly into the combustion chamber.
In a gasoline engine, however, the fuel is mixed with air, compressed by pistons and ignited by sparks from spark plugs.
The reason for this is that there is more energy in diesel, which means it ignites at a lower temperature, petrol needs a spark to ignite.
For a more in-depth explanation, including why diesel is more fuel efficient, the check out the video below. And then you can be 'that guy' the next time you're at a pub with your mates!