Ignition Of Fuels Research Articles

Understanding the role of fire retardants on the discontinuous ignition of wildland fuels

This work reports on a theoretical and experimental study on the role of fire retardant treatments on the discontinuous ignition of wildland fuels. The effect of the concentration of fire retardant in the solution applied to the vegetation is as expected to increase the ignition delay time. We found that the fire retardant modifies the fuel bed effective thermophysical properties, delaying the thermal response of the specimen when subjected to an incident heat flux. Nevertheless, the critical heat flux remains unaltered within the experimental error. We followed a proven approach based on the thermal ignition theory and testing which however has not been previously employed to study fire retardants on wildland fuels. To carry this out, we performed experiments on the I-FIT apparatus, which yields repeatable results and controlled boundary conditions. The theoretical model shows a good agreement with the experimental results, delivering simple expressions for pencil-and-paper calculations of the ignition delay time and analytical tools to evaluate effective fuel properties. These results will help CONAF and other forest services around the world to gain insight on the optimal concentrations and delivery methods for these types of products during wildfire response.

Fuel Ignition and Bottle Bubbles Snag Video Prize

Fuel Ignition and Bottle Bubbles Snag Video Prize

Physics-informed graph neural networks for predicting cetane number with systematic data quality analysis

Designing alternative fuels for advanced compression ignition engines necessitates a predictive model for cetane number (CN). In this study, the physics-informed graph neural networks are introduced for a reliable CN prediction by considering molecular features pertinent to the physical properties of molecules that affect CN. The reliability of measured data is another key factor to consider for improving the predictive model. Various experimental instruments for measuring CN exist, including standard and non-standard methods. In this regard, a systematic data quality analysis was carried out for the total 630 CNs collected from literature and new measurements in this study using Advanced Fuel Ignition Delay Analyzer (AFIDA). The results from this data curation process were reflected in the model by imposing lower sample weights on the data coming from less reliable measurement techniques. This approach effectively maximized the prediction accuracy while incorporating data from all available sources. Using the sample weights decreased the mean absolute error (MAE) up to 0.8 CN units. The accuracy was also improved by introducing the CN-related physical properties (the number of hydrogen bond donors and acceptors); the test set MAE is 5.74 and 7.01 for the model with and without such properties, respectively. Investigating molecular structural effects on CN was also carried out to gain chemical insights into factors used to design new fuel candidates. The dimensionality reduction analysis of feature vectors showed a clear clustering in terms of functional groups and CN and the structural effect derived from the model was consistent with the physicochemical insights. This physics-informed model and data curation would be helpful for accurate CN prediction and inform rational fuel design.

Modeling smoldering ignition by an irradiation spot

Irradiation spots, such as lasers, lightning strikes, and concentrated sunlight, are common ignition sources in building and wildland fires, where smoldering is generally first ignited and then transitions to flaming. In this work, a physics-based 2-D computational model that integrates heat-and-mass transfer and heterogeneous chemistry is built to investigate the smoldering ignition of typical solid fuels using irradiation spots. Simulation results predict that, given the size of the irradiation spot, the ignition time decreases as the radiant heat flux increases. However, as the diameter of the irradiation spot decreases, the modeled minimum heat flux of smoldering ignition increases significantly, agreeing well with experiments and theoretical analysis. When the irradiation spot is smaller than 20-50 mm, assumptions of constant ignition temperature and fuel-burning flux become invalid. The commonly-used physical dimensions of thermally thin/thick fuels are not applicable for smoldering spotting ignition due to the significant radial conductive heat loss in the lateral direction. Further analyses show that the minimum irradiation of smoldering ignition increases as the fuel thickness increases, but it is insensitive to the fuel moisture content. This is the first time that a sophisticated 2-D model has been used to predict the smoldering ignition using irradiation spots, which deepens the understanding of the ignition by a remote heating source and large irradiation.

Elucidating NO coupling effects on ignition of toluene reference fuels by chemical functional group analysis

Derived cetane number (DCN), Research and Motor Octane Numbers (RON and MON) have been fundamentally analyzed using Quantitative Structure-Property Relationship (QSPR) regression models with key chemical functional groups. Both RON and MON exhibit strong sensitivities to the abundances of (CH2)n and benzyl-type groups but lack sensitivity to the CH3 group, most dominant in real gasolines. Residual and EGR gases contain NOx known to synergize with fuel autoignition chemistry. Two TRF mixtures having high and low aromatic content but sharing the same RON and MON values were used to evaluate NOx coupling effects. DCN measurements with NO addition were found to be strongly correlated with the abundance of the (CH2)n group. Similar experiments of 200 ppm NO in a Rapid Compression Machine show promotion (inhibition) of ignition for the high (low) aromatic TRF fuel. Kinetic modeling attributes the promotion to the NONO2 interconversion reactions, NO + HO2 = NO2 + OH, CH3 + NO2 = CH3O + NO and NO2 + H = NO + OH. The inhibitive effect relates specifically to low temperature kinetics and high NO loading conditions, leading to the formation of meta-stable species (e.g. CH3 + NO2 (+M) = CH3NO2 (+M)) that decelerate the rate of conversion of HO2 to more reactive OH radicals. The coupling of NO with real gasolines depends on chemical composition and temperature conditions not only encompassed by RON and MON criteria, but by the chemical functional group characteristics. The relevance of this finding to the significance of preferential vaporization of multi-component gasolines on low-speed pre-ignition (LSPI) is discussed. Within the context of chemical functional group distributions of five distillation cuts of a marketed ethanol-free gasoline determined by NMR spectroscopy, the analyses identify considerable variations of key functionalities with fuel distillation properties, indicating chemical kinetic autoignition behaviors that are dependent on preferential vaporization.

Benchmarking Between COMSOL and GPYRO in Predicting Self-Heating Ignition of Lithium-Ion Batteries

Recent studies have shown that self-heating ignition is a possible cause of fires when Lithium-ion batteries (LIBs) are stacked in large numbers, for example, during storage. The understanding of this ignition type is limited, and most current studies are based on numerical modelling. The different modelling tools found in the literature differ in their assumptions, capabilities, and resources needed, and may provide significantly different predictions. This study presents a benchmarking between COMSOL Multiphysics, which is one of the most prevailing tools used in modelling thermal-electrochemical behaviour of LIBs, and Gpyro, which is widely used in modelling ignition of solid fuels. Four case studies are designed with increasing levels of complexity: (1) just chemical kinetics at the microscale, (2) just heat transfer at the mesoscale, (3) self-heating behaviour at the mesoscale for coupled chemical reactions and heat transfer of a single cell, and (4) four-cell ensemble for multiphysics at a larger scale. The results of scenarios #3 and #4 are also compared to experiments. The results show that although COMSOL and Gpyro have significant differences in their assumptions and resources needed, both tools can accurately predict the critical conditions for ignition for self-heating, which validates their use to study the safety of LIBs.

Enhancing ϕ-sensitivity of ignition delay times through dilution of fuel-air mixture

The high ϕ-sensitivity (η) of ignition delay time (τIDT) is one of the desirable fuel properties for the high-load extension of advanced compression ignition engine. Recent studies revealed the effectiveness of a high dilution rate (xD) for enhancing η at the engine-relevant conditions. This study aims to quantify the effect of dilution on the η of isooctane using a combined experiment-simulation approach. The ignition delay of the isooctane/air mixture was measured with an Advanced Fuel Ignition Delay Analyzer (AFIDA) over the temperature range of 623 – 923 K at 10 bar pressure with global ϕ = 0.3 – 0.6, with and without 28.6% of additional N2 dilution. For precise evaluation of experimental η, the facility effect of the AFIDA experiment was characterized with three-dimensional computational fluid dynamics (3-D CFD) simulation. The temperature in the combustion chamber from 3-D CFD indicated a substantial temporal dependency, varying up to ∼52 K by charge-cooling of fuel injection and heat transfer from the wall. We introduced the dimensionless number θ(t) for characterizing the temporal profile of chamber temperature. Consideration of the facility effect using θ(t) resulted in better agreement between the experimental η and zero-dimensional (0-D) kinetics simulation. The refined η were then further utilized to quantify the effectiveness of dilution to η. The extent of η enhancement with dilution strategy was maximized at the low-temperature chemistry regime, increasing η by 77% with a 28.6% dilution rate. Further analysis on the dilution effect was carried out using 0-D kinetics simulation, revealing the critical dimensionless numbers relevant to the effectiveness of dilution to η enhancement. This study is the first experiment-simulation combined research to quantify the effect of dilution on η, facilitating the kinetics model refinement for better reproduction of ϕ-sensitivity.

Assessment of lake-level fluctuation as an indicator of fire activity in boreal Canada

Fuel moisture content is a highly variable property that dictates the ignition and combustion potentials of wildfire fuels. The Canadian Fire Weather Index (FWI) System—a subset of the established Canadian Forest Fire Danger Rating System—relies solely on weather observations to track fuel moisture and compute indices of fire potential. Ancillary environmental measures, such as lake levels in non-regulated lake systems, may integrate climatic and landscape factors that better reflect environmental moisture deficits and thereby complement the FWI System. Accordingly, we investigated whether inter-annual variation in lake levels has potential to serve as an indicator of regional fire activity using a quasi-binomial regression approach. This study combines annual measurements of fire activity, lake level, and other climatic variables from the Boreal Shield and Boreal Plain ecozones of Canada from 1980 to 2019 to determine whether variation in regional area burned can be explained by lake-level fluctuation, and whether this explanatory power differs by ecozone. Results indicated that lake-level fluctuation is a significant predictor of regional area burned for many lakes (28–48%). It often performs as well as or better than traditional fire-weather metrics (such as temperature and precipitation), and this relationship is stronger on the Boreal Shield compared to the Boreal Plain. Lake-level fluctuation provides information on fuel availability unaccounted for by traditional fire-weather metrics, suggesting that this variable could be added to the suite of environmental indicators of regional fire activity in Canada.

Multiple-criteria decision analysis to substantiate the prospects of industrial and solid municipal wastes as slurry fuel components.

This article investigates the recovery of typical wastes (coal slime, sawdust, cardboard and tire pyrolysis residue) as part of high-moisture slurry fuels. Using a laboratory furnace, the ignition and combustion characteristics of fuels as well as NOx and SOx emissions were determined. Using multiple-criteria decision-making (MCDM) methods and experimental results, we access the performance of four different slurry fuels in comparison with bituminous coal. The novelty of the study is based on the following features: we consider a unique set of parameters of the fuels (economic, environmental, safety and energy indicators), as well as three countries for their potential use (the USA, India and Russia); three different methods for calculating the efficiency indicator of each fuel were used. Despite rather low energy performance, the summarizing efficiency indicator of waste-based slurries was 53-93% higher than that of coal. The use of cardboard in the composition of a fuel blend showed the best complex result (the increase in the efficiency indicator was 80-93% relative to coal). The least promising additive was the pyrolysis residue of automobile tires. Its addition resulted in a 10-15% decrease in overall efficiency relative to a slurry without additives. The research results are useful for optimizing the component composition of waste-based slurries, technical and economic development of projects for the incineration of various wastes in the form of high-moisture fuel slurries.

Hypergolic ignition of paraffin-based hybrid rocket fuels by sprays of liquid oxidizer

An experimental study is conducted to measure the ignition delay of ammonia borane doped paraffin wax with sprays of white fuming nitric acid as oxidizer. The injection pressure and injector diameter are varied to investigate the effects of spray characteristics on the ignition dynamics. A range of Weber (We) number for the oxidizer jet covering 100 < We <2700 and Reynolds (Re) number 1300 < Re <8900 is investigated, whereas the We number at the droplet scale varies from 0.8 < Wedrop <24.1. The sprays are characterized using phase-doppler anemometry to obtain the size and speed distribution of the oxidizer droplets across multiple positions. In addition to conventional high-speed imaging, the hypergolic ignition is also observed using Schlieren imaging and a high-speed mid-infrared camera. The results show that the ignition delay of a hypergolic hybrid fuel under spray conditions is unaffected by the mean droplet size of the oxidizer. The ignition delay decreases with increasing We number at the droplet scale and increasing droplet velocity. The variability in the ignition delay also decreases with Weber number and droplet velocity. The values obtained for the ignition delay when using a spray are generally higher than those from simple oxidizer drop experiments, highlighting the need to investigate the hypergolic ignition in configurations representative of engine conditions.

Plasma ignition of solid fuels at thermal power plants. Part 1. Mathematical modeling of plasma-fuel system

Plasma ignition of solid fuels at thermal power plants. Part 1. Mathematical modeling of plasma-fuel system

DETERMINATION OF KINETIC CHARACTERISTICS OF SOLID FUEL.

The combustion process begins with the ignition of the fuel - bringing it to the auto-ignition temperature, which is one of the important components of the kinetic characteristics of the fuel.&#x0D; Fuel ignition does not occur immediately - but after a certain period, during which activation energy is accumulated: heat or active centers, depending on the mechanism of the process - thermal-kinetic or chain-kinetic, sufficient to overcome the potential barrier. At the same time, the period of reaching the self-ignition temperature is the induction period of this reactive system: for self-ignition or the ignition time during ignition.&#x0D; The purpose of the work is to substantiate the kinetic characteristics of the fuel: self-ignition temperature and induction period, methods of their experimental determination for solid fossil fuels and biomass waste.&#x0D; According to the methodology, an installation was created for the experimental determination of the self-ignition temperature and the induction period of solid fuel in the layer.&#x0D; Studies of such fuels as anthracite, hard coal, buckwheat husk, millet, oats, flax husks, birch wood, peat, and paper showed the dependence of the self-ignition temperature on the degree of metamorphosis and volatiles. With an increase in the degree of metamorphism and a decrease in volatiles in solid fuel, the self-ignition temperature increases. However, the self-ignition temperature does not depend on the size of its particles, their number in the layer and the temperature of the oxidizer.&#x0D; The above allows us to conclude that the self-ignition temperature depends only on the conditions of heat exchange (accordingly, on aerodynamics), and the absolute value of the auto-ignition temperature for an infinite space, in the absence of a jet stream, is a constant value, and only then, in the presence of heat exchange (with velocity gradients) , takes one or another value.&#x0D; It was found that the induction period depends only on the initial temperature of the process, the induction period decreases with increasing temperature. This is due to the more intensive transfer of heat to the fuel particles due to the increase in the temperature gradient and the acceleration of the development of the oxidation reaction.&#x0D; The induction period, as shown by the conducted experiments, does not depend on the size of the particles. This can be explained only by the fact that the rate of thermal destruction of the fuel is close to the rate of its heating. The burning time of coal particles, on the contrary, depends on the size of its particles.&#x0D; Expressions for determining the autoignition temperature and the induction period were obtained based on the processing of the results of the conducted experiments.&#x0D; The results of the work can be used in combustion technologies, in which self-ignition of fuel is one of the main components of the process - it ensures combustion in the self-ignition mode of fuel when in contact with an oxidizer.

Characteristics of spraying and ignition of coal-water fuels based on lignite and liquid pyrolysis products of wood waste

In the modern realities of the energy market, the use of coal-water slurries with liquid industrial waste is a promising way to solve several problems (economic, environmental and energy). This article presents the results of experimental studies of the characteristics of spraying and ignition of promising coal-water slurries. Lignite, water and liquid pyrolysis products of wood waste were used as fuel components. It was found that substitution of 10% of coal with liquid pyrolysis products of wood waste decreases the dynamic viscosity of the fuel by 3.2 times in comparison with two-component coal-water fuel. Density for all the slurries studied (changes in the mass of the components: coal – from 40 to 50%; water – from 40 to 50%; pyrogenetic liquid – from 0 to 10%) differs by no more than 22%. Introduction of liquid pyrolysis products of wood waste into the coal-water fuel composition significantly changes the jet structure. Its characteristic parts – core, middle and peripheral zones – increase. The number of droplets with high velocities (30–40 m/s) increases significantly. The average size of fuel droplets in the jet decreases by 5–12% in comparison with two-component coal-water fuel. Ignition delay time of a single droplet of slurry at oxidizer temperature 1273 K increases by 23% in comparison with two-component coal-water fuel when 10% of coal is replaced by liquid pyrolysis products. In the case of water substitution with the same amount of the third component, the ignition delay time at an oxidizer temperature of 1273 K decreases by 26%. The most preferred of the studied coal-water fuels, from the point of view of application in the energy sector, are those in which water is replaced by the same amount of liquid pyrolysis products of wood waste.

Ignition and combustion of metal fuels under microgravity: a short review

Metal fuels have a high potential for applications in space propulsion owing to their superior energy density and distinct combustion characteristics. Therefore, research into the combustion properties of metal fuels in microgravity has become necessary. The principles, applications, benefits, and limitations of experimental methods for microgravity combustion of metal fuels were compared in this review. Drop towers, aircrafts, sounding rockets or microgravity balloons, acoustic or ultrasonic levitation, electrodynamic levitation, space stations, and numerical simulations are common methods used to provide microgravity for combustion research. Among them, the devices providing microgravity environment on the ground has become a good choice for simulating microgravity environment owing to its convenience, reliability and relatively low cost. Further, the physical and chemical properties of common metal fuels, such as aluminum, boron magnesium, and so on, were introduced, and the existing research achievements on the combustion of metal fuels in microgravity are succinctly summarized in this paper. The melting process, ignition temperature, combustion temperature, flame structure, and extinction of metal fuel combustion will be affected by microgravity. Moreover, the necessity and insufficiency of the research are also illustrated. Finally, the existing and potential applications of metal fuels in space propulsion and space weapons are introduced. Metal fuels’ superior energy density and combustion performance can benefit deep-space exploration, particularly Mars exploration, and bring new insights into the design of space weapons. This paper may throw some new light on the study of metal fuel combustion in microgravity.

Stages and time-scales of ignition and burning of live fuels for different convective heat fluxes

Wildland fires impact ecosystems and communities worldwide. Many wildfires burn in living or a mixture of living and senescent vegetation. Therefore, it is necessary to understand the burning behavior of living fuels, in contrast to just dead or dried fuels, to more effectively support fire management decisions. In this study, the ignition and burning behaviors of needles placed in convective heat flux were evaluated. The species included longleaf pine (Pinuspalustris), Douglas-fir (Pseudotsuga menziesii), western red cedar (Thuja plicata), ponderosa pine (Pinus ponderosa), western larch (Larix occidentalis), pacific yew (Taxus brevifolia), white spruce (Picea glauca), and sagebrush (Artemisia tridentate). The ignition and burning behaviors were related to live fuel moisture content (LFMC), pilot flame temperatures, and convective heat fluxes. The different stages of ignition and burning were captured using high-speed imaging. In general, four burning stages can be observed: droplet ejection and burning, a transition stage, flaming combustion, and smoldering combustion. Ejection and subsequent burning of droplets can occur prior to sustained flaming ignition only in live fuels. For some species (e.g., longleaf pine, ponderosa pine, white spruce), droplet ejection and burning can reduce ignition times relative to dried fuel with lower LFMC. In general, the transition stage tends to take longer than the flaming and droplet stages (when these occur). During the transition stage, the fuels are heated, and pyrolysis occurs. Time-scales to ignition and the different stages of ignition and burning vary more among live fuels than dead and dried fuels. This conclusion indicates that other parameters, such as chemical composition and structural morphology of the fuel, can significantly influence the burning of live fuels.

Hot Surface Ignition of Liquid Fuels Under Ventilation.

Mine equipment fires remain as one of the most concerning safety issues in the mining industry, and most equipment fires were caused by hot surface ignitions. Detailed experimental investigations were conducted at the NIOSH Pittsburgh Mining Research Division on hot surface ignition of liquid fuels under ventilation in a mining environment. Three types of metal surface materials (stainless steel, cast iron, carbon steel), three types of liquids (diesel fuel, hydraulic fluid, engine oil), four air ventilation speeds (0, 0.5, 1.5, 3 m/s) were used to study the hot surface ignition probability under these conditions. Visual observation and thermocouples attached on the metal surface were used to indicate the hot surface ignition from the measured temperatures. Results show that the type of metal has a noticeable effect on the hot surface ignition, while ventilation speed has a mixed influence on ignition. Different types of liquid fuels also show different ranges of ignition temperatures. Results from this work can be used to help understand equipment mine fires and develop mitigation strategies.

Acetone PLIF visualization of the fuel distribution at plasma-enhanced supersonic combustion

This study examines the mixing and flameholding characteristics of a plasma stabilized planewall supersonic combustor. Fuel injection, ignition, and flameholding are provided by Plasma Injection Modules (PIMs) installed in a M = 2, 76.2 × 76.2 mm duct. Two configurations were explored: the first involves a plasma filament collocated within a single transverse fuel jet, while the second involves combustion stabilization using a series of three PIMs. Unburned fuel distributions were assessed with acetone planar laser induced fluorescence (PLIF), where acetone vapor was seeded into the gaseous fuel. PLIF measurements were performed for both streamwise and spanwise laser sheet orientations. Supporting datasets were collected including schlieren imaging, chemiluminescent imaging, and pressure distributions. PIM actuation is found to increase jet penetration, crossflow expansion, and initiate fuel jet breakup. The average jet cross sectional area is shown to increase by >20% with the addition of plasma. PLIF imaging at PIM stabilized combustion revealed a significant unburned fuel concentration in a local separation region near the PIMs, and identified the minimum plasma pulse duration for flowfield transition from initial conditions to the combustion pattern.

Fuel ignition delay in hydrogen diesel

A new mathematical model is considered for modeling the induction period of fuel self-ignition in a hydrogen diesel engine with high-pressure injection equipment. Reconstruction of the macrokinetic equation and numerical modeling of the process of self-ignition of fuel in a hydrogen diesel engine are carried out.

Prospects and Limitations of Predicting Fuel Ignition Properties from Low-Temperature Speciation Data

Using chemical kinetic modeling and statistical analysis, we investigate the possibility of correlating key chemical “markers”─typically small molecules─formed during very lean (ϕ ∼ 0.001) oxidation experiments with near-stoichiometric (ϕ ∼ 1) fuel ignition properties. One goal of this work is to evaluate the feasibility of designing a fuel-screening platform, based on small laboratory reactors that operate at low temperatures and use minimal fuel volume. Buras et al. [Combust. Flame 2020, 216, 472–484] have shown that convolutional neural net (CNN) fitting can be used to correlate first-stage ignition delay times (IDTs) with OH/HO2 measurements during very lean oxidation in low-T flow reactors with better than factor-of-2 accuracy. In this work, we test the limits of applying this correlation-based approach to predict the low-temperature heat release (LTHR) and total IDT, including the sensitivity of total IDT to the equivalence ratio, ϕ. We demonstrate that first-stage IDT can be reliably correlated with very lean oxidation measurements using compressed sensing (CS), which is simpler to implement than CNN fitting. LTHR can also be predicted via CS analysis, although the correlation quality is somewhat lower than for first-stage IDT. In contrast, the accuracy of total IDT prediction at ϕ = 1 is significantly lower (within a factor of 4 or worse). These results can be rationalized by the fact that the first-stage IDT and LTHR are primarily determined by low-temperature chemistry, whereas total IDT depends on low-, intermediate-, and high-temperature chemistry. Oxidation reactions are most important at low temperatures, and therefore, measurements of universal molecular markers of oxidation do not capture the full chemical complexity required to accurately predict the total IDT even at a single equivalence ratio. As a result, we find that ϕ-sensitivity of ignition delay cannot be predicted at all using solely correlation with lean low-T chemical speciation measurements.

Model-based compositional predictions for a differential scanning calorimetry/thermogravimetric analysis-mass spectrometry system used for heat of vaporization measurements

A Differential Scanning Calorimetry/Thermogravimetric Analysis (DSC/TGA) procedure for determination of Heat of Vaporization (HOV) of fuel and surrogate fuel mixtures has been previously utilized for evaluation of oxygenate impacts on spark ignition fuels. This analysis has been further leveraged with mass spectrometry (MS) to elucidate vapor phase compositional changes during evaporation. In this article we focus on a simple system of three compounds (ethanol, n-hexane, and n-octane) to provide a model-based understanding of the evaporation process under these experimental conditions. An Aspen Plus model was set up to provide liquid and vapor phase concentration predictions during mixture evaporation using the initial mixture composition, and measured temperature and mass loss profiles from DSC/TGA experiments. Agreements between the trends of the MS ion count profiles and model composition predictions provide a degree of validation of this modeling approach that can allow the interpretation and extrapolation of DSC/TGA measurements for more complex fuel mixtures.