Coconut oil biofuel blends match kerosene efficiency but increase fuel consumption in jet engine tests

Researchers at Osaka Metropolitan University tested biofuel blends derived from coconut oil in a small jet engine, comparing performance and emissions against pure kerosene. The biofuel was produced using a co-solvent method that mixes acetone with alcohol and coconut oil, yielding high-purity fuel without the high heat and pressure typical of conventional SAF production. This approach leverages discarded coconut waste, such as seeds and leftover flesh, which would otherwise be discarded during processing. The method also generates biodiesel and glycerin as byproducts, potentially improving its economic viability.

Engine tests revealed that while the biofuel blends achieved thermal efficiency comparable to kerosene, they required significantly more fuel to produce the same thrust. At 80,000 rotations per minute, a 50% methanol-based blend consumed 16.8% more fuel than pure kerosene, while the ethanol-based version consumed 19.6% more. This increased consumption stems from the lower energy density of the biofuels compared to kerosene. Despite this drawback, thrust output remained consistent across all blend ratios, indicating that the biofuel can deliver equivalent performance under controlled conditions.

Emissions data showed a mixed picture. Unburned hydrocarbon emissions decreased as the proportion of biofuel in the blend increased, with reductions of up to 40% at a 50% blend ratio. This improvement is linked to the absence of aromatic compounds in the biofuel, which are present in kerosene and contribute to hydrocarbon emissions. However, carbon monoxide emissions slightly increased, and carbon dioxide levels remained unchanged. The trade-off between reduced hydrocarbons and higher fuel consumption complicates the environmental benefit calculus.

The co-solvent production method offers a potential advantage over conventional SAF refining by operating at lower temperatures and using waste materials. This could reduce the energy footprint of biofuel production, addressing a key criticism of current SAF methods. However, the scalability of this approach remains untested, particularly for large commercial engines. The study focused on a small jet engine, and performance in larger, more complex systems may differ. Additionally, the economic feasibility of sourcing sufficient coconut waste for large-scale production is unclear.

For engineers, the study highlights both the promise and the limitations of coconut oil-derived biofuels. The comparable thermal efficiency and reduced hydrocarbon emissions are encouraging, but the higher fuel consumption and unanswered questions about scalability and cost present practical challenges. Further testing in commercial-scale engines and lifecycle assessments will be necessary to determine whether this biofuel can be a viable alternative to kerosene in aviation.