Thermal runaway remains one of the most critical challenges limiting the large-scale deployment of lithium-ion batteries in energy storage and electric mobility applications. During thermal runaway, the rapid release of heat, gases, and particles in the cell ejecta can preheat and ignite neighbouring cells, leading to catastrophic propagation through the module. The temperature of this ejecta is a key parameter in propagation models, yet it remains poorly quantified due to the extreme transient nature of the release process. This work presents the first time- and spatially-resolved optical measurements of the incandescent fraction of Li-ion cell ejecta temperature during thermal runaway. Broadband emission spectra (350 – 550 nm) acquired at 5 kHz are inverted using a spectroscopic model based on Planck's law to infer the line-of-sight pyrometric temperature, accounting for system throughput and detector response. The technique is validated against the Yale E60 sooting diffusion flame to within 50 K. Application to eight repeat tests of 18650 NMC cells at 100% state of charge reveals a repeatable thermal signature: peak pyrometric temperatures of 2500 – 2900 K at thermal runaway initiation, decaying below 2000 K by 120 ms, with complete extinction of high-temperature emission by 200 – 250 ms. An uncertainty analysis of the spectral emissivity constrains the maximum temperature bias to less than 250 K, confirming that reported temperatures are upper bounds on the true pyrometric temperature. The peak pyrometric temperatures substantially exceed prior reported values, confirming that the high temperature emission is concentrated within narrow intermittent bursts that are challenging for conventional diagnostics such as thermocouples, color pyrometers and infrared imaging to resolve due to atomic emission interference or temporal blurring. These measurements establish the radiative enthalpy of the incandescent ejecta as a significant thermal load for cell-to-cell propagation modelling. Novelty and significance statement This work introduces the first time- and spatially- resolved optical measurements of incandescent ejecta temperature during Li-ion cell thermal runaway. Combining high-speed broadband emission spectroscopy with a spectroscopic model allows highly transient pyrometric temperatures to be resolved at sub-millisecond temporal resolution. The measurements reveal that the radiative thermal hazard is dominated by narrow, intermittent bursts of ejecta that can reach up to 2500 – 2900 K concentrated within the first 25 ms of thermal runaway. These quantitative boundary conditions, validated to within 50 K against a canonical sooting flame and bounded by an emissivity uncertainty analysis to less than 250 K, are directly applicable to thermal runaway propagation models where the radiative heat load from the ejecta has previously been a critical, unresolved parameter.

Ammonia is a promising carbon-free fuel and hydrogen carrier for gas turbine combustion, yet its low reactivity presents challenges for stable operation in swirl stabilized burners. This study investigates ammonia/hydrogen flame structure and stability in a dual swirl burner using high-speed planar laser-induced fluorescence (PLIF) imaging. The OH–NH PLIF measurements reveal how ammonia fraction affects the radical structures, capturing the sequential evolution of layer fragmentation, penetration, and pocket formation. One-dimensional counterflow modeling captures the qualitative ordering of OH and NH layers in dual swirl flames, though they show limited accuracy in predicting layer thicknesses due to unresolved local strain and curvature effects. Joint probability density functions and cross-correlation analyses reveal that NH and OH radicals remain segregated near the dump plane but increasingly overlap downstream due to shear. Their interaction is governed by the interplay of simultaneous transport or extinction of radicals and NH oxidation associated with OH growth following entrainment, consistent with the instantaneous PLIF images. Statistical analysis was performed to quantify flame pockets and break lengths in the OH and NH radicals and to characterize local extinction. The results identify the radical structures underlying the observed flame morphologies, providing insight for the design of stable ammonia-fueled combustors.Novelty and significance statement: While several studies exist on dual swirl hydrogen or methane combustion, the flame structure of dual swirl ammonia/hydrogen flames has not yet been characterized in detail. To the authors’ knowledge, this work presents the first high-speed OH–NH visualization of dual swirl ammonia/hydrogen flames, revealing the radical structure and its dynamics, including local extinction. These findings contribute to the fundamental understanding of flame stabilization and provide insights for combustor design in carbon-free gas turbine applications.

Lithium-ion batteries are increasingly deployed across a range of energy storage applications, heightening the need to understand failure mechanisms such as thermal runaway. This study presents a new experimental platform focusing on optical accessibility to quantify the transient ejection and ignition dynamics from a single 18650-format cell with an NMC-811 cathode. High-speed optical diagnostics, including luminosity imaging, spectral emission, photodetection, and sound measurements, were employed to characterise the spatiotemporal evolution of ejected fragments and flaming ignition. Light and sound data are temporally correlated, demonstrating that ignition is followed by flame propagation that occurs rapidly and intermittently, with significant temporal variability despite consistent thermal runaway initiation temperatures. A gaseous ignition mode is identified where solid fragments ejected from the battery coated with metallic lithium ignite pyrophorically, acting as an ignition kernel for the flammable gaseous effluent. Atomic emission of neutral lithium (Li I) at 611 nm and 671 nm is detected during ignition and flaming ignition and is hypothesised to form via lithium plating or thermal decomposition of LiC6 during thermal runaway. Atomic emission of sodium and potassium is also found, all of which is superimposed on the grey body distribution from luminous ejecta. In addition, the highspeed images are cross-correlated to provide time-resolved velocity fields and their statistical distributions of ejected particles during the entire thermal runaway event. Axial velocities possess a log-normal distribution, with peak velocities as large as 35 m s- 1. This work sets the platform for subsequent studies employing high-speed optical diagnostics to deliver a quantitative database to enable modelling of Li-ion battery thermal runaway and to understand flame-induced heating of adjacent cells in a battery module.

This paper is part of a broader program aimed at investigating the effects of co-firing clean fuels such as ammonia or hydrogen with hydrocarbons. The focus is on soot formation as well as flame stability in turbulent mixed-mode combustion, which is highly relevant in practical combustors. Ammonia substitution for nitrogen results in reduced flame stability, and this is correlated to differences in flame speed and extinction strain rate. While it is known that the addition of ammonia suppresses soot, visual inspection of compositionally inhomogeneous flames of ethylene-ammonia indicates a reduction in ammonia's ability to suppress soot formation. Measurements of soot volume fraction and laser-induced fluorescence in selected UV and visible bands are made along the centreline in selected flames to test this hypothesis. Experimental results are then compared to simulations in laminar diffusion flames, stratified counterflow flames, and partially premixed flames. All results confirm the soot-inhibiting ability of ammonia. Increasing inhomogeneity, leading to higher centreline mixture fractions, enhances soot formation, and the level of enhancement is greater for flames with ammonia than without. Moreover, it is found that partial premixing is ultimately responsible for determining the amount of soot formed as opposed to stratification of fuel mixtures near the pilot.

This paper employs a novel burner to study the effects of fuel-generated turbulence on the spatial and temporal structure of buoyant turbulent diffusion flames which are representative of large fires. Fuelturbulence levels are increased using a perforated plate that issues high-velocity jets, enabling shearing of the fuel stream. The perforated plate may be recessed to control the turbulence level at the jet exit plane. It is shown that the exit plane axial velocity fluctuations can be increased from 0.135 m/s to 1.813 m/s. Varying the levels of fuel-turbulence in the burner allows for the control of key processes defining buoyant fires such as the spatial and temporal flame structure and flame instability modes. These processes are characterised by high-speed simultaneous imaging of planar laser-induced fluorescence of the OH radical (OH-PLIF) and Mie scattering from soot particles. Increasing the fuel-turbulence level deforms the flame, which promotes non-radial lateral entrainment into the flame sheet. This results in a sharp increase in the tilting of the near-field flame sheet along the vertical flame axis. Strong angular entrainment forces are shown to overcome the diffusive and thermal expansive forces at the flame neck, which leads to a strained asymmetric sinuous flame pinch-off instability, followed by separation of the flame base. Sinuous pinch-off instabilities occur at a greater frequency than the symmetric varicose pinch-off instabilities observed for flames with low fuel-turbulence. The asymmetric stretching of the flame neck inhibits the formation of the classical puffing instability formed with an axisymmetric plume that defines classically buoyant flames. Probability density functions calculated for the flame front curvature and flame surface area are shown to monotonically broaden in the near-field region of the flame due to lateral entrainment effects. The transition to buoyancy-driven turbulence also shifts to an increasingly more upstream location. This burner, with its well-defined boundary conditions and novel data, forms a platform for advancing capabilities to model complex fire phenomena including turbulence-buoyancy interactions.& COPY; 2023 The Author(s). Published by Elsevier Inc. on behalf of The Combustion Institute. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

Simultaneous planar laser-induced fluorescence (PLIF) imaging of CH2O and OH was performed at a repetition rate of 10.kHz, jointly with chemiluminescence to explore autoigniting dimethyl ether (DME) flames in a hot vitiated coflow burner. The focus of the study is the imaging of the flame stabilization region and the temporal evolution of ignition kernels upstream of the flame base. Results detail the evolution of kernels throughout their formation, growth and final merging with the flame base. The ignition events were explored for a range of different fuel premixing and dilution ratios over two coflow temperatures which result in different lift-off heights. Images of CH2O and OH over the entire flame length show that not only is the lift-off height much higher at low coflow temperatures, but that the fluctuations are more intense and the region of kernel formation is larger both radially and axially. In these autoignition stabilized flames, increased premixing leads to the lift-off height and location of the maximum kernel formation rate being further downstream. Transient 1-D simulations of hot coflow products opposed against jet fuel mixtures identify that the overlap of CH2O and OH PLIF signals are a reliable marker of heat release in autoignition kernels. Measurements indicate that for the high coflow temperature cases, on average, the heat release of individual kernels is low, despite the high total kernel formation rate. This can be correlated to the slow growth rate and elongated aspect ratio of the kernels. For low coflow temperature cases, kernels are growing faster and have high heat release rates with near unity aspect ratios.

The telecommunications industry is undergoing a revolution-transformed by liberalisation, technological development, new customer demands and the emergence of new competitive models. The position of the incumbent public telecommunications operators (PTOs) is increasingly under threat. Their traditional domestic markets are being eroded through deregulation and competition, their bandwidth services are being commoditised, margins are falling, convergence and the advent of the Internet, mobility and Internet protocol (IP) are transforming their market space, and they are increasingly under threat from emerging new players. This article considers the new communications environment and its impact on incumbent PTOs, It discusses seven strategic issues which they will need to address in order to survive.