Higher Burning Rate Research Articles

State-of-the-art Advances in the Ignition Selay Reduction of N,N-dimethylethanamine

Propellant is a core fuel in defense and aerospace applications. However, conventional hydrazine fuel is highly volatile, toxic, and carcinogenic, resulting in huge threats to the human body and environment. N,N-dimethylethanamine (DMAZ) is a green, high-energy fuel with a low freezing point, high density, high specific impulse, and high combustion rate, and it is a promising substitute of conventional hydrazine fuel. Nevertheless, the industrial application of DMAZ is limited by long ignition delay. In this study, the mechanism of ignition of DMAZ was explored by summarizing current methods to reduce the ignition delay of DMAZ, including the addition of catalyst, fuel formulation, and tuning molecular structure. This study provides references for applications of amine azide.

Informal settlements ablaze: decoding the combustible nature of building materials used in Bangladesh through experiments and numerical analysis

ABSTRACT Fire outbreaks in informal settlements pose severe threats to residents and their properties. Despite the frequent occurrence of fire events in Bangladesh, detailed studies on fire propagation behaviour remain limited. This study addresses this critical issue by comprehensive investigations into the ignitability and burning behaviour of different materials such as cardboard, polyurethane foam, plastic bags, wood, and structural timber that are commonly found in informal settlements. Additionally, an advanced numerical model based on the finite volume method was developed in Fire Dynamics Simulator and then employed to accurately predict the fire-reaction properties of materials under the cone calorimeter environment. The results revealed that cardboard ignites quickly, burns moderately, and does not produce flaming droplets or ignite the filter paper. PU foam burns vigorously, with a high burning rate, and emits dense black smoke and a toxic odour. Plastic bags ignite rapidly, burn intensely, and are greatly influenced by the presence of airflow. The numerical model successfully quantified fire-reaction properties such as ignition time, heat release rate (HRR), and flame spread characteristics. Notably, wood and structural timber demonstrate a distinct combustion pattern with a sharp HRR peak, while PU foam exhibits the highest peak HRR values followed by timber masonite.

The effect of several factors on energy characteristicsand burning of pyrotechnic compositions based on silic and trilead tetraoxide in some pyrotechnic devices

Pyrotechnic ignition is one of the important parts of the delay timing devices found in fuses and rockets to provide operational reliability according to technical requirements. In this study, the burning rate and some energy characteristics of the pyrotechnic ignition were described. The research results showed that pyrotechnic compositions containing 85.0% Pb3O4, 15.0% Si, and 1.0% NC (over 100%) had a high and stable burning rate (109.0 mm/s) and good ignition ability.

Performance of a novel CLOU oxygen carrier (CuO/ZrO2/TiO2/MgO) in the combustion of high-rank coal: Anthracite and bituminous

Coal is the largest contributor to global CO2 emissions, and current reserves are projected to last approximately 150 years, with 71.6 % being high-rank coals (anthracite and bituminous). Chemical looping combustion is an economical CO2 capture method that uses oxygen carrier materials to supply oxygen for combustion. Copper is the most reactive due to its oxygen uncoupling capability, though it has poor stability. In our research, we developed a novel modified copper-based oxygen carrier with enhanced stability in oxygen uncoupling cycles by increasing the ZrO2 ratio at the expense of TiO2 to reduce phase interactions. The modified oxygen carrier (40 % CuO, 30 % ZrO2, 15 % TiO2, 15 % MgO) was used to combust bituminous and anthracite coal in a fixed-bed system. While bituminous coal had a high combustion rate, its efficiency was 63 %, yielding 18 mol/kg of CO2, compared to 90 % efficiency and 56 mol/kg CO2 for anthracite. The lower efficiency for bituminous was due to the rapid release of volatiles. Adding steam improved bituminous combustion efficiency to 75 % and CO2 yield to 21 mol/kg, with no significant change for anthracite. A blend of 25 % bituminous and 75 % anthracite showed better combustion efficiency, rate, and CO2 yield. This blend test was stable over 10 cycles, as confirmed by SEM, XRD, and BET analyses.

Theory-driven design of graphene-nickel gallate nanocomplex as functional catalyst for composite modified double base propellant

New graphene-nickel gallate nanocomplex (G-M-Ni) was designed, synthesized and characterized to deal with the requirement of functional combustion catalyst based on investigations of combustion mechanisms of propellant, structural analysis of catalyst and simulation results of quantum mechanics. The positive effect of G-M-Ni is not only reflected in the significantly increased burning rate, but also reflected in the reduction of friction sensitivity of composite modified double base (CMDB) propellant. The G-M-Ni nanocomplex exhibited significantly enhanced catalytic performances, and the burning rate of propellant at 20 MPa enhanced from 23.15 to 29.07 mm·s−1. Besides, the friction sensitivity of propellant reduced from 64 % to 36 % after addition of 0.5% G-M-Ni. The positive effect of G-M-Ni on CMDB propellant combustion is mainly attributed to its promotion impact on nitroglycerin (NG) pyrolysis, which significantly increased the differential charge density and decreased the decomposition activation energy (from 1.89 eV to 1.38 eV). The gas products produced by the rapid pyrolysis of NG are conducive to the heat feedback between the gas phase and the combustion surface, which makes the propellant have higher burning rate, bright flame, thin dark zone and flocculated quenching surface morphology. The findings in this study confirm the potential of G-M-Ni as a functional combustion catalyst for CMDB propellants, which has guiding significance and inspiration for the development of new combustion catalysts from the view of molecular-level insights. Novelty and significance statementRecently, graphene based functional combustion catalysts have attracted much attention in the field of solid propellants due to their excellent catalytic combustion performance, reduced sensitivity, and improved mechanical properties. Herein, novel graphene-nickel gallate nanocomplex (G-M-Ni) were designed, synthesized and characterized to deal with the to deal with the requirement of functional combustion catalyst based on investigations of combustion mechanisms of CMDB propellant, structural analysis of new material and simulation results of quantum mechanics. By taking graphene as the benchmark, the G-M-Ni nanocomplex exhibited significantly enhanced catalytic performances, and excellent effect on the reduction of friction sensitivity. The relationship between molecular structure of G-M-Ni and combustion characteristics of CMDB propellant were disclosed. The theory-driven design mode of this work may provide new pathways to tune combustion behaviors of CMDB propellants from the view of molecular-level insights.

Considerable enhancement of nanothermites propagation through worm-like expansion of expandable graphite

Metastable intermolecular composites (MICs) are known for their high energy density, high burn rate, and low diffusion distance, and they have various applications in military and civilian equipment and tasks. However, the introduction of binders, which facilitate shaping, during the processing of MICs for practical applications can lead to a decrease in the energy release rate and an increase in the required ignition energy. Herein, we incorporated graphene nanoplatelets (GNPs), multi-walled carbon nanotubes (MWCNTs), and expandable graphite (EG) into 90- wt% Al/CuO nanothermites stick using simple extrusion-based direct ink writing to improve their overall performance. The high-temperature expansion characteristics and unique structure after expansion caused EG to perform an important role during Al/CuO nanothermites system combustion, which effectively promotes heat transfer and considerably increases the burn rate (81.6%) and pressure rising rate (103.0%). This study demonstrated EG as a low-cost and efficient combustion catalyst for MICs and introduced a simple approach to modulate the energy release rate, combustion pressure and semiconductor bridge (SCB) ignition performance of MICs through incorporation of small amounts of carbon materials.

Utilization of Sengon Wood Sawdust as Bio-Pellet Feedstock: Characteristics, Potential, and Feasibility for Renewable Energy

The pellet-making process involves stages of drying, compaction, cooling, and size separation. Considering that Indonesia has great potential for biomass supply, this research aims to identify the characteristics of bio-pellets produced from sengon wood sawdust based on the pellet standard SNI8675:2018. The results showed that the highest calorific value at the Dry Basis (DB) condition was 4703 Kcal/kg, meeting national and international standards. The moisture content in the As Received (AR) condition was recorded at 10.36%, while the lowest ash content was 1.72%. The highest combustion rate was found in sample 3, with a value of 0.174 gr/min, indicating good combustion performance. The utilization of sengon wood sawdust as bio-pellets can be an efficient and environmentally friendly renewable energy solution, and has the potential to be further developed to support diversification and national energy security.

The potentials of copper chromite nanoparticles on ammonium nitrate decomposition: Towards eco-friendly oxidizers for green solid propellants

Abstract Ammonium perchlorate (AP) is the universal oxidizer for solid propellants; AP combustion is accompanied with the release of white smoke (HCl). HCl has raised an environmental concern; it could cause acidic rain and deteriorate the fertile soil. Chlorine free and eco-friendly oxidizers are highly appreciated for green solid propellants. Ammonium nitrate (AN) could be the greener substitute for AP; yet AN expose low performance. Whereas AP demonstrated exothermic decomposition with the release of -733 J/g; AN demonstrated strong endothermic decomposition process of +1707 J/g. AN with strong endothermic decomposition process could render high burning rates. Copper chromite Nano catalyst of 45 nm was developed via hydrothermal synthesis. Copper chromite was integrated into AN matrix. Catalyzed AN demonstrated advanced exothermic decomposition enthalpy of -1492 J/g. Catalysed AN experienced diminish in activation energy by - 41.5 %, and – 40.6 % using Kissinger and Ozawa models respectively. Copper chromite NPs could secure novel catalytic effect via condensed phase reactions of chromium, and copper ions with nitrate ions (NO-3) to develop NOx gases. This catalytic effect can secure alternative pathway with low energy barrier. Consequently, catalysed AN can expose novel characteristics as a green eco-friendly oxidizer.

A Lab-Scale Experiment on the Spontaneous Combustion Behavior of Chronic Naturally–Oxidized Coal in Re-Mining Coal Mine

ABSTRACT Spontaneous combustion of coal in re-mining coal mine is a serious threat to the safety recovery of coal resources. In this paper, six coal samples, including two raw bituminous coal samples from the new mining working face and four oxidized bituminous coal samples from the re-mining working face, are selected. The pore structures, thermogravimetric properties, and spontaneous combustion characteristics of raw coal and oxidized coal are studied. The pore structures show that the surface of oxidized coals has more cracks and higher macropore volume and porosity as compared with raw coal. The thermogravimetric experiments demonstrate that the oxidized coal has a higher combustion rate and turns to the combustion reaction zone in advance. Moreover, the oxidized coals perform a better combustion property by showing a comprehensive combustion index of 6.7 × 10−9 min−2·°C−3 and 8.9 × 10−9 min−2·°C−3, higher than the raw coal of 4.0 × 10−9 min−2·°C−3. The spontaneous combustion characteristics show that the oxidized coal performs a greater rate of oxygen consumption and more oxidation products released than raw coal. The CPT of raw coal is higher than 157°C, while the CPT of oxidized coal is between 132°C and 140°C. The research results can provide a risk assessment method for coal spontaneous combustion in the re-mining coal mine, and provide guidance for avoiding the occurrence of coal fires.

Characterization, performance evaluation and optimization of wheat straw – bagasse blended fuel pellets

This study was carried out to assess the fuel pellets produced from wheat straw and sugarcane bagasse. The wheat straw and bagasse were blended into four ratios including; 10:90, 30:70, 70:30 and 90:10 (wheat straw: bagasse) and developed into fuel pellets. The fuel pellets were characterized to determine the moisture content, volatile matter, fixed carbon, ash content, calorific value, bulk density and mechanical durability. The ignition time, burning rate and specific fuel consumption of the wheat straw – bagasse blended fuel pellets were studied at varying blend ratios (10:90, 30:70, 70:30 and 90:10), moisture contents (9.1%, 10.6%, 12.6% and 14.7%) and raw material particle sizes (2 mm, 4 mm, 6 mm and 10 mm). Results indicated that the wheat straw: bagasse blend ratios containing more proportion of bagasse (30:70 and 10:90) recorded a shorter ignition time, higher burning rate and lower specific fuel consumption. Larger raw material particle sizes exhibited shorter ignition time, higher burning rate and specific fuel consumption. Moreso, the fuel pellets with low moisture contents also recorded shorter ignition time, higher burning rate and lower specific fuel consumption. It was concluded that fuel pellets with high quantity of bagasse, large particle sizes and low moisture content demonstrated favorable combustion characteristics. Response surface methodology was used in the optimization so as to determine the optimum combination of blending ratio, moisture content and raw material particle size that would result in the lowest ignition time, highest burning rate and lowest specific fuel consumption. Results indicated that an optimum combination of a wheat straw: bagasse blend ratio of 10:90, moisture content of 14.70% and a particle size of 10.00 mm resulted in the lowest ignition time, highest burning rate and lowest specific fuel consumption.

Determining the influence of synthesis gas additives on the environmental performance of internal combustion engine

The object of research is the environmental parameters of a reciprocating engine when using a synthesis gas additive to the main fuel. The research is aimed at solving the problem of reducing the concentration of harmful components in the exhaust gases of an internal combustion engine by adding synthesis gas to the main fuel. Experimentally, the dependences of the effect of the addition of synthesis gas to ethanol on the change in the environmental performance of a piston engine with spark ignition were obtained. The positive effect of the addition of synthesis gas obtained by thermochemical conversion to ethanol in an amount of up to 5 % by weight on the environmental performance of a spark-ignition piston engine was established. Provided that the engine achieves the same effective power, the use of a synthesis gas additive to the main fuel made it possible to reduce the concentration of CO by 61.5 % and CH by 51.3 % in the exhaust gases. no more than 25–30 words The addition of synthesis gas contributed to the formation of radicals that activate oxidation chain reactions, and also made it possible to increase the normal combustion rate of the fuel-air mixture by 6.25 %. This ensures normal engine operation on a leaner fuel-air mixture (α=1.21) without deterioration of environmental, energy and economic performance. no more than 25-30 words The simultaneous reduction of the concentration of harmful components in the exhaust gases and engine efficiency can be achieved by using fuels with a wide concentration limit of ignition and high combustion rate in a lean mixture. The experimental data obtained can be used in the design or modernization of transport and stationary power plants with internal combustion engines as an approach to meet ever-increasing environmental standards

Experimental Observation of the Turbulent Jet Ignition for Extending the Lean Combustion Tolerance with Carbon Dioxide Diluted Mixture

ABSTRACT Exhaust Gas Recirculation (EGR) technology is widely employed to reduce NOx emissions from engine combustion, and a major challenge of this technology is to achieve stable ignition and high burning rate at higher EGR dilution ratios. Turbulent jet ignition (TJI) is a reliable ignition resource for improving ignition stability and burning rate. Therefore, in the present work, the ability of pre-chamber turbulent jet ignition for extending the lean combustion tolerance at different EGR dilution ratios was investigated in a constant volume combustion chamber. The experimental results indicate that the methane-fueled pre-chamber and the hydrogen-fueled pre-chamber cannot improve the combustion conditions as expected. On the other hand, when an appropriate quantity of air or oxygen is injected, the EGR tolerance limit can be extended due to a decrease in the EGR concentration and an increase in the mixture reactivity in the pre-chamber. However, at higher EGR dilution ratios, more air or oxygen is required to be injected to increase the mixture reactivity in the pre-chamber, which decreases the equivalence ratio of the mixture in the pre-chamber and limits further extension of the EGR tolerance. For the mixture in the active pre-chamber under EGR dilution, the competition mechanism between EGR concentration and equivalence ratio is the key that affects turbulence intensity and chemical reactivity, thereby determining the ignition and combustion results. During the extension of the EGR tolerance limit, the variations in turbulence and chemistry are accompanied by a series of ignition modes, involving jet re-ignition, re-ignition failure, and misfire. Compared to the passive pre-chamber with an EGR tolerance limit of 18%, the air-assisted pre-chamber extended the limit to 23% and the oxygen-assisted pre-chamber to 30%.

Improving the combustion of scramjet engines with struts using grooves and bumps

Grooves and bumps are arranged on both sides of a normal strut (NS) to fabricate vortex generators, and introduce streamwise vortices. Struts with sawtooth grooves (GS-1), rectangular bumps (BS-1), and trapezoidal and triangular bumps (BS-2) have been proposed. In this study, struts with V-shaped grooves (GS-2) and trapezoidal and triangular bumps (BS-3) were configured. The flow fields in the cold and hot states of scramjet combustors with NS, GS-1, GS-2, BS-1, BS-2, and BS-3 were simulated numerically using steady RANS equations and an SST k-ω turbulence model. The results show that proper arrangement of the grooves and bumps on the strut can improve the mixing and combustion performance. Compared with the NS, for GS-1, GS-2, BS-1, BS-2, and BS-3, the distance required to achieve 100% fuel mixing efficiency is shorter by 21.2%, 9.1%, 18.2%, 12.1%, and 15.2%, respectively, and to achieve 100% combustion efficiency, the distance is shorter by 42.7%, 46.9%, 47.9%, 53.1%, and 58.3%, respectively. Therefore, improvement in combustion performance does not positively correlate with improvement in the mixing performance. Large-scale heat and mass convection in streamwise vortices play a dominant role in mixing. The larger the proportion of the fuel area affected by the streamwise vortices, the more conducive it is to achieving a higher mixing performance, whereas the wall has a negative impact. However, the large-scale heat and mass convection in the streamwise vortices and small-scale heat and mass convection in the high-turbulence zones are closely related to the supply of oxygen and fuel required for the combustion zone. Large-scale streamwise vortices combined with thick high-turbulence zones are conducive to achieving a high combustion rate. When the recirculation zone has a larger combustion area and smaller wall effects, a higher combustion performance is easily achieved. Compared with the grooves, the stronger disturbance effect of the bumps on the fluid effectively increased the thickness of the high-turbulence zone, thus obtaining a higher combustion performance. However, the greater blocking area and new oblique shockwaves generated by the bumps induced a greater total pressure loss. Therefore, combining bumps and grooves can further optimize strut configurations.

Scaling up in situ combustion process for enhanced oil recovery in water-flooded light oil reservoirs from laboratory to field implementation

Aiming at low permeability, high water content light reservoir with a recovery rate higher than 20%, an improved air injection enhanced heat flooding technology is applied by combining the combustion reaction flow and flue gas flooding mechanism. The method involves the injection of air into the reservoir, which reacts with the crude oil at temperatures ranging from 220 to 300 °C. This reaction consumes part of the oil, enabling effective evaporation and flow of the remaining oil. This process combines combustion reaction flow with flue gas flooding, using high-temperature oxidation reactions to mobilize residual oil. Experimental results from combustion tube tests demonstrate stable reaction fronts, peak temperatures reaching up to 550 °C, and a significant increase in recovery rates, reaching 73.8% in some cases. Field applications of this technology require maintaining high air flux and burning rates in low-permeability zones to ensure effective heat-driven evaporation. The geological model of the well group shows that the recovery factor of the target block can be increased by more than 20% by air injection based on the water drive recovery factor of 28%–30%. The oil exchange ratio can be less than 4000 sm3/m3 by optimizing the air injection rate and oxygen content. The research results provide technical feasibility for heat flooding to significantly improve oil flow and recovery in low-permeability light oil reservoirs.

Enhancing the combustion of nAl with AlF3 coating: gas-solid reaction mechanism for reducing combustion agglomeration of Al powder.

The combustion agglomeration of nano-aluminum (nAl) powder leads to incomplete combustion, which seriously hinders its application as metal fuel. In this work, nAl@AlF3 composites were produced by coating nAl with AlF3via a facile chemical deposition method. TEM and SEM analyses indicated that the AlF3 layer was evenly coated on the surface of nAl with a thickness of 4.6-9.1 nm, thereby varying the quantity of AlF3 applied. Experimental results from combustion indicated that the prepared nAl@AlF3 composites exhibit superior combustion efficiency, a higher combustion rate, and reduced combustion agglomeration as compared to raw nAl. Contrary to the widely accepted explanation that volatilization of AlF3 hinders Al combustion agglomeration, we proved that the gas-solid reaction between nAl and AlF3 plays an important role in inhibiting the sintering of nAl particles produced. The gaseous intermediate (i.e., AlOF and HF) released from the hydrolysis of AlF3 could reduce the diffusion barrier of Al2O3 to facilitate the reaction of Al core, which enhances the combustion reaction kinetics. More importantly, these gaseous products actively participate in the reaction cycle to continuously exert their catalytic effects.

A subgrid-scale model to account for thermo-diffusive effects in artificially thickened LES models for lean turbulent premixed ammonia/hydrogen flames

With the introduction of carbon-free fuels and their rapid implementation, accurate combustion models are needed to design decarbonized engines, gas turbines or burners. Recent experimental and numerical work have highlighted the high burning rate of lean hydrogen and hydrogen/ammonia flames and their deviation from flamelet assumptions, pointing out the need to revise classical combustion models for Reynolds Averaged Navier–Stokes (RANS) or Large-Eddy Simulations (LES). In this work, a novel subgrid-scale model accounting for stretch effects for lean ammonia/hydrogen (NH3/H2) flames in the Thickened-Flame LES framework (TFLES) is proposed as an extension to the standard Charlette model Charlette et al. (2002). This model, called ESE−NH3, is based on 1-D premixed strained flames and validated a priori with Direct Numerical Simulations (DNS) and used to perform LES simulation of a turbulent slot burner configuration. To assess the performance of the novel subgrid model, LES predictions are compared a posteriori to the DNS and to LES employing the standard Charlette model. The comparison shows that the LES computation with the novel subgrid-scale model accounting for stretch effects predicts flame lengths closer to the DNS. This shows that thermo-diffusive effects can be integrated simply in the TFLES framework. Moreover, results show that these effects are significant in all lean NH3/H2 flames even at low H2 contents.

Hydrogen, methane and one of their fuel blends combustion: CFD analysis and numerical-experimental comparisons of fixed and mobile applications

The capabilities of Computational Fluid Dynamics (CFD) coupled with detailed chemistry simulations are examined in both steady jet diffusion flames and in an internal combustion engine case fuelled with hydrogen. Different approaches to turbulence-chemistry interaction such as the “Laminar Flame Concept” the “Eddy Dissipation Concept” and the “Turbulent Flame Speed Closure” are considered and tested. The results are compared with the experimental data available. Concerning the jet diffusion flames, the combustion processes of hydrogen, methane and one of their fuel blends are investigated on two burner geometries. Different sensitivities (i.e. mesh, turbulence model, turbulent Schmidt number, chemical mechanism) are performed. The study demonstrates that despite the burner geometry considered and the chemical composition of the fuel, the Complex Chemistry with “Eddy Dissipation Concept” is the model that better describes the behaviour of the turbulent flames. On the other hand, the “Laminar Flame Concept” sub-model is characterized by an higher fuel consumption rate, which causes an overestimation of the temperature peak. As for the in-cylinder unsteady simulations, the hydrogen combustion process is better described by the “Turbulent Flame Speed Closure” sub-model, which, unlike the other two, requires the specification of both laminar and turbulent flame speed. Despite different variations being considered, the “Laminar Flame Concept” adoption leads to an unphysically high burning rate, while the Eddy Dissipation Concept sub-model is characterized by an underestimation of the apparent heat release rate, and thus of the pressure peak inside the combustion chamber.

Study on the influence of some factors on the high burning rate of energy-carrying materials based on acrylonitrile butadiene rubber with end-chain carboxyl group

Heterogeneous energy-carrying materials possess outstanding advantages compared to other energy-carrying materials, therefore, research and development of this type of material to create propulsion for flying objects is an inevitable trend in the field of military science and space. This paper presents the results of research on the influence of a number of factors on the technological properties and combustion rate of heterogeneous energy-carrying materials based on acrylonitrile butadiene rubber CKH-10KTP and ammonium perchlorate (AP).The research results show that the combustion law depends on the pressure of heterogeneous energy-carrying materials based on CKH-10KTP and ultra-fine AP (specific surface area 2.61÷3.85 m2/g), using a combustion catalyst ferrocene derivative. The study also determined the optimal content of combustion catalyst - plasticiser to be 3.5÷3.8%. The research results are a solid scientific basis for optimally determining the parameters of radioactivity, energy of energy-carrying materials, supplementing the national data source in the design of aircraft engines, meeting requirements in the new context.

Visualization study on the ignition and diffusion combustion process of liquid phase ammonia spray ignited by diesel jet in a constant volume vessel

Ammonia fueled engines applying diffusion combustion mode is expected to further improve the thermal and combustion efficiencies with high burning rate and high ammonia energy replacement. However, there is a lack of the fundamental studies about ammonia diffusion combustion characteristics. Therefore, the fundamental optical experiments of liquid phase ammonia spray and combustion, which is ignited by pilot diesel injection, were performed to investigate the ignition and diffusion combustion characteristics of liquid phase ammonia. According to the high-speed photography, interaction processes between the liquid phase ammonia spray and the diesel spray had been described, and the whole ignition and combustion processes were also recorded in detail. The discussion about the effect of diesel jet ignition location on ammonia ignition process shows that the effective ammonia ignition zone by diesel spray is the region of gas entrainment zone except for the liquid phase ammonia volume under evaporated condition, where the interval on ammonia spray axis is about 16 mm ∼ 35 mm away from the ammonia nozzle exit under the current experimental conditions, and the ammonia spray is failed to be ignited at any region out of the effective ignition zone. Moreover, the ammonia diffusion combustion characteristics under various ammonia injection durations reveals that the entrainment, including both the diesel flame and the surrounding ambient gas, into the effective ignition zone of liquid phase ammonia spray, is the effective way to achieve reliable ignition and the subsequent diffusion combustion of ammonia, which can increase the energy ratio (ammonia to pilot diesel) up to at least 2.9. Finally, based on the control of combustion mode of the pilot diesel, utilizing premixed diesel flame to induce the diffusion combustion of ammonia is proved to be an effective regulation scheme to enhance the performance of ammonia combustion under engine-like thermal conditions.

Combustion Characteristics of r-GO/g-C3N4/LaFeO3 Nanohybrids Loaded Fuel Droplets

ABSTRACT Graphene oxide (GO), reduced graphene oxide (r-GO) and graphitic carbon nitride (g-C3N4) are two-dimensional carbon-based nanosheets that show promise in reducing emissions with their superior catalytic activity in capturing species such as NOx and CO2 thanks to their oxygen-based functional groups and active edges on their surfaces. These active surfaces also provide a scheme for the substitution of materials with high calorific value or high catalytic activity for combustion. This study focuses on the fabrication of functional nanohybrid structures customized for combustion with LaFeO3 metal oxide nanoparticles substituted on these nanosheets and their effect on the combustion behavior of gasoline. The fabrication of r-GO/g-C3N4/LaFeO3 nanohybrid structures was carried out by a two-step hydrothermal method. The structural characterizations of the samples were confirmed by SEM and XRD analyses and their chemical states were confirmed by Raman and XPS techniques. Combustion experiments were carried out by droplet scale combustion of gasoline-based nanofuel droplets containing dilute (0.2 wt.%) and high (0.7 wt.%) concentrations of GO, r-GO, g-C3N4, g-C3N4/LaFeO3 and r-GO/g-C3N4/LaFeO3 nanoparticles. The experimental process was recorded with a high-speed camera and a thermal camera. The nanofuel droplets containing 0.2 wt.% g-C3N4/LaFeO3 nanohybrid structures had the highest maximum flame temperature of 519 K, and the nanofuel droplets containing 0.7 wt.% r-GO/g-C3N4/LaFeO3 particles had the highest maximum aggregate temperature of 1177 K. The ignition delay time decreased for all droplets with 0.2 wt.% and 0.7 wt.% particle loadings. At 0.2 wt.% concentration, g-C3N4 doped fuel droplets exhibited the lowest extinction time, while at 0.7 wt.% concentration, the lowest extinction time was measured for r-GO/g-C3N4/LaFeO3 doped fuel droplets. Fuel droplets containing g-C3N4 particles had the highest burning rate and were the fastest extinguishing fuel droplets in the electric field. In this study, it has been demonstrated that the combustion rate and energy value of hydrocarbon fuels can be increased and soot formation can be reduced at the same time with the new generation of graphene-based functional materials to be created, and thus, many combustion problems can be solved simultaneously with these functional particles.