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Petrol Engine vs. Diesel Engine: What's the Difference?

Edited by Aimie Carlson || By Harlon Moss || Updated on October 21, 2023
A petrol engine uses spark ignition to burn fuel; a diesel engine uses compression ignition and burns diesel fuel.

Key Differences

A petrol engine and a diesel engine are both internal combustion engines, but they differ fundamentally in their ignition processes. While a petrol engine relies on a spark plug to ignite the fuel-air mixture, a diesel engine uses the heat generated from compressing air to ignite the fuel.
Regarding efficiency, petrol engines tend to provide smoother acceleration and higher RPMs, while diesel engines are generally more fuel-efficient and offer higher torque at lower RPMs.
Environmental concerns differentiate the two as well. Petrol engines generally emit more CO2, while diesel engines release higher amounts of NOx and particulates.
Maintenance perspectives offer another point of contrast. Petrol engines usually require less maintenance than diesel engines. However, diesel engines, given their robust construction, often have a longer lifespan.
The fuel used is, of course, the most obvious difference. Petrol engines run on gasoline (referred to as 'petrol' outside of North America), while diesel engines use diesel fuel, which is denser and has a higher energy content.

Comparison Chart

Ignition Method

Spark ignition.
Compression ignition.

Efficiency & Torque

Higher RPMs, smoother acceleration.
More fuel-efficient, higher torque at lower RPMs.


Emits more CO2.
Emits more NOx and particulates.

Maintenance & Lifespan

Generally requires less maintenance.
Often has a longer lifespan but might need more maintenance.

Fuel Used

Uses gasoline (petrol).
Uses diesel fuel.

Petrol Engine and Diesel Engine Definitions

Petrol Engine

An engine emitting carbon dioxide as a primary pollutant.
Environmentalists are concerned about the CO2 emissions from petrol engines.

Diesel Engine

An engine that often emits more NOx than petrol engines.
The city is regulating the use of old diesel engines due to pollution concerns.

Petrol Engine

An engine typically lighter than its diesel counterpart.
For city driving, many prefer a vehicle with a petrol engine.

Diesel Engine

A machine powered by diesel fuel.
The ship's massive diesel engine hummed steadily during the voyage.

Petrol Engine

An internal combustion engine running on gasoline.
The new model's petrol engine offers improved fuel efficiency.

Diesel Engine

An engine utilizing compression ignition.
The truck's diesel engine provides excellent torque.

Petrol Engine

An engine using spark ignition.
The sports car has a high-performance petrol engine.

Diesel Engine

An engine with a robust construction and longevity.
Farmers often choose equipment with a diesel engine for its durability.

Petrol Engine

A machine relying on petrol for power.
The boat's petrol engine roared to life with a turn of the key.

Diesel Engine

An internal combustion engine known for fuel efficiency.
For long hauls, many prefer trucks with a diesel engine.


How does a diesel engine ignite its fuel?

A diesel engine uses compression ignition.

Which engine is more fuel-efficient?

Diesel engines are generally more fuel-efficient than petrol engines.

Do petrol engines emit more CO2 than diesel engines?

Yes, petrol engines typically emit more CO2, while diesel engines emit more NOx and particulates.

What type of ignition does a petrol engine use?

A petrol engine uses spark ignition.

Why are diesel engines sometimes restricted in cities?

Diesel engines can emit higher levels of NOx and particulates, leading to pollution concerns.

Can a petrol engine be converted to run on diesel?

Converting a petrol engine to run on diesel is complex and not typically done due to design differences.

Why is diesel fuel denser than gasoline?

Diesel fuel contains more carbon atoms in longer chains, making it denser than gasoline.

Are petrol engines typically lighter than diesel engines?

Yes, petrol engines are generally lighter than their diesel counterparts.

Are diesel engines louder than petrol engines?

Diesel engines can be noisier, especially older models, compared to petrol engines.

Which engine typically provides smoother acceleration?

The petrol engine generally offers smoother acceleration.

What is the primary fuel for a petrol engine?

The primary fuel for a petrol engine is gasoline (known as petrol outside North America).

Which engine type is preferable for city driving?

Many people prefer petrol engines for city driving due to their smoother acceleration.

Why do diesel engines produce more torque at lower RPMs?

The diesel fuel's higher energy content and the engine's higher compression ratio contribute to this characteristic.

Why are diesel engines often chosen for heavy machinery?

Their high torque, fuel efficiency, and durability make diesel engines suitable for heavy machinery.

Which engine type is better for the environment?

Both have environmental drawbacks: petrol engines emit more CO2, while diesel engines release more NOx and particulates. The answer depends on the specific environmental concern.

Is it more expensive to maintain a diesel engine than a petrol engine?

Maintenance costs can be higher for diesel engines, especially if specialized parts or services are required.

Can diesel engines be used in sports cars?

While less common, some sports cars are designed with diesel engines, especially for races focusing on endurance.

Which engine usually requires more maintenance?

Diesel engines might require more maintenance compared to petrol engines.

Are diesel engines considered more durable?

Yes, diesel engines are often constructed more robustly and can have a longer lifespan.

Can petrol engines run on diesel fuel?

No, petrol engines are designed to run on gasoline and can be damaged by diesel fuel.
About Author
Written by
Harlon Moss
Harlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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