Lower Heat Release Rate Research Articles

Experimental assessment of power generation using a compression ignition engine fueled by farnesane – A renewable diesel from sugarcane

This work reports the experimental study of a single-cylinder compression ignition engine fueled with a renewable diesel from sugarcane called farnesane. The engine is representative of current small-scale power generation in very isolated rural areas existing in Brazil. A complete experimental assessment was made on engine combustion, performance, and pollutant emissions at 1800 rpm under different loads (from 4 to 7 bar IMEP). Results showed reduced values for the ignition delay, in-cylinder peak pressure and mean temperature when using farnesane compared to conventional diesel fuel, as well as lower heat release rate peaks at the premixed combustion phase and shorter diffusion combustion duration. Physicochemical properties differences, such as cetane number, H/C ratio and the biofuel paraffinic structure led to interesting emission behavior. Farnesane reduced NOx emissions by up to 34% (and further 48.6% using EGR), and particulate matter by up to 92%. Despite the higher in-cylinder peak pressure and greater fuel conversion efficiency for diesel fuel at the highest load, the biofuel exhibited gains of up to 3.3% in combustion efficiency and 5.9% in fuel conversion efficiency at intermediate and lower loads. Such improvements are closely related to the HC and CO levels depletion and the absence of aromatic compounds.

Tannin-furanic foams modified by soybean protein isolate (SPI) and industrial lignin substituting formaldehyde addition

Soybean protein isolate (SPI) was tested in this study as a crosslinker and formaldehyde substitute for preparing high biomass content sustainable rigid tannin-furanic-SPI (TFS) and lignin-tannin-furanic-SPI (LTFS) versatile foams. Additionally, flame retardancy was improved by lignin used as a natural fire-retardant. Fourier-transform infrared spectroscopy (FT-IR), coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF-MS), revealed a covalent cross-linking reaction between tannin and SPI. TFS and LTFS foams showed by scanning electron microscopy (SEM) a closed cell structure without any pores. The incorporation of SPI resulted in enhanced mechanical properties and reduced pulverization ratios, improved thermal stability and increased thermal conductivity (approximately 0.042–0.044 W/m K compared with control foam. Furthermore, the TFS foams exhibited outstanding flame retardancy and suppressed smoke generation while undergoing combustion. These results were supported by a higher limiting oxygen index (LOI) value, a lower heat-release rate, and a higher char residue, obtained by LOI and cone calorimetry. The addition of lignin further enhanced the thermal properties and flame retardancy of TFS foams although it decreased their mechanical performance. The TFS and LTFS foams were environmentally friendly, as shown by the low formaldehyde emission measurements. This novel sustainable TFS foam appears to have a good potential for industrial application.

Large eddy simulation on flame topologies and the blow-off characteristics of ammonia/air flame in a model gas turbine combustor

Ammonia (NH3) is recently identified as one of the suitable energy carriers in hydrogen energy system. However, regarding NH3 as a fuel is still facing several challenges which limit the direct use on modern combustion systems. The main challenge is the difficulty to stabilize NH3/air flames. To reveal and analyze the stabilization mechanism and the characteristics during blow-off processes in a swirl combustor, large eddy simulation with thickened flame model was performed to resolve the three dimensional swirl NH3/air flame. The CH4/air flame was also performed for comparison. The reacting flow fields and the flame structures were measured by PIV and OH-PLIF technique respectively. For NH3/air flame, flame fronts are burning to the higher equivalence ratio region, which leads to a larger trend of extinguishing. The curvature distribution at flame root is mainly dependent on the flame characteristics. Downstream the flows, the curvature distribution is mainly influenced by the flow field characteristics. Though the value of wall heat loss of NH3/air flame is less than that of CH4/air flame, the heat loss still shows greater influence on NH3/air flame stabilization when considering the lower heat release rate of NH3/air flame. The blow-off of CH4/air flame is mainly caused by the decreasing HRR and heat loss, while for NH3/air flame, it is a combined effect of the excessive stretch, the reduction of HRR as well as the greater heat loss effect.

Phosphorus-Free Vanillin-Derived Intrinsically Flame-Retardant Epoxy Thermoset with Extremely Low Heat Release Rate and Smoke Emission

Recently, the development of bio-based intrinsically flame-retardant epoxy thermosets has attracted increasing interest for the replacement of petroleum-based epoxy thermosets in fields that demand...

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.

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.

Thermal degradation and flame retardant mechanism of sulfonated polyoxadiazole fibers modified by metal ions

The sulfonated polyoxadiazole (SPOD) flame retardant fibers are prepared by wet spinning and modified by metal ions (Na+, Ca2+, Ba2+, and Mg2+). The structures of SPOD fibers are characterized by Fourier transform infrared spectrometry (FTIR), elements analysis (EA), inductively coupled plasma emission spectrometry (ICP), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Results show that sulfonate groups were successfully grafted on the POD fiber polymer, and metal ions are adsorbed in the fiber by physical and chemical adsorption. The micro-scale combustion calorimeter (MCC), limiting oxygen index (LOI), and UL-94 vertical burning tests are used to test the flame retardant properties of the fibers. Results show that the Mg-SPOD had the best flame retardant performance with LOI of 40% and the lowest heat release rate (HRR). The thermal degradation mechanism of the fiber is analyzed by thermogravimetric analysis coupled with infrared spectrometry (TG-FTIR), and the char residues were investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The rapid and sharp emission of non-flammable SO2 and high content char residue covered with dense MgO and MgSO4 improve the flame retardant properties of Mg-SPOD fibers significantly.

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.

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.

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.

A novel ceramifiable epoxy composite with enhanced fire resistance and flame retardance

A novel epoxy composite with flame retardance and fire resistance was prepared by adding silicate glass frit (SGF) and ammonium polyphosphate (APP) into the epoxy resin. In the combustion test, epoxy composites displayed obvious flame retardance feature, showing much lower heat release rate, total heat release and total smoke production than epoxy resin. The composite residue formed at 900 °C had a flexural strength of 19.05 MPa. In addition, possible mechanisms for the phase separation and crystallization reactions at high temperatures were also investigated in detail through thermogravimetric analyzer, X-ray diffraction, X-ray photoelectron spectrometer, and scanning electron microscopy. It was suggested that phosphorus element tends to migrate to the surface of the composite residue during firing process, and sodium element from SGF is selectively combined with the phosphorus element to obtain crystalline phases. With this unique phase separation and crystallization reactions, the fire resistance of the epoxy composite was significantly improved.

Effect of hydrogen and 1-Hexanol on combustion, performance and emission characteristics of CRDI CI engine

The effect of hydrogen and 1-Hexanol on engine characteristics was scrutinized in a diesel engine. The experiment was conducted at a variable load of 20% to 80% in step of 20% load and speed of the engine (2000 rpm) was constant throughout the experiment. Initially, the effect of injection time (9°BTDC, 12°BTDC and 15°BTDC) on engine characteristics were studied with 30% 1-Hexanol as fuel and compared with diesel fuel operation. 1-Hexanol showed excellent performance and emission characteristics at advanced injection time compared to standard and retard injection time. Then 10LPM of hydrogen was used in a dual fuel mode with 30% of 1-Hexanol at 15°BTDC. At 80% load, the hydrogen enrichment showed 6.77% higher cylinder pressure and 1.50% lower heat release rate compared to neat diesel. The Hydrogen enrichment improves the thermal efficiency by 5% at 80% load compared to neat diesel and also reduces the nitrogen oxide by 6.66% and hydrocarbon emission by 10% compared to neat diesel. From the experiment, it was noted that 1-Hexanol performance well at advanced injection time and further increment in the performance was made with hydrogen. It is concluded that 1-Hexanol and hydrogen will be a sustainable renewable energy source.