Both petrol and diesel are commonly used in modern cars, and one might wonder if they can be used interchangeably. Curious minds ask if petrol can be used in a diesel engine or vice versa. A simple answer is ‘No’. While both rely on combustion to power a vehicle, their respective engines are designed very differently. While operating through a similar principle, the key difference between petrol and diesel engine is in how the fuel burns.
Understanding How Car Engine Works
Both petrol and diesel engines are basically internal combustion engines. The process includes combustion of fuel and air mixture that causes a release of energy to expand the pistons and rotate the crankshaft. This in turn transfers the power to the drivetrain through a system of gears enabling the vehicle to move.
The internal combustion engine is often referred to as a four-stroke engine, due to its four-stroke cycle. Intake – piston pulls in the fuel and air by creating a vacuum through downward motion
- Compression – the fuel mixture is compressed and prepared for ignition while closing the intake and exhaust valves on the upper portion
- Power – the mixture is ignited upon completion of compression cycle either through spark plug or pressurised air compression
- Exhaust – the exhaust valve is released to expel the gases from the car exhaust system and exit the engine
Difference Between Petrol and Diesel Engine
The difference between both engines lies in how fuel injection and combustion occurs.
Fuel Injection
Petrol has the capability to mix with air easily. Hence, the fuel is introduced during the intake phase in pre-mixed condition. The pre-mixing was usually done through a carburettor but due to lack of control in exact ratio, now fuel injection is electronically controlled and prevents fuel wastage.
Diesel on the other hand does not mix well with the air, hence only air is compressed in the chamber and diesel is introduced during the combustion cycle.
Combustion
In petrol engines, the combustion of pre-mixed mixture occurs through an ignition via the car’s spark plugs. This is a rather calm operation and creates less noise as both petrol and air are mixed properly.
Diesel engines depend on a high compression ratio of air. Since only air is compressed in the chamber, high compression will increase the air temperature. When atomised diesel is sprayed during the second stage, it leads to spontaneous combustion.
Diesel engines tend to be noisier as the combustion of fuel is a bit uncontrolled.
Compression Ratio
In simpler terms, an engine compression ratio is a volumetric ratio in the combustion chamber when the piston is in an upward and downward position.
Diesel engines have to depend on a high compression ratio as the air needs to be compressed enough to raise the temperature and self-ignite when the fuel is introduced.
Petrol engines have a rather controlled compression ratio. As the air and fuel are pre-mixed, you don’t want self-ignition due to high temperature and the volatile nature of petrol itself. This can lead to non-uniform combustion as well as a secondary ignition because of spark plugs.
Furthermore, the presence of secondary hot spot leads to knocking issues that can damage both the piston and cylinder.
Fuel Efficiency
As diesel engines have a higher compression ratio, this leads to a more efficient engine cycle as compared to petrol. Moreover, diesel has a larger chain of hydrocarbons than volatile petrol and releases more energy on combustion. All these factors allow diesel engines to offer better fuel economy than petrol engines.
Engine Cost and Design
We have seen more research from automotive manufacturers towards the design of petrol engines. This is because diesel engines are bigger and expensive as they are designed for maximum compression ratio and longer strokes.
On the other hand, the petrol engines are lighter and cheaper. When we add in the environmental factor, it makes sense why manufacturers invest in innovation and research of petrol engines more than diesel engines.
Environmental Factor
The current trend is to make vehicles greener and environmentally friendly. Although diesel engines are cleaner and create fewer pollutants in terms of carbon monoxide, carbon dioxide and oxides of nitrogen. The fuel efficiency comes at a cost of higher particulate level and soot leftover that can be hazardous to the lungs.
On the other hand, petrol engines do create more oxides but the use of a catalytic converter limits the emission. Lack of particulates or afterburn fuel is the prime factor that makes petrol more environmentally friendly as compared to diesel.
FREQUENTLY ASKED QUESTIONS
Can diesel be used in petrol engines or vice versa?
If diesel is used in petrol engines, it will simply not ignite. Since it is less volatile and does not mix properly with air, the spark plug won’t be able to initiate combustion.
When we use petrol in diesel engines, we are spraying a highly volatile fuel into highly compressed hot air. Instead of smooth combustion, it will create detonations or explosions that can in turn damage the engine.
Which is more fuel-efficient, diesel or petrol?
Based on fuel compositions, diesel has larger chains of hydrocarbons as compared to petrol and emits more energy on combustion. With the addition of efficient fuel cycles due to the maximum compression ratio, diesel has a better fuel economy.
Why are diesel engines more expensive?
Diesel engines generate more heat and are designed to offer maximum compression ratio. Hence, it has to be sturdy enough to function at a high operating temperature. When we add in additional components like car turbochargers to deliver more compress and increase the overall horsepower, it costs more than an average petrol engine.
Even with the drive towards green economy to use electric and hybrid cars. Petrol and diesel cars remains a popular choice in terms of affability and variety. Check out our collection of used cars for sale across the UAE:
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Stay tuned to the UAE’s leading auto blogs for more information on car parts, market trends and automotive technology.
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