Pyrolysis Oil Utilization in Diesel Engines

Pyrolysis oil, produced by the thermochemical decomposition of organic matter in the absence of oxygen, has gained traction as an alternative or supplementary fuel for diesel engines. Feedstocks span waste tyres, agricultural residues and digestate from anaerobic digestion, yielding oils with higher viscosity, acidity and oxygen content than conventional diesel. These properties affect atomisation, combustion phasing and deposit formation. Blending strategies—such as mixing pyrolysis oil with biodiesel, short-chain alcohols or hydrotreated fractions—can adjust cetane number, density and stability to meet engine requirements. Trials in agricultural, light-duty and research-grade engines indicate that moderate blends sustain power output with minor losses in brake thermal efficiency, while often reducing smoke and particulate emissions. Challenges remain in managing elevated NOx, sulphur oxides and aromatic fractions, as well as controlling oil acidity. Advances in reactor design and post-processing aim to refine oil composition, thereby supporting waste valorisation, energy security and emissions mitigation across global transport and industrial sectors.

Research from Nature Portfolio

Recent studies have demonstrated that pyrolysis oil derived from waste tyres can substitute a proportion of diesel fuel when reactor parameters are optimised. Control of temperature and catalyst selection improves oil yield and quality, yet the resulting fuels typically exhibit higher density and lower cetane number, leading to increased brake specific fuel consumption and reduced brake thermal efficiency. Emission profiles often show elevated NOx, CO and CO₂ alongside variable particulate and hydrocarbon levels, driven by aromatic content. These findings highlight the need for tailored production methods to balance circular-economy benefits against engine performance and emissions trade-offs.

Pyrolysis Oil Utilization in Diesel Engines publication trend

The graph below shows the total number of articles in pyrolysis oil utilization in diesel engines across all publications each year (not limited to Nature Index journals).

Technical terms

Pyrolysis oil: Liquid product obtained by heating biomass or waste feedstock in the absence of oxygen, containing water, oxygenated compounds and aromatics.

Cetane number: Measure of diesel fuel ignition quality; higher values indicate shorter ignition delay and more efficient combustion.

Brake thermal efficiency: Ratio of engine mechanical output to the chemical energy input of the fuel, expressed as a percentage.

Exhaust Gas Recirculation (EGR): Emission-control technique that redirects a portion of exhaust gases into the intake to lower combustion temperatures and reduce NOx formation.

Particulate matter (PM): Solid or liquid particles emitted in engine exhaust, including soot and unburnt hydrocarbons, which contribute to air pollution and health risks.

References

1. Production of biofuel from AD digestate waste and their combustion characteristics in a low-speed diesel engine. Renewable Energy (2024).
2. Diesel engine performance and emissions with fuels derived from waste tyres. Scientific Reports (2018).
3. Tyre pyrolytic oil fuel blends in a modern compression ignition engine: A comprehensive combustion and emissions analysis. Fuel (2022).
4. Performance of a Diesel Engine Fueled by Blends of Diesel Fuel and Synthetic Fuel Derived from Waste Car Tires. Sustainability (2024).