Combustion Efficiency Research Articles

Investigating Artocarpus heterophyllus biodiesel performance using multi-walled carbon nanotubes as an additive

Fuel demand is constantly high due to the widespread use of internal combustion engines in a variety of applications, such as power generation, on-road transportation, agriculture, and marine operations etc. In order to address this need, research on biodiesel has accelerated and is now pursuing many novel directions. This research aims is to use the transesterification process to create biodiesel from the sustainable source of seeds of Artocarpus heterophyllus or jackfruits. Nano-fuels blend prepared by mixing 20 % biodiesel with 80 % diesel and adding the outsourced Multi-Walled Carbon Nanotubes (MWCNTs) at three different concentrations of 40 ppm/L, 80 ppm/L, and 120 ppm/L. The MWCNTs mixed with base fuel blend with the help of an ultrasonicator. A 5.2 kW single-cylinder four-stroke Compression Ignition (CI) engine test rig with load cell arrangement was used to test the neat diesel, neat biodiesel, B20 and nano-fuels at a constant speed of 1500 rpm and various load conditions like no-load, 1.3 kW (25 %), 2.6 kW (50 %), 3.9 kW (75 %), and 5.2 kW (100 %). Performance metrics were compared among nano-fuels, neat diesel, neat biodiesel and B20 Biodiesel blend. The nano-fuel containing 120 ppm of MWCNT was found to have exceptional properties. It achieved a maximum Brake Thermal Efficiency (BTE) of 30.19 % and the lowest BSFC of 0.282 kg/kW-hr and the resource efficiency improved at low energy consumption. Compared to conventional diesel, the 120 ppm MWCNT-enhanced nano-fuel blend produced significant emissions reductions by 31.65 % for NOx, 31.58 % for CO, 12.01 % for hydrocarbons (HC), and 29.79 % for smoke. The improved fuel properties, catalytic effects of the MWCNTs, and optimized combustion dynamics are responsible for the improved performance of the 120 ppm MWCNTs concentrated biodiesel blend. These improvements result in lower emissions and improved combustion efficiency, which makes this nano-fuel formulation ideal for internal combustion engines. By lowering emissions, it not only increases engine efficiency but also has a major positive environmental impact.

CFD Simulation of the Influence of the Type of Gas Distribution in the Burners on Thermal Aerodynamic Processes in the DKVR 10-13 Boiler

Topics related to fuel combustion and its impact on the environment will never lose their relevance, as the issues of efficient combustion and emission reduction are key in power generation and environmental protection. The countries of the European Union are massively abandoning the use of natural gas as a fuel for thermal power stations. However, in Asian countries, the ease of using natural gas as the main fuel and its environmental friendliness compared to coal made it possible to widely use natural gas in industry and energy sector. Comparing natural gas with alternative combustible gases (generator, blast furnace, mine, biogas), the main conclusion that it has the most attractive characteristics for its use in industry, including energy facilities, can be drawn. Therefore, it is impossible to replace it with alternative fuels in the chemical, heavy industry and energy sector in the near future. The paper is devoted to CFD modeling of stabilized combustion without premixing in a burner with low swirl for two operating modes of the boiler unit - nominal one and at 60% capacity. The study was carried out using numerical methods with the ANSYS-Fluent application program package. The object of the study is a burner built according to the technology based on the use of jet-niche systems with gas distribution of fuel by circular jets fed perpendicularly into the flow of the oxidizer through a single-row system of holes. Hydrodynamics and heat exchange processes were chosen as the subject of research, based on the analysis of which a model of NOx generation in jet-niche systems was obtained. The authors of the paper believe that replacing the regular burners of the DKVR-10-13 water heating boiler with a jet-niche ones can contribute to better mixing of fuel and air and ensure more complete combustion. In this paper, two types of burners are considered. In one of the burners, fuel is supplied through rectangular slits, in the other – through round holes arranged in a row. Air is supplied to both burners through rectangular slits. It was determined that gas distribution through round holes increases the spraying of the mixture and increases the area of combustion products spraying. Visualization of the distribution of pressure, temperature, kinetic energy profiles of turbulent pulsations and vorticity was carried out. The obtained results indicate that there are no changes in the flow regime, flame displacement or its instability. It was determined that both the axial velocity and the tangential velocity of the flow affect the distribution of combustion products and harmful impurities such as NOx. Gas distribution in circular jets stabilizes combustion and reduces flame expansion.

Insight into HTPB pyrolysis mechanism under high-temperature: A reactive molecular dynamics study

Hydroxyl-terminated polybutadiene (HTPB) is widely utilized in solid and hybrid rocket propellants due to its mechanical properties and combustion performance. Insight into its pyrolysis process is key to enhancing combustion efficiency in rocket engines. This study employs ReaxFF molecular dynamics (MD) simulations to explore the pyrolysis mechanism of HTPB under extreme conditions, with temperatures ranging from 1000 K to 2000 K. The results identify the primary degradation products and elucidate their formation mechanisms. The simulation reveals that C-C bond cleavage at polymerization sites is the initial step, followed by the formation of linear oligomers and butadiene. Subsequent reactions, including hydrogenation and dehydrogenation, lead to the generation of smaller molecular species. The kinetic analysis confirms that HTPB pyrolysis follows first-order reaction kinetics, with an activation energy of 8.12 kcal/mol. The findings are compared with existing experimental data, highlighting the influence of thermal environments on pyrolysis mechanisms and product distributions.

Evaluation of TiO2 Nanoparticle-Enhanced Palm and Soybean Biodiesel Blends for Emission Mitigation and Improved Combustion Efficiency.

The use of biodiesel as an alternative to conventional diesel fuels has gained significant attention due to its potential for reducing greenhouse gas emissions and improving energy sustainability. This study explores the impact of TiO2 nanoparticles on the emission characteristics and combustion efficiency of biodiesel blends in compression ignition (CI) engines. The fuels analyzed include diesel, SB20 (soybean biodiesel), SB20 + 50 TiO2 ppm, SB20 + 75 TiO2 ppm, PB20 (palm biodiesel), PB20 + 50 TiO2 ppm, and PB20 + 75 TiO2 ppm. Experiments were conducted under a consistent load of 50% across engine speeds ranging from 1000 to 1800 RPM. While TiO2 nanoparticles have been widely recognized for their ability to enhance biodiesel properties, limited research exists on their specific effects on soybean and palm biofuels. This study addresses these gaps by providing a comprehensive analysis of emissions, including NOX, CO, CO2, and HC, as well as exhaust gas temperature (EGT), across various engine speeds and nanoparticle concentrations. The results demonstrate that TiO2 nanoparticles lead to a reduction in CO emissions by up to 30% and a reduction in HC emissions by 21.5% at higher concentrations and engine speeds. However, this improvement in combustion efficiency is accompanied by a 15% increase in CO2 emissions, indicating more complete fuel oxidation. Additionally, NOX emissions, which typically increase with engine speed, were mitigated by 20% with the addition of TiO2 nanoparticles. Exhaust gas temperatures (EGTs) were also lowered, indicating enhanced combustion stability. These findings highlight the potential of TiO2 nanoparticles to optimize biodiesel blends for improved environmental performance in CI engines.

Efficient Combustion of the Fixed Coal Layer in an Advanced Combustion Chamber Design for Low-Power Boilers

In the long term, coal will remain a competitive resource in the thermal power sector, primarily due to its abundant global reserves and low costs. Despite numerous factors, including significant environmental concerns, the global share of coal power generation has remained at 40% over the past four decades. Efficient and clean coal combustion is a high priority wherever coal is used as a fuel. An improved low-power boiler design has been proposed to enhance efficiency during fixed-bed coal combustion. This design reduces harmful emissions into the atmosphere by optimizing parameters and operating modes. In this study, mathematical modeling of gas velocity and temperature distribution during fixed-bed coal combustion was conducted for a conventional grate system and an improved grate-free system. Experimental methods were employed to develop descriptive airflow models in the fixed coal layer, considering nozzle diameter and air supply pressure in the furnace chamber without a grate system. Comparative evaluations of fixed-bed coal combustion rates were performed using an experimental laboratory setup with both grate and grate-free stove systems.

An Experimental and Kinetic Modeling Study of the Laminar Burning Velocities of Ammonia/n-Heptane Blends

Ammonia is carbon-free and is a very promising renewable fuel. The ammonia/diesel dual-fuel combustion strategy is an important combustion strategy for ammonia internal combustion engines. To achieve clean and efficient combustion with a high ammonia blending ratio in ammonia engines, it is important to thoroughly investigate the combustion characteristics and chemical reaction mechanisms of ammonia/diesel fuel blends. Based on the constant volume combustion vessel experiments, the laminar burning velocities (LBVs) of ammonia/n-heptane blends were measured at the conditions of an ammonia–energy ratio of 60–100%, at initial pressures of 0.1–0.5 MPa and initial temperatures of 338–408 K, and under an equivalence ratio regime of 0.8–1.3. The experimental results indicate that the laminar burning velocities of ammonia/n-heptane fuel blends increase with a decreasing ammonia–energy ratio. Specifically, with an ammonia–energy ratio of 60%, an initial temperature of 373 K, an initial pressure of 0.1 MPa, and an equivalence ratio of 1.1, the measured LBV is approximately 20 cm/s, which is about 61% faster than that of pure ammonia flames under the same conditions. A previously developed chemical kinetic mechanism is employed to simulate the new experimental data, and the model exhibits overall good performance. The sensitivity analyses have been conducted to highlight the important reaction pathways. The elementary reaction O2 + Ḣ<=>Ö + ȮH demonstrates the most significant promotional effect on the laminar burning velocities, while the interaction reaction pathways of via H-abstraction from n-heptane by ṄH2 radicals are not showing obvious effects on the simulation results under the studied conditions.

Efficient preparation of core–shell Al@PFHP@fluoropolymer energetic composites combining corrosion resistance and high energy release properties

The study employed a two-step synthesis method to prepare Al@PFHP@fluoropolymer energetic composites with a core–shell structure. PFHP and HF acid are used for surface etching and modification of raw Al powder. PFHP bonds to the surface of Al powder, with redundant C-F providing hydrogen bonding sites, driving dissolved PVDF and P(VDF-HFP) polymer chains in the liquid phase to migrate, nucleate, and grow on the surface of the Al powder, and consequently the formation of a continuous shell layer through hydrogen-bonding self-assembly. The Al powder coated with fluoropolymer exhibited strong hydrophobic and corrosion-resistant properties, ensuring long-term storage and environmental adaptability. Compared to mechanically mixed Al@PFHP/fluoropolymer, the Al@PFHP@fluoropolymer composites show significant improvements in thermal reactivity, ignition, and combustion performance. The close integration of fluoropolymer and Al shortens the mass and heat transfer distances during the reaction process. Additionally, the low-boiling-point AlF3 does not hinder diffusion process in the combustion zone, which is conducive to the alleviation of the reaction sintering phenomenon and the rapid and concentrated release of energy. Therefore, through the dual strategy of using fluorine-containing oxidizers and structure optimization, efficient reaction of Al@PFHP@fluoropolymer is achieved, also promoting efficient combustion of Al powder. The synthesis process of this energetic composite is simple yet yields exceptionally high performance, enabling large-scale production and application potential in military ammunition and rocket propulsion systems.

Effect of combustion temperature on the unburnt carbon during ammonia co-firing with coal combustion.

Ammonia co-firing with coal seems to be the preferred approach to reduce unburnt carbon in existing pulverized coal-fired power plants. However, some operational conditions such as combustion temperature need to be carefully considered. As such, this study investigated the effect of combustion temperature on the unburnt carbon during ammonia co-firing with pulverized coal. Horizontal tube furnace with ammonia injection was employed and operating at different combustion temperature (800 to 1200 oC). Proximate analysis results showed that the raw coal sample contained 64.2 wt% fixed carbon. Additionally, based on the several analyses employed to assess the effect of combustion temperature efficacy on the unburnt carbon reduction, an effective combustion efficiency was achieved with ammonia co-firing with coal. X-ray fluorescence results revealed that SiO2 for the co-firing experiment decreased from 56.7476 wt% (800 oC) to 45.9423 wt% (1200 oC) while carbon decreased from 20.06 to 18.32 wt%, at the same combustion temperature respectively. X-ray diffraction also revealed a well-defined peak at 2θ = 25o, a graphite characteristic, which decreased significantly with increasing temperature, signifying unburnt carbon reduction. Thus, it can be confirmed that ammonia co-firing with coal can be used to improve the combustion efficiency coal fired power plants.

Effect of Torrefaction Process on the Physicochemical Properties of Solid Fuel from Palm Kernel Shells

This research investigates the effects of torrefaction on the characteristics of solid fuel made from palm kernel seed (PKS). The torrefaction process was conducted on raw PKS to improve its energy density and combustion efficiency. Torrefaction was carried out at 400°C at different durations (30, 40, and 50 minutes), with the goal of improving the energy density and combustion efficiency of raw PKS. The torrefied PKS was then ground and sieved into particle sizes of 150mm and 300mm. After being blended with high-density polyethylene (HDPE), the torrefied PKS was compacted using hot press machine into solid fuel and tested for its physicochemical properties. The results indicated that PKS torrefied for 50 minutes with particle size of 300 mm exhibited optimal characteristics, with a high heating value (HHV) of 23.22 MJ/kg. The particle size plays a role, with finer particles (150mm) having lower HHV values compared to coarser particles (300mm). Additionally, the inclusion of HDPE affected the properties of the solid fuel. Morphological analysis using scanning electron microscopy provided insights into its structural features.

TO THE ISSUE OF NON-PROJECT FUEL COMBUSTION

Nowadays, the issues of ecology and sustainable development are becoming more and more urgent, and the scientific community is actively looking for ways to more efficient and environmentally friendly use of renewable energy sources. One of such directions is the development and improvement of coal combustion technologies in aerodynamic furnaces. This paper offers a detailed analysis of this topic, looking at both theoretical aspects and practical applications. Aerodynamic furnaces are specialised devices designed to burn solid fuels such as coal with maximum efficiency and minimum environmental impact. The basic principle of operation of such furnaces is to create optimum conditions for complete combustion of the fuel, which is achieved through carefully designed aerodynamics and process control. The operation of the boiler on the coal of Karazhyra deposit is considered. This coal belongs to non-project fuel and improvement of its combustion processes is required to reduce harmful emissions and increase combustion efficiency. For the energy sector of the Republic of Kazakhstan, the conducted research is important, and the results obtained can be used to regulate and improve the operation of similar equipment, which contributes to improving environmental performance and overall efficiency of the country's energy systems.

A Numerical and Experimental Performance Assessments of an Improved Natural Draft Biomass Cook Stove

ABSTRACT This article analyses the performance of an efficiently designed biomass cook stove using standard performance parameters. The investigation was first conducted using mathematical modeling developed in the ANSYS Fluent software. The results of primary air and the temperature profiles inside the combustion chamber were found through simulation. It revealed that the flue gas left the combustion chamber with an average velocity of 1.7 m/s. The average pot bottom and fuel bed temperatures were 650 K and 1100 K, respectively. A copper coil was wrapped around the combustion chamber wall to recover its waste heat. The recovered waste heat was utilized to warm the water flowing through the copper coil. The heated water could be used for other domestic applications. The fabricated design of the improved stove was experimented with water boiling test. The maximum thermal efficiency achieved was 42% with a firepower of 8.25 kW, after incorporating the waste heat recovery system, corresponding to 7.5 L test. The overall efficiency, which is the product of the modified combustion efficiency and the maximum thermal efficiency, was found to be 41.50%. The performance was found to be significantly better than that of a commercial biomass cook stove. The developed model was also evaluated for indoor CO, CO2 and PM emissions. The highest levels of CO2 and CO were 940 ppm and 23 ppm. The average amount of PM1, PM2.5 and PM10 found out to be 18 µg/m3, 20 µg/m3 and 35 µg/m3 respectively.

Study on laminar combustion characteristics and the optimization of the coupling mechanism in a mixture of propanol and gasoline

When both isopropanol and n-propanol are incorporated, the utilization of propanol as a fuel substitute (or a gasoline additive) presents promising potential for enhancing the combustion efficiency and thermal performance in compact, turbocharged, direct-injection gasoline engines upon blending. However, the complexity of the laminar combustion behavior of propanol-blended gasoline has yet to be fully investigated, as current coupling mechanisms are insufficiently sophisticated to precisely mirror the complex experimental conditions.This study establishes a testbed specifically designed for measuring laminar burning velocity (LBV) using the heat flux method. This setup is employed to measure the LBV of pure n-heptane and isooctane, as well as the LBV of the gasoline surrogate fuel TRF with two distinct blend ratios. Additionally, it measures the LBV of propanol and its blends with TRF. The research findings reveal that isooctane demonstrates a heightened sensitivity to fuel preheating temperature, whereas the toluene proportion in TRF fuels exerts the most pronounced influence on combustion behavior. At an equivalence ratio of 1.1, the LBV of n-propanol differs from that of its isomer, isopropanol, by 4.65 cm/s. Notably, the LBV exhibits a discernible upward trend, corresponding to the increasing proportion of toluene in the blended fuel. Furthermore, there is a pronounced distinction in LBV among the propanol isomers, with blended TRF occupying an intermediate position between pure propanol and TRF. After the enhancement of the mechanism based on experimental benchmarks of LBV, a rigorous validation process demonstrated a substantial improvement in the alignment between simulated outcomes and empirical LBV measurements.

Modeling of thermo-aerodynamic and environmental parameters on the example of a two-pipe water heating boiler that has worked out the park resource

Topics related to fuel combustion and its impact on the environment will never lose their relevance, as the issues of efficient combustion and emission reduction are key in power generation and environmental protection. The countries of the European Union are massively abandoning the use of natural gas as a fuel for thermal power station. However, in Asian countries, the ease of using natural gas in industry as the main fuel, its environmental friendliness compared to coal, made it possible to widely use natural gas in industry and energy. Comparing natural gas with alternative combustible gases (generator, blast furnace, mine, biogas), the main conclusion can be drawn that it has the most attractive characteristics for its use in industry, including energy. Therefore, it is impossible to replace it with alternative fuels in the chemical, heavy industry and energy industry in the near future. The presented work is devoted to CFD modeling of stabilized combustion without premixing in a burner with low swirl for two operating modes of the boiler unit - nominal and at 60% capacity. The study was carried out using numerical methods using the ANSYS-Fluent application program package. The object of the study is a burner built according to the technology based on the use of jet-niche systems with gas distribution of fuel by circular jets fed perpendicularly into the flow of the oxidizer through a single- row system of holes. Hydrodynamics and heat exchange processes were chosen as the subject of research, based on the analysis of which a model of NO x generation in SNS was obtained. In this work, two types of burners are considered. In one of the burners, fuel is supplied through rectangular slits, in the other – through round holes arranged in a row. Air is supplied to both burners through rectangular slits. It was determined that gas distribution through round holes increases the spraying of the mixture and increases the area of spraying of combustion products. Visualization of the distribution of pressure, temperature, kinetic energy profiles of turbulent pulsations and vorticity was carried out. The obtained results indicate that there are no changes in the flow regime, flame displacement or its instability. It was determined that both the axial velocity and the tangential velocity of the flow affect the distribution of combustion products and harmful impurities such as NO x . Gas distribution in circular jets stabilizes combustion and reduces flame expansion.

Environmental assessment of the hydrogen combustion process in non-premixed gas turbines

Using cleaner fuels, such as hydrogen and developing more efficient combustion technologies are crucial in reducing NOx and N2O emissions, contributing to environmental concerns like air pollution and global warming. However, studies focusing on gas turbines using H2 as fuel often overlook the emissions resulting from H2 combustion. Given that gas turbines play a significant role in electricity generation globally, even minor improvements in their efficiency can lead to substantial cumulative benefits. Therefore, this study aims to address this gap by conducting a comprehensive environmental assessment using the life cycle assessment (LCA) methodology. By evaluating the environmental impacts of emissions from the combustion process of a conventional gas turbine and comparing them with potential emissions from H2combustion, this research seeks to provide valuable insights into the overall environmental performance of these technologies and contribute to sustainable energy development efforts. There have already been several LCA studies on H2 production. In this study, we have identified the potential emissions and environmental impacts of H2 combustion in gas turbines and compared them with the impact values of H2 production regarding reference studies. The result shows that emissions during combustion should be considered in the identified life cycle impact categories.

Effect of mainstream-forced-entrainment control strategy on the combustion performance of a cavity-based combustor

The trapped vortex combustor (TVC) displays potential for use in advanced aircraft engines because of its excellent combustion stability with a compact geometry. However, the existence of forced-entrainment phenomenon in the mainstream poses obstacles to the practical application of TVC. This study introduces passive control strategies using modified radial struts to address the issue of mainstream-forced-entrainment in a TVC. Additionally, experimental and numerical studies were conducted to investigate how the mainstream-forced-entrainment control strategy on the combustion performance of a TVC. The findings suggest that the inclined strut (case-2) and longer-vertical strut (case-3) are more effective than the short-vertical strut (case-1) in reducing mainstream entrainment into the cavity. This results in a larger vortex structure and a more concentrated fuel distribution within the cavity of case-2 and case-3, as compared to case-1. Consequently, case-2 and case-3 achieved much better ignition and lean blowout limit and combustion efficiency performances compared to case 1.

Investigation of Al-Li particle ignition dynamics with different Li content

Promoting the ignition of aluminum powder is considered an effective method to inhibit the agglomeration of aluminum powder in propellants and enhance combustion efficiency. This study utilizes laser ignition technology and high-speed photography to investigate the ignition and combustion processes of single aluminum particles and aluminum-lithium alloy particles. The focus is on comparing the effects of the diameter of micron-sized metal particles and the lithium content in aluminum-lithium alloy particles on the ignition and combustion processes of metal particles. The results show that the ignition delay time is directly proportional to the diameter of the metal particles and inversely proportional to the lithium content. For the aluminum-lithium alloy particle with a lithium content of 3.5 %, even if the diameter is close to 300 μm, the ignition delay time is only 125.5 ms, which is much smaller than that of the pure aluminum particle with a diameter of 208 μm. Compared to aluminum particles and aluminum-lithium alloy particles, there is basically no difference between the two during the combustion stage. However, in the ignition stage, aluminum-lithium alloy particles sequentially exhibit a red gas-phase flame corresponding to lithium and a yellow gas-phase flame corresponding to aluminum. This indicates that during the ignition process of aluminum-lithium alloy particles, lithium first reacts with the oxidative atmosphere and releases heat, providing a heat source for the subsequent ignition of aluminum particles. This also explains why the ignition delay time of metal particles is inversely proportional to the lithium content. An ignition model for aluminum particles in a multi-component atmosphere is established, which further considers the chemical reactions between lithium and oxidative gases, making the model applicable to aluminum-lithium alloy particles. This ignition model effectively describes the impact of particle diameter and lithium content on the ignition process of metal particles. The model is further verified, and the results show that the calculated ignition delay is in good agreement with the experimental data. Overall, this study provides deeper experimental and theoretical insights into the ignition and combustion processes of aluminum-lithium alloys, and the findings can guide the application of aluminum-lithium alloys in propellants.

High spatiotemporal resolution optical measurements of two-stage ignition and combustion in Engine Combustion Network Spray D flames

This study explores flame structures and combustion dynamics in high-pressure n-dodecane fuel sprays, focusing on the formation and consumption of formaldehyde (CH2O) during autoignition and the development of poly-aromatic hydrocarbons (PAH) as soot precursors. These processes are crucial for optimizing combustion efficiency and reducing emissions. However, traditional approaches, which rely on single-shot measurements or ensemble-averaged visualizations, often overlook critical early-stage processes during low-temperature ignition. To overcome these challenges, we employed an innovative high-speed planar laser-induced fluorescence (PLIF) technique at 50 kHz using a pulse-burst Nd:YAG laser system with an excitation wavelength of 355 nm. This approach, applied for the first time to Engine Combustion Network (ECN) Spray D flames, provides unprecedented insights into the combustion processes at varying ambient temperatures and oxygen concentrations. Additionally, simultaneous high-speed schlieren imaging at 100 kHz was used to visualize spray penetration, first-stage ignition, and thermal expansion zones. Our findings reveal that, similar to Spray A flames, CH2O forms in cold, fuel-rich zones well upstream of the combustion zone. However, in Spray D flames, the schlieren signal softening observed in the jet's head does not lead to complete disappearance, and the CH2O signal is absent from the full head of the spray. During the second-stage ignition, CH2O consumption accelerates due to high-temperature reactions, leading to a significant reduction in its signal. Unlike the mushroom-shaped structure seen in Spray A flames, Spray D flames exhibit a quasi-steady PAH phase structure, with lean peripheral mixtures insufficient for soot precursor formation. Notably, reducing ambient oxygen concentration to 13 % while maintaining or increasing temperature prolongs the presence of CH2O, highlighting its influence on ignition dynamics and oxidation processes in dodecane spray flames. This study provides new insights into the combustion mechanisms of high-pressure sprays and offers valuable data for developing next-generation combustion technologies, including models, aimed at improving efficiency and reducing emissions.

Thermal deviation mechanisms for coupled heat transfer between the combustion side and the furnace tube side in the tubular heating furnace

Temperature deviation significantly affects the safe operation of tubular heating furnaces. This is attributed to the inevitable temperature difference between the flue gas and the working medium on the tube side. To date, little research has considered the dynamic heat transfer between the furnace body and the tubes in tube furnaces, and even less attention has been paid to the thermal deviation within tube furnaces. To optimize the operational parameters of the heating furnace, a comprehensive heat transfer model is established in this paper to numerically couple the heat transfer between the combustion side and the working medium on the tube side in tube furnaces. A hydrogenation feed heating furnace with a processing capacity of 600,000 tons per year in a chemical enterprise is selected as the subject of study. Using Fluent software, on the basis of coupled simulation, a non-uniformity coefficient of temperature distribution is introduced to characterize the thermal deviation within the furnace. The impact of the thermal load and hydrogen doping in the fuel gas on the thermal deviation within the furnace is analyzed. The numerical results demonstrate that with an increase in thermal load, the flame structure in the furnace gradually becomes concentrated, the average temperature of the flue gas increases, and the outlet temperature of the furnace chamber increases by 19%, with the thermal efficiency decreasing by 5.11%; at the same time, the overall non-uniformity coefficient of the temperature distribution in the furnace fluctuates irregularly, indicating a nonlinear relationship between the thermal load and the thermal deviation within the furnace. With an increase in the hydrogen content in the fuel gas, the flame structure in the furnace becomes more dispersed, the average temperature of the flue gas increases, but the combustion efficiency of the heating furnace exhibits irregular fluctuations; the thermal deviation within the furnace initially increases and then decreases, with a lower non-uniformity coefficient of temperature at 50% hydrogen content, which is 2.48% lower than at 40% hydrogen content. Under both conditions, the thermal deviation primarily leads to localized hot spots in the radiant furnace tubes and uneven temperature distribution in the convection section, with a minimal impact on the thermal efficiency of the heating furnace.

Combination of high cetane diesel fuel and post injection mode in a diesel engine: A path towards lower exhaust emissions

The major objective of the presented work is to explore the effect of post injection (PI) strategy using neat diesel fuel (D100) blended with cetane number enhancer (CNE). The motive behind adding CNE in diesel fuel was to lower its self-ignition temperature and hence delay period subsequently. This can lead to more efficient combustion of post injected fuel which leads to lower incomplete combustion losses. The CNE used was Di-Tert-Butyl Peroxide (DTBP) which was blended with D100 in proportion of 1 % by volume. Initially experiments were conducted with D100 under various PI modes where variation of post injection timing (PIT) as well as post quantity (PQ) was considered. The experimental results showed that implementing PI resulted in lower smoke, unburned hydrocarbon (UHC), carbon monoxide (CO) and nitrogen oxides (NOx) emissions compared to single injection while affecting fuel consumption negatively. Then after similar experiments under various PI modes were repeated using blends of D100 and DTBP (D/DTBP) and results were compared with D100 case. It was found that addition of CNE in D100 resulted in more complete combustion of post fuel which further reduced CO and UHC emissions. The shorter delay period in case of D/DTBP blend compared to D100 case led to lower NOx emissions as well as higher smoke emissions. The obtained results revealed that PI mode with 3 mg PQ and 20° after top dead center (ATDC) PIT with D/DTBP blend offered 41.18 %, 17.55 %, 64 % and 62.5 % reduction in smoke, NOx, UHC and CO emissions respectively compared to single injection mode using D100 fuel.

Iron particle in liquid fuel combustion technology for nonoxidative storage and easy burning

This study investigates an iron particle in liquid fuel combustion technology with liquid fuel as an anti-oxidization agent for the iron fuel particles, which has the advantage of easy combustion and nonoxidative iron particle storage. These slurry like iron particles in liquid fuel can be ideal for furnaces and boilers. Micron and nano-sized iron particles, concentrated at a 30% mass fraction, demonstrate enhanced reductions in total combustion time and increased micro-explosion intensity. The study observes that suspensions of micron-sized particles progress through preheating, ignition, stable combustion, and intense micro-explosion. In contrast, a dense colloidal suspension of iron nanoparticles in diesel fuel undergoes preheating, classical combustion, bubble growth with low-intensity secondary atomization, and the combustion of agglomerated nanoparticles, resulting in a glowing solid residue. A hybrid dense colloidal formulation incorporating micron and nano suspensions at a combined mass fraction of 30% was introduced to prevent particle agglomeration and achieve faster micro-explosions. This formulation leads to a significant 83 % reduction in total combustion time. The distinctive behavior is attributed to iron nanoparticles’ higher specific surface area, leveraging diesel’s nucleation and bubble growth for mid-intensity puffing within the droplet. Nucleation metastability intensifies superheating values, leading to internal pressure in the bubble grown via homogeneous nucleation and culminating in intense puffing, followed by a micro-explosion. This cascade effect highlights the potential of iron particles as a clean source with high energy density, providing novel insights for practical industrial applications. The observed micro-explosion intensity underscores the promise of this innovative approach, paving the way for advancements in cleaner and more efficient iron particle slurry combustion technology.