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Coconut oil, a staple in kitchens and beauty products for generations, is now being seriously considered for jet propulsion. New research indicates that aviation biofuel derived from coconut oil can power small jet engines with an efficiency comparable to conventional kerosene, while also producing lower unburned hydrocarbon emissions. However, the study also noted that these biofuel blends consume more fuel and emit slightly higher levels of carbon monoxide.
With aviation contributing significantly to global carbon dioxide emissions, the industry faces increasing pressure to adopt cleaner fuel alternatives. The International Civil Aviation Organization (ICAO) has identified Sustainable Aviation Fuel (SAF) as the most effective strategy for reducing aviation's carbon footprint. Yet, many current SAF production methods are energy-intensive and costly, diminishing their overall environmental benefits. The new study, published in the journal 'Fuel', introduces a production approach designed to circumvent these issues, utilizing a technique that demands considerably less energy for fuel synthesis.
Researchers at Osaka Metropolitan University tested coconut oil-derived biofuels using what they termed a 'co-solvent method'. This innovative process involves blending acetone with alcohol and coconut oil to yield high-purity biofuel—exceeding 97%—without the extreme heat and pressure typically required by conventional production techniques. Beyond mere production, the team further evaluated the fuel by combusting it in a small jet engine, meticulously measuring both engine performance and exhaust emissions.
Traditional SAF production often involves rigorous industrial processes, including high-temperature refining steps that consume significant energy throughout the fuel's lifecycle before it even reaches an aircraft. The co-solvent method offers a distinct advantage: by adding acetone to a mixture of alcohol and coconut oil, normally incompatible liquids can uniformly blend and react completely at relatively low temperatures. This results in a biofuel of impressive purity.
Coconut itself presents a practical raw material advantage, as approximately 30% of the fruit is typically discarded after internal moisture extraction during processing. This study specifically utilized oil extracted from what the researchers describe as discarded and non-edible material, including large seeds and leftover flesh, effectively transforming agricultural waste into a valuable resource. The process also generates biodiesel suitable for vehicles and marine vessels, alongside high-quality glycerin as a byproduct.
Two types of biofuel were produced and thoroughly tested: one using methanol and the other ethanol. While both are plant-based fuels commonly investigated for diesel engines, this pioneering research focused on their performance within a jet engine, an area that has historically received less scientific scrutiny.
Testing was conducted in a small commercial jet engine capable of achieving speeds up to 130,000 rotations per minute. The biofuels were blended with conventional kerosene at volumetric ratios of 10%, 30%, and 50%, and the engine was operated across a range of speeds. Key measurements included fuel consumption, engine efficiency, and exhaust concentrations of four pollutants: unburned hydrocarbons, carbon monoxide, carbon dioxide, and nitric oxide.
Regarding fuel efficiency, the biofuel blends necessitated greater fuel consumption to generate equivalent thrust. At 80,000 rotations per minute, a 50% methanol-based blend consumed approximately 16.8% more fuel than pure kerosene, while the ethanol-based version required about 19.6% more. This increased consumption is primarily attributed to the biofuels possessing less energy per kilogram compared to kerosene, thus requiring more volume to maintain consistent output.
Despite the higher fuel consumption by weight, the blends converted heat into usable work at rates comparable to pure kerosene. At 100,000 rotations per minute, the thermal efficiency of the highest biofuel blend showed only a minor deviation from pure kerosene, and thrust output remained consistent across all tested blend ratios.
The most encouraging results emerged from the exhaust emissions data. Increasing the proportion of biofuel in the blend consistently led to a reduction in unburned hydrocarbon emissions. At a 50% blend ratio, hydrocarbon concentrations in the exhaust decreased by roughly 5% to 40% compared to pure kerosene, depending on engine speed. Researchers suggested this reduction is likely linked to the fuel's composition, as coconut-derived biofuels lack the ring-shaped, aromatic hydrocarbon molecules prevalent in conventional jet fuel.
Carbon dioxide emissions remained stable, aligning with levels observed for pure kerosene across all blend ratios. Although higher biofuel content correlated with increased total fuel consumption, the CO2 in the exhaust did not rise proportionally. Researchers hypothesize this pattern might indicate some unburned biofuel exiting the engine, an area they have flagged for future investigation.
Conversely, carbon monoxide emissions, a byproduct of incomplete combustion, modestly increased at higher blend ratios. A 50% blend produced approximately 3% to 17% more carbon monoxide than pure kerosene, varying with engine speed. This was linked by researchers to biofuels being harder to ignite than kerosene and carrying less energy, factors that can create fuel-rich zones within the combustion chamber where oxygen supply is limited.
Nitric oxide emissions, known to contribute to ozone depletion at high altitudes, were broadly comparable between the biofuel blends and pure kerosene. Notably, a 30% methanol-based blend exhibited nitric oxide concentrations 20% to 30% lower than pure kerosene across all tested operating conditions, a finding the authors believe warrants further in-depth study.
Several practical challenges currently hinder the routine adoption of this biofuel in aircraft. Coconut-derived biofuels are susceptible to atmospheric moisture absorption during storage, gradual oxidation over time, and can cause slight corrosion of metal components. Stainless steel exposed to the methanol-based version displayed signs of rust after one to two weeks. The authors emphasize the necessity of extended testing—spanning months to years—and suggest investigating antioxidant additives and improved sealed storage containers.
Furthermore, the oxygen content in these biofuels falls outside current international certification standards for aviation fuel. This implies that additional chemical processing, such as hydrogenation treatment, would be required to bring oxygen levels into compliance, although researchers acknowledge that such a process would subsequently reduce fuel yield.
While coconut oil-derived biofuel is not yet a direct replacement for conventional jet fuel, the performance data from this study strongly supports pursuing this concept. If the production advantages prove sustainable and the remaining fuel-quality issues can be resolved, coconut oil has the potential to become a viable candidate in aviation's ongoing quest for lower-impact fuels, rooted in a tropical nut.
It is important to note that this study utilized a small-scale micro jet engine, rather than a full-size commercial aircraft engine, meaning the results may not directly translate to larger propulsion systems. Exhaust gas measurements were taken 30 millimeters downstream from the engine nozzle exit, and the researchers acknowledge the potential for ambient air dilution of sampled gases, which could affect measurement accuracy. The study also did not measure certain toxic compounds, specifically polycyclic aromatic hydrocarbons, which the authors identify as a priority for future research. Long-term testing of fuel storage stability and material corrosion, which would require months to years of observation, was not completed. The oxygen content in both biofuels falls outside current international aviation fuel standards. Additionally, turbine inlet temperature measurements carried uncertainty due to steep temperature gradients inside the engine, and the relatively low nitric oxide concentrations measured may benefit from validation using higher-precision analytical methods in future work.
This work received support from an Osaka City Innovation Support Grant. The corresponding author, Shinichiro Ogawa, disclosed an employment relationship with Osaka Metropolitan University. All other authors declared no known competing financial interests or personal relationships that could have influenced the work.
Authors: Shinichiro Ogawa, Takuto Hongo, Yasuaki Maeda, Huynh Phuong Uyen Nguyen, and Koichi Mori, all affiliated with Osaka Metropolitan University, Sakai, Osaka, Japan.
Journal: 'Fuel', Volume 428 (2027), Article 140208, published by Elsevier.
Paper Title: 'Combustion and emission characteristics of aviation biofuel derived from coconut oil using the co-solvent method: toward eco-friendly micro jet engines'.
Received: January 9, 2025. Accepted: June 2, 2026. Available online: June 8, 2026.
Source: Fuel Journal