Propane Fuels Research Articles

Combustion stability and hetero-/homogeneous chemistry interactions for fuel-lean hydrogen/air mixtures in platinum-coated microchannels

The hetero-/homogeneous combustion and stability limits of fuel-lean hydrogen/air mixtures (equivalence ratio φ=0.40) were investigated numerically in a platinum-coated planar microchannel with a length of 10mm and a height of 1mm. A two-dimensional numerical model was used for both the gas and the solid, which included elementary heterogeneous and homogeneous reaction mechanisms, detailed transport, heat conduction in the solid, surface radiation heat transfer, and external losses via a heat transfer coefficient h. Pressures of 1 and 5bar and solid thermal conductivities ks = 1 and 16Wm-1K−1 were analyzed, while stability maps were constructed in terms of the critical extinction heat transfer coefficient hcr versus inlet velocity UIN (or mass throughput). For a given solid thermal conductivity, there existed a crossover mass throughput above (below) which the stability envelope was broader at 5bar (1bar). Simulations with a surface perfectly stirred reactor (SPSR) model qualitatively reproduced the crossover points, which originated from a shift in the pressure dependence of the catalytic reactivity of hydrogen. For the low solid thermal conductivity ks = 1 Wm-1K−1, a non-monotonic dependence of the stability limits on the mass throughput was shown, with local minima created below the crossover point. The stability limits of hydrogen were solely determined by catalytic chemistry, as it sustained combustion at temperatures down to 320–380K, at which gas-phase chemistry was frozen. Away from the critical extinction points, both catalytic and gas-phase reaction pathways were controlling. The diffusional imbalance of hydrogen, which led to catalytically-induced superadiabatic surface temperatures, and the suppression of the surface superadiabaticity by gaseous chemistry resulted in rich combustion phenomena, such as increasing peak wall temperatures with increasing heat transfer coefficients h. Critical extinction heat transfer coefficients for hydrogen were three to four orders of magnitude higher than those reported for methane and propane fuels in a similar channel geometry.

A comparative study on combustion characteristics of methane, propane and hydrogen fuels in a micro-combustor

The combustion characteristics of three hydrocarbon fuels are investigated so as to study the applicability of fuels in a micro-planar combustor. Experiments are performed to analyze the differences in flame stabilization, temperature distribution of external wall and flammable channel-heights. At different equivalence ratios, it is found that the mixture of hydrogen/air has a much wider and stable flammable range. The reaction positions of methane and propane cases will significantly move downstream along with the increase in mixture flow rate. Under the same chemical energy inputs, the external wall temperature distribution of methane case is most uniform, and the average wall temperature is also the highest among the three fuels. When hydrogen is selected as a fuel, the temperature gradient of the combustor wall becomes very large, which is caused by the flame position near the inlet. The flammable channel-heights of the three fuels in the micro-planar combustor are different. It is observed that stable combustion of methane/air cannot be achieved when the channel-height is less than 2.5 mm. However, the minimum flammable channel-height of propane/air case is 2 mm, and hydrogen/air can be ignited in a 1 mm height micro-combustor.1

Development and Test of a Fuel Cell Based Micro-CHP System

Fuel cell based micro combined heat and power (micro-CHP) systems are residential scale clean energy conversion unit. It employs fuel cells in a compact system that converts natural gas, propane or other fuels into both electricity and heat, which increases efficiency by simultaneously generating power and heat for one unit, on-site within a home. A prototype system consisting of a natural gas steam reforming unit, CO cleaning unit, PEM fuel cell stack, waste heat recovery unit and auxiliary unit is integrated. Test results of the prototype show that it can start within an hour and the syngas produced can meet the fuel cell’s requirements. The prototype’s electric power and thermal power are 200W and 530W respectively, while the electric and thermal efficiency are 15.4% and 40.9% respectively.

A Mathematical Model of a Direct Propane Fuel Cell

A rigorous mathematical model for direct propane fuel cells (DPFCs) was developed. Compared to previous models, it provides better values for the current density and the propane concentration at the exit from the anode. This is the first DPFC model to correctly account for proton transport based on the combination of the chemical potential gradient and the electrical potential gradient. The force per unit charge from the chemical potential gradient (concentration gradient) that pushes protons from the anode to the cathode is greater than that from the electrical potential gradient that pushes them in the opposite direction. By including the chemical potential gradient, we learn that the proton concentration gradient is really much different than that predicted using the previous models that neglected the chemical potential gradient. Also inclusion of the chemical potential gradient made this model the first one having an overpotential gradient (calculated from the electrical potential gradient) with the correct slope. That is important because the overpotential is exponentially related to the reaction rate (current density). The model described here provides a relationship between the conditions inside the fuel cell (proton concentration, overpotential) and its performance as measured externally by current density and propane concentration.

Layered oxygen-deficient double perovskite as an efficient and stable anode for direct hydrocarbon solid oxide fuel cells.

Different layered perovskite-related oxides are known to exhibit important electronic, magnetic and electrochemical properties. Owing to their excellent mixed-ionic and electronic conductivity and fast oxygen kinetics, cation layered double perovskite oxides such as PrBaCo2O5 in particular have exhibited excellent properties as solid oxide fuel cell oxygen electrodes. Here, we show for the first time that related layered materials can be used as high-performance fuel electrodes. Good redox stability with tolerance to coking and sulphur contamination from hydrocarbon fuels is demonstrated for the layered perovskite anode PrBaMn2O5+δ (PBMO). The PBMO anode is fabricated by in situ annealing of Pr0.5Ba0.5MnO3-δ in fuel conditions and actual fuel cell operation is demonstrated. At 800 °C, layered PBMO shows high electrical conductivity of 8.16 S cm(-1) in 5% H2 and demonstrates peak power densities of 1.7 and 1.3 W cm(-2) at 850 °C using humidified hydrogen and propane fuels, respectively.

Tip opening of premixed bunsen flames: Extinction with negative stretch and local Karlovitz number

The characteristics of tip openings in premixed bunsen flames have been studied experimentally by measuring OH radicals from laser-induced fluorescence and tip curvatures from chemiluminescent images. Results showed that the tip opening occurred at a constant equivalence ratio and was independent of the jet velocity in propane/air mixtures. The observation of a local extinction phenomenon of the negatively stretched flame due to the flame curvature could not be consistently explained based on flame stretch or the Karlovitz number, since they varied appreciably with the jet velocity. The concept of the local Karlovitz number (KaL) was introduced, which is defined as the ratio of the characteristic reaction time in the normal direction for a stretched flame to the characteristic flow time in the tangential direction for the stretched flame. The local Karlovitz number maintained a constant value under tip opening conditions, irrespective of the jet velocity. Tip opening occurred at a reasonably constant local Karlovitz number of about ∼1.72 when the nitrogen dilution level in propane and n-butane fuels was varied.

Horizontally Issuing Diffusion Flames Characterized by OH-PLIF and Visualizations

Planar laser induced fluorescence and flame visualizations characterized the effect of buoyancy on the behavior of the combustion zone of diffusion jet flames which issued from horizontally-oriented tubes into ambient air. The study focused on the mixing characteristics of propane and ethylene at Reynolds numbers ranging from 300 to 1500 in the near field of the jet (up to X/D=9) and Froude numbers ranging as low as 0.36, based on cold-flow gas properties and conditions. Performing the study with a variety of fuel tube diameters enabled independent control of Froude and Reynolds numbers. The PLIF visualizations revealed the presence of the hydroxyl radical in the mixing layer for all cases. The hydroxyl concentrations were consistently higher in the upper portion of the mixing layer, indicative of more vigorous mixing in this region. The visualizations also revealed the evolution of polycyclic aromatic hydrocarbons which were initially spatially segregated from the portion of the reaction zone containing the hydroxyl radical. The polycyclic aromatic hydrocarbons initiate in fuel-rich regions nearer to the jet core than the hydroxyl radical, though the two regions eventually combine well downstream of the tube exit. Both the hydroxyl radical and the polycyclic aromatic hydrocarbons were more prominent on the upper side of the jet flame. Both propane and ethylene fuels led to qualitatively similar features of the flow field, indicating the important role played by the buoyancy-influenced fluid dynamics of the combustion products. The resulting cross sectional PLIF images were used to produce a three-dimensional representation of the reaction zone, indicating the jet spread and trajectory. The data was empirically correlated and found to collapse when based on the Froude number consistent with the density and temperature of a fully-reacted stoichiometric mixture. Complementary visualizations provided additional insight into the trajectory of the jet flame and revealed features of the reaction zone farther from the tube exit.

Nickel Alloy Catalysts for the Anode of a High Temperature PEM Direct Propane Fuel Cell

High temperature polymer electrode membrane fuel cells that use hydrocarbon as the fuel have many theoretical advantages over those that use hydrogen. For example, nonprecious metal catalysts can replace platinum. In this work, two of the four propane fuel cell reactions, propane dehydrogenation and water dissociation, were examined using nickel alloy catalysts. The adsorption energies of both propane and water decreased as the Fe content of Ni/Fe alloys increased. In contrast, they both increased as the Cu content of Ni/Cu alloys increased. The activation energy for the dehydrogenation of propane (a nonpolar molecule) changed very little, even though the adsorption energy changed substantially as a function of alloy composition. In contrast, the activation energy for dissociation of water (a molecule that can be polarized) decreased markedly as the energy of adsorption decreased. The different relationship between activation energy and adsorption energy for propane dehydrogenation and water dissociation alloys was attributed to propane being a nonpolar molecule and water being a molecule that can be polarized.

Numerical simulations of laminar burning velocities of a major volatile organic compound involved in accelerating forest fires

This paper is dedicated to a first approach for the study of the so called eruptive fires or accelerating forest fires. It is a preliminary work to test the hypothesis of Volatile Organic Compounds (VOCs) accumulation as the cause of this phenomenon. In this work we explore the ability of the numerical code Fire Dynamics Simulator (FDS-v5.5) to simulate premixed flame spread. In a first part the burning velocities of propane/air and n-decane/air mixtures are calculated for different initial temperatures and equivalence ratio (0.7–1.3) at atmospheric pressure using a cylindrical combustion chamber. The preheat temperatures range for propane and n-decane fuels are respectively 300–423 K and 360–470 K. In a second part, the laminar burning speeds of the α-pinene, which is the main VOC emitted by Mediterranean vegetal species, is simulated for the same equivalence ratio and initial temperatures 373–453 K. The obtained results of these three fuels are compared to the experimental and computed results of the literature. These comparisons demonstrate the ability of FDS-v5.5 to deliver reliable predictions on laminar burning velocities of premixed flames.

Optimisation of biomass waste to energy conversion systems for rural grid-connected applications

Several rural farms have installed anaerobic digestion systems as manure management systems. Such systems are also used to provide electricity and heating. In these systems, biogas is generated from anaerobic digestion of biomass waste and combusted in a boiler and an engine-generator set, to produce heat and electricity respectively. This paper calculates the size and mode of operation of a biomass waste to energy conversion system that would result in maximum revenue for a given herd size. A Tabu Search optimisation technique is used. A number of equally good solutions are generated. These solutions are plotted on a Pareto front and the best solution is defined as one that lies on this Pareto front. Optimisation of a biomass waste to energy conversion system reduces reliance on electricity from the grid. It also reduces reliance on the use of propane or other fossil fuels for heating.

자발화된 층류 부상화염에 대한 점화지연시간의 영향

Autoignition characteristic is an important parameter for designing diesel or PCCI engines. In particular, diesel spray flames are lifted from the nozzle and the initial flame is formed by an autoignition phenomenon. The lifted nature of diesel spray flames influences soot formation, since air will be entrained into the spray core by the entrainment of air between the nozzle region and the lifted flame base. The objective of the present study was to identify the effect of heat loss on the ignition delay time by adopting a coflow jet as a model problem. Methane (), ethylene (), ethane (), propene (), propane (), and normal butane (n-) fuels were injected into high temperature air, and the liftoff height was measured experimentally. As the result, a correlation was determined between the liftoff height of the autoignited lifted flame and the ignition delay time considering the heat loss to the atmosphere.

Heterogeneous Reaction of NO2 on Fresh and Coated Soot Surfaces

The heterogeneous reaction of nitrogen dioxide (NO(2)) on fresh and coated soot surfaces has been investigated to assess its role in night-time formation of nitrous acid (HONO) in the atmosphere. Soot surfaces were prepared by incomplete combustion of propane and kerosene fuels under lean and rich flame conditions and then processed by heating to evaporate semivolatile species or by coating with pyrene, sulfuric acid, or glutaric acid. Uptake kinetics and HONO yield measurements were performed in a low-pressure fast-flow reactor coupled to a chemical ionization mass spectrometer (CIMS), using atmospheric-level NO(2) concentrations. The uptake coefficient and the HONO yield upon interaction of NO(2) with nascent soot depend on the type of fuel and combustion regime and are the highest for samples prepared using fuel rich flame. Heating the nascent soot samples before exposure to NO(2) removes the organic material from the soot backbone, leading to a significant increase in NO(2) uptake coefficient and HONO yield. Continuous exposure to NO(2) reduces the reactivity of soot because of irreversible deactivation of the surface sites. Our results support the oxidation-reduction mechanism involving adsorptive and reactive centers on soot surface where NO(2) is converted to HONO and other products. Coating of the soot surface by different materials to simulate atmospheric aging has a strong impact on its reactivity toward NO(2) and the resulting HONO production. Coating of pyrene has little effect on either reaction rate or HONO yield. Sulfuric acid coating does not alter the uptake coefficient, but significantly reduces the amount of HONO formed. Coating of glutaric acid significantly increases NO(2) uptake coefficient and HONO yield. The results of our study indicate that the reactivity and HONO generating capacity of internally mixed soot aerosol will depend on the chemical composition of the coating material and hence will vary considerably in different polluted environments.

Solid oxide fuel cell bi-layer anode with gadolinia-doped ceria for utilization of solid carbon fuel

Pyrolytic carbon was used as fuel in a solid oxide fuel cell (SOFC) with a yttria-stabilized zirconia (YSZ) electrolyte and a bi-layer anode composed of nickel oxide gadolinia-doped ceria (NiO–GDC) and NiO–YSZ. The common problems of bulk shrinkage and emergent porosity in the YSZ layer adjacent to the GDC/YSZ interface were avoided by using an interlayer of porous NiO–YSZ as a buffer anode layer between the electrolyte and the NiO–GDC primary anode. Cells were fabricated from commercially available component powders so that unconventional production methods suggested in the literature were avoided, that is, the necessity of glycine–nitrate combustion synthesis, specialty multicomponent oxide powders, sputtering, or chemical vapor deposition. The easily-fabricated cell was successfully utilized with hydrogen and propane fuels as well as carbon deposited on the anode during the cyclic operation with the propane. A cell of similar construction could be used in the exhaust stream of a diesel engine to capture and utilize soot for secondary power generation and decreased particulate pollution without the need for filter regeneration.

A Mathematical Model Showing Temperature Variations in a Direct Propane Fuel Cell

not Available.

Direct Propane Fuel Cell Anode with Interdigitated Flow Fields: Two-Dimensional Model

The first two-dimensional model of a direct propane fuel cell (DPFC) anode was developed and used to investigate materials and operating conditions that resulted in improved DPFC anode performance. The software used, FreeFEM++, is open source and is based on the finite element method. The anode catalyst layer (ACL) was composed of three phases. One solid phase was the platinum catalyst supported on porous carbon (an electron conductor). The second solid phase consisted of solid zirconium phosphate (a proton conductor at 150 °C). The gas phase was located within the pores of the carbon and between the solid particles. Operation at 150 °C allowed the propane gas phase concentration to be in direct contact with the catalyst at the entrance to the ACL. This was an important advantage compared to previous DPFC operations at conditions where aqueous liquids are present (PEMFC at temperatures less than 100 °C and direct propane PAFC). When aqueous liquids surround the catalyst, the propane concentration in contact with the catalyst at the ACL entrance is much smaller because the solubility of propane in aqueous liquids is small. The one-third improvement in the anode overpotential was attributed to this difference. By using interdigitated flow fields with the propane feed in one set of channels and the carbon dioxide product in another set of channels, there was no mixing of the two so that the maximum propane concentration was always present at the entrance to the ACL. The residence time could be chosen, by adjusting the distance between the feed and the product channels (length of land plus channel), to obtain large values of conversion and large values of fuel utilization. It was shown that the larger pressure drops often associated with interdigitated flow fields compared to conventional serpentine flow fields were diminished by increasing the thickness of the catalyst layer. In addition, the thicker catalyst layer permitted the Pt catalyst to be spread over a greater thickness of carbon catalyst support, thereby ensuring better catalyst dispersion and improved catalyst performance.

Near-Infrared Imaging of SOFCs with Methane and Propane Fuels

A Si-CCD camera-based imaging system is used in-situ to study the effects of hydrocarbon fuels on Ni/YSZ solid oxide fuel cell anode temperatures. Methane and propane are used as fuels. Temperature variations are investigated to explore how carbon deposition varies with fuel, and how deposition and electrochemical oxidation of carbon affect the anode. The temperature change that results from carbon growth during CH4 flow is -2.3 ºC. The temperature change due to the oxidation of carbon deposits from CH4 is +2.0 ºC. Similar experiments with C3H8 produced temperature shifts of -3.4 ºC and +2.4 ºC during fuel flow and electrochemical oxidation, respectively. The temperature drops more quickly when C3H8 is used instead of CH4. As deposits are electrochemically oxidized, the maximum temperature occurs ~2 minutes earlier in the CH4 case. The time profiles indicate that more carbon is present in C3H8 cells.

A Thermally Self-Sustaining Miniature Solid Oxide Fuel Cell

A thermally self-sustaining miniature power generation device was developed utilizing a single-chamber solid oxide fuel cell (SOFC) placed in a controlled thermal environment provided by a spiral counterflow “Swiss roll” heat exchanger and combustor. With the single-chamber design, fuel/oxygen crossover due to cracking of seals via thermal cycling is irrelevant and coking on the anode is practically eliminated. Appropriate SOFC operating temperatures were maintained even at low Reynolds numbers (Re) via combustion of the fuel cell effluent at the center of the Swiss roll. Both propane and higher hydrocarbon fuels were examined. Extinction limits and thermal behavior of the integrated system were determined in equivalence ratio—Re parameter space and an optimal regime for SOFC operation were identified. SOFC power densities up to 420 mW/cm2 were observed at low Re. These results suggest that single-chamber SOFCs integrated with heat-recirculating combustors may be a viable approach for small-scale power generation devices.

Near-Infrared Imaging of SOFCs with Methane and Propane Fuels

not Available.

Measurement and chemical kinetic prediction of detonation sensitivity and cellular structure characteristics in dimethyl ether–oxygen mixtures

In this work, experiments have been performed to measure the detonation velocities and characteristic cell sizes in the dimethyl ether (DME) fuel–oxygen mixtures. Equilibrium calculation and detailed chemical kinetics modeling of the ZND structure of detonations are also carried out to investigate the detonation characteristics of DME. Detonation cell sizes estimated using a correlation model by Ng et al. [Ng HD, Ju Y, Lee JHS. Assessment of detonation hazards in high-pressure hydrogen storage from chemical sensitivity analysis. Int J Hydrogen Energy 2007;32:93–99] are in good agreement with experimental data. It is found that the cell size values for DME–oxygen mixtures are comparable to those of propane or ethane fuels. At low initial pressure, double cell like detonation structures have been observed in all equivalence ratios considered in this study. Chemical kinetic results reveal that DME oxidation under detonation environment exhibits similarly a two-stage heat release process inside the reaction zone. This effect may play a significant role in the existence and scaling of the multi-cell detonation pattern in stoichiometric and fuel-rich DME mixtures. On the lean side, multiple cells appear to be caused primarily by the strong intrinsic instability of the unsteady detonation front. The present experimental results and chemical kinetic sensitivity analyses provide some basic information to assess detonation hazards in DME-based mixtures.

Synergistic effect of mixing dimethyl ether with methane, ethane, propane, and ethylene fuels on polycyclic aromatic hydrocarbon and soot formation

Characteristics of polycyclic aromatic hydrocarbon (PAH) and soot formation in counterflow diffusion flames of methane, ethane, propane, and ethylene fuels mixed with dimethyl ether (DME) have been investigated. Planar laser-induced incandescence and fluorescence techniques were employed to measure relative soot volume fractions and PAH concentrations, respectively. Results showed that even though DME is known to be a clean fuel in terms of soot formation, DME mixture with ethylene fuel increases PAH and soot formation significantly as compared to the pure ethylene case, while the mixture of DME with methane, ethane, and propane decreases PAH and soot formation. Numerical calculations adopting a detailed kinetics showed that DME can be decomposed to produce a relatively large number of methyl radicals in the low-temperature region where PAH forms and grows; thus the mixture of DME with ethylene increases CH 3 radicals significantly in the PAH formation region. Considering that the increase in the concentration of O radicals is minimal in the PAH formation region with DME mixture, the enhancement of PAH and soot formation in the mixture flames of DME and ethylene can be explained based on the role of methyl radicals in PAH and soot formation. Methyl radicals can increase the concentration of propargyls, which could enhance incipient benzene ring formation through the propargyl recombination reaction and subsequent PAH growth. Thus, the result substantiates the importance of methyl radicals in PAH and soot formation, especially in the PAH formation region of diffusion flames.