Combustion Behavior Research Articles

A model for the combustion behavior of AP/HTPB propellant containing ultrafine aluminum

AbstractNano‐aluminum, renowned for its remarkable efficacy in augmenting propulsion efficiency and regressive velocity, stands out as a compelling choice for incorporation into heterogeneous propellant compositions. Nevertheless, the considerable expense of this ultrafine aluminum variant, coupled with the inherent hazards associated with conducting propellant trials, may deter extensive allocation of resources and efforts towards the intricate processes of amalgamation, molding, and comprehensive analysis of the combustion characteristics of freshly devised propellant blends. To provide theoretical support for predicting the chemical properties of nano‐Al composite propellant, we establish a numerical framework to study the combustion characteristics under the working environment of a solid rocket motor. A new five‐step kinetic mechanism is developed in this model to describe the reaction process in the gas phase while accounting for heat conduction, radiative effects, and non‐planar moving surfaces. The comparison between our theoretical work and experimental results confirms that making no distinction among Al particle sizes below 3 μm is reasonable. Finally, the effects of nano‐Al on combustion, burning rate variation, and temperature sensitivity are analyzed in detail.

Nonwoven from recycled polyester fibers for thermal insulation applications

The building sector is one of the segments that most contribute to energy consumption because of the use of heating and cooling to ensure a thermally comfortable environment. Thermal insulation is a simple alternative to reduce this consumption, but the search for sustainable and efficient materials and structures is ongoing. Therefore, this study aimed to develop nonwoven in an industrial scale by dry-laid carding using polyester fibers (PES) and recycled fibers from poly(ethylene terephthalate) (PET) bottles. The influence of replacing PES fibers in a standard formulation with solid recycled fibers and siliconized fiber in different proportions (20 and 40%) was evaluated. Nonwoven samples were evaluated regarding thermal conductivity, air permeability, thermogravimetry, and burning characteristics. It was evidenced that the use of 40% recycled fiber and 20% and 40% siliconized fiber significantly reduced the thermal conductivity and air permeability of the samples. Nonwoven samples with siliconized fibers, however, showed a burning behavior with smoke generation and fire droplets. In general, the present study demonstrated that the use of 40% recycled PET fiber contributed to the improvement of the thermal insulation of nonwoven samples and is promising for more sustainable textile applications in technical textiles, specifically in the building sector.

The Structure Characteristics of Laminar Premixed Flames of Gasoline-like Fuel Under CI Engine-Relevant Conditions.

Gasoline compression ignition characterized by partially premixed and long ignition delays typically features complex flame structures such as deflagration or spontaneous ignition fronts. In this study, the flame structure and propagation characteristics of PRF90/air mixtures under compression ignition engine-relevant conditions are investigated numerically. Similar to other types of fuels, under such conditions, the propagation speed of PRF90 laminar premixed flames depends not only on the unburnt mixture properties but also on the residence time, and the transition of the flame regime depends only on the residence time. Nevertheless, due to the temperature-dependent autoignition chemistry of PRF90, flames with excessively high unburnt temperatures show different combustion behaviors after the transition from deflagration to autoignition-assisted flames. Sensitivity analysis showed that, the dominant chain branching reactions in the deflagration mode are H + O2 = OH + O and CO + OH = CO2 + H, and that in the autoignition-assisted flames with lower unburnt temperature are H2O2(+M) = 2OH(+M) and IC8H18 + HO2 = AC8H17 + H2O2, while for higher unburnt temperatures, the reactions C3H5 + HO2 = C2H3 + CH2O + OH and IC8H18 = IC4H9 + TC4H9 are more important than the fuel low-temperature oxidation reactions. In addition, a criterion based on chemical explosive mode analysis is used to analyze the local combustion mode. The results show that the difference in diffusion/chemical structure at the crossover progress variables C 0 and crossover temperature allows both C 0 and to be used as a flame location for distinguishing propagation modes in premixed flame. However, the effects of the equivalence ratio on C 0 are different from that on , which means that the selection of C 0 and may lead to different discriminant results for stratified mixtures. Comparing the applicability of C 0-based and -based locations in three-dimensional gasoline compression ignition flame, it is found that the flame location based on the value of C 0 at ϕ = 1.0 can more completely reflect the flame development characteristics in stratified premixed combustion.

Experimental investigation on diesel engine performance, combustion, and emissions characteristics with Tucuma and Ungurahui biodiesel blends

The study conducted an experimental investigation of diesel engine performance, emissions, and combustion characteristics using Tucuma and Ungurahui biodiesel blends. Higher yield (greater than 99.4%), lower viscosity than diesel, and higher cetane number of these fuels have motivated a comprehensive investigation of the effect of these fuels on diesel engines. Four blends were tested in the engine by keeping diesel as the benchmarking fuel. The engine was operated at full load conditions, and the results were investigated with respect to brake power (BP). Results indicate that biodiesel blends showed similar combustion behaviour to that of diesel. Next to diesel, TB10 and UB10 showed better brake thermal efficiency (BTE) and lower brake-specific fuel consumption (BSFC). Higher peak pressures and heat release rates (HRR) are observed for the TB10 compared to the diesel operation. Moreover, prolonged combustion was observed for the four biodiesel blends during the diffusion and late combustion phasing. With the increase in BP, slightly higher HC emissions are observed for all the blends except for TB10 compared to diesel. Similarly, a slight increase in CO emissions is also observed for all the blends at higher BP. Higher acid values of both fuels are the likely cause of increased HC and CO emissions at higher BP. NOx emissions are slightly higher for both fuels, among these UB10 has shown lower NOx than other blends. The study concludes that TB10 has demonstrated better performance (near diesel) and combustion rates (better than diesel); however, emissions like CO and NOx are slightly higher than others. The study recommends blending TB10 and UB10 with the alcohols, ethers, and nanoparticles as they can reduce NOx and CO emissions.

Relative reactivity of methyl anisole isomers: An experimental and kinetic modelling study

Due to the current interest in biomass derived carbon neutral fuels and fuel additives for gasoline engines and to the growing need of understanding the fundamentals of gas phase combustion in the context of wildfires, this study investigates the combustion behavior of key components of biomass pyrolysis oils, namely the three methylanisole isomers (ortho-, meta- and para-methylanisole). Specifically, this study presents the first experimental ignition delay time measurements for such fuels using a shock tube and a rapid compression machine. Ignition experiments were carried out for stoichiometric fuel/air mixtures (φ = 1) at compressed pressure pc = 10 and 20 bar, covering a temperature range Tc = 880–1220 K. A kinetic model based on previous efforts in the area of oxygenated aromatic hydrocarbon fuels is proposed to reproduce and interpret the experimental findings, specifically focusing on capturing the observed different reactivity of the three isomers. To this aim, thermodynamic properties of primary intermediates and bond dissociation energies were calculated highlighting relevant differences originated from the relative position of the O–CH3 and –CH3 substituents. In addition, an isomerization pathway specific to the ortho isomer was theoretically investigated and found to motivate the observed higher reactivity with respect to the meta and para isomers

Sugarcane Burning: Why?

The sugarcane harvesting practices of farmers pose a recurring problem of burning the sugarcane fields every year, leading to the release of PM 2.5, which is hazardous to health and a matter of concern for all parties involved. The objective of this research is to investigate the causes of sugarcane burning by farmers. Data is collected through participatory observation methods and group discussions with a sample group of farmers in the provinces with the highest incidents of sugarcane field fires, namely Nakhon Ratchasima, Kalasin, and Khon Kaen in the northeastern region of Thailand during the 2021/2022 production season. Content analysis techniques are employed to identify the reasons behind the behavior of burning sugarcane. The findings reveal that sugarcane burning has been a long-standing practice among farmers, and the prevalence of burning has increased due to a shortage of labor for sugarcane cutting. The available machinery for sugarcane cutting is insufficient and unsuitable for the farmers' fields. Farmers who burn sugarcane fields are aware of the health impacts and have benefited from the government's measures to address the issue of sugarcane field fires. However, it is observed that the quantity of burnt sugarcane still exceeds the government's target, because burning sugarcane is a cost-effective, convenient, and rapid method. It is found that penalizing farmers at a rate of 30 Baht per ton of burnt sugarcane and providing assistance at a rate of 120 Baht per ton of fresh-cut sugarcane does not sufficiently motivate farmers to change their sugarcane burning behavior.

Investigation of Hydrothermal Carbonization of Exhausted Chestnut from Tannin Extraction: Impact of Process Water Recirculation for Sustainable Fuel Production

This study explores the hydrothermal carbonization (HTC) process applied to the exhausted chestnut produced by the tannin extraction industry, utilizing process water recirculation to enhance the efficiency and sustainability of the conversion process. Tannin extraction from wood typically involves hot water treatment, leaving behind residual wood biomass known as exhausted wood. These by-products maintain their renewable properties because they have only been exposed to hot water under a high pressure, which is unlikely to cause major alterations in their structural components. Hydrothermal treatment was carried out at temperatures of 220 °C and 270 °C for 1 h, with process water being recirculated four times. This investigation focused on analyzing the effects of recirculation on the yield and fuel properties of hydrochar, as well as characterizing the combustion behavior of the obtained hydrochar. The results indicated that recirculation of process water led to improvements in both the mass and energy yields of hydrochar. The mass yield of the hydrochar samples increased by 5–6%, and the ERE of the hydrochar samples increased by 5–8% compared to the HTC reference sample. However, alterations in the combustion characteristics were observed, including decreases in ignition temperature and combustion reactivity. The results indicate that, with PW recirculations, the combustion index decreased by about 14% and 18% for 220 °C and 270 °C, respectively. Overall, this research demonstrates the potential of utilizing HTC on chestnut tannin residue with process water recirculation to produce stable solid fuel and provides insights into the combustion behavior of the resulting hydrochar.

Ignition and combustion behavior of pressure treated wood and wood-plastic composite exposed to glowing firebrand piles: Impact of air flow velocity, firebrand coverage density and pile orientation

Pressure treated wood (PTW) and wood-plastic composite (Trex®) were exposed to glowing firebrand piles in a bench-scale wind tunnel. The air flow velocity was 0.9–2.7 m s−1, the firebrand coverage densities were 0.06 and 0.16 g cm−2, and the pile footprint was 5 × 10 cm2 with either the 10-cm or 5-cm sides perpendicular to the incident air flow. Several types of flaming ignition events were observed including flames attached to the substrate surface in front of the pile (preleading zone ignition), and flames attached to the pile that sometimes spread onto the substrate downstream of the pile (downstream ignition). The most frequent and long-lasting flaming combustion occurred in experiments performed at 2.4–2.7 m s−1 using 0.16 g cm−2 firebrand coverage density piles with 10-cm sides perpendicular to the air flow. Trex® was less prone to preleading zone ignition but was more prone to downstream ignition. Unlike Trex®, PTW exhibited a propensity for sustained smoldering for a wide range of air flows.

Investigation on spray combustion modeling for performance analysis of future low- and zero-carbon DI engine

Global warming issues and fossil fuel depletion crisis have forced transportation industry to seek clean engine fuels both liquid and gaseous. Dual-fuel mode with high-pressure direct injection (HPDI) has been recognized as mainstream method in developing flexible-fuel internal combustion engines (ICEs). But flexible-fuels’ physicochemical properties and spray combustion characteristics under HPDI have changed a lot. Unfortunately, there is currently no universal model for predicting spray combustion behaviors and analyzing performance of flexible-fuel ICEs. Therefore, this paper aims to develop a novel spray combustion model and provide optimal injection and combustion strategies for performance improvement of low- and zero-carbon HPDI ICEs. Based on balance of momentum change and vortex ring drag force, the jet spray effective injection velocity is obtained. Then the jet spray penetration under varying injection rate is solved. Finally, the developed model is established and validated experimentally, with the spray combustion characteristics of various fuels investigated. The results show that the developed model has a good accuracy and robustness for flexible-fuels’ characteristic analysis. Meanwhile, multiple-injection could increase the combustion efficiency (CE) over 10.27 % than single-injection, and CE increases with dwell time. Moreover, CE of H2 in nitrogen-oxygen (N2–O2) atmosphere is 10.15 % higher than that in argon-oxygen (Ar–O2) atmosphere.

Composite combustion behaviors of tubular flame and central jet flame in a reduced-diameter vortex combustor

The characteristics of the tubular flame and the flow field mixing mechanism in a reduced-diameter vortex combustor are investigated by varying the fuel flow rate and equivalence ratio through experiments and numerical simulations. Single-layer tubular flame and double-layer composite tubular flame are found in the combustor under the coupling effect of the cyclone and the central jet. The composite tubular flame will be formed when the air in the combustor is more abundant (Ф>1.00), and the center flame frequency is linearly and positively correlated with the Reynolds number of the central jet air. When the Reynolds number exceeds 2000, the double-layer composite flame tends to stabilize, with the center flame frequency higher than 9 Hz. The turbulence of the central jet air promotes the mixing of reactants by enhancing the recirculation near the nozzle, guaranteeing the central flame's stable combustion. Through analysis of the burn rate of methane at the outlet and the emission species of CO and CO2, it is evident that the double-layer flame achieves the methane burn rate exceeding 95 %, while also exhibiting lower CO emissions compared to the single-layer flame.

V-shaped effect of primary and secondary airflow momentum ratio on performance of a 660 MW tangentially fired lignite boiler: Identification and verification

To explore how the primary and secondary air ratios affect the overall performance of lignite-fired power generation boilers, a 660 MW wall-tangentially fired lignite boiler was chosen as research subject. 17 combustion scenarios were designed and then numerically simulated through a validated model, and the in-furnace coal combustion behavior, heat transfer process, and NOx conversion characteristics under various conditions were analyzed in detail. Results show that, except for the monotonous increase in NOx emission, the overall boiler performance follows a V-shaped trend with the continuous increase in primary air ratio (PAR). Initially, as PAR is slightly increased, the in-furnace combustion temperature, heat transfer intensity and coal utilization rate notably decrease, followed by a subsequent increase in these parameters as PAR is significantly increased. The separated over fire air (SOFA) ratio doesn’t alter this V-shaped pattern; however, a higher SOFA ratio does reduce the critical PAR at which the overall boiler performance is most compromised. This is attributed to changes in the momentum ratio between primary and secondary airflow caused by varying PAR. Boiler performance deteriorate significantly when their momentum ratios are nearly equal, and a higher SOFA ratio makes it easier. These observations are confirmed under different thermal load conditions, where the close proximity of primary and secondary air momentum is avoided by reducing SOFA ratio. Based on these findings, a substantial increase in PAR should be avoided in practice, if necessary, lowering the SOFA ratio helps mitigate significant deterioration in boiler performance.

Iron powder particles as a clean and sustainable carrier: Investigating their impact on thermal output

The utilization of iron powder as a sustainable energy carrier, conducive to a carbon-free future, has garnered substantial attention due to its commendable attributes such as high energy density, widespread availability, and absence of emissions. To harness its potential optimally, a comprehensive understanding of the combustion behavior of iron powder and the development of corresponding combustion technologies are imperative. This study endeavors to investigate the influence of iron powder particle size, as well as the flow rate of air and iron powder, on the temperature at the exit of the ignition chamber. Experimental trials were conducted utilizing a metal cyclonic combustor (MC2) equipped with a system for feeding iron powder. The findings reveal that an increase in the diameter of iron particles corresponds to an elongation of the path from the ignition chamber to the outlet. Consequently, this elongation induces prolonged ignition delay time and burning duration. Notably, larger particles exhibit enhanced combustion efficiency in comparison to their smaller counterparts. The outcomes demonstrate that particles approximately 50 µm in size achieve an efficiency of 94%, as opposed to 72% for particles below 20 µm. Temperature measurements and spectrometric analysis expose a discernible relationship between particle size and temperature during combustion, elucidating that larger particles yield higher temperatures. Comprehending the intricate correlation between particle size and combustion behavior is crucial for optimizing combustion systems when utilizing iron powder as an energy carrier. By controlling particle size and combustion conditions, the efficiency and efficacy of iron powder combustion processes can be enhanced, thereby contributing to cleaner and more sustainable energy solutions. The implications of this study extend to the enhancement of burner system design and functionality, along with an overall improvement in combustion efficiency. These findings hold significance within the realm of combustion science, presenting opportunities for the development of more sustainable and environmentally friendly energy solutions. Implementing the insights derived from this research empowers researchers to harness the potential of iron powder as an energy carrier, thereby advancing progress toward a greener future through environmentally conscious combustion processes.

Combustion characteristics of refuse-derived fuel pellets having varying plastic compositions.

The plastic fraction of refuse-derived fuel (RDF) pellets influences fuel's physico-chemical, and mechanical properties, which in turn might affect the combustion behavior of RDF. In the present study, the combustion behavior of different plastic fraction-simulated RDF pellets is reported. The simulated pellets were prepared based on the Indian commercial RDF composition. Initially, the plastic content varied from the existing fraction in Indian commercial RDF, i.e., 35% (RDF-1), to a lower plastic content of 5% (RDF-2). Physico-chemical characterization showed that a higher plastic fraction in RDF-1 reduces its pellet density by 25% as compared to RDF-2. The changes in RDF physico-chemical properties due to plastic variation are reflected in the RDF conversion process. Single-particle and packed-bed studies concluded that the lower density for higher plastic RDF-1 leads to lower conversion times (36%), and higher flame front speed (11%), which are desirable conditions for faster conversion. However, packed-bed studies also showed limitations regarding the utilization of high plastic RDF as RDF-1 has a narrow range of operating air mass flux due to the early advent of convective cooling of the bed. Finally, considering the constraints associated with the utilization of high plastic fraction (~ 35%) RDF and to maximize the effective utilization of plastic in RDF, a workable plastic fraction of 15% in RDF was proposed and tested for its combustion properties. RDF with 15% plastic showed faster conversion, higher flame front speed, and a wider range of operating air mass flux before the advent of convective cooling of the bed.

A Novel Benchmarking Approach to Assess Fire Safety of Liquid Electrolytes in Lithium‐Ion Batteries

AbstractEstablishing authoritative electrolyte safety assessment methods at laboratory levels is crucial for addressing conflicts from thermal runaway of lithium‐ion batteries. However, self‐extinguishing time (SET), as the most widely used evaluation method now, lacks benchmarks and heavily relies on the specific implementation of test procedures. This work systematically summarizes and investigates key test parameters. Based on repeatability and reliability, burning a glassfiber separator (Φ16 mm) with absorption of 0.1 g liquid electrolyte (LE) can be proposed as a unified method. The concept of self‐extinguishing efficiency (SEE) is further proposed with a new evaluation criterion of i) SEE≤70, Flammable; ii) 70<SEE<90, Flame Retarded; iii) 90≤SEE≤100, Nonflammable. The feasibility of the new protocol is verified by employment in evaluating the effects of 15 representative flame retardants (FRs) on combustion behaviors of LEs. Meanwhile, the underlying flame retardancy mechanism is revealed, indicating that preceding or simultaneous vaporization and pyrolysis of FRs in conjunction with the decomposition of LE promote mitigating electrolyte fire risk. In addition, machine learning is employed to aid in analyzing the significance of various features on SEE, providing further validation of the proposed mechanism. This work provides a benchmark for the safety evaluation of LEs, facilitating the advancement of fire‐safe batteries.

VOF based model of numerical simulation for single aluminum droplet evaporation and combustion

ABSTRACT This study investigates the combustion of a single aluminum droplet in a high-temperature convective setting, focusing on the interplay between the environment and droplet evaporation combustion. Using the VOF numerical method, a two-dimensional multiphase flow combustion model for micron-sized aluminum droplets is developed. Experimental validation compares predicted droplet diameter with experimental data. The combustion behavior of aluminum droplets in high-temperature convective environments is analyzed, emphasizing gas-phase combustion during stable stages. Parametric variations in flow velocity and oxygen concentration reveal the formation of vortices around the droplet, influencing aluminum vapor accumulation and evaporation rates. Combustion primarily occurs at the droplet’s windward side, with reaction rates decreasing downstream. Increasing gas velocity from 1.5 m/s to 3 m/s thins the aluminum vapor concentration boundary layer, boosting combustion rates by 35%. Elevating oxygen concentration from 20% to 50% brings the flame closer to the droplet, accelerating combustion rates by 2.7 times, suggesting oxygen concentration’s role in reaction acceleration and combustion duration reduction. This research offers insights for simulating aluminum droplets in propellant applications.

Effect of lignin, cellulose and hemicellulose from biomass on sulfur release behavior from dyeing sludge combustion

Co-combustion with biomass is recommended for treating dyeing sludge (DS) from the view of minimizing sulfur emissions. However, the sulfur emission from DS combustion depends on the lignin (L)/cellulose (C)/hemicellulose (H) ratio in the biomass, which is frequently overlooked. This study reveals the effect of biomass on the combustion characteristics and sulfur evolutions of DS combustion using triphenylmethyl mercaptan (TM) and L/C/H as model representative compounds of DS and biomass, respectively. Results indicated that the combustion behavior of the TM–biomass mixture was dominated by TM and secondarily by L/C/H. Although L/C/H brought forward the TM combustion, these biomass components (especially L) deteriorated the combustibility and burnout performances of the combustion. L/C/H promoted CH3SH and SO2 release at low temperatures but inhibited these emissions at high temperatures. The sulfur retention ratios of L, C, and H were 7.53 %, −5.75 %, and 0.17 %. TM–L interaction initially promoted and later inhibited the co-combustion process and the CH3SH and SO2 release. L/C/H addition reduced the E values of the mixtures and the co-combustion kinetics were dominated by Dn models. Residue analysis also indicated a dominant role of L in sulfur fixation, mainly because L additive created abundant adsorption sites in the co-combustion residue.

Flame-retardant wire burning behavior by jet flame heating: Ignition, charring, and secondary flame spread

This research presents an in-depth examination of the combustion characteristics of flame-retardant electrical wires, contrasting behavior with non-flame-retardant counterparts under jet flame heating. The study systematically investigates the pyrolysis process, ignition patterns, charring behavior, and the development of secondary flames in wires with different core diameters and insulation materials. Findings indicate the heightened susceptibility of thinner wires to rapid heating, pyrolysis and charring, leading to faster ignition and more intense secondary flame development. This insight is crucial for tailoring flame-retardant formulations to specific wire dimensions. The research also delves into the thermal dynamics within the wires, highlighting how the core diameter influences axial heat conduction and, consequently, the overall flame spread behavior and pyrolysis rate. A critical discovery is the relationship between heating duration and flame sustainability, establishing a specific range of heating times for sustaining secondary flames in flame-retardant wires. Theoretical models used in the study explained the critical heat flux heating time for wire ignition, offering insights into improved fire prevention strategies, particularly in prolonged heat exposure scenarios. These findings not only advance our understanding of flame-retardant wire behavior under fire conditions but also provide guidance for selecting and using electrical wires, thereby optimizing fire safety in diverse applications.

Combustion Characteristics, Kinetics and Thermodynamics of Peanut Shell for Its Bioenergy Valorization

To realize the utilization of peanut shell, this study investigates the combustion behavior, chemical kinetics and thermodynamic parameters of peanut shell using TGA under atmospheric air at the heating rates of 10, 20, and 30 K/min. Results indicate that increasing the heating rate leads to higher ignition, burnout, and peak temperatures, as observed in the TG/DTG curves shifting to the right. Analysis of combustion performance parameters suggest that higher heating rates can enhance combustion performances. Kinetic analysis using two model-free methods, KAS and FWO, shows that the activation energy (Eα) ranges from 93.30 to 109.65 kJ/mol for FWO and 89.72 to 103.88 kJ/mol for KAS. The data fit well with coefficient of determination values (R2) close to 1 and the mean squared error values (MSE) less than 0.006. Pre-exponential factors using FWO range from 2.19 × 106 to 8.08 × 107 s–1, and for KAS range from 9.72 × 105 to 2.25 × 107 s–1. Thermodynamic analysis indicates a low-energy barrier (≤±6 kJ/mol) between activation energy and enthalpy changes, suggesting easy reaction initiation. Furthermore, variations in enthalpy (ΔH), Gibbs free energy (ΔG), and entropy (ΔS) upon conversion (α) suggest that peanut shell combustion is endothermic and non-spontaneous, with the generation of more homogeneous or well-ordered products as combustion progresses. These findings offer a theoretical basis and data support for the further utilization of agricultural biomass.

Combustion Diagnosis in a Spark-Ignition Engine Fueled with Syngas at Different CO/H2 and Diluent Ratios

The gasification of residues into syngas offers a versatile gaseous fuel that can be used to produce heat and power in various applications. However, the application of syngas in engines presents several challenges due to the changes in its composition. Such variations can significantly alter the optimal operational conditions of the engines that are fueled with syngas, resulting in combustion instability, high engine variability, and misfires. In this context, this work presents an experimental investigation conducted on a port-fuel injection spark-ignition optical research engine using three different syngas mixtures, with a particular focus on the effects of CO/H2 and diluent ratios. A comparative analysis is made against methane, considered as the baseline fuel. The in-cylinder pressure and related parameters are examined as indicators of combustion behavior. Additionally, 2D cycle-resolved digital visualization is employed to trace flame front propagation. Custom image processing techniques are applied to estimate flame speed, displacement, and morphological parameters. The engine runs at a constant speed (900 rpm) and with full throttle like stationary engine applications. The excess air–fuel ratios vary from 1.0 to 1.4 by adjusting the injection time and the spark timing according to the maximum brake torque of the baseline fuel. A thermodynamic analysis revealed notable trends in in-cylinder pressure traces, indicative of differences in combustion evolution and peak pressures among the syngas mixtures and methane. Moreover, the study quantified parameters such as the mass fraction burned, combustion stability (COVIMEP), and fuel conversion efficiency. The analysis provided insights into flame morphology, propagation speed, and distortion under varying conditions, shedding light on the influence of fuel composition and air dilution. Overall, the results contribute to advancing the understanding of syngas combustion behavior in SI engines and hold implications for optimizing engine performance and developing numerical models.

A numerical determination of complex solid gun propellant burn rates through closed bomb simulation

AbstractClosed bomb testing is a prominent means of characterizing the combustion behavior of solid gun propellants. This sub‐scale test allows the propellant to burn in a constant volume environment, where the resulting pressure‐time trace can be collected via a pressure transducer. Historically, numerical procedures have been developed to determine the burn rates of the gun propellants from these pressure‐time traces; however, no standardized procedure exists to determine the burn rates of grains with variable surface thermochemistry and ignition criteria. To address this capability gap, a non‐linearly constrained, multivariate optimization algorithm has been developed to decouple propellant grain surfaces and determine surface‐specific burn rates [1]. In this work, the optimization algorithm as well as the legacy Excel‐based Closed Bomb (XLCB) program [2] were used to determine the burn rates of homogeneous, deterred, and layered propellants from experimental data. Closed bomb simulations using these burn rates were then conducted with the two‐phase, multidimensional, interior ballistics solver, iBallistix [3]. The maximum mean error between the simulated and experimental pressure‐time curves was 6.8 % for the optimization algorithm and 23.8 % for XLCB, showing a marked improvement with our new approach. Furthermore, the approach discussed herein improves burn rate predictions of complex solid gun propellants when compared with legacy closed bomb data reduction analysis programs.