The diesel engine was invented by Rudolph Diesel and granted a German patent in 1892. Diesel's aim was to create an efficient engine, the petrol engine that had been invented in 1876 was very inefficient at the time. Diesel was the first to prove fuel could be ignited without a spark. In the diesel engine air is compressed to such a degree that the temperature exceeds that needed to ignite the fuel.
How a diesel engine works?
In a petrol engine, petrol and air are mixed, compressed and then ignited with a spark. A diesel engine takes in just air, compresses it and then injects fuel into the compressed air. The air is compressed to such a high temperature it ignites the fuel as soon as it is introduced.
Why is a diesel engine more fuel efficient than a petrol one?
A diesel engine compresses at a far higher ratio than a petrol engine. A petrol engine compresses at a ratio of 8:1 to 12:1, while a diesel engine compresses at a ratio of 14:1 to 25:1. This makes the diesel engine far more efficient. Diesel fuel also contains a higher energy density than petrol. On average, 1 gallon of diesel fuel has 147,000 BTU while 1 gallon of petrol has 125,000 BTU.
Diesel engines also have a higher thermal efficiency than petrol engines. This is the ratio of chemical energy converted into mechanical force. In all engines some of the chemical energy in the fuel will be wasted through heat (which is then released through the vehicles cooling system). Diesel engines waste less energy than their petrol counterparts.
What are the advantages of diesel engines over petrol engines?
Economy: This is normally the first thing people associate with diesel engines. Higher compression ratios, higher BTU per gallon and higher thermal efficiency all add to making the diesel engine more economical than a petrol engine.
Lower maintenance & Reliability: Because diesel engines do not use electricity to ignite the fuel, they do not need the complex ignition systems (spark plugs, coils, HT leads, distributor etc) associated with petrol engines. Petrol engines also require a carburettor or injection system to mix the fuel and air, diesel engines do not need them. This all means there is far less to go wrong with a diesel engine.
Longer life: Diesel engines, because of their application in industry, are normally built far stronger than petrol engines. From farming to Taxis, they are expected to work harder in a shorter period of time. Normal wear of piston rings in petrol engines is far slower in a diesel engine as the nature of the diesel fuel itself acts as a lubricant. You will also hear of diesel being referred to as ‘heavy oil’ and diesel vehicles as ‘oil burners’.
Emissions: Diesel engines in comparison to petrol engines produce less carbon dioxide, the gas responsible for global warming, and less Nitric Oxide (NO).
What are the disadvantages of diesel engines over petrol engines?
Noise: Diesel engines are far noisier, especially when cold, than petrol engines. However, modern diesels are becoming more refined all the time and are far more acceptable amongst private car users.
Higher Cost: Because of higher stresses within a diesel engine over petrol, the increased strength built into the engine means a higher initial cost. However, this is easily offset by the long term economy
Emissions: Eventhough diesel engines produce some less harmful gases associated with petrol engines they also produce more particulates (soot). These particulates are considered carcinogenic (cancer causing) and also contribute to smog.
Still interested in learning more click on the link for more information about traditional and modern systems. This is a fairly long and detailed explanation, so before you proceed go and grab a coffee.