Petrol vs Diesel - What Are The Differences?

Both petrol and diesel can be obtained from the crude oil that is trapped within the earth's soil. Both these fuels are found everywhere around the world where diesel is used to power up big vehicles such as trucks, boats, and cranes whereas petrol is commonly used for smaller engines on cars and motorcycles.

Have you ever given it a thought on why that would be the case? And what is found in diesel that made it more efficient and suitable for fixed motion as petrol often causes what is known as shoulder jolting?

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Both have their equal importance and flaws but nevertheless, petrol and diesel will have their own differences.

Differences Between Petrol and Diesel

Crude oil is a combination of disorganized hydrocarbons. The hydrogen molecules and carbon form a chain or long linear ring known as a cyclic compound. The boiling point of these chains will be dependent on their size.

This is pretty clear as it will be much more difficult to break longer molecular chains than shorter ones. We can exploit these features while filtering the oil or splitting the chain between one another.

Firstly, the crude oil being extracted will be poured into a giant furnace where it will be heated. The heating that occurs will distill the crude oil in a process known as fractional distillation as we witness the separation of the crude oil.

In a vertical position, different areas of the furnace will be subjected to different temperatures. The lowest temperature will be at the head and this will increase as we reach the bottom part. As we have mentioned previously, the longer the chain, the more difficult it would be to break it apart.

Due to that, the difference in temperatures being set in this furnace will allow us to extract different types of hydrocarbon chains from the crude oil. At the top part, we can see a much lighter hydrocarbon with lower boiling points such as LPG and petrol.

In the middle, a more compact fuel with a slightly higher boiling point is obtained like diesel while the bottom part will be the most compact hydrocarbon like lubricating oil and heavy gas oil.

Since petrol is much lighter than diesel, this explains why it will be much more likely to cause shoulder jolting and it can light up much easier than diesel. But because diesel is more compact as it contains more hydrocarbons, it will have a much higher energy output per volume compared to petrol.

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Generally speaking, petrol is comprised of repeated chains of not more than 9 carbon atoms whereas the one in diesel will be at least 14 carbon atoms. Diesel is not as volatile as petrol but it is more sticky and viscous with it containing 132 x 106 J for every gallon compared to petrol of 155 x 106 J per gallon.

Consequently, vehicles powered by diesel are more oriented on distance compared to petrol-powered vehicles. We all know that trucks are not able to produce a significant RPM but they are able to generate a huge torque and thus the capability to move a higher load.

The inability of smaller vehicles not being able to produce as much torque is due to their engine. The operation of a diesel engine is relatively different from that of a petrol engine.

Diesel Engine VS Petrol Engine

Petrol can easily be lit up than diesel. If you were to conduct an experiment by putting fire in a tank filled with petrol, the petrol will be burnt instantly. Due to this attribute, petrol engines utilize spark plugs.

In a petrol engine, the mixture of air and petrol is compressed by pistons and later lit up by sparks of fire. However, diesel does not easily burn as petrol. In a diesel engine, the air will be compressed first before the diesel is filled.

The compressed air is burned and since it is so powerfully compressed, the diesel will instantly light up as it is filled into the chamber. A stable ignition requires more compression which will generate more heat and a bigger torque to perform its job.

The chemical energy that is exchanged for mechanical energy by a diesel engine is far greater than the amount of energy generated by a petrol engine. Due to this, the efficiency of diesel engines surpasses that of petrol engines.

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But to generate and maintain a bigger torque, the engine must also be powerful. The drawback is that the heavier the engine is, the bigger the vibration it produces. This strong vibration will also mean that the engine is more prone to damage.

In contrast, a diesel engine will require more maintenance than a petrol engine. In addition to this, due to the bigger mass of diesel engines, it is more exposed to a vigorous environment.

So a diesel engine must be able to reach a bigger compression to produce a bigger torque to move the vehicle. And to generate such torque, it will also need heavier components that will add up its mass.

Aside from that, the combustion of diesel will produce a much thicker smoke which consists of black particles produced by this partial combustion. Smog produced by these vehicles will also result in acid rain which will later damage our eyes and skin.

Since diesel engine requires more air for combustion, this additional air will result in more chemical reactions and ultimately releases a significant amount of air pollutants. Thus making it less environmentally friendly than petrol.

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