Combustion Dynamics and Emissions Characterization

Combustion dynamics and emissions characterization address how fuel‐air mixtures ignite, propagate and interact with flow fields, and how these processes give rise to pollutant formation. Research spans detailed studies of flame stability, acoustic coupling leading to thermoacoustic instabilities, and the chemical pathways that govern the generation of nitrogen oxides, unburned hydrocarbons and particulate matter. High‐fidelity numerical models – including large‐eddy simulation and detailed chemical kinetics – now resolve flame front structure, turbulent stretch and curvature, enabling prediction of localised extinction and reignition events. Experimental approaches couple optical diagnostics with laser‐based methods to measure species concentration, temperature and velocity fields. Together, these tools reveal the influence of parameters such as equivalence ratio, pressure, temperature and fuel composition on flame behaviour and pollutant yields. Emissions characterisation has become critical for the adoption of new fuels, from ammonia and hydrogen blends to renewable producer gas, by quantifying trade‐offs between carbon reduction and NOx or N2O formation. Advances in combustion control – such as exhaust gas recirculation (EGR), staged combustion and in‐cylinder reforming – aim to optimise thermal efficiency while minimising pollutant output. The global significance of this work is underscored by stringent air quality regulations and the drive towards net-zero greenhouse gas emissions, motivating both fundamental insights and practical strategies for low-emission combustor design across power generation, transportation and industrial applications.

Research from Nature Portfolio

A novel approach to ammonia‐fuelled marine engines introduces in-cylinder reforming coupled with targeted exhaust gas recirculation. One cylinder operates rich of stoichiometry to decompose excess ammonia into hydrogen, which is then recirculated into adjacent cylinders. This configuration leverages hydrogen-enriched combustion and EGR to achieve a 15.8 % gain in indicated thermal efficiency at low engine speeds, while reducing unburned NH₃ by nearly 90 % and N₂O by over 90 %. Concurrently, greenhouse gas emissions are cut by more than 90 %, demonstrating a viable pathway to decarbonise maritime propulsion without compromising performance or regulatory compliance.

Combustion Dynamics and Emissions Characterization publication trend

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

Technical terms

Combustion dynamics: The study of flame behaviour, including instability, propagation speed and interaction with flow and acoustic fields.

Emissions characterization: The analysis and quantification of pollutants produced during combustion, such as NOx, particulate matter and unburned hydrocarbons.

Premixed combustion: A mode of burning in which fuel and oxidiser are mixed prior to ignition, promoting uniform flame propagation.

Equivalence ratio (φ): The actual fuel-to-air ratio divided by the stoichiometric fuel-to-air ratio, indicating lean (φ < 1) or rich (φ > 1) mixtures.

Lean combustion: Operation with an excess of oxidiser (φ < 1), which typically reduces peak temperatures and NOx formation but may lead to instabilities.

Nitrogen oxides (NOx): Reactive nitrogen species (NO and NO₂) formed at high temperatures via thermal and prompt pathways, major contributors to smog and acid rain.

Exhaust gas recirculation (EGR): A technique that recirculates a portion of exhaust gases back into the intake stream to lower combustion temperature and reduce NOx emissions.

References

1. Air Quality Implications of Using Ammonia as a Renewable Fuel: How Low Can NO x Emissions Go?. ACS Energy Letters (2023).
2. Ammonia marine engine design for enhanced efficiency and reduced greenhouse gas emissions. Nature Communications (2024).
3. Influence of steam addition and elevated ambient conditions on NOx reduction in a staged premixed swirling NH3/H2 flame. Proceedings of the Combustion Institute (2019).