This study aims to clarify the effect of inner-diameter differences on the delayed onset of flashback, where the H₂/air premixed flame, after being trapped near a wire mesh, passes through the mesh and flashback occurs with a time delay. In the experiment, as the inner diameter decreased, the flashback range decreased, and the time from the flame trap near the mesh to the flashback increased. This is because the heat loss to the tube wall increased as the inner diameter decreased. On the other hand, the mesh temperature just before the start of flashback decreased as the inner diameter decreased. This is because heat recirculation is greater as the inner diameter decreases due to the longer time from the flame trap near the mesh to the flashback and the low flow rate of the mixture. Additionally, flame-front position was calculated using image analysis, and flame propagation behavior was examined in terms of the apparent flame speed. As a result, the findings of this study clarified the effects of heat loss and heat recirculation differences due to variations in the inner diameter on flame behavior near the mesh. This study provides knowledge on flame behavior near the flame arrester under flow conditions and contributes to the safe use of hydrogen.

A biomass briquette, which are highly densified biomass raw material and a type of renewable energy are expected to suppress the global warming. To effectively utilize biomass briquettes, it is important to know their combustion characteristics. It is reported that the flaming combustion duration is proportional to the product of briquette density and inverse square of specific surface area, and the char combustion duration is proportional to the product of fixed carbon density and inverse square of specific surface area, with a single cylindrical briquette of which aspect ratio is 2 in the constant hot air condition. Each proportional constant, C_f for flaming combustion and C_c for char combustion, can be considered as the indicators of the biomass briquette combustion rate, may change with the briquette’s aspect ratio. Previous studies have reported that the flaming combustion duration and the char combustion duration are both affected by the aspect ratio. However, the extent and tendency of each influence and the reason why such influences occur have not been clarified. In the present study, combustion experiments of a single cylindrical briquette were conducted to clarify the trends and extent of the influence of the briquette aspect ratio on both combustion durations.

This study examines the combustion, performance, and emission characteristics of a gasoline direct injection compression ignition (GDCI) engine. A conventional single cylinder, water-cooled, direct injection, stationary diesel engine was modified to operate in GDCI mode by replacing mechanical fuel injection system with gasoline direct injection system. The engine features a flat cylinder head, hemi-spherical re-entrant piston bowl, central-mounted injector, with a compression ratio of 16.5 developing 7.46 kW at 1500 rpm. Injection, exhaust gas circulation, and intake boost systems were employed as control strategies. Experiments were conducted at No load, Part-load, and Full load conditions under partially premixed compression ignition mode without switching to diffusion-controlled combustion. At no load conditions without EGR, NO, UBHC, CO, and smoke opacity were 53 ppm, 5 ppm, 0.21% and 5%, respectively. The coefficient of variation of IMEP remained below 5% and the exhaust temperature was under 180 °C. The engine achieved a BSFC of 240 g/kWh at 1500 rpm and 2 bar BMEP. At full load condition, emissions of NO, HC, CO, and smoke opacity were 642 ppm, 4 ppm, 0.48% and 19%, respectively. Near-Stoichiometric mixtures without EGR delivered a peak BMEP of 5.28 bar at 1500 rpm. The results demonstrate stable combustion with reduced noise, optimized combustion phasing, and improved efficiency under all operational conditions.

In this study, we extend the principle of frequency-domain Soret forced Rayleigh scattering (SFRS) to ternary mixtures for the determination of ternary Soret coefficients. We derived an analytical expression for the frequency-dependent phase lag in ternary systems, revealing the mathematical relationship between the measured phase lag and the coupled transport coefficients. Similar to time-domain SFRS, theoretical analysis demonstrates that the use of two-wavelength probe lasers enables the simultaneous determination of Soret and thermodiffusion coefficients. To validate the proposed theory, preliminary experiments were conducted on a ternary benchmark mixture composed of n-dodecane, isobutylbenzene, and 1,2,3,4-tetrahydronaphthalene using an existing single-wavelength probing setup. The measured frequency response was well-described by the derived analytical expression. This work provides a new foundation for characterizing mass transport in complex multicomponent mixtures that have remained challenging to investigate, by virtue of lock-in detection scheme offering minimal system disturbances and high robustness against scattered light.

Taking rice-wheat straw blends (1:1, wt%) as the research object, thermogravimetric analysis (TGA) was used to investigate the co-pyrolysis behavior of the untreated sample (RA) and the alkali-treated blend (RB) at four heating rates. The Kissinger-Akahira-Sunose (KAS) method, Friedman (FR) method and Coats method were combined to analyze the kinetic parameters, thermodynamic parameters and pyrolysis mechanism, and the product distribution was characterized. The results showed that the average activation energy (E_α) of RA was 173.82 kJ/mol (KAS method) and 176.57 kJ/mol (FR method), with the average Gibbs free energy change (ΔG) of 171.68 kJ/mol, enthalpy change (ΔH) of 171.63 kJ/mol, and entropy change (ΔS) of −0.07 J/(mol·K). After alkali treatment, the average E_α of RB increased to 180.18 kJ/mol (KAS method) and 186.67 kJ/mol (FR method), along with the average ΔG of 180.50 kJ/mol, ΔH of 181.49 kJ/mol, and ΔS of 1.58 J/(mol·K). The pyrolysis mechanism of RA evolved from the three-dimensional diffusion model (D3) to the random nucleation model (F2), while RB followed the D3 model throughout the entire pyrolysis process. Through comparison with individual feedstocks, RA exhibited a complex coexistence of positive (lowered E_a and ΔH) and negative (elevated temperature) synergies, whereas RB showed predominantly negative synergy with elevated E_a, ΔG, ΔH and a shifted temperature range to 260–407°C, suggesting that alkali treatment shifts the predominant synergistic effect from coexistence to a predominantly inhibitory mode. In terms of product distribution, the biochar proportion of RB (36.70%) was markedly higher than that of RA (24.32%), while the bio-oil proportion of RB (31.12%) was lower than that of RA (44.44%). The average pre-exponential factors (A) of RA and RB were 2.0 × 10¹⁶ s^-1 and 1.8 × 10¹⁵ s^-1, respectively. This study shows that alkali treatment slightly increases the pyrolysis difficulty of the rice-wheat straw blends, but can effectively regulate the product distribution and promote biochar formation, providing theoretical support for the thermochemical conversion and efficient utilization of rice straw and wheat straw.

The functional resonance analysis method (FRAM) is one of most brilliant methods in complex systems to conduct the risk analysis and/or accident analysis. To conduct the risk assessment which consists of the risk analysis and risk reduction on the control of gaseous fuel flow, the semi-quantitative FRAM was adopted in this research. The accumulated coupling variability was newly propounded, and the expected values obtained by simple calculations were used to evaluate variabilities semi-quantitatively. The accumulated coupling variability was closely related with risk, and then we analyzed the sensitivity of output variability of each function to the accumulated coupling variability of the top event. Significant functions, which had large values in sensitivity, i.e. greatly affected the risk of system, were identified through the risk analysis. The accumulated coupling variability of the top event, corresponding to the risk of system, was effectively suppressed, based on the semi-quantitative results derived from the risk analysis. We proposed the effective measure of risk reduction in this research. Using the expected values in the semi-quantitative FRAM, the risk analysis was conducted with reasonable accuracy, considerably reducing the effort and time spent on evaluations. Compared with the downlink functional coupling variability as the representative of previous methods, the superiority of the proposed method was confirmed.

When using carbon-free fuels (H₂/NH₃), achieving total heat recovery via an economizer—specifically complete recovery including latent heat—is desirable to compensate for their low calorific values LHV (kJ/mol). To the best of the authors' knowledge, this is the first numerical study on economizers under H₂/NH₃ combustion exhaust gas conditions. Analysis of heat transfer around the heat transfer tube placed in a combustion exhaust gas flow of H₂/NH₃ yielded the following results: (1) A liquid film formed downstream of the tube, creating a region of locally high heat flux. (2) The heat flux into the tube increased with the gas velocity at the economizer inlet, and the heat flux upstream of the tube wall increased significantly. The contribution of latent heat to the heat transfer downstream of the tube wall exhibited a similar moderately increasing trend along the tube wall starting from the vicinity of the 70-degree position, regardless of the inlet gas velocity. (cf. stagnation point: 0°) (3) The effects of the inlet gas temperature on condensation phenomena in the boundary layer and the recovery rates of sensible and latent heat were clarified. This knowledge will facilitate the preliminary design of a multi-tube structure based on the local gas temperature at each tube row of the economizer.

Thermal therapy, including hyperthermia and thermal ablation, is minimally invasive and associated with minimal side effects. To ensure effective and safe thermal therapy, the temperature distributions inside the patient’s body must be accurately measured. In clinical practice, thermal sensors are often adopted but are invasive and limited to point measurements. Alternatively, noninvasive temperature monitoring can be achieved through magnetic resonance imaging but presents several disadvantages, including expensive implementation and numerous contraindications. To address these drawbacks, this study investigates the feasibility of estimating two-dimensional temperature distributions from ultrasound images using a generative adversarial network (GAN). Because the speed of sound in the propagation medium depends on temperature, the increasing temperature induced by thermal therapy causes apparent scatterer displacements between ultrasound images acquired before and after heating. The proposed GAN-based method was trained using paired ultrasound images and corresponding ground-truth temperature distribution images generated by extending one-dimensional theoretical temperature profiles. Experiments were conducted using an agar phantom under first- (Dirichlet) and second-kind (Neumann) boundary conditions to evaluate whether the proposed GAN-based method could learn the mapping between paired ultrasound images and the corresponding model-generated ground-truth temperature distributions. The mean absolute error (MAE) between the theoretical model and estimated temperature distributions was evaluated within the effective thermal region, where the theoretical temperature increase was at least 10% of its maximum value at each heating time. The MAE within this region was 0.80 ± 0.78 °C under the first-kind condition and 0.88 ± 0.62 °C under the second-kind condition. Although larger local errors were observed in regions with steep temperature gradients, these results demonstrate the feasibility of the proposed GAN-based method as a proof-of-concept for noninvasive temperature estimation from ultrasound B-mode images using model-generated ground-truth temperature distributions.