Effect Of Fuel Composition Research Articles

Effects of Wildland Fuel Composition on Fire Intensity

Assessing the characteristics of fuel flammability during fire is of major significance regarding fire intensity and fire spread control. Under the background of shifting forest composition from heliophytic to mesophytic species in mixed-oak forests, our objective is to determine the impacts of species-driven changes in fuel flammability characteristics and the specific relationships between fuel ignition variations at the species level. Oak and maple fuels were collected from ninety-four plots established in Zaleski State Forest, Ohio. A total of 30 combustion samples were separated (15 oak samples and 15 maple samples), with each combustion sample weighing 20 g to ignite under a laboratory fume hood. Our results determined that oak fuel showed significantly higher flame temperatures than maple fuel, and the fuel consumption and combustion duration time both varied between oak and maple fuel. These findings indicated that the shift from oak forest to mesophytic species could change a fire’s behavior. Combined with the cooler, moister, and less-flammable forest conditions generated by these mesophytic species, fires may not be able to reach their historical fire intensities, suggesting that updated data and new insights are needed for fire management.

Micro-Mixing Combustion for Highly Recuperated Gas Turbines: Effects of Inlet Temperature and Fuel Composition on Combustion Stability and NOx Emissions

Abstract The micromix combustion concept offers an elegant compromise between premixed and nonpremixed combustion. By mixing the fuel and air at the smallest scale possible, one can achieve NOx emissions comparable to premixed combustion while removing the risks of auto-ignition and flashback. Current literature reports multiple micromix designs that achieve low NOx emissions (<10 ppm) with hydrogen or hydrogen-rich fuels at combustor inlet temperatures (CIT) representative of low to medium pressure ratio gas turbines (<650 K). This paper seeks to bridge the gap between current literature and the design requirements of highly recuperated ceramic gas turbines, which should allow low NOx operation with various fuels at combustor inlet temperatures upwards of 900 K. To this end, micromix injection nozzles were designed and tested at small scale to investigate the effects of fuel composition and inlet temperature on combustion stability and NOx emissions. The nozzles were additively manufactured in Inconel 625 having hundreds of holes as small as 0.25 mm. An axial swirler is used to induce recirculation of the products behind the nozzle, which helps stabilize combustion with hydrocarbon fuels due to their longer reaction times and slower flame speeds. Experimental results show that NOx emissions can be decreased down to premixed levels if the jet Damköhler number is kept under a critical value, which requires increasingly smaller holes or higher jet velocities as the inlet temperature increases. Combustion instabilities are observed at low inlet temperatures with hydrocarbons, which are also correlated to the jet Damköhler number.

Effect of Fuel Composition on Carbon Black Formation Pathways

Differences in lamellae length, stacking, and particularly a difference in the core-to-shell radial structure are observed for carbon blacks produced using different feedstocks. Carbon black (CB) produced using a coal tar (CT) feedstock formed particles with amorphous cores exhibiting a sharp transition to extended lamellae oriented about the periphery of the particle. In contrast, the carbon black produced from fluidized catalytic cracker (FCC) decant oil as feedstock formed particles with a single nucleated core possess a rather uniform radial transition—reflecting the presence of ordered, concentric lamellae across most of the particle radius. Minimal disorder was observed in the core while the undulations in perimeter lamellae were fewer. Our interpretation for these structural dissimilarities is premised on differences in fuel composition, specifically component classes as found by saturate, aromatic, resin, asphaltene (SARA) analysis. These in turn lead to variation in the relative rates of particle nucleation and particle growth by pyrolysis products, moderated by temperature. Electron energy loss spectroscopy reveals radial variation in the sp2 content between the different feedstocks consistent with observed nanostructures. Collectively these results are interpreted in terms of an offset in nucleation and growth—dependent upon the relative contributions of feedstock aromatic content and pyrolysis processes to particle nucleation and growth. To further test the postulate of different formation conditions for the two carbon blacks pulsed laser annealing was applied. The high temperature heating accentuated the dissimilarities in nanostructure and chemistry—leading to stark dissimilarities. These differences were also manifested by comparing oxidative reactivity.

Effects of Fuel Composition at Varying Air-Fuel Ratio on Knock Resistance During Spark-Ignition Combustion

Effects of Fuel Composition at Varying Air-Fuel Ratio on Knock Resistance During Spark-Ignition Combustion

Computation of conventional and alternative jet fuel sensitivity to lean blowout

Large Eddy Simulations (LES) are performed to compute the sensitivity of a conventional (A-2) and an alternate bio-jet (C-1) fuel to Lean Blowout (LBO). A realistic aviation gas turbine engine combustor configuration is considered. Reliable experimental LBO data and OH∗ chemiluminescence data for the conventional and alternate jet fuel in the combustor configuration have recently become available. The present work utilizes a highly automated, on-the-fly meshing strategy, along with adaptive mesh refinement, to demonstrate the feasibility of capturing the realistic combustion processes. A Lagrangian framework, with initial conditions specified using measurements of spray statistics, is used to model the fuel spray. Newly developed compact reaction mechanisms based on fuel surrogates are validated for the A-2 and the C-1 fuels. The compact reaction mechanisms are implemented using a detailed finite rate chemistry solver. Spray statistics computed by the present LES simulations compare well with available measurements at stable flame conditions near the lean blowout limit. The computed shape of the stable flame as represented by line integrated OH concentrations compares well with the experimental OH∗ chemiluminescence data. Lean blowout is reached by gradually decreasing the fuel flow rate in the computations, similar to that in the experiments. The results of the LES simulations effectively capture the fuel composition effects and estimate the sensitivity of the LBO limits to the fuel type. The computed trends in LBO limits agree within engineering accuracy with the experimental results for conventional and alternative aviation fuels. The methodology for predicting the fuel composition effects on the lean blowout limits in a fully resolved realistic, complex combustor is established for the first time.

Reduction of Nonvolatile Particulate Matter Emissions of a Commercial Turbofan Engine at the Ground Level from the Use of a Sustainable Aviation Fuel Blend.

Nonvolatile particulate matter (nvPM) emissions from aircraft turbine engines deteriorate air quality and contribute to climate change. These emissions can be reduced using sustainable aviation fuels (SAFs). Here, we investigate the effects of a 32% SAF blend with fossil fuel on particle size distributions and nvPM emission indices of a widely used turbofan engine. The experiments were conducted in a test cell using a standardized sampling and measurement system. The geometric mean diameter (GMD) increased with thrust from ∼8 nm at idle to ∼40 nm at take-off, and the geometric standard deviation (GSD) was in the range of 1.74-2.01. The SAF blend reduced the GMD and GSD at each test point. The nvPM emission indices were reduced most markedly at idle by 70% in terms of nvPM mass and 60% in terms of nvPM number. The relative reduction of nvPM emissions decreased with the increasing thrust. The SAF blend reduced the nvPM emissions from the standardized landing and take-off cycle by 20% in terms of nvPM mass and 25% in terms of nvPM number. This work will help develop standardized models of fuel composition effects on nvPM emissions and evaluate the impacts of SAF on air quality and climate.

A Novel Large-Eddy Simulation-Based Process for NOx Emission Assessment in a Premixed Swirl Stabilized Combustion System

Abstract This paper presents a new computational fluid dynamics (CFD) approach for the assessment of NOx emission. The methodology is validated against the experimental data of a heavy-duty gas turbine annular combustor. Since the NOx formation involves time scales that are different from the fuel oxidation time, this work defines the transport equation source terms for NOx basis on a dedicated NOx-Damköhler number. The latter parameter allows to properly distinguish the “in-flame” contribution from the “postflame” one. While the former is a mix of several mechanisms (prompt, N2O-pathway, thermal), the latter is dominated by the thermal contribution. The validation phase is developed in a large-eddy simulation (LES) framework where the extended turbulent flame speed model is implemented to consider the influence of both heat loss and strain rate on the progress variable source term. The accuracy of the model against the most important operability parameters of the combustor is verified. A strong focus on the fuel composition effect onto NOx is presented as well. For any simulated operating condition, the present methodology is able to provide a limited percentage error if compared with the data, considering also different combustion regimes. Leveraging this alignment, the last portion of the paper is dedicated to detailed postprocessing highlighting the role of some key factors on NOx formation. In particular, the focus will be dedicated to the impact of the fuel gas composition and the pilot split.

The effects of distillation characteristics and aromatic content on low-load gasoline compression ignition (GCI) performance and soot emissions in a multi-cylinder engine

The DOE Co-Optima initiative focuses on investigating the ability of fuel properties to work in tandem with advanced combustion engines to increase fuel economy. One of the most promising advanced compression ignition strategies (ACI) is gasoline compression ignition (GCI). GCI leverages the relative auto-ignition resistance of gasoline-like fuels to enable highly premixed combustion processes at a range of air–fuel stratifications. In practical applications, engines must operate over a wide range of conditions, which associated with the inherent limitations and benefits of different ACI modes, suggests the engine should be capable of operating across multiple combustion modes. Operating the engine in multiple combustion modes effectively requires a fundamental understanding of fuel composition effects. The fact that GCI can operate with fuels designed for spark ignition engines enables the engine to be operated in either combustion mode when most suitable. This effort investigates the effects of fuel physical properties and aromatic content on GCI NOx, unburned hydrocarbons (HC), CO and particulate emissions. Three fuels with the same research octane number (RON) but different distillation curves and aromatic content are compared to isolate the impact of the two properties in a production, multi-cylinder engine. Different injection strategies targeting increasing levels of fuel stratification (100%, 70% and 0% premixed fuel) at a constant combustion phasing are utilized. Results showed that changes in fuel stratification had little impact on emissions of NOx, HC and CO until the fuel was injected completely near top dead center (TDC). Particulate sampling showed that the aromatic content of the fuel had greater impact on elemental carbon particulate matter (PM) emissions than the fuel distillation characteristics.

Kinetic Modeling of the Ignition of Droplets of Fast Pyrolysis Bio-oil: Effect of Initial Diameter and Fuel Composition.

Fast biomass pyrolysis is an effective and promising process for high bio-oil yields, and represents one of the front-end technologies to provide alternative, sustainable fuels as a replacement of conventional, fossil-based ones. In this work, the effect of droplet initial diameter on the evaporation and ignition of droplets of crude fast pyrolysis bio-oil (FPBO) and FPBO/ethanol blend (50% vol) at ambient pressure is discussed. The experimental tests were carried out in a closed single droplet combustion chamber equipped with optical accesses, using droplets with a diameter in the range of 0.9–1.4 mm. The collected experimental data show a significant effect of droplet diameter and initial fuel composition on the evaporation and combustion of the droplets. At the same time, 1-dimensional modeling of the evaporation and ignition of different droplets of crude FPBO and its blend with ethanol is performed to understand the complex physical and chemical effects. To this purpose, an 8-component surrogate was adopted, and a skeletal mechanism (170 species and 2659 reactions) was obtained through an established methodology. The comparison of numerical and experimental results shows that the model is able to capture the main features related to the heating phase of the droplet and the effect of fuel composition on droplet temperature and evaporation, particularly the increased reactivity following ethanol addition and the variation of diameter with time. Also, a sensitivity analysis highlighted the reactions controlling the autoignition of the droplets in the different conditions. It was found that the autoignition of pure FPBO droplets is governed by dimethyl furane (DMF), because of its high volatility and in spite of not being the most abundant species. On the other side, ethanol chemistry drives the gas-phase ignition in the case of the blended (50/50 v/v) mixtures, due to its higher volatility and reactivity.

A Numerical Investigation of the Effects of Fuel Composition on the Minimum Ignition Energy for Homogeneous Biogas-Air Mixtures

The minimum ignition energy (MIE) requirements for ensuring successful thermal runaway and self-sustained flame propagation have been analysed for forced ignition of homogeneous stoichiometric biogas-air mixtures for a wide range of initial turbulence intensities and CO2 dilutions using three-dimensional Direct Numerical Simulations under decaying turbulence. The biogas is represented by a CH4 + CO2 mixture and a two-step chemical mechanism involving incomplete oxidation of CH4 to CO and H2O and an equilibrium between the CO oxidation and the CO2 dissociation has been used for simulating biogas-air combustion. It has been found that the MIE increases with increasing CO2 content in the biogas due to the detrimental effect of the CO2 dilution on the burning and heat release rates. The MIE for ensuring self-sustained flame propagation has been found to be greater than the MIE for ensuring only thermal runaway irrespective of its outcome for large root-mean-square (rms) values of turbulent velocity fluctuation, and the MIE values increase with increasing rms turbulent velocity for both cases. It has been found that the MIE values increase more steeply with increasing rms turbulent velocity beyond a critical turbulence intensity than in the case of smaller turbulence intensities. The variations of the normalised MIE (MIE normalised by the value for the quiescent laminar condition) with normalised turbulence intensity for biogas-air mixtures are found to be qualitatively similar to those obtained for the undiluted mixture. However, the critical turbulence intensity has been found to decrease with increasing CO2 dilution. It has been found that the normalised MIE for self-sustained flame propagation increases with increasing rms turbulent velocity following a power-law and the power-law exponent has been found not to vary much with the level of CO2 dilution. This behaviour has been explained using a scaling analysis and flame wrinkling statistics. The stochasticity of the ignition event has been analysed by using different realisations of statistically similar turbulent flow fields for the energy inputs corresponding to the MIE and it has been demonstrated that successful outcomes are obtained in most of the instances, justifying the accuracy of the MIE values identified by this analysis.

Probabilistic modeling of forced ignition of alternative jet fuels

Fast and reliable high altitude re-ignition is a critical requirement for the development of alternative jet fuels (AJFs). To achieve stable combustion, a spark kernel needs to transit in a partially or fully extinguished flow to develop a flame front. Understanding the relight characteristics of the AJFs is complicated by the chaoticity of the turbulent flow and variations in the spark properties. The focus of this study is the prediction of such characteristics by high-fidelity simulations, with a specific focus on fuel composition effect on the ignition process. For this purpose, a previously developed computational framework is applied, which utilizes high-fidelity LES simulations, a hybrid tabulation approach for modeling forced ignition and detailed quantification of uncertainty resulting from initial and boundary conditions to predict ignition probability. The method is applied to two alternative fuels (named C1 and C5) and Jet-A fuel (named A2) under gaseous conditions. Results show that the mixing of kernel and fuel–air mixture is not affected by the ignition process, but chemistry effects strongly dominate ignition probability. In particular, C1 exhibits much lower ignition probability than the other two fuels, especially at lean operating conditions. More importantly, this behavior is contradictory to ignition delay experiments which predict longer delay times for C5 compared to C1. Comparisons with experiments show that the comprehensive modeling approach captures the ignition trends. Analysis of kernel trajectories in composition space shows that the variations are caused by the relative effects of kernel mixing, response to strain, and ignition properties of the fuel.

Fuel Composition Effects on Carbonyls and Quinones in Particulate Matter from a Light-Duty Diesel Engine Running Biodiesel Blends from Two Feedstocks

Several studies have linked diesel engine exhaust particulate matter (DPM) to adverse health effects. To examine the effects of biodiesel blends on light-duty diesel engine exhaust composition, concentrations of a select number of target compounds were determined in petrodiesel-biodiesel [waste vegetable oil (WVO) and soybean (SOY) feedstocks] fuel blends, lubricating oil, and exhaust particulate matter (PM). Particulate matter was generated from a light-duty diesel engine running on a transient drive cycle and fueled with WVO (B10, B20, B50, and B100 where Bxx refers to volume % biodiesel in fuel blend) and SOY (B20 and B100) biodiesel fuels blended with ultralow sulfur diesel (ULSD) reference fuel (B00). As expected, concentrations of individual n-alkanes (C12–C24) decreased with increasing biodiesel content but were absent from B100 for both WVO and SOY feedstocks. No target PAHs, carbonyls, and quinones were detected in B00 fuel, biodiesel fuel blends (for both WVO and SOY), or lubricating oil. No FAM...

High-Speed Imaging of Forced Ignition Kernels in Nonuniform Jet Fuel/Air Mixtures

This paper describes experimental measurements of forced ignition of prevaporized liquid fuels in a well-controlled facility that incorporates nonuniform flow conditions similar to those of gas turbine engine combustors. The goal here is to elucidate the processes by which the initially unfueled kernel evolves into a self-sustained flame. Three fuels are examined: a conventional Jet-A and two synthesized fuels that are used to explore fuel composition effects. A commercial, high-energy recessed cavity discharge igniter located at the test section wall ejects kernels at 15 Hz into a preheated, striated crossflow. Next to the igniter wall is an unfueled air flow; above this is a premixed, prevaporized, fuel–air flow, with a matched velocity and an equivalence ratio near 0.75. The fuels are prevaporized in order to isolate chemical effects. Differences in early ignition kernel development are explored using three synchronized, high-speed imaging diagnostics: schlieren, emission/chemiluminescence, and OH planar laser-induced fluorescence (PLIF). The schlieren images reveal rapid entrainment of crossflow fluid into the kernel. The PLIF and emission images suggest chemical reactions between the hot kernel and the entrained fuel–air mixture start within tens of microseconds after the kernel begins entraining fuel, with some heat release possibly occurring. Initially, dilution cooling of the kernel appears to outweigh whatever heat release occurs; so whether the kernel leads to successful ignition or not, the reaction rate and the spatial extent of the reacting region decrease significantly with time. During a successful ignition event, small regions of the reacting kernel survive this dilution and are able to transition into a self-sustained flame after ∼1–2 ms. The low-aromatic/low-cetane-number fuel, which also has the lowest ignition probability, takes much longer for the reaction zone to grow after the initial decay. The high-aromatic, more easily ignited fuel, shows the largest reaction region at early times.

Fuel composition effect on cathode airflow control in fuel cell gas turbine hybrid systems

Cathode airflow regulation is considered an effective means for thermal management in solid oxide fuel cell gas turbine (SOFC-GT) hybrid system. However, performance and controllability are observed to vary significantly with different fuel compositions. Because a complete system characterization with any possible fuel composition is not feasible, the need arises for robust controllers. The sufficiency of robust control is dictated by the effective change of operating state given the new composition used. It is possible that controller response could become unstable without a change in the gains from one state to the other.In this paper, cathode airflow transients are analyzed in a SOFC-GT system using syngas as fuel composition, comparing with previous work which used humidified hydrogen. Transfer functions are developed to map the relationship between the airflow bypass and several key variables. The impact of fuel composition on system control is quantified by evaluating the difference between gains and poles in transfer functions. Significant variations in the gains and the poles, more than 20% in most cases, are found in turbine rotational speed and cathode airflow. The results of this work provide a guideline for the development of future control strategies to face fuel composition changes.

The Effect of Fuel Composition on Knock in Lean Burn SI Engine

The Effect of Fuel Composition on Knock in Lean Burn SI Engine

The Performance of Syngas-Fueled SOFCs Predicted by a Reduced Order Model (ROM): Temperature and Fuel Composition Effects

An electrochemical reduced order model (ROM) has been developed in this study to simulate the performance of syngas-fueled anode-supported SOFCs with coupled bulk chemical reactions and multi-species gas diffusion in the electrodes. Experimental V-I curves with syngas fuel were used to validate the model to ensure its high fidelity. The model was used to investigate the effects of fuel composition and temperature on the electrochemical performance of the cell, chemical reaction rate and concentration distributions of gaseous species across the anode. The results show that H2 electro-oxidation dominates the overall cell performance, and that CO contributes to the performance indirectly via water gas shift (WGS) reaction, especially at low CO:H2 ratio and low current densities. Increasing the temperature enhances the performance of syngas-fueled SOFCs by increasing the rates of total electrochemical oxidation and the WGS reaction. The present work provides fundamental knowledge and framework for future performance simulations of large-scale and more complex syngas-fueled SOFC systems.

Effects of fuel composition on the economic performance of biogas-based power generation systems

Biogas to fuel is an attractive method to reduce global warming potential of methane emission and providing a renewable source of energy. In this study, exergoeconomic assessment of a biogas-based gas turbine system with preheater is conducted. In the present work, effects of fuel composition on the exergetic and economic performance of a plant are studied, and comparison between two fuel pricing methods has been carried out. Fuel composition effects have not been studied before and fuel pricing mostly conducted in terms of lower heating value (LHV) in previous studies. In this study, percentage of methane content in the fuel is changed. Two definitions for fuel pricing are used, one based on the exergy and the other based on the LHV of the biogas and the results are compared. In addition, the cost factors are defined and the cost of generated power are evaluated. To add more generality to the work, system sizes ranged from 1 to 10MW is taken into consideration to understand the effect of system size as well. Results reveal that fuel pricing based on the exergy gives more realistic evaluations. Furthermore, when methane content is changed from 0.95 to 0.6, total cost rate of the plant rises around 1% and electricity cost augments. Exergetic efficiency mitigates when methane content reduces. Based on the system size and biogas fuel price, the cost of generated electricity varies from 0.05$/kWh to 0.18$/kWh in this assessment.

Measurements of Stretch Statistics at Flame Leading Points for High Hydrogen Content Fuels

Fuel composition has a strong influence on the turbulent flame speed, even at very high turbulence intensities. An important implication of this result is that the turbulent flame speed cannot be extrapolated from one fuel to the next using only the laminar flame speed and turbulence intensity as scaling variables. This paper presents curvature and tangential strain rate statistics of premixed turbulent flames for high hydrogen content (HHC) fuels. Global (unconditioned) stretch statistics are presented as well as measurements conditioned on the leading points of the flame front. These measurements are motivated by previous experimental and theoretical work that suggests the turbulent flame speed is controlled by the flame front characteristics at these points. The data were acquired with high-speed particle image velocimetry (PIV) in a low-swirl burner (LSB). We attained measurements for several H2:CO mixtures over a range of mean flow velocities and turbulence intensities. The results show that fuel composition has a systematic, yet weak effect on curvatures and tangential strain rates at the leading points. Instead, stretch statistics at the leading points are more strongly influenced by mean flow velocity and turbulence level. It has been argued that the increased turbulent flame speeds seen with increasing hydrogen content are the result of increasing flame stretch rates, and therefore, SL,max values, at the flame leading points. However, the differences observed with changing fuel compositions are not significant enough to support this hypothesis. Additional analysis is needed to understand the physical mechanisms through which the turbulent flame speed is altered by fuel composition effects.

Size evolution of soot particles from gasoline and n-heptane/toluene blend in a burner stabilized stagnation flame

The evolution of soot particle size distribution function (PSDF) in premixed flames of gasoline (34% aromatics by volume) and a n-heptane/toluene blend (66% n-heptane/34% toluene by volume) was investigated in the burner stabilized stagnation (BSS) flame configuration, using the micro-orifice probe sampling and scanning mobility particle sizer (SMPS). The aim of this study is to illustrate the similarities and differences of sooting propensity between the real fuel and the simple hydrocarbon blend in premixed flame conditions. The mole ratio of carbon to oxygen (C/O) in the unburned gas was kept constant at 0.6 and similar maximum flame temperatures and temperature-time histories were kept between the two cases, so that we could focus on the fuel composition effects on sooting propensity. In addition, the size distribution, the total number density, and the volume fraction of soot were also compared to those previously measured for ethylene and propene flames under comparable conditions. It was observed that the particle size distributions of both gasoline and heptane/toluene flames evolve from the unimodal distribution (nucleation mode only) to the bimodal (both nucleation and coagulation mode) distribution. Compared to the heptane/toluene blend, the soot formation in gasoline flame features more persistent nucleation and much faster growth rate.

Vapour Space Flammability Measurements of High Ethanol (“E85”) and Low Ethanol (“E10”) Winter Automotive Fuels: Effects of Fuel Composition and Vapour Pressure

Vapour Space Flammability Measurements of High Ethanol (“E85”) and Low Ethanol (“E10”) Winter Automotive Fuels: Effects of Fuel Composition and Vapour Pressure