Cleaner diesel engines may come from water itself
image: Advancements in diesel emission reduction strategies: a focus on water-in-diesel emulsion technology
Credit: Chukwuemeka Fortunatus Nnadozie, Chiamaka Prisca Onuoha, Emeka Emmanuel Oguzie & Enos Ihediohamma Emereibeole
A new study led by Nigerian researchers suggests a simple ingredient could make diesel engines cleaner: water. By blending precise amounts of water with diesel fuel, scientists have shown that emissions of several harmful pollutants can be dramatically reduced without major engine modifications.
The review, published in Carbon Research, analyzed decades of studies on reducing emissions from diesel engines, which remain vital in transportation, agriculture, and power generation but also emit soot, nitrogen oxides, and other air pollutants. Traditional solutions, such as exhaust filters and catalytic converters, are effective but costly and difficult to retrofit on older engines. The new analysis finds that a fuel‑based method called Water‑in‑Diesel Emulsion (WiDE) technology offers a practical and sustainable alternative.
WiDE consists of tiny water droplets evenly dispersed within diesel fuel using stabilizing surfactants. When injected into an engine, the water evaporates rapidly, creating microscopic “micro‑explosions” that improve fuel mixing and combustion. This physical effect lowers engine temperatures, which in turn reduces the formation of nitrogen oxides, while the improved air‑fuel mixing cuts down particulate matter and unburned hydrocarbons.
According to lead author Chukwuemeka Fortunatus Nnadozie of the Federal University of Technology Owerri, “WiDE technology can reduce nitrogen oxides by up to 67 percent and soot emission by roughly 68 percent while maintaining high engine efficiency.” The study also notes improved brake thermal efficiency in several experiments, meaning engines using WiDE not only run cleaner but can also use fuel more effectively.
The key to success lies in maintaining a stable emulsion. The researchers report that using surfactant blends allows WiDE fuels to remain uniform for up to 60 days without separating, an important step toward commercial adoption. They also identify opportunities to combine WiDE with other green technologies, such as diesel oxidation catalysts, for even greater pollutant reduction.
Future research, the authors suggest, should focus on optimizing surfactant chemistry, studying long‑term effects on engine components, and developing large‑scale testing standards. If widely adopted, WiDE could help countries meet emission targets while extending the life of existing diesel fleets.
“Simply adding water could help us make diesel engines part of a cleaner‑energy future,” said co‑author Emeka Emmanuel Oguzie. “It is an innovation that bridges environmental responsibility with engineering practicality.”
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Journal Reference: Nnadozie, C.F., Onuoha, C.P., Oguzie, E.E. et al. Advancements in diesel emission reduction strategies: a focus on water-in-diesel emulsion technology. Carbon Res. 4, 45 (2025). https://doi.org/10.1007/s44246-025-00210-y
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About Carbon Research
The journal Carbon Research is an international multidisciplinary platform for communicating advances in fundamental and applied research on natural and engineered carbonaceous materials that are associated with ecological and environmental functions, energy generation, and global change. It is a fully Open Access (OA) journal and the Article Publishing Charges (APC) are waived until Dec 31, 2025. It is dedicated to serving as an innovative, efficient and professional platform for researchers in the field of carbon functions around the world to deliver findings from this rapidly expanding field of science. The journal is currently indexed by Scopus and Ei Compendex, and as of June 2025, the dynamic CiteScore value is 15.4.