Scientists from the Federal University of Technology Owerri (FUTO) in Nigeria have conducted one of the most comprehensive reviews of modern methods for reducing emissions from internal combustion engines. Analysis of dozens of major international studies has shown that Water-in-Diesel Emulsion (WiDE) is currently the most efficient and simple technology for emissions reduction. This method consists in adding a small amount of water to diesel fuel. Evidently, this simple procedure can significantly reduce harmful emissions (by more than 60% for some components) while maintaining engine efficiency, and even improving it in some cases.
Diesel engines continue to be one of the main sources of urban air pollution. They release nitrogen oxides, soot, carbon monoxide and unburned hydrocarbons. Although modern purification systems, such as diesel particulate filters and catalytic converters, effectively reduce these emissions, they entail high costs, complicate system design and require the internal combustion engine to be replaced from time to time. Meanwhile, WiDE technology offers a simple solution: mixing diesel with water and special emulsifier additives to modify the combustion process.
The Nigerian researchers have demonstrated that the key effect of this technology is related to microexplosions. When water droplets that are evenly distributed in the diesel fuel enter the hot combustion chamber, they vaporize instantly. The resulting vapor breaks the fuel droplets into smaller fragments, improving the fuel’s ability to mix with air. This simultaneously brings peak cylinder temperatures down (which means fewer nitrogen oxides) and improves combustion efficiency, reducing soot formation. According to the reviewed studies, it is possible to reduce nitrogen oxide emissions by up to 67% and particulate matter emissions by up to 68% compared to conventional diesel fuel.
However, special surfactants are needed to prevent water and diesel fuel from separating. The researchers examined the principles for selecting the surfactants in detail. They found that the best results come from a combination rather than a single component, such as a mix of sorbitan monooleate (Span 80) and polysorbate 80 (Tween 80, or polyoxyethylene sorbitan monooleate). The former interacts better with the fuel, or the oily phase, and helps retain water within the diesel fuel, forming a water-in-oil emulsion. The latter, meanwhile, gravitates towards the water phase. Together, they create a stable system in which water and fuel do not separate.
This balance is described by the HLB value (hydrophilic-lipophilic balance). In simple words, this is a scale indicating whether the emulsifier gravitates more towards water or oil. Low and high values indicate a strong affinity for oils and water, respectively. For a water-in-diesel emulsion, the range between 4 and 8 was found to be optimal, meaning that the mixture should consist mainly of fuel while interacting with water enough to distribute it evenly throughout the volume.
A properly selected combination of emulsifiers makes it possible to maintain fuel stability for up to 60 days without phase separation. However, the efficiency of WiDE is highly dependent on the proportion of water. With a water content of about 5–15%, the engine can operate even more efficiently than usual, improving heat transfer and combustion efficiency. If the water content is too high (over 20%), it can cause problems: ignition delays, increased fuel consumption and potentially higher carbon monoxide and hydrocarbon emissions. In addition, some experiments have shown increased CO₂ emissions due to more complete fuel combustion.
The researchers also compared WiDE with other water injection methods, such as vapor injection into the intake manifold or direct water injection into the cylinder. They found that the emulsion is more efficient because the water is initially contained in the fuel and microexplosions occur right in the combustion zone. This increases the efficiency of the process and eliminates the need for complex engineering solutions.
However, widespread adoption of this technology will only be possible if developers address the following challenges: optimizing emulsifier composition, assessing the long-term impact of mixtures on engine wear and testing their compatibility with existing exhaust control systems. Nevertheless, WiDE is already being viewed as a practical transitional solution capable of quickly reducing the environmental impacts of an internal combustion engine.
