Low Burning Rate Research Articles

Smoldering characteristics of high bulk density peat

Low-density peats from many countries have long been studied by many authors. They are mostly forest and moss peats. Different peat types, from different locations in the world, may present degradation behavior that differs significantly. Bulk density, which is one the most important physical parameters governing the smoldering dynamics of solid fuels, varies among countries’ peatlands. This work compares experimental data for low (200 kg m−3) and high (450 kg m−3) bulk density peat smoldering in a test bench. Peat samples with different densities, organic matter contents, and particle sizes were considered in this work. The physicochemical characterization included ultimate analysis, ash composition, the density of the solid, and thermogravimetric and differential thermogravimetric analysis. The influences of the organic matter content, as well as the bulk surface area to volume ratio on peat burning, are also discussed. It is showed that, for the same organic matter and bulk surface area to volume ratio, the high bulk density peat burning rate is as low as one-third of the low bulk density peat burning rate. Once the High Heating Value of both peats is found similar, this lower burning rate is related to chemical kinetics, which shows higher oxidation temperature, around 500 °C for the high bulk density peat, and 300 °C for the low bulk density peat. For the high bulk density peat, the higher the bulk surface area to volume ratio the higher both horizontal and vertical smoldering spread rates.

Investigation on premixed methane/air combustion characteristics in heat recirculation micro combustor with separating cylinder

Nowadays, the low combustion efficiency and combustion instability are the two major challenges in the design and development of meso/micro combustor. Heat recirculation and catalytic combustion are one of the best methods to solve those problems. The low combustion rate far from catalytic surfaces in micro combustor is a serious issue in catalytic combustion. To solve this problem, the novel micro combustor with separating cylinder is proposed. The fuel combustion efficiency in HRMCC is higher than that of HRMC at the same inlet velocity. When the inlet velocity is 0.5 m/s, the combustion efficiency gap between HRCC and HRMCC reaches up to the maximum value of 7.4 %. The methane conversion per unit catalyst in HRMCC is higher than that of HRMC, and it also increases as inlet velocity increases. Besides, the location of separating cylinder in HRMCC does not show obvious influence on combustion efficiency and methane conversion per unit catalyst. However, it has a great influence on the size of high temperature region in HRMCC. The high temperature area size becomes larger as the separating cylinder in HRMCC becomes further from outlet.

Combustion performance of composite propellants containing core-shell Al@M(IO3)x metastable composites

Aluminum (Al) has been widely used in solid composite propellants (SCPs) to increase the specific impulse. However, Al always subjects to coalescence, sintering to large agglomerations during combustion of SCPs resulting in larger two-phase flow losses. Herein, core-shell μ-Al@M(IO3)x composites have designed and synthesized as a replacement for micron-sized Al (μ-Al) in the Al/AP/RDX/HTPB propellant with tunable combustion behavior. The results show the thermal reactivity and heat releases of SCP are largely enhanced by using these novel metal-based composites. With the inclusion of μ-Al@EGCG@Fe(IO3)3 (EGCG: Epigallocatechin gallate), the major exothermic peak is reduced by 29.1 °C compared to the reference propellant with a heat release increase up to 5475 J g−1, exceeding that of the reference sample (86 J g−1 higher). The burn rates are increased with the inclusion of μ-Al@(MIO3)x, while the pressure exponent is higher. The SCP-1 (0.3), SCP-2 (0.18) and SCP-4 (0.25) that have relatively low pressure exponent and high burn rates are good candidates for future applications. The major condensed combustion products (CCPs) of these SCPs are Al2O3, Al2.81O3.56N0.44, Al4C3, Al2OC, AlN and C7H18ClN. The agglomeration can be reduced with a minor inclusion of μ-Al@M(IO3)x due to the enhanced interfacial reactions, and the average CCP sizes (0.5 μm for SCP-1 and SCP-4) are even smaller than that of initial μ-Al (1.2 μm).

Fabrication and investigation of 3D-printed gun propellants

Gun propellant is the energy source of barrel weapons. A 3D printed gun propellant based on “Stereolithography (SLA)” was developed to overcome the limitation of traditional extrusion technologies. A demonstration formulation composed of 50 wt% 1,3,5-Trinitro-1,3,5-triazinane (RDX), 25 wt% epoxy acrylate, 12.5 wt% N-n-butyl-N-(2-nitroxyethyl) nitramine (Bu-NENA), 12.5 wt% reactive diluent and additives were fabricated. The 3D-printed propellants were characterized in terms of inner structure, mechanical strength and combustion behavior. Finally, a ballistic assessment of multi-perforated disk (MPD) propellant was carried out using a 30 mm test gun. The results showed that no signs of porosity or defects existed in the propellant printed by the SLA technique. The compression strength and tensile strength were 21.6 MPa and 7.3 MPa, respectively. The 3D-printed propellant exhibited a relatively low linear burn rate and a high pressure exponent value of 1.46. In the gun test, a muzzle velocity of 420 m/s was achieved without crushing the MPD.

Combustion of Nanoaluminum and Magnesium in Fuel‐Rich Propellants

AbstractFuel‐rich propellants are used in ducted rocket technology. The reduced content of oxidizer and the use of atmospheric air improve the gravimetric specific impulse far above the level of standard rocket motors, granting longer operating range. Peculiar requirements of ducted rockets favor either high or low‐pressure exponent propellants, depending on the pressurization strategy of the gas generator. The introduction of metal additives further improves the volumetric specific impulse and plays in favor of system compactness but combustion is difficult due to the intrinsic lack of oxidizer. Agglomeration of metal and low burning rates are observed. In this paper, the combustion of a set of fuel‐rich propellants with nanoaluminum and magnesium is investigated. The reported data set comprises ideal performance, burning rate, incipient agglomeration, and metal content of the agglomerates.

Preparation of Al/Ni Reactive Multilayer Foils and its Application in Thermal Battery

The conventional heating materials of thermal battery have the disadvantages of low combustion rate and less heat release, so it is necessary to develop new heating materials. Al/Ni Reactive Multilayer Foils (RMFs) is an ideal heat source due to its high heat release, fast burning speed and no gas generated during combustion. Al/Ni RMFs were prepared by magnetron sputtering, and the heat transfer process of thermal battery using Al/Ni RMFs as heating material was simulated by the COMSOL MULTIPHYSICS simulation. The Al/Ni RMFs combustion reaction mechanism with different Al/Ni ratios was proposed according to DSC and XRD results. The effects of Al/Ni atomic ratio of RMFs on the melting time of electrolyte were investigated, and the temperature distribution during the activation was obtained, indicating the rapid activation process of the thermal battery.

Oxidation and ignition of a heterogeneous Al-Zn alloy powder metallic fuel

In this work, a heterogeneous Al-Zn alloy was developed as a metallic fuel to overcome the ignition time delay and low combustion rate of Al energetic materials. Al-Zn alloy powders were prepared by a high-speed centrifugal atomization method, which distributed Al and Zn uniformly on the surfaces and insides of the resulting spherical particles. The temperature at which the particles’ oxide shells cracked was lower and the laser ignition delay was 35 ms shorter for the Al-Zn alloy than for Al, based on TG-DSC results. The reason is that the low-temperature vaporization of Zn exacerbated the breakage of Al2O3 shells, and the heat accumulated during the vapour-phase combustion of Zn heated the particle to the reaction temperature of Al. Therefore, the addition of Zn enhances the combustion behaviour of Al by accelerating the rate of heat release.

The Performance of Red Flare Pyrotechnic Compositions Modified with Gas Generating Additives

AbstractIn this work, an effective, but still not well‐explored area of red flare pyrotechnic formulations was investigated. High magnesium content (40–60 % w.t.) and the presence of conventional gas generating materials were the specific features of formulations explored herein. Such illuminant compositions possessed a low burning rate and high specific luminous intensity. The investigated system was based on strontium nitrate, rounded magnesium powder, chlorinated rubber, binder and gas generating additives. Emission spectra, light intensity and burning time have been measured during the experiment and recalculated to the specific luminous intensity and color purity. Additives in the form of 2‐cyanoguanidine, Melamine, Azodicarbonamide, Calcium resinate, Shellac, Strontium oxalate, Lactose, Dextrin, Phenolic resin, Lignin sulfonate, 5‐aminotetrazole, Urea, Guanidinium nitrate (GN), Hexamine and Sulfur were evaluated in Mg‐rich flare compositions. The use of GN was studied more carefully as an exceptionally efficient additive that increased the flares light intensity by 60 %, in comparison to the standard GN‐free composition, while maintaining high color purity of 90–97 %.

Combustion of crude glycerol and its blends with acetals

In spite of its relevance, the prospective energetic valorization of crude glycerol (CG), a major by-product of biodiesel production, remains nowadays unfulfilled in the industry because of the significant challenges posed by its combustion properties. Besides some basic post-treatments such as desalting (to obtain desalted crude glycerol, DG), its blending with other industrial by-products could improve crude glycerol properties, while maintaining the renewable nature of the fuel. A secondary product obtained from the FAGE process, consisting in a mixture of acetals named GF*, has been proposed in this work as a suitable fuel for this purpose. The combustion characteristics of these by-products have been tested along with different CG-GF* and DG-GF* blends by employing single droplet combustion experiments and semi-industrial furnace tests. Single droplet results point to widely different behaviors between GF* and the glycerols, the latter displaying much lower burning rates and violent microexplosions ascribed to salt content as well as to the broad differences in their constituent's boiling points. Relevant differences were noted between DG and CG modes of microexplosion, presumably due to the lower salt content of the former. Both CG-GF* and DG-GF* mixtures presented similar behaviors to CG, although with a noticeably faster conversion. The furnace tests revealed that GF* addition widened the range of stable conditions in the burner, significantly improving flame stability and reducing CO emissions. NOx emissions slightly increased, although they could be reduced through burner aerodynamics optimization, facilitated by the improvement in flame stability. The reported results support the potential use of GF* as auxiliary fuel for enhancing the combustion behaviors of crude glycerol.

Tuning the agglomeration and combustion characteristics of aluminized propellants via a new functionalized fluoropolymer

Fluorine-containing organic substances (FCOS) are often added to aluminized solid propellants to improve their ignition and combustion characteristics, but existing FCOS coatings tend to have poor mechanical strength, limiting their reliability in practical applications. In this experimental study, we investigate the effect of adding a new functionalized FCOS to aluminized solid propellants. Specifically we focus on the oxidation and ignition characteristics of Al-FCOS composite particles and on the combustion of fluorine-containing propellants. By altering the surface pre-ignition reaction, FCOS-modified particles are found to ignite more quickly and produce more gaseous products. For pressures above 5 MPa, adding FCOS can both increase and decrease the burning rate relative to a baseline Al propellant, depending on the precise Al-FCOS content used, with 8.5 wt% and 17 wt% Al-FCOS producing a higher and lower burning rate, respectively. Compared with the baseline Al propellant, the FCOS-modified propellants are found to produce smaller agglomerates. This shows that the ignition, combustion and agglomeration characteristics can be readily tuned by adjusting the content of the new functionalized fluoropolymer. These findings can help guide the development of FCOS additives for aluminized propellants in solid rocket motors.

Droplet combustion of kerosene augmented by stabilized nanoaluminum/oxidizer composite mesoparticles

Inclusion of energetic and chemically active nanoparticles into liquid fuels and propellants is known to affect resultant combustion dynamics. Recently, the activity of such nanoparticle additives has been promoted using electrospray to preassemble said particles into nitrocellulose-bound mesoparticle (MP) clusters of either nanoaluminum (nAl) or oxygen-carrying nanoparticle primaries. In either case, stability in kerosene with TOPO surfactant and isolated droplet burning rates estimated in a free-droplet combustion experiment increase substantially with the MP additive architecture. Burning rates benefit from violent physical mixing of droplet systems which occurs when the carried nanoparticles are energetic and/or chemically active, causing gas generation, additive transport to the flame, energy or oxygen release, and further gas liberation accelerating the process. In this study, this same physical underlying mechanism is seen superimposed with the effects of another advantage of electrospray particle assembly: MP composition flexibility. By mixing nAl with oxide nanoparticles to form composite MPs, these novel additives for hydrocarbons are employed to modify kerosene and their effects are found to be dependent on the oxidizer chosen. Most notably, nAl/CuO MPs show evidence of interparticle thermite reaction in the droplet system yielding a cooperative benefit of the two constituents relative to either alone in MPs. Use of oxidizer co-additives and the MP architecture with nAl represents a flexible and promising method of overcoming low burning rates of hydrocarbons with high as-received nAl loadings and provides expansive means of tunability to tailor nanofuel properties.

An analysis of heat feedback effects of different height embedded plates on promotion of pool fire burning using a variable B number

In this study, heat feedback effects of embedded plates with various heights on the enhancement of the pool fire burning were investigated through a variable Spalding B number. The study showed that the embedded plate had a significant effect on the increase in flame height and pool fire burning rate, but longer plate inhibited the effect, where a critical point arose. Besides, by increasing plate height, the solid temperature increased with a high growth rate before the critical point, while the growth rate decreased after the critical point. Below the liquid surface, the plate temperature of ethanol was generally lower as compared with n-heptane due to the lower boiling point of ethanol. While above the liquid surface, it was the opposite due to its less soot production with higher flame temperature. Secondly, the flame height had a significant positive effect on the heat feedback energy from solid radiation and solid-liquid nucleate boiling. For n-heptane fire, as its latent heat of gasification (hfg) was about 1/2.6 of ethanol, the nucleate boiling dominated total solid heat feedback. Finally, the solid heat feedback led the modified heat of gasification (Lm) to change oppositely, which first decreased then increased with the increasing plate height. Thus the B number decreased after a rise that made the same change in burning rate for both fires. Ethanol pool fire had a lower burning rate as compared with n-heptane fire because of its smaller values of B number affected by larger original heat of gasification.

Production and droplet combustion characteristics of waste tire pyrolysis oil

This work aims to study the pyrolysis of scrap tires as an end-to-end process, from its production to the combustion characteristics of the tire pyrolysis liquid (TPL) obtained. The TPL was produced in a continuous auger reactor (150 kWth) and its combustion characteristics were acquired through a drop tube facility, where the TPL burning behavior was compared to that of conventional heating oil (FO). The evaluated combustion characteristics included droplet and flame size evolution, burning rates, soot shell morphology, microexplosion occurrence and soot analysis. When compared to FO, TPL displayed considerably lower burning rates, although the consistent occurrence of microexplosions effectively shortened the TPL droplets lifetimes below those of FO. TPL also presented smaller flames and a higher propensity to soot. A TPL-FO blend of interest for heating applications (with only 5% of TPL due to its high sulfur content), was also tested, showing identical results to those of neat FO for all the studied combustion characteristics. The reported results are thought to provide valuable experimental data regarding the combustion behavior of a well characterized tire pyrolysis oil, which could also be used as the fuel-specific input data required for the simulation of realistic spray flames.

Facile preparation of Si/CuO energetic materials by electrophoretic deposition and their exothermic studies

Silicon (Si) with a thinner oxide layer than aluminum (Al) has attracted considerable interest in the fields of energetic materials. Herein, we report novel Si/CuO energetic materials fabricated by electrophoretic deposition methods. Electrophoretic deposition dynamics and exothermic behaviors of Si/CuO energetic materials were systematically analyzed in this study. Besides, chemical compositions and morphologies of samples were characterized by X‒ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, respectively. The results demonstrate clearly that Si/CuO energetic materials can be employed as a secure energetic composite because of its high ignition temperature and low combustion rate. The insights obtained in this work provide inspiration for the investigation and development of Si‒based energetic materials.

Methodology to separate the two burn stages of natural-gas lean premixed-combustion inside a diesel geometry

Heavy-duty diesel engines can be modified to natural-gas spark-ignition operation by replacing the fuel injector with a spark plug and fumigating the gas inside the intake manifold. As natural gas premixed combustion in a diesel geometry is a two-stage combustion process with each stage influencing engine efficiency and emissions, determining the end of the fast burn inside the bowl can help optimize engine operation. This study proposed a methodology that identifies the burn inside the bowl using the inflection points of the heat release rate. A 3D CFD simulation that changed spark timing, equivalence ratio, and engine speed showed that this methodology can separate the fast combustion stage from the rest of the combustion event compared to the conventional spark-ignition theory that could not. In addition, this methodology showed that operating conditions controlled the flame location and combustion behavior inside the squish. For example, advanced spark timing, higher equivalence ratio, and lower engine speed advanced the transition point between the fast and the slow combustion stages but increased the mass of fuel inside the squish region. Moreover, the flame speed inside the bowl was ∼3 times higher than that inside the squish region. In addition, the lower burning rate after the transition point can decrease engine efficiency. Moreover, a higher engine speed optimized in-cylinder conditions at the transition between the two combustion events (which would suggest a better late combustion stage) but decreased the time available to complete the late combustion, which will probably increase emissions compared to conventional spark-ignition engines.

Detonation properties of ammonium nitrate/nitramine-based composite propellants

ABSTRACTAmmonium nitrate (AN) propellants have attracted attention because of their low cost and ecofriendliness despite certain major disadvantages such as low burning rate, poor ignitability, low energy, and volume change due to phase transition of AN. The addition of nitramine to AN propellants is one of the approaches to overcome these disadvantages. However, AN/nitramine propellants are characterized by easy initiation, high sensitivity, and high detonation velocity because of the high energy of nitramine. The detonation properties of AN/nitramine propellants were investigated in this study. It was observed that the AN/nitramine propellant required a booster to detonate the propellants, as detonation did not occur while using only a commercial electric blasting cap. It was further observed that the detonation velocity (D) increased linearly as the mass of nitramine per unit propellant volume was increased, and AN had a negligible effect on the detonation properties. An approximate equation was derived from the relationship between D and the mass per unit propellant volume of nitramine. The dominant factors that can be used to estimate the detonation/no-detonation boundaries of the propellants were identified, and the experimental boundary equations were determined using these factors.

An Approach to Analysing Erosive Characteristics of Two-Channel Combustion Chambers

To acquire the erosive characteristics of two-channel combustion chambers, a quasi-one-dimensional internal ballistics model is proposed. Combining the model with two different erosive burning models, the modified L-R expression, and the Mukunda-Paul expression, the flow parameters and the internal ballistics performance of a test solid rocket motor are computed. The results show good agreement with experimental data. According to the results, the more severe the erosion is, the earlier, longer, and gentler the tail-off stage becomes. During the tail-off stage, the dramatic drop of pressure leads to a low normal burning rate and makes it easier for erosion burning to occur. For this reason, notable erosive burning might appear during tail-off if the case-to-throat area ratio is extremely low. The results also show that flows in the inner channel and the outer channel are similar but not identical. This leads to different erosive burning behaviours in the two channels. Also, the two erosive burning rate models involved in this paper are compared. It seems that the M-P expression provides better results than the modified L-R expression does, since it reveals the threshold phenomena. Besides, the M-P expression has great advantages for its universality for most propellants and different SRM geometries.

Development and Characterization of Sisal Fiber Reinforced Polypropylene Composite Materials

In most of the developing countries, plastic polypropylene is not fully recycled and converted in-to use after it is once used. Sisal fiber is also widely available in different developing countries like Ethiopia. Adding this two materials and developing automotive interior part was taken as a primary motive for it reduces cost and is environmentally friendly. Thus, the main purpose of this research is to develop composite material from natural fibre (sisal fiber) reinforced with recycled plastic waste (polypropylene) for interior automobile accessories specifically for internal door trim panel application. This research examines effect of fiber length, fiber loading and chemical treatment of fiber on the physical and chemical properties of the sisal fiber reinforced polypropylene (SFRPP) composite material. The waste polypropylene and the treated and untreated sisal fiber with variable length and weight ratio (fiber/matrix ratio) were mixed. Flammability of sisal fiber reinforced Polypropylene (SFRPP) composites material was examined by a horizontal burning test according to ASTM D635 and chemical resistance of the sisal fibre reinforced PP composites was studied using ASTM D543 testing method. The result on the flammability test shows that treated fiber has lower burning rate than untreated fiber and decreases with increase in fiber length and fiber loading. The resistance of the composites to water has increased as the fiber length increases and decreased as the fiber loading increase. Generally, SFRPP composite is found to have better resistance to water than NaOH and H2SO4 and treating the fiber has brought considerable improvement on chemical resistance of the composite. Fiber loading and fiber length has positive and negative effect on the flammability of the SFRPP composite respectively.

Effect of Tris(1,3-Dichloroisopropyl) Phosphate as Flame Retardant on Mechanical Properties and Fire Resistivity of PU Composites

Palm oil based polyurethane composites that are reinforced with Tris(1,3- dichloroisopropyl) phosphate TDCPP which function as flame retardants (FR) at different proportions of 3, 6 and 9% were synthesized. The polyurethane composite’s influence on the mechanical (tensile strength, impact and flexural limits and modulus) and thermal characteristics (fire test) of the polyurethane composites were examined. Increased loading of TCPP resulted in increased hardness (up to 39%) which translates to a marginal increase in Shore D hardness as the TDCPP content increases. With higher TDCPP loading, the impact and flexural capabilities decreased because of the fragile interfacial bonding between the TDCPP and PU matrix. Loading of 3%, 6% and 9% of TDCPP resulted in the decrease of impact strength by 25%, 24% and 23% respectively. Lowest flexural ability (at a reduction of 21%) was exhibited with the highest amount of TDCPP loading (9%) and the modulus had decreased by 23%. When the percentage of TDCPP loading increased, this resulted in a lower heat of combustion of the composites which manifested in the form of lower burning rate from 5.4 mm/s to 2.7 mm/s in the fire test operated.

Wastage pomegranate rind extracts (PRE): a one step green solution for bioactive and naturally dyed cotton substrate with special emphasis on its fire protection efficacy

Pomegranate rind (Punica granatum) extracts (PRE), a widely available wastage material, are explored as new multifunctional finishing agent (fire retardant, natural dye, mordanting and antimicrobial agent) on cellulosic textiles. PRE has been applied on the cellulosic cotton fabric at higher temperature (90 °C, 30 min) in different concentrations. 400 g/L PRE extract treated fabric showed 15 times lower burning rate as compared to the control cotton fabric. Thermo-gravimetry of the PRE treated fabric showed earlier dehydration phenomenon and more amount of char mass formation. The resulting fire retardancy of the treated fabric is the combined reaction effect of the acid source (carbamic acid, ammonium salt, hexacontanoic acid, etc.), carbon source (carbonic dihydrazide, nona hexacontanoic acid, 1 hydroxy 2 pentanone, sugar based material) and blowing agent [nitrogen containing bases like guaninidine, asparigine (amino acid of protein), di amino guanidine and ethanamine, piperidine] present in the PRE extracts as observed from the Gas Chromatography Mass Spectroscopy analysis. Antimicrobial efficacy of the PRE extract on cotton substrate has also been demonstrated successfully against both the Gram-positive and the Gram-negative bacteria because of its tannin and positively metal ion as well as amino acid contents. Furthermore, cotton fabric dyed from the PRE medium with anionic acid dye showed dark colour compared to the acid dyed cotton fabric from water medium, characteristics of the mordanting efficacy of the extract. Extract also has been explored as natural dye for the dyeing of the cotton textile substrates because of the presence of natural colouring material (betacyanin, coumarin, etc.) in it as observed from the phytochemical analysis of the extracts.