What is the difference between a diesel engine and a petrol engine?

Answer 1

The major difference between diesel and gasoline is the way explosions happen. In a gasoline engine, fuel is mixed with air, compressed by pistons and ignited by sparks from spark plugs. In a diesel engine, however, the air is compressed first, and then the fuel is injected. Because air heats up when it's compressed, the fuel ignites.

In brief, a petrol engine uses sparks to ignite its fuel/air mixture but a diesel engine uses only air compression to ignite its fuel.

Petrol engines use spark plugs to ignite the fuel which is a mixture of air and petrol. A diesel engine uses a higher compression ratio when it compresses the incoming air, which creates a temperature inside the cylinder which is high enough to ignite the fuel when it is injected into the compressed air.

Over long periods of running-time a petrol engine can be allowed to turn (revolve) much faster than a diesel engine - thus delivering much more power from a given size engine - which is why diesel engines are not really suitable for use in race cars such as Formula 1.

Until the latest electronic engine and fuel management systems became available, diesel engines used their fuel much more efficiently than equivalent-size petrol engines.

But even today, if you drove a vehicle that has a diesel engine, you should get up to approximately 30% more miles per gallon than if you used a gasoline engine which had the same power output.

However, whichever type of fuel you use, the fuel economy you can achieve will depend very much on how you drive: if you thrash your engine it will use a lot more fuel than if you drive gently!

If you do lots of short journeys - or leave your engine running unattended while you shop (which is illegal in some countries, e.g. the UK) - you'll use a lot more fuel per mile than if you drive freeways most days.

Another consideration to take into account is that diesel engines cost a lot more to make than gasoline engines, so diesel vehicles sell at a higher price, but if you do a high annual mileage it is worth running a diesel because of all the money you will save on fuel.

The gasoline in a petrol engine is fired by the spark plugs. The diesel fuel in a diesel engine is fired by compression. The compression ratio of the average gas engine is around 10 to 1. The compression of a diesel is around 25 to 1.

Therefore a diesel engine must be built much stronger and heavier. A diesel will produce much more torque that a gas but a gas will produce more h.p. The diesel is better at pulling heavy loads which requires the extra torque or pulling power.

In a Diesel engine, the fuel and air mixture is compressed about 20 times atmospheric pressure and is ignited by the compression heating of the gas mixture. Diesel engines have to be stronger to resist this higher pressure and so are heavier than petrol engines.

One can be a lot more technical about it, but that is the basic information.

To tell if an engine is a diesel or a petrol (Gas) engine, my favorite way is look for spark plugs.

A diesel engine uses high pressure to ignite the diesel, a gasoline (petrol) engine uses a high voltage spark to ignite the engine. Similarly check for a distributor, which is required for spark plugs.