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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]

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]

Ammonia is emerging as a promising alternative fuel for longer range decarbonised heavy transport, particularly in the marine sector 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 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 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 ammonia 'slip'). With a geometric compression ratio of 12.4:1, it was possible to run the engine on pure ammonia at low engine speeds (1000-1800 rpm) at low to moderate engine loads in a fully warmed up state. When progressively dropping down below a threshold load limit, an increasing amount of gasoline co-firing was required to avoid engine misfire. Due to the favourable antiknock characteristics, pure ammonia operation was up to 5% more efficient than pure gasoline operation under stable operating regions. A maximum net indicated thermal efficiency (ITE) of 40% was achieved, with efficiency tending to increase with speed and load. For the co-fuelling of gasoline and ammonia in a pure ammonia attainable operating region, it was found that addition of gasoline improved the combustion, but these improvements were not sufficient to translate into improved thermal efficiency. Emissions of ammonia slip reduced with increased gasoline co-fuelling, albeit with increased NOx. However, the reduction in ammonia slip was nearly ten times the increase in NOx emissions. Comparing pure ammonia and pure gasoline operation, NOx reduced by ~60% when switching from pure gasoline to pure ammonia (as the latter is associated with longer and cooler combustion). Results were finally compared to those obtained a modern multicylinder Volvo 'D8' turbo-diesel engine modified for dual-fuel operation with ammonia port fuel injection (PFI), with the focus of the comparison being ammonia slip and NOx emissions. [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]

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]

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]

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]

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.

• In situ resource utilization of carbon dioxide. • Detailed analysis of multilayer oxidation shell structures provided. • Moving micron-scale single-particle combustion was observed and measured. • Temperature data enhances burning time measurement and mode classification. An experimental system integrating micro-sized single particle generation, ignition, and observation was proposed and constructed for investigating the combustion characteristics of magnesium single particles in carbon dioxide. Defining the onset of combustion using the boiling point temperature allows for precise measurement of combustion time without artificial interference. Results revealed four modes of combustion for magnesium particles (Vapor-phase combustion, surface reaction, Micro explosion and flash-out mode) in carbon dioxide. Vapor-phase combustion is diffusion-controlled (with a D 0 1.76 scaling, where D 0 is the initial particle diameter). Additionally, the micro-explosion mode primarily occurs in particles with diameters exceeding 70 μm, and the combustion time is rather insensitive to the particle size (Typically 0.5 ∼ 2.2 ms in this study). The characteristic temperatures of the particles were determined using two-color pyrometry, indicating that the particle combustion temperature decreases with increasing particle size. Magnesium particles typically reach temperatures approximately 800 K higher than normal vapor-phase combustion temperatures before experiencing micro-explosions. Analysis of combustion products shows that the oxide shell formed by the combustion of magnesium particles has a three-layer structure. Both the outer and inner layers are mixed layers of magnesium oxide and solid carbon produced during combustion reactions, and the middle layer is the initial oxidation layer of the particles. [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]

• 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]

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]

• Measuring the enthalpy of combustion of methane gas with a reference gas calorimeter. • Description of reference gas calorimeter system elements. • Comprehensive uncertainty calculation for enthalpy of combustion measurement. • Determination of enthalpy of combustion of methane with low uncertainty. • Importance of temperature measurements in enthalpy of combustion calculations. Natural gas is a plentiful and adaptable energy source among other gases that is used all over the world with an increasing demand nowadays. It is therefore of utmost importance to measure the energy content of the natural gas with high precision for both users and sellers. In this study, methane gas, the main component of natural gas, was combusted using the reference gas calorimeter developed at TUBITAK UME (The Scientific and Technological Research Council of Turkey) - (National Metrology Institute) to determine the enthalpy of combustion. The objective was to measure the enthalpy of combustion of the methane, perform a detailed uncertainty calculation and to compare the enthalpy of combustion of the methane specified in ISO 6976:2016 with the obtained experimental results. The reference gas calorimeter was designed using the temperature, mass, power, flow control, waste water absorption, and waste gas measurement systems with the highest precision and circulating water bath with temperature control insulated so as not to exchange heat from the external environment. All measurements were performed with the instruments having calibration certificates. Experiments were carried out at the temperature of 298.15 K and a constant pressure (101.325 kPa) using the methane with a purity of 99.995 % as a reference gas. The mass of the burnt methane in combustion process was approximately 10-3 kg. As a consequence of the measurements, mean experimental enthalpy of combustion was obtained as −55518.2 kJ kg−1 with the error of 0.2 % (k = 2). The evaluations indicated that the largest source of error in the enthalpy of combustion measurements originated from the temperature and mass measurements. [ABSTRACT FROM AUTHOR]

This work implements astigmatic dual-beam interferometric particle imaging (ADIPI) in propellant combustion diagnostics to enable the measurement of the three-dimensional (3D) spatial position and particle morphology of opaque particles. The ADIPI allows the discrimination of different substances, such as metal droplets, flames, and pyrolysis residues. A general theoretical model based on the generalized Huygens-Fresnel integral and the ray transfer matrix model is developed to describe the identification of ADIPI signals for regular and irregular particles. An experimental system combining a 13 kHz time-resolved ADIPI with digital in-line holography (DIH) is built to enable simultaneous measurements of the propellant combustion field. The typical ADIPI signals presented by different substances in the combustion field are analyzed by comparing the experimental results of DIH. The time-resolved 3D trajectory reconstruction of burning particles and the measurement of irregular particle size and morphology are realized. Due to the effect of the flame, the average deviation of the depth locating of the particles is 1.4 mm with a standard deviation of 1.0 mm. The average deviation value of the depth position relative to the measured distance is 1%. In propellant combustion measurements, the motion of burning particles can be accurately determined, proving its feasibility and practicality. [Display omitted] • ADIPI is applied to propellant combustion diagnostics. • Theoretical model and experimental study are both carried out. • 3D trajectory, particle size and morphology of burning particles are measured. [ABSTRACT FROM AUTHOR]