Powering transport with the densest energy carrier on earth
The role of liquid hydrocarbons in transportation, particularly aviation, is a story of efficiency, energy density, and practicality.
From the early days of petrol-powered cars to the jet-fuelled aircraft that cross continents today, liquid fuels have consistently offered the best balance between weight, storage, and range — essential qualities for long-distance travel. As hard-to-abate transport sectors navigate the path toward sustainability, alternatives to fossil-derived liquid fuels are vital for the net-zero transition.
A brief history of liquid fuels in transportation
Liquid fuels became indispensable with the invention of the internal combustion engine in the 1800s. In 1886, Karl Benz introduced the first petrol-powered car, demonstrating the advantages of a lightweight, energy-dense fuel that outperformed steam power. The aviation industry soon followed suit, with the Wright brothers’ first flight relying on petrol. This innovative use of liquid hydrocarbons extended into space when Robert H. Goddard launched the first liquid-fuelled rocket in 1926, using petrol and liquid oxygen — the same fundamental technology that later propelled the Saturn V rocket to the moon. By the 1940s, the development of high-octane fuels became critical to the war efforts of World War II, cementing the role of liquid hydrocarbons in aviation.
The power of liquid hydrocarbons as transport fuel
Liquid hydrocarbons, including petrol, diesel, and kerosene, are molecular compounds composed of carbon and hydrogen atoms linked in chains. The strong chemical bond between carbon and hydrogen means a large amount of chemical energy is stored in the bond and is released when burned in an engine. Additionally, the compact structure of hydrocarbon chains allows these fuels to pack substantial energy into a small volume. In fact, liquid hydrocarbons are the densest chemical energy carrier on earth. To quantify this, the energy densities of hydrocarbon fuels are:
- Petrol: 34.2 MJ/L
- Jet A-1 kerosene: 35 MJ/L
- Diesel: 38.6 MJ/L
These high energy values make them highly efficient for powering both ground vehicles and aircraft, where fuel weight directly affects performance and range.
Alternative fuel transition
The standard fuel for modern commercial aircraft is kerosene, specifically Jet A or Jet A-1. In addition to its high energy density, Jet A-1 fuel has a freezing point of -47°C, making it suitable for high-altitude flights where temperatures can plummet. For long-haul flights, the combination of energy density and resistance to freezing makes kerosene an optimal choice, ensuring both efficiency and operational reliability across vast distances.
As the aviation industry seeks a more sustainable future, alternatives to fossil fuel-derived kerosene are being explored, with hydrogen emerging as one such solution. Hydrogen offers an impressive energy per unit mass — roughly three times that of kerosene — but its low density presents significant challenges. Liquid hydrogen has a density of only 0.070-0.071 kg/m³ at cryogenic temperatures (-253°C), resulting in an energy density of just 8.5-10 MJ/L. This means that, although hydrogen is extremely lightweight, it requires around four times the volume of kerosene to store the same amount of energy. The challenge is even greater with gaseous hydrogen, which contains only 4.5-5.3 MJ of energy per litre, requiring even more storage volume.
While hydrogen-powered aircraft are an active area of research and an emerging technology for zero-emission flights, the low energy density of liquid hydrogen makes it less practical for long-haul journeys. As a result, the aviation industry considers sustainable aviation fuel (SAF) the most viable solution, especially in the short to medium-term. SAFs are synthetic fuels that can directly replace fossil-based kerosene, which means they can be used in existing aircraft without significant modifications to engine or fuelling infrastructure. This compatibility makes SAF a practical and scalable step toward greener aviation.
At Avioxx, we are developing a novel process to efficiently convert residual household waste into liquid hydrocarbons suitable for powering planes, trucks, and ships. Harnessing the energy of waste hydrocarbons, we aim to produce sustainable fuels at a price that’s comparable to fossil-derived fuels, offering a more sustainable alternative to transport. To learn more about our projects, please get in touch at info@avioxx.com.