Petrol vs. Diesel What is the difference?

When choosing a car, one of the first considerations used to be (before electric cars became popular): Should it run on diesel or petrol? Both fuel types have advantages and disadvantages, and the engines behind them differ significantly in both technology, performance, and application. In this article, we review the most important differences between diesel and petrol – both as fuels and engine principles.

The difference in the fuel

Petrol and diesel are both products of crude oil, but their chemical composition and properties are different:

• Petrol is more volatile and evaporates more easily. It is ignited by a spark (spark plug) and is ideal for rapid combustion and higher revolutions.
• Diesel is heavier and less volatile. It is ignited by compression (without a spark plug) and is more energy-dense, which means better fuel economy.

Diesel contains on average about 10–15% more energy per liter than petrol. This makes diesel cars more economical for longer journeys. On the other hand, diesel typically pollutes more with NOx and particulates – unless advanced filters and AdBlue systems are used.

Technical difference

The petrol engine

The petrol engine works by a mixture of air and petrol being supplied to the cylinder. Here, the mixture is compressed and then ignited by a spark plug, creating a controlled explosion that pushes the piston down.

Petrol engines typically operate at lower compression and higher revolutions. They are known for their quick response, quiet operation, and ability to produce high power in small engines.

The diesel engine

The diesel engine works differently. Here, only air is compressed in the cylinder – to a very high pressure – which causes the temperature to rise sharply. When diesel is then injected, it self-ignites at the high temperature.

Diesel engines have higher compression, lower revolutions, and more torque at low revs. They are more fuel-efficient and durable, but often heavier and noisier than petrol engines.

Advantages and disadvantages of petrol and diesel

Petrol – advantages

• Less noise and vibration
• Cheaper cars and maintenance
• Better suited for short trips and city driving
• Lower emissions of particulates and NOx

Petrol – disadvantages

• Higher fuel consumption
• Less torque at low revs

Diesel – advantages

• Lower consumption and longer range
• High torque – good for heavy vehicles and trailers
• Long lifespan with proper maintenance

Diesel – disadvantages

• More complex technology (turbo, particulate filter, AdBlue)
• Higher emissions of NOx and particulates
• Can cause problems with many short trips (soot in the filter)
• Often higher weight and price

Environment and future

Diesel cars have for many years been preferred because of their fuel economy – especially in Europe. But with increasing focus on air quality and CO₂ emissions, diesel has gained a worse reputation, particularly in urban areas with particulate pollution and NOx problems.

Modern petrol cars with turbo engines and direct injection have reduced the difference in consumption and emissions. At the same time, both petrol and diesel cars have received advanced emission systems that reduce environmental impact.

As we transition to electric and hybrid cars, the difference becomes less relevant for many. Nevertheless, both petrol and diesel are still widespread – especially for commuting, commercial driving, and heavy transport.

What should you choose?

The choice between petrol and diesel primarily depends on your driving needs:

• Do you drive many short trips and mainly in the city? Choose petrol or electric/hybrid. Diesel engines have difficulty reaching optimal operating temperature on short trips.
• Do you drive many kilometers on the motorway or transport heavy loads? Diesel may be the best choice due to low consumption and high torque.
• Do you want to reduce your environmental impact? Modern petrol engines often emit less NOx and particulates, but electric and hybrid are the greenest choices today.

Conclusion

Petrol and diesel differ both as fuels and in the way the engines are constructed. Petrol engines are lighter, quieter, and good for shorter trips, while diesel engines are fuel-efficient and strong for heavy loads and long distances.

The best choice depends on your driving style and needs. With more alternatives like electric and hybrid today, it is more important than ever to consider both economy, environment, and functionality before choosing a powertrain.