Combustion and Emission Characteristics of Diesel Engine Fuels

Diesel engine combustion is governed by high-pressure injection of liquid fuel into hot, compressed air, leading to rapid auto-ignition and flame development. Key fuel properties—cetane number, density, viscosity and oxygen content—mediate ignition delay, heat release rate and pollutant formation. Conventional petroleum diesel typically delivers high energy density and reliable performance but generates nitrogen oxides (NOx) and soot under lean-burn conditions. Strategies to mitigate emissions include precise control of injection timing and multiple injections, exhaust gas recirculation to lower peak temperatures, after-treatment systems and alternative fuel blending. Advanced fuels such as Fischer–Tropsch-derived diesel and oxygenated compounds (for example polyoxymethylene dimethyl ethers) offer higher cetane numbers and intrinsic oxygen, reducing soot and carbon monoxide, yet often involve trade-offs in fuel consumption, NOx emissions or power output. Understanding these interlinked processes is crucial for meeting stringent global regulations and advancing cleaner combustion technologies.

Research from Nature Portfolio

Recent studies have explored coal-based Fischer–Tropsch diesel blends and heavy-duty engines meeting stringent emission standards. Coal-derived diesel blended with hydrogenated diesel at varying ratios showed comparable brake specific fuel consumption to petroleum diesel, with slight reductions in brake thermal efficiency. Introduction of polyoxymethylene dimethyl ethers (PODE) up to 30% by volume into the most petroleum-diluted blend decreased hydrocarbon, carbon monoxide and smoke emissions by up to 82%, while marginally raising NOx emissions. In a separate investigation on a common-rail heavy-duty engine compliant with China VI standards, blends of 10–30% PODE advanced combustion phasing, shortened ignition delay by up to 2.8°CA, and improved thermal efficiency by as much as 2.6%. Emissions of soot, hydrocarbon and CO declined significantly (up to 76%), with only a modest increase in NOx and a net decrease in equivalent fuel consumption.

Combustion and Emission Characteristics of Diesel Engine Fuels publication trend

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

Technical terms

Brake thermal efficiency (BTE): Ratio of useful mechanical work output to the total energy input from fuel.

Cetane number: Indicator of diesel fuel’s ignition quality; higher values signify shorter ignition delay.

Ignition delay: Time or crank-angle interval between start of fuel injection and onset of combustion.

Particulate matter (PM): Solid or liquid particles suspended in exhaust gases, including soot, measured by mass or number concentration.

Polyoxymethylene dimethyl ethers (PODE): Synthetic oxygenates composed of methylene ether chains, enhancing combustion and reducing soot.

Stoichiometric combustion: Fuel–air mixture ratio in which all fuel and oxygen are exactly consumed.

Soot: Carbonaceous particulate produced under fuel-rich or poorly mixed combustion conditions.

Exhaust gas recirculation (EGR): Technique whereby a fraction of exhaust gases is reintroduced to the intake to lower combustion temperature and NOx formation.

References

1. Performance and emissions of a diesel engine fueled by coal-based diesel fuels and their blends with polyoxymethylene dimethyl ethers. Scientific Reports (2023).
2. Experimental study on the effects of blending PODEn on performance, combustion and emission characteristics of heavy-duty diesel engines meeting China VI emission standard. Scientific Reports (2021).
3. Exploring the Potential of Lignocellulosic Biomass-Derived Polyoxymethylene Dimethyl Ether as a Sustainable Fuel for Internal Combustion Engines. Energies (2023).
4. Experimental Study of Fuel Combustion and Emission Characteristics of Marine Diesel Engines Using Advanced Fuels. Polish Maritime Research (2023).
5. Effects of Polyoxymethylene Dimethyl Ethers Addition in Diesel on Real Driving Emission and Fuel Consumption Characteristics of a CHINA VI Heavy-Duty Vehicle. Energies (2022).