Combustion Problems Research Articles

Influence of Blending Ratio on Spray Characteristics of Gasoline–Hydrogenated Catalytic Biodiesel Blended Fuel

Blending gasoline with hydrogenated catalytic biodiesel has the potential to improve combustion problems of gasoline direct-injection compression combustion, and the spray characteristics of the blending fuel can directly affect the combustion effect. In order to understand the spray characteristics of a gasoline–hydrocatalyzed catalytic biodiesel mixture, a numerical spray model of constant volume combustion chamber was established, and the accuracy of the model was verified by experimental data in the literature. Based on this model, the spray penetration, sauter mean diameter, spray velocity field and concentration field of gasoline–hydrocatalyzed catalytic biodiesel at different blending ratios were studied. The results show that under the conditions of 850 K ambient temperature, 5 MPa ambient pressure, and 80 MPa injection pressure, as the proportion of hydrogenated catalytic biodiesel in the blending fuel increases, the spray penetration increases, the sauter mean diameter decreases slightly, and the area of high velocity and high concentration at the spray center increases. The results of this study will contribute to the development of blended fuels for superior combustion performance and reduced pollutant emissions at appropriate blending ratios.

Impact of mixed boundary conditions and nonsmooth data on layer‐originated nonpremixed combustion problems: Higher‐order convergence analysis

Impact of mixed boundary conditions and nonsmooth data on layer‐originated nonpremixed combustion problems: Higher‐order convergence analysis

Benchmarking of primary measures to achieve lowest NOx emissions in small-scale biomass grate furnaces

Despite recent progress, NOx is still a major problem in biomass combustion, especially when using fuels with high nitrogen contents. The aim of this work was to determine the minimum NOx emissions achievable by applying primary measures in small-scale biomass grate furnaces. For this purpose, a new benchmark for furnaces using double air staging was defined on the basis of three different plants. An experimental study with different biomass fuels was conducted in two of these plants to systematically improve this benchmark.The results show that the new NOx benchmark using double air staging is up to 39 % lower than values achieved with conventional single air staging. Furthermore, this new benchmark was improved by extending the reduction zone, additionally reducing the NOx by up to 30 %. Secondary flue gas recirculation and partial load further reduced the NOx emissions.By combining the primary measures investigated in the 70-kW furnace, NOx emissions were achieved that were up to 70 % lower than those from other small-scale furnaces described in the literature. This efficiency also applies to fuels with a high nitrogen content, so that secondary NOx reduction measures can be avoided in most cases in furnaces in the future by taking this approach.

An experimental study of surrogates of diesel from indirect coal liquefaction and the development of an improved kinetic mechanism

The increasing energy shortage and environmental pollution make the use of clean and efficient alternative fuels an effective way to solve the emission problem. Diesel from indirect coal liquefied (DICL) is a clean and efficient alternative fuel for diesel engines. The composition and chemical kinetics mechanism of DICL research contributes to a better understanding of combustion and pollutant formation process. The components of DICL were analysed by gas chromatography-mass spectrometry (GC-MS). The proportion of normal alkanes contained in DICL is particularly high, 93.82%, which proves that its reactivity is particularly good. The mixture of n-dodecane and iso-octane was selected as the surrogates of DICL. The oxidation process of DICL surrogates was examined by a jet-stirred reactor (JSR) over the temperature range of 500–890 K. A detailed kinetic mechanism of surrogates encompassing 1356 species and 6008 reactions was constructed. The critical reactions associated with the reactivity of surrogates were adjusted by the sensitivity analysis method to increase the accuracy of mechanism prediction. The predicted value of the improved mechanism is in good agreement with the experimental value. The improved mechanism can reasonably predict the oxidation process and the ignition characteristics of DICL and the improved mechanism can provide a good reference value for the subsequent analysis of combustion and emission problems of DICL. Abbreviations: C/H, C/H ratio; CN, cetane number; DDCL, direct coal liquefy diesel; DICL, Diesel from indirect coal liquefied; GC-MS, gas chromatography-mass spectrometry; HMN, 2,2,4,4,6,8,8-heptamethylnonane; HXN, n-hexadecane; IDT, ignition delay time; JSR, jet-stirred reactor; LHV, low heating value; LLNL, Lawrence Livermore National Laboratory; NSRL, National Synchrotron Radiation Laboratory; NTC, negative temperature coefficient; PICS, photoionization cross section; PRF, gasoline substitute; PSR, perfectly stirred reactor; SVUV-PIMS, Synchrotron VUV photoionization mass spectrometry; TOF-MS, time-of-flight mass spectrometer

ReactionMechanismSimulator.jl: A modern approach to chemical kinetic mechanism simulation and analysis

AbstractWe present ReactionMechanismSimulator.jl (RMS), a modern differentiable software for the simulation and analysis of chemical kinetic mechanisms, including multiphase systems. RMS has already been applied to problems in combustion, pyrolysis, polymers, pharmaceuticals, catalysis, and electrocatalysis. RMS is written in Julia, making it easy to develop and allowing it to take advantage of Julia's extensive numerical computing ecosystem. In addition to its extensive library of optimized analytic Jacobians, RMS can generate and use Jacobians computed using automatic differentiation and symbolically generated analytic Jacobians. RMS is demonstrated to be faster than Cantera and Chemkin in several benchmarks. RMS also implements an extensive set of features for analyzing chemical mechanisms, including a library of easy‐to‐call plotting functions, molecular structure resolved flux diagram generation, crash analysis, traditional sensitivity analysis, transitory sensitivity analysis, and an automatic mechanism analysis toolkit. RMS implements efficient adjoint and parallel forward sensitivity analyses. We also demonstrate the ease of adding new features to RMS.

Projection-based reduced order modeling of multi-species mixing and combustion

High-fidelity simulations of mixing and combustion processes are computationally demanding and time-consuming, hindering their wide application in industrial design and optimization. This study proposes projection-based reduced order models (ROMs) to predict spatial distributions of physical fields for multi-species mixing and combustion problems in a fast and accurate manner. The developed ROMs explore the suitability of various regression methods, including kriging, multivariate polynomial regression (MPR), k-nearest neighbors (KNN), deep neural network (DNN), and support vector regression (SVR), for the functional mapping between input parameters and reduced model coefficients of mixing and combustion problems. The ROMs are systematically examined using two distinct configurations: steam-diluted hydrogen-enriched oxy-combustion from a triple-coaxial nozzle and fuel-flexible combustion in a practical gas-turbine combustor. The projected low-dimensional manifolds are capable of capturing important combustion physics, and the response surfaces of reduced model coefficients present pronounced nonlinear characteristics of the flowfields with varying input parameters. The ROMs with kriging present a superior performance of establishing the input–output mapping to predict almost all physical fields, such as temperature, velocity magnitude, and combustion products for both test problems. The accuracy of DNN is less encouraging owing to the stringent requirement on the size of training database. KNN performs well in the region near the design points but its effectiveness diminishes when the test points are distant from the sampling points, whereas SVR and MPR exhibit large prediction errors. For the spatial prediction at unseen design points, the ROMs achieve a prediction time of up to eight orders of magnitude faster than conventional numerical simulations, rendering an efficient tool for the fast prediction of mixing and combustion fields and potentially an alternative of a full-order numerical solver.

Adaptive detached eddy simulation of turbulent combustion with the subgrid dissipation concept

Detached eddy simulation has become a widely used method in eddy simulations due to its balance between cost and accuracy. The recently developed subgrid dissipation concept (SDC) combustion model [Liu et al., “On the subgrid dissipation concept for large eddy simulation of turbulent combustion,” Combust. Flame 258, 113099 (2023)] is found to be more reasonable and accurate than the conventional eddy dissipation concept model in large eddy simulation (LES). In this paper, the SDC model is adapted to the ℓ2-ω adaptive detached eddy simulation framework, named DES-SDC. The required key quantities, including the fine structure mass fraction and dissipation rate, are appropriately blended across Reynolds-averaged Navier–Stokes and LES regions. The DES-SDC approach is validated using premixed bluff body stabilized flame, non-premixed swirl flame, and premixed swirl flame with complex geometry. It is much more tolerant to coarse mesh resolution than pure LES, yet it preserves the capability of resolving the key unsteady feature critical for the combustion process, as it is designed to be. The DES-SDC approach is relatively insensitive to the grid resolution. The present research provides a promising approach for accurately simulating practical unsteady turbulent combustion problems at an affordable computational cost.

Variable Time-stepping Exponential Integrators for Chemical Reactors with Analytical Jacobians

Chemical combustion problems are known to be stiff and therefore difficult to efficiently integrate in time when numerically simulated. Implicit methods, such as backwards differentiation formula (BDF), are widely considered to be the state-of-the-art methods owing their capability of taking relatively large time-steps while maintaining accurate combustion characteristics. Exponential time integration methods have recently demonstrated the ability to accurately and efficiently solve large scale systems of ordinary differential equations. This study introduces a novel adaptive time stepping exponential integrator named EPI3V. Its performance is measured on spatially homogeneous isobaric reactive mixtures involving three hydrocarbon fuel mechanisms. The full combustion process is simulated using gas compositions with sufficient temperature to obtain auto-ignition. Simulations are run until the steady state is obtained, then a comparison of the computational efficiency and accuracy between a BDF and EPI3V method is made. The novel EPI3V method exhibits comparable computational efficiency to a well-established implementation of the variable time-stepping BDF implicit methods for two of the mechanisms investigated. In certain situations it even demonstrates a slight advantage over the implicit solver. However, in one specific case, the EPI3V shows relative performance degradation compared to the implicit method, but it still converges for this case. These results indicate that exponential time integration methods may be applicable to a larger variety of combustion problems.

Preparation and performance study of OPC-MF-PEG microcapsules based on strong antioxidant groups against spontaneous coal combustion

In order to solve the problem of spontaneous combustion of coal in the air-mining area, flame-retardant microcapsules were prepared by in-situ polymerization. OPC-MF-PEG flame-retardant microcapsules were prepared by selecting proanthocyanidin (OPC) as the core material of the microcapsules, polyethylene glycol-modified Melamine resin (hereinafter referred to as modified resin) as the shell. The microcapsules were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), stability analysis experiments, thermogravimetric analyzer (TG), and other experiments in terms of their surface morphology, dispersion, encapsulation, pyrolysis, and other properties. On this basis, the microcapsules were mechanically mixed with coal samples to prepare chemically inhibited coal samples. The effects of microcapsules with different core-to-wall ratios on the spontaneous combustion characteristics of coal were investigated by TG experiments. The results showed that the flame retardant effect was best when the core-to-wall ratio was 3:1. According to the analysis of the combustion experiment results, the CO concentration of the coal samples treated with microcapsules was reduced by 57.5% and 22.5% compared with that of the pure coal and OPC-treated coal samples.

Impact of flash boiling spray on soot generation of a rich fuel–air mixture under various ambient pressures

Particulate emission is one of the critical challenges for the modern gasoine direct injection (GDI) engines. Especially under cold start conditions, the global equivalence ratio inside the cylinder is often set quite rich, leading to the generation of a large amount of soot. The fuel distribution state, such as homogeneous mixing and heterogeneous mixing with local rich pockets prior to the combustion is the key factor affecting soot generation under cold start conditions in GDI engines. Flash boiling injection, as a method to promote fuel air mixing, could be a potential solution to sooting problems of rich mixture combustion under cold start conditions. However, the unclear influences of flash boiling spray to fuel–air mixing state and subsequent soot generation pose a challenge to soot reduction in GDI engines. This work aims to study the effect of various flash boiling degrees on fuel–air mixture formation and subsequent soot generation utilizing a customized constant volume combustion chamber (CVCC) incorporated with the gasoline direct injection scheme under moderately cold start ambient temperature of 30 °C. A global high equivalence ratio of 1.7 representing extremely rich combustions under cold start conditions is selected for strong sooting propensity. By setting different fuel temperatures (Tf= 30 °C and 120 °C) and various ambient pressures (Pa= 40 kPa, 100 kPa and 160 kPa), various spray flash boiling states (subcooled, transitional flash boiling and flare flash boiling sprays) are achieved, and finally various fuel distribution states of rich mixtures prior to combustion are obtained. High speed color camera and soot sampling TEM grids were used to capture and evaluate the characteristics of spray atomization, combustion and soot aggregate structures. Based on this investigation, the effect of flash boiling degree on fuel–air mixing and subsequent soot generation is analyzed. The results show that flash boiling spray enhances fuel atomization and produces much more homogeneous rich mixture with smaller local rich pockets and richer global premixed gaseous portion. Over-rich global premixed mixture combustion is prone to nuclei inception and agglomeration, producing soot aggregates with small primary particles. While the local rich pocket combustion is prone to surface growth, producing larger primary particles. Flash boiling spray could reduce the size of soot particles under cold start conditions by generating smaller local rich pockets.

PeleMP: The Multiphysics Solver for the Combustion Pele Adaptive Mesh Refinement Code Suite

Abstract Combustion encompasses multiscale, multiphase reacting flow physics spanning a wide range of scales from the molecular scales, where chemical reactions occur, to the device scales, where the turbulent flow is affected by the geometry of the combustor. This scale disparity and the limited measurement capabilities from experiments make modeling combustion a significant challenge. Recent advancements in high-performance computing (HPC), particularly with the Department of Energy's Exascale Computing Project (ECP), have enabled high-fidelity simulations of practical applications to be performed. The major physics submodels, including chemical reactions, turbulence, sprays, soot, and thermal radiation, exhibit distinctive computational characteristics that need to be examined separately to ensure efficient utilization of computational resources. This paper presents the multiphysics solver for the Pele code suite, called PeleMP, which consists of models for spray, soot, and thermal radiation. The mathematical and algorithmic aspects of the model implementations are described in detail as well as the verification process. The computational performance of these models is benchmarked on multiple supercomputers, including Frontier, an exascale machine. Results are presented from production simulations of a turbulent sooting ethylene flame and a bluff-body swirl stabilized spray flame with sustainable aviation fuels to demonstrate the capability of the Pele codes for modeling practical combustion problems with multiphysics. This work is an important step toward the exascale computing era for high-fidelity combustion simulations providing physical insights and data for predictive modeling of real-world devices.

The synergistic effect mechanism of H2 generation during coal/ammonia co-pyrolysis

Coal/ammonia (NH3) co-combustion faces the problem of unstable ignition and combustion due to the high ignition temperature and low flame propagation speed of NH3. The pre-pyrolysis of coal and NH3 generates combustible gases such as hydrogen (H2) that aid in enhancing the stability of the subsequent ignition and combustion process. In this paper, the synergistic effect mechanism of H2 generation during coal/NH3 co-pyrolysis are investigated by constant temperature thermogravimetric experiments and reactive molecular dynamics (ReaxFF MD) simulations. The experimental results show that NH3 promotes coal pyrolysis, leading to an increase in the release of coal pyrolysis volatiles during coal/NH3 co-pyrolysis. Furthermore, both experimental and ReaxFF MD simulations results affirm a synergistic effect on H2 generation during coal/NH3 co-pyrolysis. The atomic labeling method is employed to reveal the mechanism of the synergistic effect on H2 generation during coal/NH3 co-pyrolysis. It is found that H2 generated solely from either coal or NH3 during co-pyrolysis is lower than that from the individual pyrolysis of coal or NH3, respectively. The synergistic effect on H2 generation during coal/NH3 co-pyrolysis is mainly attributed by the interactions between coal and NH3, resulting in the generation of coupling H2. The main reaction pathways for H2 generation during coal/NH3 co-pyrolysis are determined by analyzing the frequencies of H2 generation reactions. The mechanisms of the coupling H2 generation are revealed by tracing to the source of the important reactants in the main reactions for H2 generation. The coupling H2 are mainly formed through the directly pyrolysis of the coupling NHi, and the dehydrogenation reactions of the coupling hydrocarbons.

Effects of Turbulence‐Induced Blade Position on Flow and Combustion in a Wankel Rotary Engine

Aiming at the problem of low turbulent velocity and incomplete combustion in the combustion process of the Wankel rotary engine (WRE), and setting turbulence‐induced blade (TIB) in the combustion chamber recess is an effective means to enhance the turbulent motion and promote combustion. Carifying the optimal arrangement position of TIB can get better combustion performance. Therefore, a computational fluid dynamics (CFD) simulation model of a WRE with TIB was established in this paper. Based on the differential pressure perturbation mechanism, the influence of the arrangement position of the TIB on the flow field and combustion performance were analyzed. The results showed that when the ratio of blade arrangement distance is less than 0.66, the pressure difference between the leading and trailing of the blade is small. At this time, the in‐cylinder flow is mainly disturbed by the forced disturbance of the TIB, the increase of the turbulent velocity is not obvious, and the diffusion velocity of the flame to the rotor direction is small. When the ratio of blade arrangement distance is greater than 0.66, the pressure difference between the leading and trailing of the blade is large. At this time, the In‐cylinder flow is affected by the pressure difference flow in addition to the forced disturbance of the TIB. The turbulent velocity is effectively enhanced, and the flame velocity is fast to the rotor direction. When the ratio of blade arrangement distance is 0.66, it shows the best combustion performance, and the indicated work is the largest. Compared to the scheme without TIB, the indicated work is increased by 16%.

Transformation and migration of key elements during the thermal reaction of coal spontaneous combustion

As deep coal mining continues to expand, the problem of coal spontaneous combustion (CSC) becomes increasingly severe, posing a significant threat to the safe extraction of energy resources. For preventing CSC, it is of great significance to determine the relationship between the content changes of major elements in the constituent coals and CSC, and it is a necessary study to reveal the mechanism of CSC. By utilizing elemental analyzers, it was found the coal experienced dominant changes in O/C ratios up to 120 °C, H/C ratios between 120 and 270 °C, and O/C ratios beyond 270 °C; By employing a correlation approach, it was determined that the key elements influencing heat release during CSC, i.e., C, H, and O. Additionally, with the key elements as monomers, the migration and transformation process of its mutual composition and structure was investigated, and mastered the influence of elemental migration on the thermal reaction properties in the CSC, as well as uncovering migration and transformation pathways in the CSC. Meanwhile, both the critical groups and temperatures that promote CSC generation were obtained, i.e., –CH2, –CO, and 150 °C, It is expected that the study results may provide theoretical support for the development of fire extinguishing materials.

Preparation and characteristic study of the hydrogel of coal spontaneous combustion environmental protection

In order to solve the problem of spontaneous combustion of coal in mined-out areas, a new type of P/S/T/H environmentally friendly hydrogel was designed by using polyvinyl alcohol, sodium alginate and di(triethanolamine) titanate diisopropyl to form a gel system and adding the environmentally friendly material hybrid shell bio-filler. The formulation of P/S/T/H gel was studied by orthogonal experiment, and the forming time was precisely controlled. The synthesis mechanism and flame-retardant properties of the gels were investigated by various experimental methods. The results show that: There are folds and three-dimensional pore structures inside the P/S/T/H gels, and the two cross-linked networks strengthen the stability of the gels. Compared with WG gel and single cross-linked network gel, P/S/T/H gel has the best water retention, water absorption/salt resistance and flame-retardant effect. The water retention rate of P/S/T/H gel is still as high as 20% after 12 h, the water-absorbing multiplicity is more than 400 after 90 min, and the salt-resistant multiplicity is 54 after 90 min. When P/S/T/H gel is added to the coal samples, the combustion end temperature lags 8.4 °C, the heat release is reduced by 19.9%, the average CO inhibition rate is 45.9%, the maximum heat release rate is reduced by 20.1 KW/m2, the total heat release rate is reduced by 36.6%, and the maximum flue gas inhibition rate is 87.1%. Therefore, the highly efficient and environmentally friendly P/S/T/H gel is expected to play an important role in the work of fire prevention in mined-out areas.

Influence of LES Inflow Conditions on Simulations of a Piloted Diffusion Flame

This study investigates the influence of different turbulent inflow conditions on the Large Eddy Simulation (LES) of turbulent combustion problems. Four turbulent inflow conditions are studied, including two Synthetic turbulence methods (White Noise and Random Spot), and two Precursor simulation methods (Library and Library-Rescale). The simulation results are compared with experimental measurements. While the White Noise method yields a longer flame with poor agreement against experiments, the Random Spot method has good predictions initially but overpredicts turbulent fluctuations downstream. The results obtained by the Library and Library-Rescale methods are similar, and the discrepancies mainly lie in the region around the centerline. By rescaling the turbulent inlet library to match the experimental profiles, the Library Rescale method improves the prediction of turbulence fluctuations near the nozzle. The present study shows the pronounced sensitivity of LES accuracy in turbulent jet flames to the choice of turbulent inflow 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.

Catalytic Effects on Combustion Behavior of Oil Shale: Thermal Conversion, Kinetic, Mechanism Analyses

ABSTRACT In order to solve the problem of traditional energy combustion and to achieve the comprehensive use of oil shale. This work investigated the impact of potassium-containing catalysts on the combustion reactivity of Beipiao oil shale through TG, FTIR, and SEM analysis. Results showed that the catalyst of different proportions reduced the oil shale ignition temperature by 9.34–17.67°C and burnout temperature by 9–51.67°C, optimal catalyst addition (5%) exhibited the most effective catalytic effect. The catalyst effect was affected by heating rates, the lower the heating rate, the more favorable the oil shale combustion. In addition, the hydroxyl and ether oxygen groups of combustion residue increased with catalyst, the absorption peak intensity of carbonate reduced. Suggesting that the catalyst promoted the decarbonization cracking of oil shale, thereby accelerating the release of volatiles and the decomposition of inorganic mineral carbonate. Finally, activation energy was calculated using the Friedman and FWO methods. The results obtained from both kinetic methods were highly consistent, obviously reductions in activation energy under catalytic action.

Efficacy of performance and mitigate pollution of CI engine: Delonix regia biodiesel with n‐butanol and exhaust gas recirculation

AbstractThe primary aim of this research study was to examine the effectiveness and environmental consequences of using Delonix regia biodiesel (DRB) in combination with butanol (BUT), exhaust gas recirculation (EGR), and diesel fuel (D) on a direct injection compression ignition engine operating at a constant speed. This study involved the formulation of five distinct biodiesel blends, namely DRB10% + D90%, DRB20% + D80%, DRB10% + BUT10% + D80%, DRB10% + BUT20% + D70%, and DRB20% + D80% + EGR10%. The inclusion of n‐butanol in a biodiesel blend serves to tackle the problem of inadequate combustion in fuel blends by alleviating the oxygen deficiency that occurs during the combustion process. The findings of the study revealed that the combination of DRB at 10%, BUT at 20%, and D at 70% produced in a significant reduction in specific fuel consumption (SFC) by 11.19% and brake thermal efficiency by 2.62%. Additionally, this combination led to a decrease in exhaust emissions of CO and Smoke, with the exception of HC and NOx, when compared to the use of diesel fuel. The control of HC and NOx emissions can be achieved through the implementation of an exhaust gas recirculation system. The results of this investigation suggest that Delonix regia biodiesel, in combination with a 20% concentration of n‐butanol, has potential as a viable alternative fuel choice that may be utilized without necessitating any engine modifications.

Experimental Studies on Preheating Combustion Characteristics of Low-Rank Coal with Different Particle Sizes and Kinetic Simulation of Nitrogen Oxide

Low-rank coal, accounting for 45% of the global coal reserves, is easier to use in terms of realizing ignition and stable combustion due to its relatively high levels of volatile content. But the problem of low-rank coal combustion is that its NO formation is in the range of 300–600 mg/m3, which makes the emission’s meeting of the environmental regulation quite difficult or uneconomic. Preheating combustion was a prospective combustion technology which involved preheating in a circulating fluidized bed (CFB) first and then combustion in a combustor for preheated fuel. With three particle sizes (0–0.355 mm, 0–0.5 mm, and 0–1 mm), some experiments were carried out in a 30 kW test rig. The results showed that, in the CFB preheating, a particle size of 0–1 mm had the highest coal-gas heating value due to a long residence time. The release of species in the CFB preheating always followed the order H > N > C > S. For preheated fuel combustion, a particle size of 0–0.355 mm showed the fastest combustion velocity, with the highest temperature point near the nozzle. For all three particle sizes, the combustion of preheated fuel showed a uniform temperature distribution with a small temperature difference. The lowest NO emission was 105 mg/m3 for the particle size of 0–0.5 mm. A GRI-Mech 2.11 mechanism was used to simulate the formation of NO with different influencing factors, such as temperature, oxygen concentration, and secondary-air ratio. There was a good agreement between the experimental data and the simulation’s results. The simulation showed that the NO formation could be further decreased with an optimal secondary-air ratio. This investigation provides support for the basic understanding of preheating-combustion technology and potential industrial applications in the future.