Fuel Types

Dara de Bruijn


Diesel or Petrol

Diesel and Petrol are both extracted from the same raw material – crude oil – however due to a different refining process, both fuels have quite different characteristics, and levels of energy efficiency.

Calorific Value 

The calorific value of a fuel means the amount of energy present within the fuel which is released as heat when burned. Petrol has a calorific value of 45.8 MJ/kg, where Diesel has a value of 45.5 MJ/kg. Both fuels are similar in value, however diesel has a higher density, so less fuel is required to generate the same amount of energy.


The nature of Petrol is more volatile than Diesel. Higher volatility means that there is a greater chance of ‘knocking’ to occur in the engine (for the fuel to combust before the optimum timing) – this is bad for fuel efficiency and for the overall health of the car.


Due to the differences in the nature of Petrol and Diesel, the kind of residues that result from combustion vary. Gasoline produces more greenhouse gasses than Diesel, such as carbon monoxide and hydrocarbons – this contributes to environmental pollution. Diesel on the other hand will produce more nitrogen oxide and soot particles – this combination results in heavy black deposits which pose a health hazard for those exposed to the exhaust, more so than Petrol, as such a special filter must be installed on diesel exhausts to counteract this.

Fuel Efficiency

Diesel is a more energy-efficient fuel when compared to Petrol, however the cost of parts and servicing is notably higher for Diesel cars.

“Depending on the car as well as the engine used, a diesel engine uses 15-20% less fuel compared to a petrol engine. However, the price of this efficiency is a higher premium compared to the petrol variant of the same car.”

The question of which type of fuel is better for the environment lies in selecting the correct car for your needs. If you are just making short trips, a petrol car may be more economical for you – if you are driving 40 minutes to work every day, diesel could be a better option.


Biofuel is the term used for any fuel that has been derived from biomass (materials produced by living organisms such as plants and animals). This process comes with some advantages and disadvantages. When we look at the current biofuel market, the majority of fuel is being produced in the form of biodiesel for trucks, however biofuel compatible cars are becoming more readily available.


Biofuel is significantly more clean when we compare it to fossil fuels. When burned, biofuel gives off less greenhouse gasses and particulates. Biofuel also has the added benefit of oil spill security – biofuel is biodegradable, so in the event of an oil spill or breach somewhere along the production-distribution line, there is much lower risk to the environment.


The downside of biofuels is that they are currently less energy-efficient than fossil fuels – biodiesel has a calorific value of 38 MJ/kg. They also have the disadvantage of not being completely compatible with most cars on the market today – in order to use biofuel in your car without causing damage, it must come in the form of 10E, which contains 9-10% bioethanol and the rest comprised of unleaded petrol.

There is now also a rising concern in how valuable agricultural land is being utilized for production of biofuels as opposed to food. These crops also use artificial fertilizers, so the positive impact on the environment by having a cleaner material to burn could be negated to some extent by the negative impacts as a result of production.


Electric cars have established themselves as the most economical and eco-friendly vehicles on the market today. On average, electric cars emit three times less CO2 than their fossil fuel powered equivalents. 

“Even in the worst case scenario, an electric car with a battery produced in China and driven in Poland still emits 22% less CO2 than diesel and 28% less than petrol… In the best case scenario, an electric car with a battery produced in Sweden and driven in Sweden can emit 80% less CO2 than diesel and 81% less than petrol.”

Energy Sources

Where electricity is sourced from is a common topic of discussion. The energy in an electric motor could just as easily have been generated by fossil fuels as it could have been by wind or solar methods. However, the capacity for electric motors to turn energy into torque is far more efficient than fossil fuel motors. This means that if we were to put the same fuel we used to generate the electricity in the e-car, into a petrol motor, we would still be getting better energy output from the electric engine.

With the world’s supply of fossil fuels diminishing, and affordable electric cars becoming increasingly accessible, we find ourselves in the midst of a great shift from non-renewable to renewable forms of energy. See also our article on Renewable Sources for Central Heating

For the moment electric cars are generally still more expensive than their fossil fuel alternatives, so here are some helpful tips on how you can save on gas during your next drive


[1]: “Petrol vs diesel: A fuel efficiency comparison – spinny,” Spinny Car Magazine, 26-Aug-2022. [Online]. Available: https://www.spinny.com/blog/index.php/petrol-vs-diesel-efficiency-and-cost-of-running/ [Accessed: 02-Dec-2022].

[2]: “Does an electric vehicle emit less than a petrol or diesel?,” Transport & Environment, 28-Jun-2022. [Online]. Available: https://www.transportenvironment.org/discover/does-electric-vehicle-emit-less-petrol-or-diesel/ [Accessed: 03-Dec-2022].

About the Author

Dara de Bruijn is a freelance writer, musician, and yoga instructor based in Dublin, Ireland. His main focus is exploring the benefits of co-operative living and leading a life orientated around social service.

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