Comparing Diesel and Petrol Engines

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Comapring diesel and petrol engines

Diesel vs Petrol

The age old question, Diesel vs Petrol. Which is better? Which costs less to maintain? Which is more environmentally friendly, and at the end of the day, which should you buy? While there are differences between petrol and diesel engines, in theory they both do the same thing, which is use a combustible air/fuel mixture to ignite the fuel, creating rotational energy and moving us down the road.

The internal combustion engine (ICE) is exactly that. An engine that creates torque or usable energy by the means of internal combustion. Petrol is a more unstable energy source, interestingly enough, the liquid its self is not what is combustible, rather the fumes that are evaporating. These fumes can be ignited by a simple spark or an open flame. It is exactly this spark that ignites the air/fuel mixture inside an ICE engine. This ignited fuel rapidly expands pushing the piston down and creating rotating motion. As mentioned earlier, the fuel enters the cylinder as a fine mist created by the fuel injector. This injector atomizes the fuel, which is essential for ignition as we mentioned earlier.

The petrol engine draws in an air and fuel mixture, compresses it and ignites it using a spark plug. Diesel engines work on a similar principal. The fuel is injected into the cylinder as a mist, it is then compressed by the piston, but instead of a spark plug igniting the fuel, a glow plug is used to ignite the combusted mixture. The key difference here is that liquid diesel, much like petrol, is not combustible, and in the case of diesel, neither is the vapour. Diesel is combusted using a glow plug, but the conditions need to be perfect in order for the diesel to ignite. This is created using the compression stroke. Diesel engines compress the air/fuel mixture to an extremely high pressure. This high pressure raises the temperature of the mixture allowing it to be ignited easier using the glow plug. Diesel has a higher energy value then petrol, which means you use less of it. It is exactly this reason that gives diesel the fuel efficiency advantage over petrol. The diesel internal combustion engines also provide much more torque then petrol engines, making them ideal for towing.