Low Heat Release Research Articles

Tannic acid based super‐intumescent coatings for prolonged fire protection of cardboard and wood

AbstractTannic acid (TA) has gained increased attention in recent years for its application in fire safety due to its natural abundance and char‐forming ability. In this paper, TA‐based composites were developed and evaluated against control composites containing pentaerythritol (PER), a common intumescent char‐forming agent. Individual component analysis was performed to provide a fundamental material understanding, followed by compounding in epoxy resin with other intumescent ingredients for intumescent testing (especially compared against PER control). In all TA systems, time to failure was elongated from seconds or minutes to over 15 min (up to 27 min). Quantitative analysis followed using cone calorimetry. TA composites displayed lower peak heat release values (211 vs. 108 kW/m2), lower total heat release values (37.2 vs. 24.4 MJ/m2), and lower fire growth rates (2.43 vs. 1.27 kW/m2s−1) relative to PER composites. X‐ray photoelectron spectroscopy analysis revealed that TA char is more carbonaceous, containing 54.71 at% C (relative to only 39.63 at% C in PER char). This work presents TA‐containing composites that offer superior fire protection as compared to previous reports using TA composites and hence offer significant advancement in fire protection related and packaging industries.

Enhanced residue stability and strength of epoxy-based coating for fire protection via ceramifiable strategy

A combination of talc and ammonium polyphosphate (APP) was used to fabricate the novel epoxy-based fire resistive coatings via ceramifiable strategy designed for steel substrates. The effects of individual and various combinations of fillers on the fire protection, dimensional stability and strength of coating residues fired at high temperatures were evaluated. The optimized formulation (ETA4) exhibited much lower heat release rate, total heat release and smoke production rate, indicating good flame retardance feature. The results of fire protection test indicated that the backside temperature of steel substrate with ETA4 coating decreased significantly (below 200 °C). After firing at 1000 °C, creamic-like foam residue was formed and it showed excellent dimensional stability and good mechanical strength. Furthermore, the possible fire resistive mechanisms of coatings at high temperatures were also proposed by performing different measurements. The decomposition products of APP-cohered talc were obtained at high temperatures, accompanied by the gradual disappearance of talc phase and generation of crystallization reaction. Finally, a ceramic-like residue was formed, leading to enhanced stability of coating residues.

Conversion of natural gas jet flame burners to hydrogen

In a study of conversion from CH4 to H2, jet flame characteristics of these gases and their blends are compared on a burner diameter scale of mm. Low velocity H2 and CH4 jets, burned on pipes of different diameters, indicate higher blow-off limits for H2, but lower heat release rates, a consequence of its lower specific energy. Compensation for this might be obtained through increased H2 flow velocity, or a small increase in pipe diameter. Blended CH4/H2 flames have lower heat release rates than CH4 alone, yet small proportions of H2, with CH4 might still be burned, on a CH4 burner. Throughout, fundamental understanding is enhanced through two dimensionless groups: laminar flame thickness normalised by burner diameter, δk/D, and the dimensionless flow number, U∗. These suggest an optimal role for H2 combustion, utilizing its high acoustic and blow-off velocities, in high intensity, subsonic, combustors, at low δk/D, and high U∗.

Performance, emission and combustion characteristics of various biodiesel blends

This experimentation explores the usage of three types of biodiesel consisting of palm, jatropha and cottonseed incorporated in a single-cylinder four-stroke CI engine to evaluate the performance, emission and combustion indices. The objective of this study is to prepare biodiesel blends of three types: (i) primary, (ii) binary and (iii) ternary, and investigate their behaviors to identify the optimal blends that produce the lowest emissions and adequate performance with no significant engine modifications. Experimental investigations carried out in this study indicate that by increasing biodiesel quantity in the blend, a rise in brake thermal efficiency and a marginal increase in brake specific fuel consumption were deduced. P30 blend was superior among the biodiesel blends, showing a maximum thermal efficiency of 36.83%. Biodiesel blends were reported to emit lower NOx emissions at higher loads and increased NOx at low loads compared to diesel. Culminated values of NOx were shown by CS30 (601 ppm); similarly, binary blend PJ30 showed a curtailed amount of NOx (497 ppm) at 20 N-m loading. Lower emissions of unburnt hydrocarbon and carbon monoxide are noticed for biodiesel blends with values lying in a range of 35–40 ppm and 0.04%, respectively, while the smoke emissions escalated for biodiesel blends reaching up to 76% for PJCS20. Among combustion indices, biodiesels showed lower heat release rate (HRR) and lower maximum pressure than diesel and increasing blend ratio resulted in lower HRR and higher pressure. P10 blend was observed to be providing better performance and emissions (lowered HC and CO) compared to all other blends.

Eco-friendly synergistic cross-linking flame-retardant strategy with smoke and melt-dripping suppression for condensation polymers

Conventional methods to improve the flame retardancy of polymeric materials usually involve the use of flame-retardant elements such as Cl, Br and P, however, their use may bring more smoke and toxic gases hazards, and more importantly, cause non-negligible environmental and ecological problems. In this work, we put forward a novel green strategy that eliminates the use of any conventional flame-retardant elements to improve the flame retardancy by incorporating a synergistically cross-linkable structure (named PN) containing phenylacetylene and phenylimide groups. The resulting PN copolymer exhibited an excellent 55% lower smoke release rate and 68% lower heat release rate than the pure polymer, as well as a high LOI value of 32% and UL-94 V-0 rating with excellent anti-dripping performance. TG-DSC, rheological and FTIR results proved the high cross-linking ability of the PN copolymer due to the synergistic cross-linking effect between the “imide-isoimide” rearrangement of phenylimide and the “self-cross-linking” of phenylacetylene. The SEM, Raman and Py-GC/MS results further upheld the condensed phase flame-retardant mechanism. This eco-friendly synergistic cross-linking strategy provided new perspective for the design and synthesis of polymeric materials with excellent flame retardancy, great anti-dripping performance, and low release of heat, smoke, and toxic gas.

Microstructure, Thermal Conductivity, and Flame Retardancy of Konjac Glucomannan Based Aerogels.

With abundant renewable resources and good biodegradability, bio-based aerogels are considered as promising insulating materials for replacing the conventional petroleum-based foam. In this study, konjac glucomannan (KGM)-based aerogels were prepared as thermal insulation materials via a convenient sol–gel and freeze-drying progress with different content of plant polysaccharides, proteins, and wheat straw. The morphology, thermal conductivity, and flame retardancy of KGM-based aerogels were determined. The KGM-based aerogels showed a uniform three-dimensional porous microstructure. The addition of wheat straw could significantly reduce the pore size of aerogels due to its special multi-cavity structure. KGM-based aerogels showed low densities (0.0234–0.0559 g/cm−3), low thermal conductivities (0.04573–0.05127 W/mK), low peak heat release rate (PHRR, 46.7–165.5 W/g), and low total heat release (THR, 5.7–16.2 kJ/g). Compared to the conventional expanded polystyrene (EPS) and polyurethane (PU) foam, the maximum limiting oxygen index (LOI) of KGM-based aerogels increased by 24.09% and 47.59%, the lowest PHRR decreased by 79.37% and 94.26%, and the lowest THR decreased by 76.54% and 89.25%, respectively. The results demonstrated that the KGM-based aerogels had better performance on flame retardancy than PU and EPS, indicating high potential applications as heat insulation in the green advanced engineering field.

Effect of Cyclotriphosphazene-Based Curing Agents on the Flame Resistance of Epoxy Resins.

Epoxy resins are characterized by excellent properties such as chemical resistance, shape stability, hardness and heat resistance, but they present low flame resistance. In this work, the synthesized derivatives, namely hexacyclohexylamino-cyclotriphosphazene (HCACTP) and novel diaminotetracyclohexylamino-cyclotriphosphazene (DTCATP), were applied as curing agents for halogen-free flame retarding epoxy materials. The thermal properties and combustion behavior of the cured epoxy resins were investigated. The obtained results revealed that the application of both derivatives significantly increased flame resistance. The epoxy resins cured with HCACTP and DTCATP exhibited lower total heat release together with lower total smoke production compared to the epoxy materials based on conventional curing agents (dipropylenetriamine and ethylenediamine). Comparing both derivatives, the HCACTP-cured epoxy resin was found to provide a higher flame resistance. The designed novel class of epoxy materials may be used for the preparation of materials with improved flame resistance properties in terms of flame spreading and smoke inhibition.

Properties of alkali-activated mortars with salt aggregate for sealing structures in evaporite rock

Concrete structures for sealing of tunnels in the host rock are an essential part of systems for nuclear waste storage. However, concretes based on blended cements or magnesium oxychloride cements, which are commonly considered for this application, can deteriorate severely due to a significant heat of hydration and associated deformation and cracking. Alkali-activated materials (AAMs) offer a potential solution to this problem because of their low heat release during hardening. To explore their suitability for the construction of sealing structures in evaporite rock, various AAMs with salt aggregate were studied regarding fresh properties, heat release, mechanical properties and microstructure. The heat of reaction of the AAMs was up to 55% lower than that of a blended cement designed for sealing structures, indicating significant benefits for the intended application. Other relevant properties such as mechanical strength and permeability depended strongly on the mix-design of the AAMs and curing conditions.

Temperature-dependent rheological, mechanical and hydration properties of cement paste blended with iron tailings

With this research, the authors intend to investigate the effects of particle size and curing temperature on the properties of cement paste blended with iron tailings (IT). The research work found that the partial replacement of ordinary Portland cement (OPC) by iron tailings (IT) accelerated the hydration of cement in the initial stage, but low cumulative heat release was noticed after long curing. Both the yield stress and plastic viscosity of fresh cement paste blended with IT were decreased due to the IT replacement. The initial setting was found to be delayed by the addition of IT. Besides, the introduction of IT led to enhanced pore volume resulting in reduced UCS and the UCS decreased with the increase of IT particle size. On the other hand, the properties of cement in the presence of IT were found to be more temperature dependent. Increasing temperature accelerated the early-stage hydration of paste with IT more strongly than that of the control paste. Temperature rising was more favorable to the UCS development of samples with IT replacement. The grow rates of both yield stress and plastic viscosity increased due to the replacement of OPC by IT when the temperature rising.

Preparation of a novel lignin-based flame retardant for epoxy resin

A renewable and eco-friendly lignin-based flame retardant was prepared to improve the flame retardant performance of epoxy resin (EP) by green and convenient one-step reaction of Ammonium Polyphosphate (APP), Melamine (MEL) and Al-lignin. Thermal and flame retardant properties test results showed that the properties of epoxy resin were significantly improved after adding 20% of flame retardant. Its carbon residue increased by 15.3 wt % and limit oxygen index value increased from 26.7% to 36.1%. In addition, it also showed excellent smoke suppression effect and low heat release rate. Its total smoke production (TSP) was 9.9 m2 and total heat release (THR) rate was 53.1 MJ/m2. In contrast, the TSP and THR of EP were much higher than 9.9 m2 and 53.1 MJ/m2, respectively. Kinetic analysis showed that the conversion rate ranging from 0.05 to 0.85 corresponded to activation energy between 97.83 kJ mol−1 and 327.45 kJ mol−1. Flame retardant mechanism showed that the performance of this renewable and eco-friendly lignin-based flame retardant was excellent in fire suppression and smoke suppression.

Numerical Analysis of the Effects of Direct Dual Fuel Injection on the Compression Ignition Engine.

In this work, the influence of direct dual fuel injection on a compression ignition engine fueled with gasoline and diesel has been investigated. To do this, closed cycle combustion simulations have been performed. Gasoline has been supplied through port injection and early direct and late direct injection to achieve fuel stratification and emission reduction. Simulations have been done for various start of injection (SOI) timings of diesel fuel. A detailed discussion on a low temperature heat release (LTHR) mechanism has been done. Results revealed that the maximum gross indicated thermal efficiency (GITE) of 39% is obtained for port injection of gasoline mode. Direct dual fuel combustion (type 2) (DDC2) mode shows approximately 2% and 38% less GITE and oxides of nitrogen (NOx), respectively, and 40% more soot as compared to the port injection gasoline mode. DDC2 mode shows lower oxides of carbon and hydrocarbon emissions as compared to other dual fuel modes. More than 99% of combustion efficiency and less maximum pressure rise rate have been noticed in the DDC2 case. Strong LTHR and high temperature premixed combustion region have been found in advanced SOI timing cases (in DDC2). In-cylinder contours for the DDC2 case show that diesel and gasoline fuels combusted successively cause less in-cylinder temperature than that for the conventional dual fuel combustion case.

Combining Mechanical Fortification and Ultralow Flammability in Epoxy Networks

AbstractMultifunctional organophosphorus additives present opportunities to engineer epoxy networks with both enhanced mechanical properties and ultralow flammability. This paper describes a systematic investigation of the effect of dimethyl methylphosphonate (DMMP) on the mechanical and heat release properties of both conventional and inherently low flammability epoxy resins. The findings demonstrate that integration of DMMP into epoxy networks produces materials with outstanding flame retardance and increased stiffness. Thermogravimetric analysis of DMMP‐containing networks show that DMMP promotes considerable char formation, with char residue reaching very high levels, up to 55%, for DMMP‐containing deoxybenzoin networks. Microscale combustion calorimetry of all the DMMP‐containing networks exhibit 50% lower heat release capacity and total heat release rate values relative to formulations without DMMP. Moreover, vertical burn tests demonstrate that DMMP‐containing formulations burn slowly and self‐extinguish. Morphological analysis of the charred DMMP‐containing formulations shows a porous structure and mechanical characterization reveals 50% higher elastic modulus, and comparable yield stress, for networks containing DMMP relative to those without DMMP. Overall, this organophosphorus additive represents an opportunity to combine materials chemistry with mechanical enhancement mechanisms to achieve low heat release properties without the need for halogenated flame‐retardant additives.

Hierarchical Cellular Poly(m‐phenylene isophthalamide) with High Flame Retardancy, Mechanical Robustness, and Heat Resistance at Extreme Situation

AbstractHigh‐performance cellular foams with superior mechanical properties and heat resistance are urgently needed to fulfill the applications in extreme environments. However, they are difficult to be prepared because of low gas diffusion rate in high‐performance polymers. In this work, a facile solution‐foaming strategy to prepare multifunctional foams based on poly(m‐phenylene isophthalamide) (PMIA) is reported. The achieved PMIA foams show a hierarchically cellular structure containing macropores and mesopores. Due to their high porosity, the PMIA foams exhibit low thermal conductivity (0.0447–0.0498 W m−1 K−1) and high sound absorption coefficient at different frequency. A bimodal distribution on acoustic absorption is observed. With a bulk density range of 0.089–0.122 g cm−3, PMIA foams possess compressive moduli of 3.2–14.2 MPa and bending strength of 1.1–2.1 MPa, respectively. Moreover, they exhibit a recoverable deformation of 55.4% after 10 cycling 10% strain compressions and maintain a dimensional stability under harsh environment (–196 to 250 °C). Despite generated byproducts like polyurea, they still show a limiting oxygen index (25.2–26.3%) and relatively low heat release rate (178.3 kW m−2). This work provides a facile strategy to efficiently prepare high‐performance PMIA foams for broad application prospects.

Development of a combined flash and binary geothermal system integrated with hydrogen production for blending into natural gas in daily applications

This paper concerns a novel integrated system for geothermal-based power and hydrogen generation and blending of hydrogen into natural gas to feed household devices, such as gas stove and combi boiler. The system includes a combined flash and binary geothermal subsystem, an alkaline electrolyzer, a blending unit and a combustion reactor. The design and modelling of the proposed system are conducted with Aspen Plus software. The overall energy and exergy efficiencies of the investigated system are found to be 46.8% and 77.9%, respectively. The highest exergy efficiency belongs to January as 86.63% when the average ambient temperature is 5.8 °C, while the lowest exergy efficiency belongs to July as 76.98% when the average ambient temperature is 27.2 °C in Denizli, Turkey. The hydrogen fraction into natural gas is changed from 0% to 20% and analysed the combustion of the blend. The results show that syngas composition has higher oxygen output rate and lower carbon dioxide, steam and heat release rates with higher hydrogen addition.

Use of Am-241 in RTGs

Currently, transuranic elements are a serious problem. They are formed in spent nuclear fuel as a result of the operation of reactors. These elements have a sufficiently high radioactivity and a huge half-life, thus they remain dangerous for a very long time and must be burned out on specialized reactors. However, not all of them can be classified exclusively as waste. Am-241, which has a low heat release due to its alpha decay, can be used as a radionuclide source for RTGs. However, this nuclide can maintain a fission chain reaction and emits gamma rays as a result of decay. The article investigates some properties of possible devices, as well as an assessment of the radiation protection for such devices.

Combining Low-Emissivity Thin Coating and 3D-Printed Original Designs for Superior Fire-Protective Performance.

Three-dimensional (3D) printing is a very flexible process to design various objects of original shapes. Previous works highlighted the preparation of new multimaterials composed of an original sandwich structure made of the ethylene vinyl acetate copolymer containing 30 wt % of aluminum trihydroxide in which a hydrogel phase made of agar and vermiculite was incorporated. This original material revealed an extremely low heat release rate (HRR) (with a reduction of 86 and 64% with regard to the peak of the HRR and total heat release, respectively, when compared to the same sample without hydrogel filling) during its heat exposure at 50 kW/m2 according to the mass loss cone calorimetry test. However, the time to ignition (TTI) of this material was not improved. This work consequently focuses on delaying the time to ignition of this hydrogel sandwich 3D-printed multimaterial. Solution consists in depositing by pulsed DC magnetron sputtering a low-emissivity thin coating on the exposed skin surface. This coating reflects most of the infrared rays responsible for heat absorption and thus delays the ignition of the underlying material. The thermal resistance performances of this coated sandwich 3D-printed multimaterial were evaluated, and a mechanism of action was proposed to explain the dramatic enhancement of the properties.

Effect of sidewall on the flame extension characteristics beneath a ceiling induced by carriage fire in a channel

Laboratory tests were firstly conducted in a reduced scale channel to investigate the conditions for flame ejections when the carriage was at the centre of the channel. The ejected flames were recorded by two cameras and the temperature inside the enclosure and on the ceiling were measured. The lower critical heat release rate (HRR) which would result in intermittent flame ejection and upper critical HRR which would lead to continuous external flame were analysed with regards to their variations with the ventilation factor. Correlations for the longitudinal and transverse flame extension lengths and flame extension area beneath the ceiling were proposed. Subsequently further experimental investigations were conducted to study the effect of sidewall constraint on flame extension by changing the position of the carriage along the transverse direction to vary the distance between the sidewall and the carriage opening, which was also systematically varied. With the decrease of the sidewall-to-opening distance, the longitudinal flame extension length was found to increase whereas the transverse flame extension length decreased. The changes are most significant when sidewall-to-opening distance was relatively small. These trends are different from those observed in previous wall-attached fires or corner fires in channels, where the flame extension length beneath the ceiling firstly increased with the decrease of sidewall-source distance, and then decreased slightly when the fire source was attached to the wall. New correlations were proposed to account for the effect of sidewall-to-opening distance for longitudinal and transverse flame extension lengths under the ceiling. They captured well the measurements for all the present cases and some published cases not used in their derivation, demonstrating the potential for fire safety engineering applications.

Analysis of low-temperature chemistry in a turbulent swirling spray flame near lean blow-out

An n-dodecane swirling spray flame from the Cambridge flame series is simulated using large-eddy simulation (LES) at conditions near the lean blow-out (LBO) limit. The focus of this study is to examine effects of low-temperature chemistry (LTC) and spray evaporation in turbulent spray combustion. To this end, a first simulation is performed using a finite rate chemistry model with a 55-species skeletal mechanism including LTC in a fully compressible Eulerian-Lagrangian formulation. A second simulation is performed using the same formulation, but with the LTC chemical sub-mechanism deactivated. The interactions of spray and gas-phase mixing and combustion are investigated through the consideration of mean and instantaneous LES results. Chemical explosive mode analysis (CEMA) is extended to account for droplet evaporation in the context of spray combustion, the results of which reveal that the flame is dominated by non-premixed combustion without significant auto-ignitive behavior. CEMA results further show that the effect of spray evaporation on the reaction is two-fold, namely to inhibit reaction near the injector through heat absorption, and to facilitate reaction further downstream by supplying fuel to the gas phase. Mixture fraction-conditioned analysis is then performed to evaluate the importance of LTC in the turbulent spray flame, showing its effect on heat release despite the flame not exhibiting auto-ignitive behavior. A polar mapping is proposed for analyzing the complex interplay of low and high temperature chemistry heat release. The results have consequences for numerical modeling of spray combustion systems where LTC effects are commonly neglected.

A study of the spray ignition characteristics of hydro-processed renewable diesel, petroleum diesel, and biodiesel using a constant volume combustion chamber

The spray ignitions of hydro-processed renewable diesel (HRD), petro-diesel and biodiesel were investigated in a constant volume combustion chamber at low combustion temperatures (LTC) spanning from 600 K to 818 K and various chamber pressures of 10, 15, and 20 bar. These experiments were determined by the reactivity of the fuel and the spray ignition acceleration under engine-related operating conditions. It was found that the first stage and total stage ignition delays were shortened exponentially with increases in the chamber temperature. The HRD fuel was found to obtain the fastest ignition delay compared to diesel and biodiesel. The ignition delays of biodiesel and diesel were similar at the highest chamber pressure and temperature even though biodiesel has a slightly higher cetane number. HRD had the highest reactivity among the fuels, followed by diesel and biodiesel. Additionally, the global equivalence ratio under the lean condition resulted in a lower heat release rate amplitude. Slower fuel reactivity was observed with the maximum amount of carbon double bond in the biodiesel at the lower chamber temperature. The diesel with isomer chain branching had longer reactivity compared to the HRD, which obtains mostly normal alkanes. The NTC zone was clearly observed at a chamber pressure of 15 bar. The region was extended from 725 K to 781 K for the HRD fuels and from 725 K to 818 K for both diesel and biodiesel fuels.

Lifted flame in fire whirl: An experimental investigation

This paper presents an experimental study on the flame and flow characteristics of the lifted flame in a fire whirl. A small-scale rotating screen facility was used for experiments with finely controlled imposed circulation (Γ) and heat release rate (Q˙=2.0−8.0kW), by using methane as the fuel. The instantaneous three-dimensional velocity fields in the vertical plane passing through the flame centerline were measured by stereo particle image velocimetry (SPIV) technique. It is found that the flame of fire whirl can be lifted off the burner under relatively weak Γ, for which, the lifted flame is mainly blue partially premixed flame under a certain lower heat release rate (Q˙=2.0kW in this work), while when the heat release rate is beyond a certain value (Q˙≥4.0kW in this work), the lifted flame is structured by blue partially premixed flame at the bottom and yellow diffusion flame downstream. For these two different lifted flames, the flame length and the flame base diameter have significantly different dependence on Γ. Experimental data indicate that under a specified Q˙, the flame liftoff height firstly increases slowly and then decreases quickly with increasing Γ after reaching the maximum value. The maximum liftoff height decreases with Q˙ slightly and Γ dominates the variation of liftoff height. It is also found that the instantaneous axial velocity in the lifted fire whirl increases quickly in the bottom inflow layer, then decreases with height upstream of the flame base and increases again in the hot flame region. The flow field diverges as the instantaneous flame base is approached. The mean axial velocity conditioned on the instantaneous lifted flame base generally increases with Q˙ and is less than two times the maximum laminar flame speed. The lifted fire whirl and the triple flame share similar characteristics of the flame front and velocity fields.