Have you ever thought about how does a car or a local transport runs in which you travel daily? Or if you knew that they run either on the diesel or petrol engines? The second thing that must have striked your mind would be that what is a difference between a Diesel and petrol engine. And after this question you would have stopped asking anything further because things would have got a bit technical from there on.

It is common for a non-technical person to get confuse between a diesel and a petrol engine mostly in terms of their technicality and uses. In this article, a non-technical person will easily understand the difference between the two engines.

Firslty, the internal combustion engines came into existence in the early 19th century and since then they outdated many of the previously used engines. Since then internal combustion engines have their application in various fields of machines. Apart from internal combustion engines, there are many other engines in the existence which are used for specific purposes like electric engines, steam engines, etc.

An internal combustion engine operates either in two strokes or four strokes. In simple terms, we can say that in two strokes every revolution of the crankshaft has a power stroke and in four strokes, there is one power stroke for every two revolutions of the crankshaft.

What is a CI Engine?

Compression-Ignition (CI) engine is also known as the Diesel engine. It was named after Rudolf Diesel. They were initially designed to replace the steam engines. Perhaps their existence later revolutionized the whole auto industry. It is also an internal combustion engine like the SI engine which uses fuel and air for combustion. Contrarily to the SI engine, in the CI engine, there is no spark plug.

The combustion is initiated by increasing the temperature of the air inside the chamber. A diesel engine is built robustly to withstand high temperature and high compression ratio, therefore they have more weight than an SI engine. In addition, it produces more torque and better fuel economy than an SI engine.

Generally, heavy-duty vehicles have diesel engines but it can be a problem during winters. As it doesn’t use a spark plug to initiate combustion it is dependent on the temperature created inside the engine block by compression stroke, therefore it has a starting problem during winters. It also produces more hydrocarbons in its exhaust gases which create pollution.

It has the highest thermal efficiency in internal combustion engines because of its high compression ratio which lies between 14:1 and 25:1. This makes it to reach upto an efficiency of 55%.

What is an SI Engine?

The SI engines are generally known as a petrol engines. It runs on the otto cycle. In the later 19th century, Nicolaus Otto invented the otto cycle for internal combustion engines. SI engine uses a spark plug to initiate combustion in the combustion chamber. There is a carburetor in the SI engine which sucks the air from outside and mixes it with the fuel. As air fuel mixture is injected in the combustion chamber and spark plug provides a spark. It uses petrol as the working fluid.

The air-fuel mixture ratio is provided and controlled by the carburetor. The compression ratio is lower and lies between 10:1 and 14:1. Its efficiency lies between 20% and 35%. Due to presence of the spark plug in the SI engines, it easily starts during winters. Moreover, it has low vibration and low noise production. The cylinder block is also lightweight and maintenance cost is lower than a diesel Engine.

Difference between SI and CI engine?

Here are some of the key differences between both these engines:

Diesel engine Petrol engine
Operates on the diesel cycle. Operates on the otto cycle.
It has constant volume cycle It has constant pressure cycle
Air fuel is mixed inside the combustion chamber Air fuel is mixed outside the combustion chamber
Fuel injector only injects fuel in the combustion chamber Carburettor mixes air and fuel and supply to the combustion chamber
Its efficiency is high thus provides good fuel economy. Its efficiency is low thus it give low fuel economy
The power production is high The power production is low compared to CI engines
It has high maintenance cost It has low maintenance cost

These are some of the basic differences between diesel engines and petrol engines. Apart from these, internal combustion engines is differentiated in terms of their designs, mounting, fuel type used, positioning of the spark plug in SI engines and positioning of the fuel injector in CI engines, power capacity, etc.

Well, now you can say which type of the engines you travel on and how do they work.

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