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Ethylene plays a crucial role as an intermediate component in the cracking and combustion processes of large molecular alkane and olefins. In this article, the laminar flame speed of ethylene–air mixtures was measured using the heat flux method. The mechanism of ethylene was simplified by utilizing the error propagation directed relationship graph (DRGEP) and sensitivity analysis (SA), and the Arrhenius pre‐exponential factors for 20 selected reactions in the skeletal mechanism were optimized using the particle swarm optimization (PSO) algorithm. Finally, an ethylene optimization mechanism including 39 species and 85 reactions was obtained. The prediction results for flame speed, ignition delay time, and species concentration were compared with experimental data and other mechanisms, covering a wide range of temperatures (298–1725 K), pressures (1–22.8 atm), and equivalence ratios (0.5–2.0). The findings demonstrate that the optimization mechanism not only improves the prediction results of laminar flame speed in the rich combustion zone and low oxygen environment but also enhances the prediction accuracy of the ignition delay time at high pressure and in the lean combustion zone, as well as the prediction accuracy of C2H4 and H2O radicals. In conclusion, the optimized mechanism exhibits higher accuracy and broader applicability. [ABSTRACT FROM AUTHOR]

Laminar flame speeds of methanol/air mixtures at 338–398 K are measured by the heat flux method, extending the range of equivalence ratio up to 2.1. And a new optimized methanol mechanism with 94 reactions is proposed by using the particle swarm algorithm, adjusting 20 Arrhenius pre‐exponential factors in their uncertainty domains. The optimized model is compared with eight methanol combustion mechanisms and experimental data published in recent years, covering a wide range of initial temperatures (298–1537 K), pressures (0.04–50 atm) and equivalence ratios (0.5–2.1). The results show that the optimized mechanism not only improves the accuracy of ignition delay time with rapid compression machine at low temperature but also moderately improve the description of laminar flame speed in lean and stoichiometric conditions. Meanwhile, the optimized model significantly enhances the prediction accuracy of CH3 and CH2O radical, and perfectly captures the evolution trend of HCO radical in laminar flat flame. Overall, the optimized mechanism provides the best overall description of the currently available measurements, leading to more accurate and comprehensive prediction of ignition delay time, laminar flame speed and species concentration. [ABSTRACT FROM AUTHOR]

Tunable diode laser absorption spectroscopy (TDLAS) technology, combined with chromatographic imaging algorithms, is commonly used for two-dimensional temperature and concentration measurements in combustion fields. However, obtaining critical temperature information from limited detection data is a challenging task in practical engineering applications due to the difficulty of deploying sufficient detection equipment and the lack of sufficient data to invert temperature and other distributions in the combustion field. Therefore, we propose a sparse projection multi-view synthesis model based on U-Net that incorporates the sequence learning properties of gated recurrent unit (GRU) and the generalization ability of residual networks, called GMResUNet. The datasets used for training all contain projection data with different degrees of sparsity. This study shows that the synthesized full projection data had an average relative error of 0.35%, a PSNR of 40.726, and a SSIM of 0.997 at a projection angle of 4. At projection angles of 2, 8, and 16, the average relative errors of the synthesized full projection data were 0.96%, 0.19%, and 0.18%, respectively. The temperature field reconstruction was performed separately for sparse and synthetic projections, showing that the application of the model can significantly improve the reconstruction accuracy of the temperature field of high-energy combustion. [ABSTRACT FROM AUTHOR]

Measurement of the combustion temperature field is an extremely important issue in industrial production. Temperature is one of the key parameters in combustion studies. With the temperature field distribution of the combustion field obtained, heat transfer, heat convection, and heat radiation can be calculated directly and efficiently. Traditional background oriented Schlieren (BOS) is an effective method for non-axisymmetric temperature field measurements, but it requires simultaneous Schlieren imaging at multiple angles for tomographic reconstruction, which will greatly limit its application. In this paper, the compressive sensing algorithm is introduced into the temperature field reconstruction, which establishes the system of equations between the deflection angle and the refractive index gradient. Then, the reconstruction of the non-axisymmetric temperature field is realized by solving the underdetermined system of equations by the method of solving the sparse solution through the compressive sensing. First, light offsets across the non-axisymmetric temperature field are measured by the under-angled BOS system and image processing method. Second, the spatial refractive index field is reconstructed by the compressive sensing BOS method proposed in this paper. Finally, the spatial temperature field is obtained. The experimental results show that by comparing the iRadon reconstruction algorithm and the compressive sensing reconstruction algorithm, the temperature field reconstructed by the compressive sensing under the condition of the under-angled sampling of projection data had a higher accuracy than that reconstructed by the tomographic reconstruction algorithm under the same condition. The average error of the temperature field was reduced from 34.6 to 29.7 K under the same measurement conditions; however, the accuracy is better maintained by using the compressive sensing algorithm under the condition of undersampling projection. [ABSTRACT FROM AUTHOR]

Accurately measuring the combustion and destruction removal efficiency of flaring is important when accounting for methane emissions from oil and gas production. Despite this, the amount of experimental data from full-size flares is limited, especially for flares built without air or steam assistance. The use of a single destruction value of 98% is commonly applied. In this paper, we present new empirical measurements of flare efficiency using three common flare designs employed in upstream applications. Combustion products were analyzed using an extractive sampling method. The results demonstrate that whilst destruction efficiencies in excess of 98% are achievable, if the gas composition falls below a critical heating value of ~300 BTU/scf, the efficiency deteriorates leading to elevated methane emissions. This is further complicated by accurately measuring the flow of combustible gas and the impact of crosswinds. In an operational setting, continuous tracking of flare conditions is therefore a key resource in reducing methane emissions but further work is required to standardize how continuous performance tracking is evaluated if such measurements are to attain full traceability. [ABSTRACT FROM AUTHOR]

An experimental stagnation pressure measurement technique is presented for a rotating detonation combustor (RDC). Schlieren imaging enables rotating detonation wave passage to be correlated with oscillations observed in the under-expanded exhaust plume. By measuring the spatiotemporal variation in exhaust plume divergence angle, stagnation pressure measurements of the RDC were acquired at a rate of 1 MHz. Combustor mass flux was varied between 202 and 783 kg/m2s, producing equivalent available pressures (EAPs) in the range of 3.42–13.5 bar. Time-averaged stagnation pressure measurements gathered using this technique were in agreement with the measured EAP within ±1.5%. Time-resolved stagnation pressure measurements allow for the pressure ratio produced across detonation wave cycles to be determined. For the conditions tested, detonation pressure ratios and wave speeds decreased while increasing the mean operating pressure of the combustor. Numerical modeling of the conditions tested indicates that the decrease in pressure ratio and wave speed is a result of elevated levels of combustion prior to the detonation wave arrival (i.e., "preburning"). Simultaneous OH* chemiluminescence measurements within the combustion chamber show an increase in preburned heat release relative to detonative heat release for increasing operating pressures of the RDC, in agreement with the results of the numerical model. Modeled chemical kinetic timescales decrease by approximately the same magnitude by which the preburning mass fraction increased in the range of operating pressures tested, suggesting that the faster reaction rates associated with higher pressure combustion may be the reason for increased preburning within the combustor. [ABSTRACT FROM AUTHOR]

The effects of the burnt-to-unburnt temperature ratio (T b / T u) (reciprocal density ratio) on thermoacoustic combustion instability were investigated in a hydrogen-rich ram combustor by controlling the inlet air temperature under cruising conditions. Steady and unsteady combustion dynamics were investigated with the simultaneous measurement of combustion pressure and near-infrared (NIR) emissions. Time-resolved NIR images were analyzed using dynamic mode decomposition (DMD) to extract modes of the combustion instability, which show two oscillation modes: longitudinal (500 Hz) and flame-vortex interaction modes (2000 Hz) with a Strouhal number of approximately 0.5. The thermoacoustic combustion instability was not excited at T b / T u = 3.3, but was excited at T b / T u = 2.6 and 2.9. The DMD modes show that the structure of the vortex mode is similar to that of the fourth longitudinal mode at T b / T u = 2.6 and 2.9, indicating that the coupling of the vortex and the fourth longitudinal modes excited the thermoacoustic combustion instability. • The burnt-to-unburnt temperature ratio T b / T u influenced thermoacoustic instability (TI) in a hydrogen-rich combustor. • Dynamic mode decomposition analysis extracted a longitudinal mode (500 Hz) and a vortex mode (2000 Hz). • At low T b / T u , TI was excited owing to the similar structures of the vortex and fourth longitudinal modes. • Vortex mode was changed by the enhanced vortex formation near the injectors at high T b / T u. • At high T b / T u , TI was not excited owing to the low correlation between the vortex and fourth longitudinal modes. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) is emerging as a potential favoured fuel for longer range decarbonised heavy transport, particularly in the marine sector, predominantly due to highly favourable characteristics as an effective hydrogen carrier. This is despite generally unfavourable combustion and toxicity attributes, restricting end use to applications where robust health and safety protocols can always be upheld. In the currently reported work, a spark ignited thermodynamic single cylinder research engine equipped with gasoline direct injection was upgraded to include gaseous ammonia port injection fuelling, with the aim of understanding maximum viable ammonia substitution ratios across the speed-load operating map. The work was conducted at varied effective compression ratios under overall stoichiometric conditions, with the spark timing re-optimised for maximum brake torque at all stable logged sites. The experiments included industry standard measurements of combustion, performance, and engine-out emissions (including NH3 "slip"). With a geometric compression ratio of 11.2:1, it was found possible to run the engine on pure ammonia at low engine speeds (1000-1800 rpm) and loads of 12 bar net IMEP. When progressively dropping down below this load limit an increasing amount of gasoline co-firing was required to avoid engine misfire. When operating at 1800 rpm and 12 bar net IMEP, all emissions of carbon (CO2, CO, unburned hydrocarbons) and NOx decreased considerably when switching to higher NH3 substitution ratios, with NOx reduced by ~ 45% at 1800 rpm/12 bar when switching from pure gasoline to pure NH3 (associated with longer and cooler combustion). By further increasing the geometric compression ratio to 12.4 and reducing the intake camshaft duration for maximum effective compression ratio, it was possible to operate the engine on pure ammonia at much lower loads in a fully warmed up state (e.g., linear low load limit line from 1000 rpm/6 bar net IMEP to 1800 rpm/9 bar net IMEP). Under all conditions, the indicated thermal efficiency of the engine was either equivalent to or slightly higher than that obtained using gasoline-only due to the favourable anti-knock rating of NH3. Ongoing work is concerned with detailed breakdown of individual NOx species together with measuring the impact of hydrogen enrichment across the operating map. [ABSTRACT FROM AUTHOR]

Since hydrogen does not emit carbon dioxide when it is burned, burning hydrogen directly is one option. However, as the hydrogen ratio in the total fuel increases, the visible flame emission becomes weaker. Therefore, when using fuels with hydrogen mixed with city gas, it is necessary to have a system that monitors incomplete combustion to ensure safe use of combustion equipment. In this study, we measured the C2 and CH chemiluminescence intensities of a laminar premixed flame of hydrogen and methane. These chemiluminescence intensities were evaluated using the ICCD camera, compared with flame images taken by the commercially available digital camera. Especially, we proposed a method to determine the C2 and CH chemiluminescence intensities simultaneously in terms of the signals composed of three primary colors of red (R), green (G), and blue (B) obtained by the digital camera images. The G signal of the flame obtained by the digital camera is almost proportional to the C2 chemiluminescence intensity. The B signal also shows a good linear relationship when data are divided into two groups according to the presence or the absence of the outer flame. We concluded that if the C2 and CH chemiluminescence intensities are predicted from the G signal and the B signal.

Sensitive and fast mid‐infrared (MIR) spectroscopy is highly attractive in a variety of applications including astronomical observation, pharmaceutical synthesis, and environmental monitoring. However, the performance of conventional MIR spectrometers has long been hindered by the limited sensitivity of narrow‐bandgap detectors and/or the deficient brightness of broadband light sources. Here, an ultra‐sensitive and broadband MIR upconversion spectrometer, which integrates a supercontinuum source covering 1.5–4.2 μ$\umu$m based on a silicon nitride nanophotonic waveguide, is devised and integrated. High‐efficiency and low‐noise nonlinear frequency upconversion is realized based on coincidence pulsed pumping with spectro‐temporal optimization, which enables leverage of silicon detectors for facilitating MIR single‐photon spectroscopy at 0.2 photons/nm/pulse. Furthermore, the upconversion‐based array spectrometer is manifested with high‐speed spectral acquisition rates beyond 200 kHz, which is about tenfold faster than the state‐of‐the‐art scan rates for FTIR‐based spectrometers at a comparable spectral resolution. The achieved features of broadband spectral coverage, single‐photon sensitivity, and sub‐MHz refreshing rate might open up new possibilities for infrared transient spectral measurements in combustion analysis, high‐throughput sorting, and reaction tracking, among others. [ABSTRACT FROM AUTHOR]

α‐Si3N4 powder was prepared by combustion synthesis method. The propagation characteristics of combustion wave were investigated by thermocouple temperature measurement and "resistance—combustion wave displacement response device." The results show that the combustion reaction takes place in a narrow area, and there is a maximum temperature gradient of 180°C/mm in the combustion front. The "resistance—combustion wave displacement response device" was innovatively used to realize the in situ measurement of combustion wave propagation process. The test results showed the pulse combustion mode in which the combustion front took 10 s as a cycle, and the quantitative data of Si–N2 discrete combustion characteristics were obtained for the first time. [ABSTRACT FROM AUTHOR]

Bio-based polymers can reduce dependence on nonrenewable petrochemical resources and will be beneficial for future sustainable developments due to their low carbon footprint. In this work, the feasibility of bio-based polyamide 56 (PA56) substituting petroleum-based PA66 is systematically investigated. The crystallization, melting, and decomposition temperature of PA56 were all lower than that of PA66. PA56 formed a γ crystal type with larger grain size and took a longer amount of time to complete the crystallization process since its crystallization rate was lower than that of PA66. Compared with PA66, PA56 exhibited a higher tensile strength of 71.3 ± 1.9 MPa and specific strength of 64.8 ± 2.0 MPa but lower notched impact strength. More importantly, the limited oxygen index and vertical combustion measurement results indicated that the flame retardancy of PA56 was better than PA66, and the LOI values and the UL94 result of PA56 were 27.6% ± 0.9% and V-2. It is worth noting that the PA56 fiber had superior biodegradability compared to the PA66 fiber. PA56 showed significant biodegradation from the eighth week, whereas PA66 remained clean until the sixteenth week (without obvious biodegradation taking place). Eventually, PA56 did not show significant differences compared to PA66 in terms of thermal and mechanical properties. However, PA56 had great advantages in flame retardancy and biodegradability, indicating that the bio-based PA56 could potentially replace petroleum-based PA66 in many fields. [ABSTRACT FROM AUTHOR]

As a high energy density hydrogen-rich carrier, ammonia (NH3) is a highly promising carbon-free fuel. The large-scale industrial application of NH3 is limited by its low reactivity and high NOx emission. In this work, the flame and emission characteristics of ammonia/methane (NH3/CH4) non-premixed combustion were investigated under ultrasonic excitation. An experimental system was designed and built, including non-premixed combustion system, loading ultrasonic system, deflectionmography temperature measurement system and flue gas measurement system. Combustion and measurement experiments at different ultrasonic frequencies and NH3/CH4 blending ratios were carried out. Flame images and flue gas species concentrations under ultrasonic excitation were acquired. The 3-D temperature field was reconstructed. The influence of ultrasonic excitation at different frequencies on flame characteristics, flame temperature field and emission characteristics of the combustion process was analysed. The mechanism of NH3/CH4 combustion enhancement and emission reduction was revealed when the flame was ex-cited by ultrasonic waves. Results showed that part of the hydrocarbon fuels was replaced by NH3 to reduce CO2 emission. The height and color of the NH3/CH4 flame were changed and the high temperature area of the flame gradually expanded as ultrasonic acted on the flame. As ultrasonic frequency increased, the emission concentrations of unburned CH4, unburned NH3, and NO decreased significantly. The flame was ex-cited by ultrasonic waves, which reduced its local equivalent ratio, improved combustion efficiency and suppressed NOx generation. [ABSTRACT FROM AUTHOR]

Aluminum is characterised by its high calorific value, stable performance, and abundant reserves. It is a commonly used additive in solid propellants that are widely used in aerospace and underwater propulsion applications. As aluminum is a key component of these solid propellants, combustion temperature measurement of aluminum particles is crucial in investigating their combustion characteristics. This paper presents a method to determine the combustion temperature of aluminum particles in solid propellants. A combination of radiation imaging and Monte Carlo probability simulation is applied in the proposed method. Further, a numerical model is established to determine the surface temperature of aluminum particles. The method is validated through numerical simulation considering a target with a pre-set temperature distribution, as well as a practical implementation in solid-propellant combustion experiments. Results of the experimental analysis establish the reliability of the proposed method and also demonstrate the method's ease of operation, good practicability, and potential for future application. • A method to determine the combustion temperature of aluminum particles is proposed. • The proposed method is based on Planck's radiation law and Monte Carlo simulation. • The method validated through numerical simulation with pre-set temperature and experiments. [ABSTRACT FROM AUTHOR]

In this study a fast-response Atomic Layer Thermopile (ALTP) based heat flux measurement system is used for wall heat-flux determination in the combustion chamber of a commercially available SI-gasoline combustion engine. The ALTP system provides further process variables that supplement conventional cylinder pressure data with data that are highly resolved in time and location. The newly developed sensor modules were precisely calibrated and compared with other measurement techniques with radiation- and convection-based procedures. Quantitative highly time-resolved measurements with frequency resolutions up to 1 MHz are performed in the engine from low to full load and up to full speeds. Single-cycle and cycle-to-cycle measurements display the quality and high temporal resolution of the measurement system. The comparison of pressure and the heat-flux measurements shows the benefits of ALTPs for detection of engine, combustion and flow characteristics. The time progression of the heat flux curves and their autocorrelated signals show only minor noise interference. The measured results display significantly higher local peak heat flux densities with values up to 1250 Wcm−2 for certain measurement points and engine conditions than reported previously in literature for SI engines. A regression analysis suggests that the high peak heat flux densities obtained are caused by the significant higher engine power-levels per cylinder. The measured data compare well with regressions extrapolated from reported literature data. A provided uncertainty analysis revealed significant influencing parameters. The variation of thermal wall parameters with 20%–30% uncertainty are playing an essential role in particular. [ABSTRACT FROM AUTHOR]

The combustion effect of biomass fuel made by mixing straw and coal, the heat of combustion measurement device was used to determine the heat of combustion of mixed fuels at different blending ratios, and the synergistic effect of the combustion of the two mixed fuels and the combustion at different amounts of oxygen were investigated by changing the type of straw and the origin of coal.The result showed that the blended fuels produced favorable combustion aid under both oxygen-rich and oxygen-poor conditions with specific blending ratios. Infrared spectroscopic analysis of the changes in functional groups of the experimental raw materials further revealed that blending straw with coal could increase the content of hydroxyl and oxygen-containing functional groups and thus promote combustion and heat release.The differential thermal and thermogravimetric analysis found that straw has a dual effect on the combustion of coal, and the peak area of the thermal effect of its DTA curve is positively correlated with the heat of combustion of coal and straw at each blending ratio. [ABSTRACT FROM AUTHOR]

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Accurate and high-speed transient surface-temperature measurements of combustion devices including internal combustion (IC) engines, gas turbines, etc., provide validation targets and boundary conditions for computational fluid dynamics models, and are broadly relevant to technology advancements such as performance improvement and emissions reduction. Development and demonstration of a multi-infrared-channel pyrometry-based optical instrument for high-speed surface-temperature measurement is described. The measurement principle is based on multi-spectral radiation thermometry (MRT) and uses surface thermal radiation at four discrete spectral regions and a corresponding emissivity model to obtain surface temperature via non-linear least squares (NLLS) optimization. Rules of thumb for specifying the spectral regions and considerations to avoid interference with common combustion products are developed; the impact of these along with linear and non-linear MRT analysis are assessed as a function of temperature and signal-to-noise ratio. A multi-start method to determine the MRT-solution global optimum is described and demonstrated. The resulting multi-channel transient pyrometry instrument is described along with practical considerations including optical-alignment drift, matching intra-channel transient response, and solution-confidence indicators. The instrument demonstrated excellent >97% accuracy and >99% 2-sigma precision over the 400–800 °C range, with ~20 µs (50 kHz, equivalent to 0.2 cad at 2000 RPM IC-engine operation) transient response in the bench validation. [ABSTRACT FROM AUTHOR]

This article discusses current testing methods for motor vehicle engines. Traction engines have so far been tested, for example, according to WLTP (Worldwide Harmonized Light Vehicle Test Procedure) driving tests, but due to the "VW—gate" incident, these are now to be supplemented by RDE (Real Driving Emissions) tests, conducted under real road conditions. The analyses of the state of knowledge and the directions of research to date unequivocally indicate the need for the construction of a stand that allows: testing of a complete vehicle admitted to traffic; testing of a motor vehicle with the possibility of simulating real operating conditions; load setting with the possibility of its regulation; feeding the engine with various fuels; modification of the software of controllers having a direct impact on the control strategies of the engine; transmission and traction control system; reading, recording and analysis of the parameters of the operation of control systems in real time; detailed recording and analysis of the combustion process occurring directly in the combustion chamber; and the measurement of emitted toxic substances. On a bench with the above features, tests were carried out on a diesel motor vehicle, which were based on recording changes in the parameters of the combustion and injection process. The tests were conducted under static and dynamic conditions. Tests under static conditions were conducted on a chassis dynamometer. They consisted of indicating the engine for different fuel dose control maps. The vehicle equipped with the test engine was driven at a constant speed on the chassis dynamometer and loaded with a drag force of 130 Nm. Tests under dynamic conditions were conducted under real traffic conditions. They were limited to the presentation of results under static conditions. The main results of the tests are given in the conclusion and include a general summary. In particular, the presented results of the diesel tests demonstrate an attempt to adapt the engine to co-power with hydrogen. [ABSTRACT FROM AUTHOR]

Sustainable aviation fuels (SAFs) have different compositions compared to conventional petroleum jet fuels, particularly in terms of fuel sulfur and hydrocarbon content. These differences may change the amount and physicochemical properties of volatile and non-volatile particulate matter (nvPM) emitted by aircraft engines. In this study, we evaluate whether comparable nvPM measurement techniques respond similarly to nvPM produced by three blends of SAFs compared to three conventional fuels. Multiple SAF blends and conventional (Jet A-1) jet fuels were combusted in a V2527-A5 engine, while an additional conventional fuel (JP-8) was combusted in a CFM56-2C1 engine. We evaluated nvPM mass concentration measured by three real-time measurement techniques: photoacoustic spectroscopy, laser-induced incandescence, and the extinction-minus-scattering technique. Various commercial instruments were tested, including three laser-induced incandescence (LII) 300s, one photoacoustic extinctiometer (PAX), one micro soot sensor (MSS+), and two cavity-attenuated phase shift PM SSA (CAPS PM SSA) instruments. Mass-based emission indices (EI m) reported by these techniques were similar, falling within 30 % of their geometric mean for EI m above 100 mg per kg fuel (approximately 10 µ g PM m -3 at the instrument); this geometric mean was therefore used as a reference value. Additionally, two integrative measurement techniques were evaluated: filter photometry and particle size distribution (PSD) integration. The commercial instruments used were one tricolor absorption photometer (TAP), one particle soot absorption photometer (PSAP), and two scanning mobility particle sizers (SMPSs). The TAP and PSAP were operated at 5 % and 10 % of their nominal flow rates, respectively, to extend the life of their filters. These techniques are used in specific applications, such as on board research aircraft to determine particulate matter (PM) emissions at cruise. EI m reported by the alternative techniques fell within approximately 50 % of the mean aerosol-phase EI m. In addition, we measured PM-number-based emission indices using PSDs and condensation particle counters (CPCs). The commercial instruments used included TSI SMPSs, a Cambustion differential mobility spectrometer (DMS500), and an AVL particle counter (APC), and the data also fell within approximately 50 % of their geometric mean. The number-based emission indices were highly sensitive to the accuracy of the sampling-line penetration functions applied as corrections. In contrast, the EI m data were less sensitive to those corrections since a smaller volume fraction fell within the size range where corrections were substantial. A separate, dedicated experiment also showed that the operating laser fluence used in the LII 300 laser-induced incandescence instrument for aircraft-engine nvPM measurement is adequate for a range of SAF blends investigated in this study. Overall, we conclude that all tested instruments are suitable for the measurement of nvPM emissions from the combustion of SAF blends in aircraft engines. [ABSTRACT FROM AUTHOR]

• A current literature overview on biomass oxy-combustion identifies research gaps. • Pulverized walnut shell combustion investigated by optical and sampling methods. • Optical measurements provide the size statistics for the whole particle ensemble. • Burnout was analyzed using a solid sample probe for chemistry and porosity. • Temperature, size and sampling data combined in one comprehensive data set. Despite the extensive literature on single-particle biomass combustion measurement, there is a significant gap between the abundance of conducted experimental investigations and the inadequacy of the resulting database for calibrating predictive burnout models. This research aims to address this gap by providing an experimental database for single-particle combustion of walnut shells, chosen as a representative lignocellulosic biomass, in a laminar flow reactor for oxy-fuel combustion. Eight different oxy-fuel atmospheres were examined. A stereoscopic imaging system, utilizing four intensified CCD cameras, enables in-situ measurements of temperature, size, shape, velocity and residence time of solid fuel particles. The system's optical resolution is approximately 10 µm and its temporal resolution is 1 μs. In addition to the optical measurements, partially converted solid samples were extracted from the reactor with a sampling probe. The elemental composition, the proximate analysis, pore evolution during the burnout and the morphology of particles were analyzed using samples collected at different residence times. Notably, walnut shells always ignite heterogeneously in oxy-fuel atmospheres and the volatile flame is of low luminosity. With increasing burnout, spheroidization of particles occurs. The novel dataset is presented, compared, and discussed alongside results from current literature. [ABSTRACT FROM AUTHOR]

We report micrometric imaging measurements of the ignition of micron-sized aluminum (Al) wires and the consequent combustion processes of single micron-sized Al droplets in hot steam and steam with oxygen. The specially designed flames were anchored on a modified burner where a small central H 2 /O 2 diffusion flame in the center jet provided a hot flow (>2330 K) for Al ignition, and the diffusion flame together with a laminar co-flow of premixed H 2 /N 2 /O 2 flame provided the vitiated flow of desired combustion environment. As soon as the horizontally arranged Al wire was moved to the center hot jet, a high-speed color camera was triggered to record the transient event of the ignition and combustion process. The high imaging quality and spatial resolution allow direct observation of the structure of the burning particles, i.e., the liquid core, the bright flame front encapsulating the center droplet, and the coalescent alumina agglomerates downstream above the burning Al droplets. A distinct thin condense sheet was observed defining the flame front in all symmetric and asymmetric combustion modes, indicating that homogeneous oxidation dominates the heat-release reactions as a diffusion flame. A color ratio RGB pyrometry was calibrated to provide temperature distribution over the burning particles. In the steam condition, the center droplet temperature in the symmetric phase was analyzed to be ∼2650 K and the temperature of the flame front ∼3400 K, while in the oxygenated environments, the droplet temperature was evaluated to be ∼2790 K, and the temperature of the flame front ∼4150 K. The transient temperature evolution of different parts of the burning elements was recorded and analyzed. To the authors' awareness, the current study represents the first structure-resolved temperature measurement of the combustion of single aluminum particles in high-temperature steam. These measurements can provide unprecedented spatiotemporally resolved information on Al combustion for improved insight into the governing mechanism. [ABSTRACT FROM AUTHOR]

In the present work, an optical sensor was developed and calibrated for the purpose of non-intrusive equivalence ratio measurements in combustion systems. The sensor incorporates a unique four-line, single-sensor chemiluminescence imaging-based approach, which relies on the ratio of C2* and CH* radical-species intensities to obtain measurements of equivalence ratios. The advantage of the four-line sensor is the use of additional filtering to mitigate broadband luminescence signals, and its improvements over conventional two-line chemiluminescence diagnostics are discussed. The sensor was calibrated using a premixed bluff-body jet burner with a propane–air flame operating over a wide range of equivalence ratios. The results showed that the four-line processing technique improved the signal-to-noise ratio of the chemiluminescence images for all test cases. Calibrations of C2*/CH* intensity ratio to equivalence ratio were developed for both the four-line and two-line techniques. The calibrations were then used to create maps of local equivalence ratios in the flame-holding region. The maps revealed a non-uniform field of equivalence ratios due to the nature of the radical-species intensity profiles within the flame. Therefore, special consideration is required for calibration in order to accurately quantify equivalence ratios and apply these to diffusion flames. [ABSTRACT FROM AUTHOR]

The U.S. Environmental Protection Agency (US EPA) requires residential wood heaters (RWHs) to meet particulate matter (PM) emission limits in order to lower ambient concentrations and reduce public exposure. The current US EPA dilution tunnel PM measurement methods for RWHs were developed several decades ago and use manual filter samples to generate a single PM value for tests that can last more than 12 hours for stoves and 30 hours for central heating appliances. This approach results in averaging periods of high and low emissions together and provides limited data on emissions over the entire burn profile. Over the last decade, the U.S. ambient fine particulate monitoring network has transitioned to the routine use of online automated methods. However, stationary source measurement methods have not made this transition. There are no substantial technical issues in implementing real-time automated methods to measure PM for RWH emission certification purposes. The Thermo Scientific Tapered Element Oscillating Microbalance (TEOM™) has been widely used for ambient PM measurements. It is a true inertial mass measurement with high time resolution and sensitivity. This work compares measurements obtained using a Thermo 1400 or 1405 TEOM with ASTM E2515 manual filter samples, the current US EPA Federal Reference Method, for 172 test runs across a wide range of stoves and PM loading conditions. The TEOM measurements used the same filter media, similar filter face velocities, and filter temperatures as manual methods. PM measurements were well correlated (R2 > 0.9), with TEOM values typically lower by 5% to 10%. TEOM data capture was high, with filter changes resulting in ~5 minutes of lost data, usually once or twice during a multi-hour test. We discuss differences between the two methods, such as post-sampling equilibration and measurement of PM on sample train surfaces (probe "catch"). We also provide examples of substantial non-water semi-volatile mass loss during sampling. Implications: Measurement methods for continuous PM and our understanding of their performance has dramatically improved over the last thirty years. Highly time-resolved measurements of PM from residential wood heating appliances in an appliance certification testing context provide additional insight into both appliance performance and the suitability of the test method to assess that performance. This continuous measurement approach offers new opportunities to replace traditional US regulatory PM sampling integrated manual source methods like ASTM E2515 or EPA Method 5G testing. For measurement of combustion products that can have a wide range of physical and chemical characteristics, the TEOM's actual mass measurement principle has advantages over the sensitivity of surrogate methods to different aerosols for use in a regulatory program. Although the TEOM is commonly used to measure ambient PM, it can readily be configured to meet the needs of continuous emission testing. [ABSTRACT FROM AUTHOR]

This paper assesses the effect of the Miller cycle upon the internal aerodynamics of a motored transparent spark ignition engine via CFD simulation and particle image velocimetry. Since the transparent Miller engine does not allow for measurements in the roof of the combustion chamber, the extraction of information regarding the aerodynamic phenomena occurring here is based on CFD simulation, i.e., the results of the CFD simulation are used to allow for the extrapolation of the experimental data; thus, they are used to complete the picture regarding the aerodynamic phenomena occurring inside the whole cylinder. The results indicate that implementing the early intake valve closing strategy to obtain the Miller cycle has a negative impact on the mean kinetic energy, turbulent kinetic energy, and fluctuating velocity toward the end of the compression stroke, thus affecting, the combustion process. This supports the need to intensify the internal aerodynamics when applying the Miller cycle such that the turbulence degradation is not too big and, consequently, to still gain efficiency in the Miller cycle. [ABSTRACT FROM AUTHOR]

This publication presents changes in sawdust of selected deciduous trees as a consequence of impulse electric field (PEF) stimulation. The analyzed changes concerned the time–temperature characteristics created during the measurement of the heat of combustion of the audited material. Based on experience from previous studies, two alternatives of electric field strength and one variant of capacitor discharges (pulses) were adopted. The results were compared with the sample not treated with PEF. The selected parameters were the result of previous studies, in which the applied variants seemed to be the most promising, i.e., they gave the most diverse results. The research presented in this work has shown that the pulsed electric field affects the time and temperature characteristics of biological material. The changes are most pronounced for the last period of the combustion process, from the moment the maximum temperature was reached to the end of the process. The obtained results indicate that birch and ash react to PEF conditioning in a similar manner. The second group, due to the similarity of the obtained results, is oak and linden. It seems that, apart from the electric field strength, the obtained results are also influenced by the cellulose content in the tested wood. The described process has a very low energy-efficiency, but the reduction of the energy needed to generate the impulse could lead to the possibility of applying the obtained results in industry. [ABSTRACT FROM AUTHOR]

In the work, the combustion regimes of iron particles (d10 = 4.7 µm) in a laminar pre-mixed flame (LPF) and in an axisymmetric laminar diffusion flame (LDF) are studied. For (LPF), we studied the effect of variations in gas suspension of the concentrations of fuel Cf = 0.4 ÷ 0.6 kg/m3 and oxygen CO2 = 21 ÷ 40%, and for (LDF), pure oxygen blowing and variation in the iron concentration Cf = 0.4 ÷ 1.5 kg/m3. The results of particle temperature measurements in the combustion zone of LPF and LDF, the dispersed and phase composition of the combustion products (depending on the concentration of fuel and oxidizer) are presented. It is shown that, under certain conditions, iron particles in LPF switch to a "high-temperature" diffusion mode of combustion. This mode is accompanied by intensification of gas-phase reactions and leads to a two-mode particle size distribution of combustion products. In this mode of combustion of a gas suspension (at temperatures much lower than the boiling point of iron), the mass yield of a nanoscale fraction of combustion products reaches tens of percent and increases with increasing oxygen concentration in LPF. This mode of iron particles combustion was not observed in LDF. The features of the thermal structure of the diffusion dust flame are analyzed. It is shown that in LDF the burning time of metal particles in the diffusion mode is proportional to the particle radius r p ( \~ r p in the kinetic mode), and should depend on the concentration of fuel and the size of the burner. [ABSTRACT FROM AUTHOR]

Combustion diagnostics play an essential role in energy engineering, transportation, and aerospace industries, which has great potential in combustion efficiency improvement and polluting emission control. The three-dimensional (3D) visualization of the combustion field and the measurement of key physical parameters such as temperature, species concentration, and velocity during the combustion process are important topics in the field of combustion diagnostics. Benefiting from the non-contact and non-intrusive advantages of the optical detection method as well as the advantages of the 3D fullfield measurement of the measured field by computational tomography, flame chemiluminescence tomography (FCT) has the ability to realize non-intrusive and instantaneous 3D quantitative measurement and 3D full-field visualization of key physical parameters in the combustion process, which has crucial research significance in combustion diagnostics. In this study, we review the progress of FCT technique. First, we provide an extensive review of practical applications of FCT in state-of-the-art combustion diagnostics and research. Then, the basic concepts and mathematical theory of FCT are elaborated. Finally, we introduce the conventional reconstruction algorithm and proceed to more popular artificial intelligence-based algorithms. [ABSTRACT FROM AUTHOR]

Measurements of multi-scalar field within a combustor are of particular interest for engine performance promotion and failure diagnosis. Due to the harsh operating conditions and extremely limited space, direct measurements of combustion state in a near-real conditioned engine combustor were rarely reported. Therefore, this paper reports spontaneous Raman scattering (SRS) measurements of temperature and major species, such as N2, H2O, O2, and CO2 within a single sector reverse-flow model combustor fuelled with kerosene under elevated incoming pressure and temperature. Geometry of the model combustor was designed to simulate a real engine combustor as much as possible and the point SRS measurement was conducted at 10 characteristic locations of the main combustion region. The measured temperature and major species concentration exhibited a non-uniform distribution in space and highly dynamic variation in time. Strong turbulence-chemistry interaction and deviation from chemical equilibrium were observed according to the measurement. This research demonstrates the feasibility of conducting detailed thermochemistry measurements in a combustor with complicated geometry. [ABSTRACT FROM AUTHOR]

• Beam-steering-effect immune DAS method is proposed. • A cost-effective and compact distortion detection scheme is introduced. • The SNR of the raw transmitted laser signal increases by 35 dB. • 4、Temperature successful fitting rate up to 100 % from 93.7 % over the 1000 repetitions. • 5、Temperature standard deviations have decreased from 296.6 K to 61.8 K. Tunable diode laser absorption spectroscopy is widely used for temperature measurement in combustion monitoring due to its merits of rapidity, non-contact capability, and high precision. In actual applications, the beam-steering effect will cause time-varying distortion in the laser intensity signal, resulting in a low signal-to-noise ratio and inaccurate extraction of the absorption spectrum. This work proposes a cost-effective distortion detection scheme and adaptive distortion filter and compensation algorithm for the extraction of the beam-steering effect immune laser absorption spectrum. Turbulent flame monitoring experiment results prove the proposed method can improve the signal-to-noise ratio of the raw transmitted absorptive laser signal by 35 dB after the beam-steering distortion has been compensated. When compared with the temperature results calculated from the distorted absorptive laser signal, the results from the distortion-compensated absorptive laser signal show a significant improvement in both robustness and precision. The experimental results demonstrate that the successful temperature fitting rate has increased from 93.7 % to 100 % (over 1000 repetitions), and the average standard deviations of temperature have decreased from 296.6 K to 61.8 K. The proposed method is cost-effective and compact, which will potentially play an important role in dynamic combustion monitoring and diagnosis. [ABSTRACT FROM AUTHOR]

Tomographic absorption spectroscopy (TAS) is a promising temperature and concentration monitoring technology because it has fewer optical access requirements and species selectivity. However, the inhomogeneous distribution of temperature and species concentration in a practical reaction flow can cause laser deflection, which may affect the imaging quality. Thus, this study aimed to develop a novel tomographic absorption deflection spectroscopy (TADS) technology for in-situ, quantitative, and simultaneous measurements of temperature and H 2 O concentration. The proposed system is based on the gas mixing equation and ray tracing, considering the inhomogeneous gradient refractive index and laser bending. Moreover, multi-prior information, including smooth regularization, non-negative constraints, and topological shape constraints, is coupled to mitigate the ill-posedness of inverse problems, thereby improving the accuracy and robustness of multiparameter tomography. Numerical verification and a comparison of algorithms for multimodal flames indicate that the proposed TADS technology exhibits excellent anti-noise performance and can significantly improve reconstruction quality. Additionally, a proof-of-concept based on experimental data of a steady methane diffusion flame is performed to demonstrate the feasibility of TADS as a practical combustion diagnostic. The reconstruction results of instantaneous temperature and H 2 O concentration on six different cross-sections show that the topological structure, dynamics, and parameter distribution can be quantitatively demonstrated. This technology is expected to enhance the practicability of laser absorption spectroscopy in the in-situ measurement of complex combustion reaction flows with high temperature, high pressure, and strong distortion. [ABSTRACT FROM AUTHOR]

Cigarette smoke is a dynamically changing aerosol system and the operando measurement of its complex chemical compositions is challenging. In this work, the gas- and particle-phase components of combustion cigarette smoke aerosols, which usually have different adverse influences on environment and human health, have been separated and their individual compositions are measured online by using a novel vacuum ultraviolet (VUV) photoionization time-of-flight mass spectrometer. The gas-phase compositions are clearly identified and ascribed to low-mass volatile organic compounds (VOCs), while the particle-phase are more complicated and dominated with abundant semi- or non-volatile organics. The present results demonstrate that some compositions only present in gas- or particle-phase, but some can exist in both phases. In addition, the signals of the gas- and particle-phases increase with the puff number of smoking and their dynamical processes are discussed. The puff-by-puff increase of the gas-phase components is more obvious than that of the particle-phase, implying their different mechanisms involved in the smoking. • Operando measurements of gas/particle phases of combustion cigarette smoke aerosol. • Gas-phase dominates with VOCs, while particle-phase to semi-/non-volatile organics. • Some species only present in gas or particle phase, while some exist in both phases. • Gas and particle phase releases increased with puff number, but at different rates. [ABSTRACT FROM AUTHOR]

This study investigated the behavior and temperature of condensed combustion products (CCPs) in a magnesium–water vapor flame. The experiments were conducted using magnesium plates with a surface area of 5 × 5 mm 2 and an oxidizer pressure in the range of 10–100 kPa, in consideration of potential applications in microspacecraft. Compared with the air and oxygen cases, a substantial quantity of white residue remained around the fuel when the oxidizer was water vapor. Scanning electron microscopy revealed that this was deposited by submicron CCPs formed in the flame. Additionally, the laser light extinction method revealed the spatial distribution of the CCP. In the case of water vapor, the point of maximum CCP density was closer to the fuel than to the oxygen, which caused a difference in residue formation. Next, the temperature of the CCP in the combustion flame was calculated using Planck's law with a spectrometer. This study utilized six types of emissivity indices, ranging from 0 to -4, for power fitting. A more plausible temperature range was determined using the coefficient of determination, leading to an uncertainty of 20% in the temperature calculation using Planck's law. The observed temperature was approximately 600 K lower for water vapor than for oxygen, a discrepancy exceeding the difference predicted by the adiabatic flame temperatures. The two-dimensional temperature distribution was measured with CCD cameras using the two-color pyrometer method, and the distance to the point of maximum reaction temperature was shorter for water vapor than for oxygen. This study concluded that the decrease in the reaction distance in the water vapor case owing to the lower temperature significantly influenced the spatial distribution of CCPs within the flame. Novelty and significance statement : The present study is novel in that the condensed combustion products in a magnesium flame were identified, and their temperature was measured distinctly from the fuel. These observations explain why the oxide residue accumulated only in water vapor cases. Our research stands out, recognizing the limited experimental forays into magnesium combustion with pure water vapor. The combustion research on these materials, which are safe and obtainable from space bodies, has profound implications for advancing space propulsion and energy. [ABSTRACT FROM AUTHOR]

High quality of three-dimensional particle swarm images is always highly desired in some important areas like experimental fluid mechanics and combustion field measurement, etc. as particle distributions in these fields can characterize the field properties well. Recently, deep learning techniques have been applied for the computed tomography to improve three-dimensional image reconstruction quality of an object. However, how to promote the network processing efficiency and quality to reduce artifact noise, missing-particles and ghost-particles in the reconstruction image is still a challenge at present. For this purpose, we propose a lightweight dual-residual deep learning approach for improvement of tomographic image reconstruction of particle swarms in this paper. It includes the innovative designs in lightweight dual-residual down-sampling, fast feature convergence module and high-SNR network input datasets to acquire image features more effectively. Numerical analysis and experimental test have demonstrated that the proposed method can effectively reduce not only the missing particles and ghost-particles in the reconstructed images under sparse-sampling, but also the network training time, in contrast to the performances of some typical deep learning networks under the same conditions. • A lightweight dual-residual neural network to achieve high-quality particle image reconstruction in computed tomography. • The new network involves lightweight dual-residual down-sampling, fast feature convergence and high-SNR input dataset. • The artifact noise and particle image errors are effectively reduced, and the network training efficiency is promoted. [ABSTRACT FROM AUTHOR]

Seven energetic salts of 3,6-dinitramino-1,2,4,5-tetrazine (DNAT), named as (NH4)2(DNAT) (1), (NH2NH3)2(DNAT) (2), (NH3OH)2(DNAT) (3), G2(DNAT) (4) (G = guanidine), (AG)2(DNAT) (5) (AG = aminoguanidine), (DAG)2(DNAT)·H2O (6) (DAG = diaminoguanidine) and (TAG)2(DNAT) (7) (TAG = triaminoguanidine) were synthesized and fully characterized. Molecular structures of 1, 4, 6, and 7 were confirmed by single-crystal X-ray diffraction for the first time, which constituted by the nitrogen-rich cations and DNAT2- through electrostatic and H-bond interactions. The thermal behaviors of 1–7 were also investigated, all of these salts have a higher thermal decomposition temperature than DNAT. Enthalpies of formation of these salts were evaluated according to the measurement results of combustion energies, and the detonation performances were calculated via the EXPLO5 v6.01 program. Compound 7 (P: 31.7 GPa, Dv: 9333 m s−1) exhibits the highest detonation performance among them. Sensitivities toward mechanical stimuli of 1–7 were tested by using BAM standard methods, 4 is insensitive to impact and frication (IF>40 J, FS>360 N). Moreover, the relationship between the sensitivity and intermolecular interactions were analyzed by using Hirshfeld surfaces calculations. All studies demonstrated the salts for potential energetic materials. [ABSTRACT FROM AUTHOR]

SUMMARY: Performance‐based design of the timber structures' fire resistance is often based on the reduced cross section and thus relying on empirical and numerical assessment of the charring propagation. The current work aims to construct models for the pyrolysis of spruce and pinewoods to allow coupled simulations of the cross‐section reduction and burning rate in fire models. Kinetic models are formulated based on thermogravimetric data and supported by the heats of pyrolysis and combustion measurements by differential scanning calorimetry and microscale combustion calorimetry, respectively. The results from these small‐scale measurements are consistent with each other, and the heats of pyrolysis and combustion are determined for the wood primary components by fitting the simulations to the experimental results. Heat release models are constructed based on the small‐scale tests, and cone calorimeter experiments are used for the estimation of the physical properties and for the heat release model validation. [ABSTRACT FROM AUTHOR]

Compared to the ordinary RDX, nano‐sized RDX has many more excellent properties. Therefore two kinds of CMDB propellant were prepared for comparison. One is the normal CMDB propellant called M‐CMDB propellant, the other is N‐CMDB propellant which adds nano‐sized RDX to CMDB propellant. The morphology characterization, tensile properties, sensitivity, and combustion performance of the propellants were investigated, the results for N‐CMDB propellant were compared with that for the normal one. It has been found that the interface of N‐CMDB propellant showed no stratification and fewer overall defects than the normal one. The value of σm and ϵm for N‐CMDB propellant are increased by 32.6 % and 25.2 % at 323.15 K, respectively. At 293.15 K, the σm and ϵm values of N‐CMDB propellant also increased by 25.4 % and 46.9 % and increased by 17.5 % and 23.7 %, respectively, at 233.15 K. The friction and impact sensitivities of N‐CMDB propellant are decreased by 51.3 % and 50.4 %, respectively. The TG/DSC study indicated that, compared with M‐CMDB propellant, the thermal decomposition peak temperature of N‐CMDB propellant is advanced, and the apparent activation energy is reduced by about 6.0 % to 144.3 kJ ⋅ mol−1. Combustion performance measurements were carried out. It was observed that nano‐sized RDX is a good burning rate enhancer, because of the burning rate coefficient value of N‐CMDB propellant is relatedly increased by 36.9 %. Besides, the pressure exponent of N‐CMDB propellant is relatively decreased by 21.6 %. All the results indicate that the application of nano‐sized RDX will help to improve the comprehensive performance of CMDB propellant. [ABSTRACT FROM AUTHOR]

This article describes the development of the first single-shot ultrafast-laser-absorption-spectroscopy (ULAS) diagnostic for simultaneous measurements of temperature and concentrations of CO, NO and H 2 O in flames and aluminized fireballs of HMX (C 4 H 8 N 8 O 8 ). Ultrashort (55 fs) pulses from a Ti:Sapphire oscillator emitting near 800 nm were amplified and converted into the mid-infrared through optical parametric amplification (OPA) at a repetition rate of 5 kHz. Ultimately, pulses with a spectral bandwidth of ≈ 600 cm - 1 centered near 4.9 μ m were utilized in combination with a mid-infrared spectrograph to measure absorbance spectra of CO, NO, and H 2 O across a 30 nm bandwidth with a spectral resolution of 0.3 nm. The gas temperature and species concentrations were determined by least-squares fitting simulated absorbance spectra to measured absorbance spectra. Measurements of temperature, CO, NO and H2O were acquired in a HMX flame burning in air at atmospheric pressure and the measurements agree well with previously published results. Measurements were also acquired in fireballs of HMX with and without 16.7 wt% H-5 micro-aluminum. Time histories of temperature and species column densities are reported with a 1 - σ precision of 0.4% for temperature and 0.3% (CO), 0.6% (NO), and 0.5% (H 2 O), and 95% confidence intervals (CI) of 2.5% for temperature and 2.5% (CO), 11% (NO), and 7% (H 2 O), thereby demonstrating the ability of ULAS to provide high-fidelity, multi-parameter measurements in harsh combustion environments. The results indicate that the addition of the micron-aluminum increases the fireball peak temperature by ≈ 100 K and leads to larger concentrations of CO. The addition of aluminum also increases the duration fireballs remain at elevated temperatures above 2000 K. [ABSTRACT FROM AUTHOR]

The wet dichromate methods for the quantification of soil organic carbon on the basis of the reductant ability of soil organic matter have been widely used and they are still nowadays. The results obtained with these methods depart from the reference dry combustion with CO2 measurement and the discrepancies are interpreted in terms of incomplete oxidation under the wet dichromate conditions. However, in the calculations accompanying the dichromate methods a carbon valence (VC) equal to four is systematically used, even though the actual VC could be different. To assess the importance that an actual VC different from four could have in the mismatch between the wet dichromate methods and the reference dry combustion, the relationship between VC and the average formal oxidation state of carbon (zC) in soil organic matter should be known. On the basis of the definition of the equivalent weight and the average formal oxidation state, it is shown that a simple linear expression of the form VC = 4 – zC relates both concepts in carbon‐hydrogen‐oxygen‐nitrogen‐phosphorus‐sulphur compounds, which are representative of soil organic matter. On the basis of this equation the actual VC in soil organic matter can be assessed, thus helping in the interpretation of soil organic carbon determinations with the wet dichromate methods and, therefore, in the comparison between the dichromate methods and the reference dry combustion. Highlights: Although questioned, a carbon valence of four is always used in the wet dichromate methods for SOC.How the valence of carbon depends on its average formal oxidation had not been previously shown.Both concepts are related through a simple linear equation: VC = 4 – zC.The mismatch between the dichromate oxidation and the dry combustion will be better interpreted. [ABSTRACT FROM AUTHOR]

This paper presents the measurement process of the emissions from marine diesel engines. The emission measurement was carried out by the certified TESTO 350 Maritime exhaust gas analyzer on the Juraj Dalmatinac ferry Caterpillar C32 engines. The gas analyzer records the concentrations of nitrogen oxides (NOx), carbon monoxide (CO), carbon dioxide (CO2), oxygen (O2) and sulfur dioxide (SO2). TESTO 350 emission sampling probe was set at the end of the exhaust pipe. A combustion emission measurement was performed during a Split – Supetar (Brač) trip and backwards with the total duration of 110 min. The emissions are estimated for two trip phases: “maneuvering” and “at sea”. [ABSTRACT FROM AUTHOR]

A new method for real-time measurements of potassium and sodium containing aerosol particles is described and verified. The method is based on surface ionization technique and may be used to explore the alkali chemistry related to high temperature chemistry processes. The measurement device is a further development of the simple and cost-effective surface ionization detector previously used for online alkali measurements in combustion and gasification research. The discrimination between sodium and potassium is possible due to differences in their surface desorption kinetics and facilitated by rapidly reversing the field potential between the ion source and the nearby collector. The instrument is evaluated in a series of laboratory experiments using size-selected alkali salt particles containing KCl, NaCl, K2SO4, Na2SO4, KNO3 and NaNO3. The filament temperature was found to be a key influencing factor in order to optimize the strength and Na–K deviation of the observed ion current. The ability to simultaneously report absolute concentrations of Na and K makes the instrument attractive for solid fuel conversion of alkali-rich fuels such as low-grade biomass and to explore behavior deviations of Na and K in high temperature processes. [ABSTRACT FROM AUTHOR]

Particulate matter (PM) generated by residential wood combustion is a major environmental concern in Europe. This study focuses on the influence of potassium chloride (KCl) on fine particle emissions from a modern wood stove. Wood logs with and without KCl impregnation were subjected to batch combustion and emission measurements. A bi-modal particle number-size distribution characterized by a nucleation mode and an accumulation mode was identified for all types of wood fuel. However, in the presence of KCl, a lower number emission of ultrafine particles and a higher number emission of larger particles (size ∼200–500 nm) were observed. In addition, the emission factor of condensed organic compounds (COC) increased with increasing KCl content, from 0.16 g/kg dry wood for normal wood (NW) to 0.48 g/kg dry wood for wood impregnated with the 2 mol/L KCl solution (HKW), most likely due to the facilitated heterogeneous condensation of semi-volatile hydrocarbons on pre-existing ash particles. In addition, the emission factor of soot particles also increased slightly when the KCl content was high, from 1.47 g/kg dry wood for NW to 2.23 g/kg dry wood for HKW. • PM emissions from the combustion of KCl-impregnated wood in a domestic stove were characterized. • The emission of accumulation mode particles from the wood stove increased in the presence of KCl. • The organic carbonaceous emissions from the wood stove increased with increasing KCl content in the fuel. • A high KCl content in the fuel slightly promoted the soot emissions from the wood stove. [ABSTRACT FROM AUTHOR]

A method is proposed to assess the thermal safety of solid propellant charges by measuring the temperature and pressure of propellant specimens during cook-off tests and determining the reaction kinetics. In this work, two propellants—ammonium perchlorate/hydroxy-terminated polybutadiene/aluminum (AP/HTPB/Al), and ammonium perchlorate/hydroxy-terminated polyether/aluminum (AP/HTPE/Al)—are taken as examples to demonstrate this method in detail. Specifically, by implementing two kinds of cook-off tests—viz., multipoint temperature monitoring, and combustion pressure measurement—the thermal reaction temperature before ignition and the combustion pressure after ignition of the two propellants were respectively determined. Then, the kinetic parameters of the thermal decomposition reaction model and the parameters of the combustion reaction model were numerically simulated and calibrated to achieve mathematical descriptions of the entire process of cook off of two solid propellant charges. On this basis, the technology of grid-node separation calculation was employed to simulate and predict the rupture of a solid rocket motor case, thereby quantitatively describing the severity of the cook-off reaction. The results demonstrate that, at a heating rate of 1 K min−1, the ignition positions of the two propellant charges in the solid rocket motor are located in the annular area where the side wall and the front of the casing are joined. Compared with those of the AP/HTPE/Al charge, the ignition time of the AP/HTPB/Al charge is longer (12,714 s for AP/HTPB/Al vs. 9701 s for AP/HTPE/Al), the temperature of the casing before ignition is higher (501.5 K for AP/HTPB/Al vs. 466.2 K for AP/HTPE/Al), the reaction after ignition is more intense, and the deformation of the casing is more serious. [ABSTRACT FROM AUTHOR]

In this study, OH chemiluminescence of methane-hydrogen premixed flames formed on a Bunsen burner was investigated. As for the chemiluminescence intensity, we obtained the values at the edge of the flame and at the central axis of the flame, compared with the value calculated by the inverse Abel transform. It was found that the value at the central axis of the flame was less dependent on the measurement position than that at the edge of the flame, because the effect of integrated chemiluminescence intensity on the optical path was small. In addition, four filters with different center wavelengths were tested. Although the chemiluminescence intensity was changed by the filter, the dependence of the chemiluminescence intensity on the equivalence ratio was almost the same. For more discussion, the OH concentration and the heat release rate predicted by the numerical simulation of a one-dimensional methane-hydrogen flame were compared with the OH chemiluminescence and the burning velocity in experiments. It was revealed that, even when hydrogen was added by keeping the total equivalence ratio constant, the OH chemiluminescence intensity was proportional to the production rate of excited OH* produced by the reaction of CH and O2 concentrations. Similarly, the OH chemiluminescence intensity was apparently related with the heat release rate.

Attempts were made to reproduce the laboratory measurements of flameless combustion systems using numerical simulation tools, for different chambers designs. In many cases, a significant discrepancy is reported between the experimental measurements and the numerical results. In this work, we have successfully reproduced the reported experimental results (velocity field, temperature field, and the outlet dry NOx emissions) of the "FOUR" MILD combustion facility (proposed by C. Rottier). An acceptable accuracy was achieved in two reference test cases. A concise discussion is presented on the available literature on the subject of numerical modeling for the flameless combustion mode. The use of two turbulence models was explored (standard k-ε, and modified k-ε), along with two kinetic mechanisms (a global 2-step CH4 combustion mechanism, and the more detailed KEE-58 mechanism). The commercial ANSYS FLUENT® software was used in these simulations. The results of seven different modeling setups are presented, comparing the predictions of temperature fields, and NOX emissions. Features such as the onset of premature ignition and the reactants entrainment ratio are also discussed. Our results show that the most accurate model setup employs the following: SKE – KEE-58 – EDC with a reduced volume fraction constant. In regards to reproducing the measurements from the "FOUR" facility, we are not aware of a similar research that runs a concise discussion on the predictions of such broad and different modeling setups. [ABSTRACT FROM AUTHOR]

Since aqueous film-forming foams (AFFFs) are major sources of per- and polyfluoroalkyl substances (PFAS), understanding the quantity and type of PFAS present in AFFFs is crucial for assessing environmental risk and remediation. We characterized 25 foams from Canada and Europe, including two non-AFFFs and two fluorine-free AFFFs. We used liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS) to identify novel PFAS, as well as total oxidizable precursor assays (TOP) and total organofluorine (TOF) measurements for comparison. LC-HRMS showed that the two non-AFFF foams and two PFAS-free AFFFs contained little or no PFAS, confirmed by TOF measurement using combustion ion chromatography (CIC). The PFAS-containing AFFFs, however, spanned a wide concentration range of TOF (2200–45,000 mg F/L) and contained 22 new classes of polyfluoroalkyl substances not previously reported. As a result of identifying new compounds, LC-HRMS was fully able to capture the oxidizable precursors determined by TOP assay in all tested fluorotelomer (FT) AFFFs, while unknown compounds still constituted a significant fraction (19–53 mol%) in most electrochemical fluorination (ECF) AFFFs. A fluorine mass balance was achieved by comparing the amounts of compounds identified by LC-HRMS with those detected by CIC, although LC-HRMS overestimated TOF with a recovery of 127 ± 36%. [Display omitted] • 25 firefighting foams were characterized, revealing diverse PFAS concentrations and types. • LC-HRMS identified 22 classes of novel PFAS of various chemistry • Non-AFFF foams and fluorine-free AFFFs contained minimal PFAS. • PFAS-containing AFFFs showed a wide range of total organofluorine content. • LC-HRMS and CIC aided in fluorine mass balance despite slight LC-HRMS overestimation. [ABSTRACT FROM AUTHOR]

• Single-cylinder engine (SCE) experiment using renewable diesel and methanol as fuels. • Dual-fuel combustion and emissions performance comparison with conventional diesel combustion. • Effect of different methanol substitution rates at different engine load conditions. Methanol (MeOH) and renewable diesel (RD) are being considered promising alternative fuels for the de-fossilization of internal combustion engines (ICE). This study provides an experimental investigation on the use of both fuels under dual-fuel combustion mode: port fuel injection (PFI) of MeOH and direct injection (DI) of RD. The combustion mode is labeled as RMDF (renewable diesel methanol dual fuel). The experiment was performed in a heavy-duty single-cylinder engine (SCE) equipped with combustion and emissions measurements and analysis for engine efficiency and emissions of soot and NO X (oxides of nitrogen). MeOH substitution rate, which is the mass ratio of injected MeOH fuel to total injected fuels of both MeOH and RD, was varied to study its effect on engine efficiency and emissions. Different MeOH substitutions were tested from low (6.9 bar gIMEP) to full (23.5 bar gIMEP) engine load conditions at a fixed engine speed of 1200 RPM. Test results showed that higher MeOH substitution rates can reduce NO X emissions effectively while improving engine thermal efficiency. However, a higher MeOH substitute rate can result in longer ignition delay at low load, and increased emissions of carbon monoxide (CO) and unburned hydrocarbon (UHC). Increased maximum pressure rise rate (MPRR) at high load condition was observed as the MeOH substitution rate increased. MPRR is not sensitive to the change in MeOH at low load condition. While ignition delay became longer at low load, it was shorter at high load as MeOH substitution rate increased. Overall, the results from this study suggest that RMDF can be considered as an option to achieve a cleaner and more efficient engine. However, further optimization of combustion designs and engine operating strategy need to be considered to improve combustion loss from RMDF emissions, possibly due to the lower reactivity of MeOH. [ABSTRACT FROM AUTHOR]