Alternative Fuels and Emissions in Internal Combustion Engines

Internal combustion engines remain dominant in land transport and off‐grid power generation, but their reliance on petrol and diesel contributes significantly to global CO₂ and pollutant emissions. Alternative fuels—including bio‐LPG, biodiesel, alcohols (methanol, ethanol, acetone), compressed natural gas and dual‐fuel combinations—offer varied pathways to decarbonise mobility and improve urban air quality. Bio‐LPG and biodiesel can be drop‐in replacements, reducing lifecycle carbon emissions by up to 80%, while gaseous fuels often lower particulate and carbon monoxide outputs. Oxygenated alcohol blends enhance combustion stability and reduce soot but can accelerate lubricant oil ageing and elevate NOₓ formation. Dual‐fuel diesel engines combine a gaseous pilot with a liquid pilot to achieve low smoke–NOₓ trade‐offs at modest efficiency penalties. Key challenges include variable energy density, cold‐start behaviour, material compatibility, fuel distribution infrastructure and optimising combustion timing and aftertreatment to control NOₓ and unburnt hydrocarbons. Cross‐disciplinary advances in catalyst‐based fuel synthesis, engine mapping and exhaust‐gas recirculation strategies underpin progress towards more sustainable transport.

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Alternative Fuels and Emissions in Internal Combustion Engines publication trend

The graph below shows the total number of articles in alternative fuels and emissions in internal combustion engines across all publications each year (not limited to Nature Index journals).

Technical terms

Brake thermal efficiency: Ratio of engine output work to the fuel’s energy input, indicating how effectively chemical energy is converted into mechanical work.

Brake specific fuel consumption (BSFC): Mass of fuel required to produce one unit of power over time; a key metric of an engine’s fuel economy.

NOₓ: Oxides of nitrogen formed during high‐temperature combustion; primary contributors to smog and regulated by emission standards.

Bio-LPG: Renewable liquefied petroleum gas derived from biomass or waste feedstocks, interchangeable with fossil LPG but with a lower lifecycle carbon footprint.

Biodiesel: Ester-based diesel substitute produced from vegetable oils or animal fats, characterised by oxygen content that promotes cleaner combustion.

Dual-fuel operation: Combustion strategy using two distinct fuels (e.g., diesel and gas) to balance efficiency, power and emissions control.

References

1. Decarbonized automotive fuel: Liquefied petroleum gas biosynthesis, benefits and drawbacks. Results in Engineering (2024).
2. Acetone–Gasoline Blend as an Alternative Fuel in SI Engines: A Novel Comparison of Performance, Emission, and Lube Oil Degradation. ACS Omega (2023).
3. The Impact of Diesel/LPG Dual Fuel on Performance and Emissions in a Single Cylinder Diesel Generator. Applied Sciences (2018).
4. Comparative Analysis of Performance and Emission Characteristics of Biodiesels from Animal Fats and Vegetable Oils as Fuel for Common Rail Engines. Energies (2024).