Emulsified Fuels in Diesel Engine Performance and Emissions

Emulsified fuels—most commonly water-in-diesel blends stabilised by surfactants—have emerged as a practical strategy to curb harmful exhaust in compression-ignition engines while retaining or enhancing thermal efficiency. By dispersing fine water droplets within the fuel, combustion is marked by secondary atomisation and micro-explosions that promote more uniform spray breakup, lower peak flame temperatures and accelerate fuel–air mixing. As a result, reductions in nitrogen oxides (NOx), particulate matter and unburned hydrocarbons are routinely reported, with many studies also noting marginal gains in brake thermal efficiency. These attributes render emulsified fuels attractive for road vehicles, marine engines and stationary power plants without requiring major engine modifications. However, real-world deployment hinges on overcoming challenges in droplet coalescence, long-term stability, surfactant compatibility and changes to viscosity and density. Recent efforts have explored both novel biosurfactants and advanced formulation techniques, as well as the integration of data-driven optimisation to tailor water content and operating conditions. Together, these developments underscore the global significance of emulsified diesel as a low-cost, near-term pathway to lower engine emissions and support decarbonisation objectives.

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Emulsified Fuels in Diesel Engine Performance and Emissions publication trend

The graph below shows the total number of articles in emulsified fuels in diesel engine performance and emissions across all publications each year (not limited to Nature Index journals).

Technical terms

Water-in-diesel emulsion: A two-phase mixture in which micron- to nano-scale water droplets are dispersed within diesel fuel by surfactants to modify combustion dynamics.

Micro-explosion: A secondary atomisation event where rapid vapourisation of dispersed water droplets causes fuel droplets to fragment, enhancing mixing and lowering flame temperature.

Surfactant: A surface-active agent added to emulsified fuel to reduce interfacial tension and maintain homogenous dispersion of water and oil phases.

Brake thermal efficiency (BTE): The ratio of engine brake power output to the fuel’s chemical energy input, indicating how effectively fuel energy is converted into work.

Brake-specific fuel consumption (BSFC): The mass of fuel consumed per unit of brake power produced per hour, used to evaluate engine fuel economy.

References

1. The investigation of lecithin and cocamide DEA Biosurfactant concentrations on emulsified biodiesel fuel stability, properties, and the micro-explosion phenomenon. Results in Engineering (2024).
2. Applied Intelligent Grey Wolf Optimizer (IGWO) to Improve the Performance of CI Engine Running on Emulsion Diesel Fuel Blends. Fuels (2023).
3. Optimal Water Addition in Emulsion Diesel Fuel Using Machine Learning and Sea-Horse Optimizer to Minimize Exhaust Pollutants from Diesel Engine. Atmosphere (2023).