Heat Release Research Articles

The emission of pollutants from ornamental shrubs during forest fires

AbstractThis study investigates the combustion behavior, emissions, and aerosol production of four plant species: Laurus nobilis, Cistus monspeliensis, Photinia fraseri, and Cupressus sempervirens. The Heat Release Rate (HRR) and Smoke Production Rate (SPR) were measured, revealing that Cupressus sempervirens had the highest HRR and longest flame duration due to its higher bulk density. Emission Factors (EFs) for key compounds such as CO₂, CO, NO, and aerosols showed significant variation by species. Aerosol analysis indicated that the combustion of all plants primarily emitted fine particles, with the majority being ultrafine particles (PM0.1), particularly in the 25–130‐nm range. Particle size distributions were bimodal in number but monomodal in volume. These findings highlight the impact of plant characteristics on fire behavior and emissions, with significant implications for understanding fire dynamics in wildland–urban interfaces.

Performance Characteristics of a Compression Ignition (CI) Engine Using an Environmentally Friendly Waste Plastic Fuel

Due to growing demands and depleting reserves of petroleum-based fuel, there is a necessity to find an alternative fuel for IC engines. Also, environmental concerns and globally faced problems like lots of garbage generated through plastics is a major issue in India. There is a significant disparity between plastic production and waste plastic generation. Therefore, the need for alternative fuels derived from municipal plastic waste has emerged to enhance the performance of IC engines, decrease emissions, and address other environmental concerns in line with the “Swachh Bharat Mission of India”. In this study, the alternative fuel was produced from a municipal mix of plastic waste by pyrolysis process. The experiments were carried out with a constant speed of 1500 rpm at different load conditions and fueled with standard diesel, waste plastic fuel and other blends to investigate IC engine performance and combustion and emissions in terms of brake thermal efficiency, brake power, brake specific fuel consumption, cylinder pressure, net heat release, mean gas temperature, rate of pressure rise, andbrake specific CO2, NOx, CO and HC emissions parameters were investigated and it is compared with standard diesel. The overall result shows that WPO20D80 and WPO30D70 exhibit the peak performance (torque, BP, BTE and BSFC) and lowest emissions (HC, CO, NOx) at all load conditions. Moreover, according to all the performance results, the lowest BSFC with maximum brake thermal efficiency and variations was 24.01% and 0.346 Kg/kWh for the WPO30D70 blend at part load condition. The minimum brake-specific NOx produced by the diesel blend at peak load conditions (WPO20D80) is 138.66 ppm, which is higher than other blends. This phenomenon may be attributed to an elevated proportion of pre-combustion and an extended ignition duration, resulting in a high cylinder temperature and an enhanced rate of heat release. This analysis contributes to a deeper understanding of the environmental implications associated with different fuel blends and load conditions. Notably, the blends ranging from 10% to 50% showed good tendencies to be utilized with diesel engines and consistently exhibit favourable brakespecific emission profiles, suggesting its potential as an environmentally friendly alternative fuel.

Experimental study on an improved direct-contact thermal energy storage container

Direct-contact thermal energy storage (TES) systems characterized by high heat density and rapid heat transfer rates have been exploited for the collection of industrial waste or surplus heat for subsequent utilization. In order to address blockage issue at the initial stage of charging process, an improved direct-contact TES container was developed by incorporating a double-pipe structure at both the inlet and outlet. Within the container, a U-shaped tube serving as the inner tube was concentrically positioned from the inlet to the outlet. Erythritol was selected as the phase change material (PCM), while heat transfer oil (HTO) functioned as the heat transfer medium during experimentation. During the charging process, hot HTO initially flowed through the U-shaped tube, establishing an indirect contact with the PCM. The high thermal conductivity of the U-shaped tube wall expedited the formation of a flow channel within the solid PCM. The duration of forming flow channel was 6 to 13 min. In the discharging phase, the liquid PCM was segregated into convection and conduction zones. The indirect-contact TES experiments were also conducted in the same container. Comparison between indirect-contact and direct-contact TES were analysed from the aspects of phase change behavior, charging and discharging time with the identical container structure and theoretical heat capacity. Results indicated that the direct-contact TES container exhibited superior heat storage and release rates, with the direct-contact discharging time being approximately a quarter of the indirect-contact duration. The phase change behavior of the PCM was notably influenced by the movement of HTO within the direct-contact storage container.

Association of anthropogenic heat with asthma and related symptoms among children in China: A novel index reflecting climate change

BackgroundAnthropogenic heat (AH) is defined as the significant release of waste heat into the environment due to human activities, serving as a controllable heat source contributing to global climate change. However, epidemiological evidence establishing a clear association between AH and childhood asthma is currently lacking. ObjectivesTo explore the relationship between children's exposure to AH and asthma, as well as its related symptoms. MethodsThis population-based cross-sectional study, part of the National Chinese Children Health Study from 2012 to 2018, involved 188,145 children aged 6 to 18 years. We used multisource remote sensing images and ancillary data to estimate AH exposure. Data on asthma symptoms were collected through validated self-reported questionnaires. A generalized linear mixed model was applied to determine the associations. ResultsOur findings indicate a positive correlation between AH exposure and asthma risk in children. An interquartile range (IQR) increase in total AH was linked to higher odds of current asthma (OR: 1.15, 95 % CI: 1.10, 1.20) after adjusting for covariates. Categorizing AH by source, industrial AH exhibited the strongest effect, with an increased risk of current asthma (OR: 1.16, 95 % CI: 1.11, 1.22). Notably, younger children exhibited stronger associations between AH exposure and asthma-related symptoms, with boys showing heightened susceptibility, particularly for persistent cough. ConclusionThis study suggests that exposure to AH may elevate the risk of asthma and related symptoms, particularly in boys and younger children. Providing a foundation for developing practical strategies to mitigate the adverse impacts of global warming on respiratory health, while also guiding the formulation and evaluation of climate action and public health policies, and supporting sustainable urban development.

Comparison of different geometry trees in fire simulation

AbstractWildfire simulations can help to better understand the dynamics and effects of forest fires. The basis of wildfire simulation is the tree-burning simulation. In this paper, the fire simulation of 7 different geometry Hungarian trees in the case of arson is presented. It was observed that the trees were burned down fast. The maximum mass loss rate and maximum heat release rate were larger as the tree was larger. The largest intensity fire could be observed in the case of the smallest tree. The maximum temperature was higher in the case of a large crown diameter. The maximum aerosol reached high pollutant concentrations. In the case of large crown height, the maximum CO2 concentration was higher. The results presented in this paper can be the basis of the following forest fire simulations.

Assessing the Fire Properties of Various Surface Treatments on Timber Components in Ancient Chinese Buildings: A Case Study from the Xianqing Temple in Changzhi, Shanxi, China

Traditional and modern coatings play a key role in enhancing the fire resistance of ancient Chinese buildings. However, further comparative analysis is needed on the fire properties of the two coatings and their effects on different timber structural components. This study focuses on the main hall of the Shanxi Changzhi Xianqing Temple, a typical traditional column and beam construction built between the Song and Jin periods. Firstly, the combustion characteristics of various timber structural component samples with different surface treatments (traditional “Yi-ma-wu-hui” and modern flame retardants) were analyzed using cone calorimeter. Secondly, the fire development process of the Xianqing Temple building model was analyzed by a fire dynamics simulator (FDS), and the effect mechanism of different surface treatments on the burning process was further studied. The results show that the fire resistance of timber structural components is significantly improved after modern and traditional surface treatments. The traditional method is more effective in delaying the peak heat release rate and reducing the surface temperature during combustion, while the modern surface treatment significantly prolongs the ignition time of the timber structural components. The FDS results confirm that modern and traditional surface treatments significantly improve the fire resistance of the building, delaying the flashover time by about 300 s, with no collapse occurring within 800 s. In addition, the fire resistance of buildings after traditional surface treatment is better compared to traditional methods. The above research results can provide direct data support for the selection and optimization of fireproof coatings and treatment methods for ancient buildings.

Robust, self-lubricating and injectable dECM-loaded hydrogels based on rapid photo-crosslinking for articular cartilage regeneration

The restoration of articular cartilage poses a significant clinical challenge due to its avascular nature and the limited presence of chondrocytes. Recently, there has been a growing emphasis on developing materials that emulate the properties of cartilage to facilitate high-quality repair. Here, an injectable dECM-loaded hydrogel (HS-dECM) with potent compressive strength and self-lubricating ability was prepared by photo-crosslinking for cartilage regeneration. The HS-dECM hydrogel was formed by integrating cartilage decellularized extracellular matrix (dECM) with hyaluronic acid methacrylate (HAMA) and sulfobetaine methacrylate (SBMA). Once injected into irregular defects, a robust hydrogel was rapidly formed in situ by UV irradiation with negligible heat release. The HS-dECM hydrogel exhibited robust compressive strength (898 ± 86 kPa), excellent fatigue resistance and a low friction coefficient, and had the feasibility of minimally invasive implantation. Besides, HS-dECM hydrogel promoted chondrogenic differentiation of BMSCs in vitro and repaired articular cartilage defects in rats. Therefore, the high-performance injectable HS-dECM hydrogel represents a novel minimally invasive strategy that significantly promote the cartilage injuries repair and regeneration.

Co Hybrids modified piperazine pyrophosphate towards efficient flame retardancy, smoke suppression, and high mechanical properties of styrenic thermoplastic elastomer

The highly flammable nature of thermoplastic elastomers (TPE) results in poor fire safety performance. The large addition of flame retardants leads to a significant decrease in mechanical properties. To solve above challenges, we design a multilayer core-shell flame retardant, piperazine pyrophosphate@ tannic acid@ Co amorphous hybrids (PAPP@TA@Co-2-MIM) and add it to TPE to enhance the fire safety and mechanical performance simultaneously. It was found that the addition of 32 wt% PAPP@TA@Co-2-MIM achieved a UL-94 V-0 rating of TPE composites, with a limiting oxygen index of 27 %. Compared to pure TPE, the peak heat release rate, total heat release, total smoke production, and peak CO release rate of TPE/PAPP@TA@Co-2-MIM were reduced by 79.8 %, 37.1 %, 42.9 %, and 82.5 %, respectively, effectively suppressing the release of heat, smoke, and toxic gases. Besides, the flame-retardant mechanism was also explained. In terms of mechanical performance, benefiting by the bridging effect of the core-shell structure, the tensile strength of TPE/PAPP@TA@Co-2-MIM increased by 52.7 %, compared to TPE/PAPP. This study designed a TPE composite material that showed good thermal stability, high fire safety performance and enhanced mechanical properties.

Highly efficient flame retardancy and fire spread behavior of rigid polyurethane foams with extremely low content of flame retardant

In recent years, flame-retardant rigid polyurethane foam (RPUF) has once again captured the scholars’ attention due to the growing the growing demands in the field of building energy efficiency. However, the inherent flammability of RPUF is high and the complexities of its flame-retardant mechanisms remain inadequately understood. In this study, a modified biomass material, amino starch phosphate ester was successfully synthesized which was then combined with expandable graphite (EG) and incorporated into RPUF. The research delved into the optimal ratio and minimal flame-retardant additive required to achieve the stringent UL-94 V-0 rating, while also thoroughly investigating the flame retardancy and thermal properties of the composite system. The findings revealed that with just 6 wt.% of flame retardants, the RPUF achieved the UL-94 V-0 rating, with a 41.1 % reduction in peak heat release rate (pHRR) and a 23.7 % decrease in total heat release (THR). Additionally, it diminishes the flame's size and width, leading to quicker extinction, while also lowering the internal combustion temperature of the polyurethane, thereby delaying both preheating and combustion times. The synergistic interaction between amino starch phosphate ester and EG during combustion results in the formation of a dense, continuous char layer, effectively inhibiting the pyrolysis and combustion of RPUF. This study provides a theoretical foundation for the development of efficient flame-retardant systems for RPUF.

Assessing and mitigating building fire risk based on the scenario clusters in Bangladesh

The increasing occurrence of fire hazards in residential buildings in Bangladesh has led to severe property damage, physical injuries, and fatalities, underscoring a critical research gap in effective fire risk management. This study aims to address this gap by identifying key fire risks and proposing mitigation strategies using BIM technology. The research employs a comprehensive survey and scenario clustering methodology to identify these risks and assess the efficacy of various fire-resistant materials. Data collection involved questionnaires distributed to 200 respondents, including building owners, occupants, engineers, and firefighters. These clusters are based on the metrics of fatality numbers and property damage to quantify fire risk. Findings highlight the significant role of wall and ceiling lining materials (RII = 0.919) in contributing to fire risk. Further analysis was conducted using a residential building model developed in Autodesk Revit and simulated in Pyrosim software, assessing various lining materials. Quantitative results demonstrated that fire brick is the most effective material, exhibiting the lowest heat release rate (968 kW/m2), minimum adiabatic surface temperature (28°C), minimum heat transfer coefficient (1.75 W/m2/K), and lowest surface burning rate (7.5e−08 Kg/m2/s). These results suggest that fire brick is the optimal choice for enhancing fire resistance in residential buildings.

Synergistic Effect of GO and MXene Enables Ultrasensitive, Reversible, and Self-Powered Fire Warning of a GO/MXene/Chitosan Aerogel.

Graphene oxide (GO)-based fire alarm materials have garnered extensive attention because the thermal reduction of GO to reduced GO (RGO) enables rapid fire warning. However, they suffer from poor flame retardancy, irreversible fire warning, and dependence on an external power supply. Herein, a GO/MXene/chitosan aerogel with a low density of 0.018 g cm-3 and good compressibility has been developed. The experimental results demonstrate that (i) MXene effectively reduces the peak and mean heat release rate of GO, while RGO nanosheets compensate for the structural instability of MXene in the flame due to thermal oxidation into TiO2; as such, long-lasting fire warning (>120 s) has been achieved; (ii) the reducibility and conductivity of MXene contribute to the ultrasensitive response of GO, with a fire response time of 1 s; and (iii) notably, the thermoelectric effect of MXene enables the reversible and self-powered fire warning of the GO/MXene/CS aerogel without an external power supply. Compared to pure MXene/CS aerogel, the presence of GO improves the sensitivity and stability of self-powered fire warning, owing to the formation of the highly conductive RGO nanosheets. The results of this work highlight the cooperation between GO and MXene in realizing ultrasensitive, long-lasting, reversible, and self-powered fire warning.

Investigation of Ammonia/Hydrogen Mixtures and Pilot-Split Strategies in a Laboratory-Scale Radial Swirl Combustor

Abstract The transition to a decarbonized energy future relies on identifying the most suitable alternative fuels that can meet the needs of various energy sectors. While both ammonia and hydrogen are zero-carbon energy vectors, their physical properties and burning characteristics sit on either side of that of natural gas. Hence, mixtures of ammonia and hydrogen are being increasingly looked at as having the potential to fuel current energy systems without requiring significant combustor redesign. However, the combustion characteristics and operation limits for different ammonia/hydrogen mixtures still need to be evaluated. For gas turbine applications in particular, the effect of ammonia/hydrogen mixture composition and operating condition on flame behavior and stability is not well understood. The current work was carried out in a laboratory scale, radial swirl-stabilized turbulent combustor. A systematic study of two ammonia/hydrogen blend ratios (70:30 and 80:20 by volume) and a range of equivalence ratios were tested for different pilot-split ratios, to understand the effect on flame shape, stability and dynamics. Time-resolved pressure and integrated heat release fluctuations were measured to evaluate combustor dynamics, and NH2* chemiluminescence flame images were captured to understand spatial differences in flame structure. When comparing blend ratios, differences were observed in flame macrostructures and combustor dynamics, which could be largely attributed to the considerable difference in the laminar flame speeds of the blends. The addition of pilot generally improved the stability and lean operation for both blend ratios.

Prediction of the Flame Characteristics of an Industrial Gas Turbine Operated With CO2-Diluted Air Through a High-Fidelity Numerical Analysis: A Comparison Between Flamelet Generated Manifolds and Artificially Thickened Flame

Abstract In light of the global commitment to decarbonize industrial processes, carbon capture and storage (CCS) plays a pivotal role in mitigating greenhouse gas emissions from gas turbine (GT) power generation processes. Achieving an efficient GT–CCS coupling requires the employment of high percentages of exhaust gas recirculation (EGR) to maximize the CO2 content at the CCS inlet. Nevertheless, such operating conditions pose critical challenges for conventional combustion systems due to reduced oxygen levels associated with higher EGR, limiting engine operability. To address this challenge, the development of innovative technical solutions is essential to extend the combustor operational capabilities at high EGR rates. For this goal, a significant number of computational fluid dynamics (CFD) simulations are required to identify the flame stability limits across various EGR levels and burner designs. It is imperative, in this context, to minimize computational costs while maintaining high accuracy. In this work, a comprehensive comparative study of an extended version of the flamelet generated manifolds (FGM) and the artificially thickened flame (ATF) model is performed through a large eddy simulation (LES)-based CFD analysis. The investigation is performed within the context of an industrial lean-premixed burner manufactured by Baker Hughes, operating with natural gas and CO2-diluted air at atmospheric pressure. While the extended-FGM has been previously presented by the authors in a study on the same test rig under standard air conditions, the current work aims to extend its application to critical oxygen-depleted conditions, where near-blowout phenomena such as flame liftoff and length elongation may become significantly pronounced. Numerical validation is carried out through a direct comparison of the computed averaged heat release, representing the flame topology, with detailed OH* chemiluminescence images from a test campaign conducted by the technology for high temperature (THT) Lab of the University of Florence. The experimental data will serve as the primary benchmark for assessing the models’ effectiveness in capturing the main dynamics of such critical operating conditions. Furthermore, potential disparities in both thermal and flow fields at the burner exit region between the two models will be discussed.

Experimental investigation on maximum ceiling temperature and longitudinal attenuation in a closed tunnel with an inclined shaft

For tunnel fires with open and closed tunnel ends, the smoke flow pattern and air supply conditions vary considerably, resulting in different maximum excess ceiling temperature (ΔTmax) and its longitudinal distribution (ΔTx). However, few studies have focused on the tunnel closed at both ends with an inclined shaft (typical tunnel structure during construction). Hence, tunnel model 1 (tunnel closed at both ends with an inclined shaft) and tunnel model 2 (tunnel open at both ends) are built for comparison and analysis. The results show that tunnel model 1 has higher ceiling temperatures and slower attenuation than tunnel model 2. Therefore, the ΔTx in tunnel model 1 needs to be re-analyzed in detail. Different inclined shaft slopes, fire heat release rates, longitudinal and vertical fire positions are considered. In tunnel model 1, for h (lifting height of burner surface) = 0, the ΔTmax value tends to be constant for the same heat release rate, irrespective of the longitudinal fire position. For h = 5 cm, the ΔTmax value takes on a rising trend with the fire moving downstream. Moreover, the inclined shaft slope within this study has little influence on ΔTx. As the fire moves downstream, the downstream ΔTx/ΔTmax value decreases more rapidly. From h = 0 to h = 5 cm, the value of ΔTx/ΔTmax drops slightly faster, but the gap is small and can be ignored. Finally, the experimental correlations are proposed to estimate the longitudinal ceiling temperature distribution in a closed tunnel with an inclined shaft.

Surface layer reinforcement modification for wood with high strength and flame retardancy performances

The high-value utilization of low-value wood can effectively address the shortage of wood resource, while also contributing to the global green sustainable development and the implementation of “dual carbon” strategy. The present study employed an innovative technology to achieve controllable surface reinforcement modification of fast-growing poplar wood, resulting in improved strength and exceptional flame retardancy for structural applications. The achievement was realized through a three-step method, involving delignification, impregnation, and surface densification, while minimizing the loss of wood volume. The results demonstrated that surface functional densification can significantly improve the mechanical properties of fast-growing poplar wood, with the modulus of rupture (MOR) and modulus of elasticity (MOE) reaching 140.6 MPa and 11.8 GPa, respectively, representing a 3.4-fold and 2.5-fold increase compared to the control group (CK). The samples were found to possess thin surface-densified layers, while the core layer remained unaltered, thereby exhibiting a sandwich structure with significant disparity in density between the layers, reaching up to a factor of 2. The pores structure of the surface layers underwent significant densification, with a gradual deformation distributed throughout its thickness direction. A process optimized for surface densification involving a 2-hour delignification duration and a pressure of 3 MPa. The sample subjected to surface functional modification exhibited a 90-second delay in the peak of heat release compared with the CK. The heat release rate (HRR) experienced a significant deceleration, accompanied by notable reductions in total heat release (THR) and smoke production rate (SPR). The mechanisms underlying the enhancement of surface functionality were elucidated from the perspectives of physical mechanics, microstructure, and flame retardancy, providing a theoretical foundation for the efficient utilization of fast-growing wood.

Waste to Energy: Combustion, Performance, and Emission Characteristics of Waste Animal Fats/Diesel Blends Premixed with Various Alcohols as Port Fuels

AbstractAnimal flesh is a major food source with economic and industrial value for consumer demand. These meats produced biowaste during and after preparation and use. Chicken intestines make up most of the waste thrown away after processing or frying. This study considers it a biodiesel source. Transesterification turns chicken intestine waste fat oil into biodiesel. This oil is used in compression ignition (CI) engines but performs poorly compared to diesel. Diesel, the base fuel, is mixed with 20% biodiesel. The remaining 10% and 20% of butanol and pentanol are port fuels, improving combustion and lowering emissions in the 5.2 kW, 1500 rpm CI engine. 20% pentanol premixing outperformed butanol premixing, blending, and engine CIWFOB operation. The greater heating value improves combustion, therefore 20% pentanol premixing with blend produces 32.76% BTE, 10.57% more than diesel. It produced 55.18% less CO and 50.92% less smoke than diesel, which has a greater heat release rate (48.86 J/CAD) and peak pressure (64.76 bar). This premixing costs NOx emissions. The CIWFOB blend with 20% pentanol premixing improves engine performance. For SDGs 7, 9, 12, and 13, this study is supported.

High fire-safety epoxy resin with functional polymer/metal–organic framework hybrids

Petroleum-derived bisphenol A-type epoxy resins are highly flammable and vulnerable to fires, limiting their wide applications. The addition of inorganic flame retardants to the epoxy resin improves the flame retardancy of the epoxy resin, but it is difficult to distribute them evenly in the polymer matrix. Here, we introduce flame-retardant epoxy resins supported by the functional polymer/metal–organic framework hybrids. The hybrids, consisted of polyaniline, poly (4-styrenesulfonic acid), and Zr-based organic frameworks, demonstrate effective flame-retardant effects with homogeneous distribution in the epoxy based on their synergistic effects of each material. Compared with pure epoxy resin, the presence of 1 wt% of hybrid flam-retardant remarkably decreases the combustion, the heat release, and the smoke production.

Evaluation of soot emission and wall heat loss for the fuels with high aromatic contents using the coupled analysis of chemical luminescence images with heat flux

The stricter regulations on the sulfur content of marine fuel oil in the general sea area that came into effect in January 2020 have led to a prediction of the increase of light cycle oil with high aromatic contents. The higher aromatic content is expected to result in higher soot in the exhaust gas. During combustion, soot emits radiant heat because of blackbody radiation, some of which passes through the walls of the combustion chamber and is released outside. Therefore, the exhaust emission characteristics and wall heat loss are affected if soot formation during combustion differs depending on the aromatic content of the fuel oil. This study developed an analytical method that combines the temporal and spatial distributions of C2 and OH radicals (these species contribute to soot formation and oxidation) to evaluate the emission and wall heat loss characteristics of different aromatics in fuel oils via combustion and heat flux analysis. The method was applied to test fuels containing different aromatic contents. Two test fuels containing 60 vol% each of toluene (monocyclic) and 1-methylnaphthalene (bicyclic) were evaluated in a rapid compression machine with a 100 mm wall-to-wall distance combustion chamber. The results suggested that the differences in soot emissions were observed because of differences in aromatics, and no differences in the wall heat flux were observed. The distributions of C2 and OH radical luminescence intensities between the walls were examined, and the differences in soot production were attributed to differences in the C2 radical production upstream of the flame in the region of low air entrainment. The lack of difference in the heat flux between the test fuels can be attributed to the the differences in the C2 and OH luminescence intensities, which are related to the heat release rate and heat flux, being almost nonexistent near the walls.

Prediction and Simulation of Biodiesel Combustion in Diesel Engines: Evaluating Physicochemical Properties, Performance, and Emissions

Environmental and energy sustainability concerns have catalyzed a global transition toward renewable biofuel alternatives. Among these, biodiesel stands out as a promising substitute for conventional diesel in compression-ignition engines, providing compatibility without requiring modifications to engine design. A comprehensive understanding of biodiesel’s physical properties is crucial for accurately modeling fuel spray, atomization, combustion, and emissions in diesel engines. This study focuses on predicting the physical properties of PODL20 and EB100, including liquid viscosity, density, vapor pressure, latent heat of vaporization, thermal conductivity, gas diffusion coefficients, and surface tension, all integrated into the CONVERGE CFD fuel library for improved combustion simulations. Subsequently, numerical simulations were conducted using the predicted properties of the biodiesels, validated by experimental in-cylinder pressure data. The prediction models demonstrated excellent alignment with the experimental results, confirming their accuracy in simulating spray dynamics, combustion processes, turbulence, ignition, and emissions. Notably, significant improvements in key combustion parameters, such as cylinder pressure and heat release rate, were recorded with the use of biodiesels. Specifically, the heat release rates for PODL20 and EB100 reached 165.74 J/CA and 140.08 J/CA, respectively, compared to 60.2 J/CA for conventional diesel fuel. Furthermore, when evaluating both soot and NOx emissions, EB100 displayed a more balanced performance, achieving a significant reduction in soot emissions of 34.21% alongside a moderate increase in NOx emissions of 45.5% compared to diesel fuel. In comparison to PODL20, reductions of 20.4% in soot emissions and 3% in NOx emissions were also noted.

Numerical Study on the Influence of the Slope Composition of the Asymmetric V-Shaped Tunnel on Smoke Spread in Tunnel Fire

Asymmetrical V-shaped tunnels often appear in tunnels crossing the river or urban underground road tunnels. The smoke flow inside is affected by a lot of factors. A full understanding of the smoke flow in this kind of tunnel is the basis of the smoke control. In this study, the effects of slope composition and fire heat release rate (HRR) on the longitudinal induced airflow velocity, the smoke back-layering length at the small slope side, and the maximum ceiling temperature were studied by the numerical method. The results show that when the fire occurs at the slope change point of the V-shaped tunnel, the maximum ceiling temperature decreases with the increase in the slope of the large-slope side tunnel. The longitudinally induced velocity is primarily related to the slope of the large-slope side tunnel and the fire HRR. When the slope difference between the side tunnels or the slope of the large-slope side tunnel is large, the smoke in the small-slope side tunnel flows back toward the fire source after reaching its maximum dispersion distance and then reaches a quasi-steady state. The smoke back-layering length is mainly affected by the slope and length of the large-slope side tunnel. When the slope of the large-slope side tunnel is 9%, the induced airflow velocity from the small-slope side can prevent the spread of smoke. The empirical models of the smoke back-layering length and the longitudinal induced airflow velocity in the small-slope side tunnel are drawn, respectively, by the theoretical analysis and the numerical results. This study can provide technical support for the design and operation of smoke control systems in V-shaped tunnels.