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Showing papers on "Combustion published in 2005"


Journal ArticleDOI
TL;DR: A comprehensive review of CO2 capture in coal-fired combustion plants can be found in this article, where the status of the technology development and assessments providing comparisons with other power generation options, and suggests research needs.

1,450 citations


Journal ArticleDOI
TL;DR: In this paper, the potential applications of renewable energy sources to replace fossil fuel combustion as the prime energy sources in various countries, and discusses problems associated with biomass combustion in boiler power systems.

973 citations


Journal ArticleDOI
TL;DR: In this paper, a subset of 154 biomass samples of very different origin (for instance wood, grass, rye, rape, reed, brewery waste, and poultry litter) have been selected from the database BIOBIB.

720 citations


Journal ArticleDOI
01 Jan 2005
TL;DR: In this paper, a H2-CO kinetic model was proposed to predict a wide variety of H2 and CO combustion data, from global combustion properties (shock-tube ignition delays, laminar flame speeds, and extinction strain rates) to detailed species profiles during H 2 and CO oxidation.
Abstract: We propose a H2–CO kinetic model which incorporates the recent thermodynamic, kinetic, and species transport updates relevant to high-temperature H2 and CO oxidation. Attention has been placed on obtaining a comprehensive and kinetically accurate model able to predict a wide variety of H2–CO combustion data. The model was subject to systematic optimization and validation tests against reliable H2–CO combustion data, from global combustion properties (shock-tube ignition delays, laminar flame speeds, and extinction strain rates) to detailed species profiles during H2 and CO oxidation in flow reactor and in laminar premixed flames.

626 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present results from a sensitivity analysis and from experimental fires conducted to investigate the relationship between fire radiative energy (FRE) and fuel mass combusted, and they conclude that FRE assessment offers a powerful tool for supplementing existing burned-area based fuel consumption measures.
Abstract: Estimates of wildfire aerosol and trace gas emissions are most commonly derived from assessments of biomass combusted. The radiative component of the energy liberated by burning fuel can be measured by remote sensing, and spaceborne fire radiative energy (FRE) measures can potentially provide detailed information on the amount and rate of biomass consumption over large areas. To implement the approach, spaceborne sensors must be able to derive fire radiative power (FRP) estimates from subpixel fires using observations in just one or two spectral channels, and calibration relationships between radiated energy and fuel consumption must be developed and validated. This paper presents results from a sensitivity analysis and from experimental fires conducted to investigate these issues. Within their methodological limits, the experimental work shows that FRP assessments made via independent hyperspectral and MIR radiance approaches in fact show good agreement, and fires are calculated to radiate 14 ± 3% [mean ± 1S.D.] of their theoretically available heat yield in a form capable of direct assessment by a nadir-viewing MIR imager. The relationship between FRE and fuel mass combusted is linear and highly significant (r2 = 0.98, n = 29, p < 0.0001), and FRP is well related to combustion rate (r2 = 0.90, n = 178, p < 0.0001), though radiation from the still-hot fuel bed can sometimes contribute significant FRP from areas where combustion has ceased. We conclude that FRE assessment offers a powerful tool for supplementing existing burned-area based fuel consumption measures, and thus shows significant promise for enhancing pyrogenic trace gas and aerosol emissions estimates

606 citations


Journal ArticleDOI
TL;DR: In this paper, the fundamental concepts for how to devise and apply quantitative measurement techniques for studies of fuel concentration, temperature, and fuel/air ratio in practical combustion systems, with some emphasis on internal combustion engines.

561 citations


Journal ArticleDOI
01 Jan 2005
TL;DR: In this paper, a cylindrical quartz tube with an inner diameter of 2mm was used as a model channel, and the downstream part of the tube was heated by an external heat source, and hence the temperature gradient in the axial direction was formed in the tube.
Abstract: Characteristics of premixed combustion in a heated channel with an inner diameter smaller than the conventional quenching distance of the employed mixture were investigated experimentally, analytically, and numerically. A cylindrical quartz tube with an inner diameter of 2 mm was used as a model channel. The downstream part of the tube was heated by an external heat source, and hence the temperature gradient in the axial direction was formed in the middle of the tube. Flat and stationary conventional premixed flames were stabilized at a point in this temperature gradient. In addition to these flames, various other flames that exhibit dynamic behaviors such as cyclic oscillatory motions, and repetitive ignition and extinction were also observed experimentally. These flames with large amplitude oscillatory motion might be utilized as a heat source with high speed temporal temperature variations in microsystems for future application. Another stable flame region in extremely low speed criteria at a mixture velocity of 2–3 cm/s was also experimentally confirmed. This flame was inferred to be an example of mild combustion, and it might also be used as a mild heat source for microdevices. The overall stability criteria of these flame regimes were analytically examined, and the detailed structure of each flame on the stable solution branches was numerically examined by employing 1D computation with detailed chemistry. The two results qualitatively agreed with each other and clarified the mechanism of the present various flames and their dynamic characteristics.

438 citations


Proceedings ArticleDOI
TL;DR: In this article, the effects of charge dilution on low-temperature diesel combustion and emissions were investigated in a small-bore single-cylinder diesel engine over a wide range of injection timing.
Abstract: The effects of charge dilution on low-temperature diesel combustion and emissions were investigated in a small-bore single-cylinder diesel engine over a wide range of injection timing. The fresh air was diluted with additional N 2 and CO 2 , simulating 0 to 65% exhaust gas recirculation in an engine. Diluting the intake charge lowers the flame temperature T due to the reactant being replaced by inert gases with increased heat capacity. In addition, charge dilution is anticipated to influence the local charge equivalence ratio Φ prior to ignition due to the lower O 2 concentration and longer ignition delay periods. By influencing both Φ and T, charge dilution impacts the path representing the progress of the combustion process in the Φ-T plane, and offers the potential of avoiding both soot and NO x formation. In-cylinder pressure measurements, exhaust-gas emissions, and imaging of combustion luminosity were performed to clarify the path of the combustion process and the effects of charge dilution and injection timing on combustion and fuel conversion efficiency. Based on the findings, a postulated combustion process in the Φ-T plane is presented for different dilution levels and injection timings. Although the ignition delay increased with high dilution and early injection, the heat release analysis indicated that a large portion of the combustion and emissions formation processes was still dominated by the mixing-controlled phase rather than the premixed phase. Because of the incomplete premixing, and the need to mix a greater volume of charge with unbumed or partially-burned fuel to complete combustion, the diluted mixtures increased CO emissions. Injecting the fuel at earlier timings to extend the ignition delay helped alleviate this problem, but did not eliminate it. Fuel conversion efficiencies calculated for each dilution level and start of injection provide guidance as to the appropriate combustion phasing and practical levels of charge dilution for this low-temperature diesel combustion regime.

350 citations


Journal Article
TL;DR: In this article, the influence of cetane number improver on heat release rate and emissions of a high-speed diesel engine fueled with ethanol-diesel blend fuel was investigated.
Abstract: The influence of cetane number improver on heat release rate and emissions of a high-speed diesel engine fueled with ethanol-diesel blend fuel was investigated.Different percentages of cetane number enhancer(0~0_0,0.2~0_0,0.4~0_0) were added to blends,and the engine tests were performed on a high speed diesel engine.The results show that the engine power decreases slightly; the thermal efficiency improves remarkably,and the NO_x and smoke emissions decrease simultaneously when diesel engine is fueled with blends.Besides, the engine power can be recovered,NO_x and smoke emissions are further reduced when cetane number improver is added to blends.By the combustion analysis,it can be found that the ignition delay prolongs;the total combustion duration shortens,and the maximum heat release rate increases for ethanol-diesel blend fuel when compared to diesel fuel; in addition,the combustion characteristics of ethanol-diesel blend fuel at large load may be recovered to diesel fuel by cetane number improver. However a large difference still exists at lower load.

327 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of the mixing ratio of biodiesels on the emission characteristics and engine performance was investigated at various mixing ratios of the biodiesel and engine operation conditions, and physical properties such as kinematic viscosity and cetane number were analyzed to study relations with fuel atomization and combustion characteristics.
Abstract: In this paper we describe the atomization and combustion characteristics of biodiesel fuels in a common-rail diesel engine. To investigate the effect of the mixing ratio of biodiesels on the emission characteristics and engine performance, the experiments were conducted at various mixing ratios of the biodiesel and engine operation conditions. In addition, the physical properties such as kinematic viscosity and cetane number of the biodiesel-blended fuel were analyzed to study relations with the fuel atomization and combustion characteristics. The atomization characteristics of biodiesel-blended fuels were investigated in terms of spray tip penetration, SMD, and mean velocity distributions by using a spray visualization system and phase Doppler particle analyzer. The effect of the mixing ratio on the combustion characteristics was studied on the basis of the results of the combustion pressure obtained from the single-cylinder engine at various experimental conditions. The emission characteristics of HC, N...

324 citations


Proceedings ArticleDOI
TL;DR: In this paper, the authors examined the effects of a wide range of parameters (injection pressure, orifice diameter, and ambient gas temperature, density and oxygen concentration) on lift-off length under quiescent diesel conditions.
Abstract: The reaction zone of a diesel fuel jet stabilizes at a location downstream of the fuel injector once the initial autoignition phase is over. This distance is referred to as flame lift-off length. Recent investigations have examined the effects of a wide range of parameters (injection pressure, orifice diameter, and ambient gas temperature, density and oxygen concentration) on lift-off length under quiescent diesel conditions. Many of the experimental trends in lift-off length were in agreement with scaling laws developed for turbulent, premixed flame propagation in gas-jet lifted flames at atmospheric conditions. However, several effects did not correlate with the gas-jet scaling laws, suggesting that other mechanisms could be important to lift-off stabilization at diesel conditions. This paper shows experimental evidence that ignition processes affect diesel lift-off stabilization. Experiments were performed in the same optically-accessible combustion vessel as the previous lift-off research. The experimental results show that the ignition quality of a fuel affects lift-off. Fuels with shorter ignition delays generally produce shorter lift-off lengths. In addition, a cool flame is found upstream of, or near the same axial location as, the quasi-steady lift-off length, indicating that first-stage ignition processes affect lift-off. High-speed chemiluminescence imaging also shows that high-temperature self-ignition occasionallymore » occurs in kernels that are upstream of, and detached from, the high-temperature reaction zone downstream, suggesting that the lift-off stabilization is not by flame propagation into upstream reactants in this instance. Finally, analysis of the previous lift-off length database shows that the time-scale for jet mixing from injector-tip orifice to lift-off length collapses to an Arrhenius-type expression, a common method for describing ignition delay in diesel sprays. This Arrhenius-based lift-off length correlation shows comparable accuracy as a previous power-law fit of the No.2 diesel lift-off length database.« less

Journal ArticleDOI
01 Jan 2005
TL;DR: In this paper, the fundamental and industrial application aspects of combustion of natural gas, heavy and light fuel oils, and coal in highly preheated air are examined in an experimental furnace at 0.58 MW thermal input based on fuel.
Abstract: This paper examines the fundamental and industrial application aspects of combustion of natural gas, heavy and light fuel oils, and coal in highly preheated air. The experiments have been carried out in an experimental furnace at 0.58 MW thermal input based on fuel, and the combustion air has been preheated to 1300 °C. The fuel injectors are positioned outside of the combustion air stream. Detailed in-furnace measurements of temperature, chemistry (O 2 , CO, NO x , and particulates), and heat transfer have been performed. Combustion of natural gas and light oil takes place without a visible presence of flame. Although the furnace was operated with an overall excess air of 10%, the combustion process occurs in strongly sub-stoichiometric conditions due to entrainment of large amounts of recirculated flue gases into the fuel jets before ignition. The experiments demonstrated an effective technology for efficient and environmentally friendly combustion of a wide range of fuels. The technology discussed in the main text offers the potential of high furnace efficiencies, uniform heat flux distribution, and dramatic reductions in CO 2 , CO, and NO emissions. Therefore, this technology should be considered for future design of industrial furnaces.

Journal ArticleDOI
01 Jan 2005
TL;DR: In this paper, the influence of gas excitation by a pulsed nanosecond discharge with a high-voltage pulse amplitude up to 25kV on the properties of a premixed propane-air flame has been investigated over a wide range of the equivalence ratios (0.4-5).
Abstract: Oxidation of molecular hydrogen and different hydrocarbons in stoichiometric mixtures with air and oxygen in the pulsed nanosecond discharges was studied at room temperature, and the detailed kinetics of the process has been numerically investigated. In the discharge afterglow, the reactions including electron-excited particles play a dominant role for the time up to 100 ns, ion–molecular reactions—for the time of microsecond range, and reactions including radicals mostly contribute for the time interval of several milliseconds. The principal role of processes with formation of excited components that support the development of the chain mechanism of oxidation has been shown. The spatial uniformity of the gas-mixture combustion initiated by a high-voltage nanosecond volume discharge is investigated at gas pressures of 0.3–2.4 atm and temperatures of 1000–2250 K. The self-ignition time and the time of discharge-induced ignition are determined. It is found that the discharge significantly (by 600 K) decreases the ignition temperature with very low energy in the discharge (∼10−2 J/cm3). The influence of gas excitation by a pulsed nanosecond discharge with a high-voltage pulse amplitude up to 25 kV on the properties of a premixed propane–air flame has been investigated over a wide range of the equivalence ratios (0.4–5). It was experimentally found that the flame’s blow-off velocity increased more than twice at a discharge energy input less than 1% of the burner power. Efficient production of active radicals under the action of a barrier discharge has been observed. The increase in the flame’s propagation velocity is explained by the production of atomic oxygen in a discharge by the quenching of electronically excited molecular nitrogen N2 and the dissociation of molecular oxygen on electron-impact. A numerical model has been developed, which describes the influence of pulsed electric discharges on the ignition, combustion, and flame propagation.

Journal ArticleDOI
01 May 2005-Fuel
TL;DR: In this article, the authors compared coal combustion in air and the mixtures of O2/CO2 mixtures in a 20kW down-firing combustor and found that coal combustion with 30% CO2/70% O2 can produce matching gas temperature profiles.

Journal ArticleDOI
TL;DR: In this paper, the effects of molecular transport on turbulent flame propagation and structure are critically discussed and the results of relevant studies of perturbed laminar flames (unstable flames, flame balls, flames in vortex tubes) are reviewed.

Journal ArticleDOI
TL;DR: In this article, the behavior of composite systems composed of aluminum (Al) and molybdenum trioxide (MoO3) were studied as a function of Al particle size, equivalence ratio and bulk density.
Abstract: Combustion behavior of energetic composite materials was experimentally examined for the purpose of evaluating the unique properties of nano-scale compared with traditional micron-scale particulate media. Behavior of composite systems composed of aluminum (Al) and molybdenum trioxide (MoO3) were studied as a function of Al particle size, equivalence ratio and bulk density. Samples were prepared by mechanically mixing individual fuel and oxidizer particles and combustion experiments included measurements of ignition and flame propagation behavior. Ignition was achieved using a 50-W CO2 laser and combustion velocities were measured from photographic data. Reaction kinetics were studied with differential scanning calorimetry (DSC). Results indicate that the incorporation of nano-Al particles (1) significantly reduces ignition temperatures and (2) produces unique reaction behavior that can be attributed to a different chemical kinetic mechanism than observed with micron-Al particles.

Journal ArticleDOI
01 Jan 2005
TL;DR: The potential of combustion diagnostics has been discussed in this article, highlighting selected application examples and guiding the reader to recent literature, in particular, techniques which permit measurement of important features of the chemical composition, sometimes in conjunction with flow field parameters.
Abstract: Fifty years after the foundation of the Combustion Institute and almost 150 years after Michael Faraday's famous lectures on the combustion of a candle, combustion diagnostics have come a long way from visual inspection of a flame to detailed analysis of a combustion process with a multitude of sophisticated techniques, often using lasers. The extended knowledge on combustion phenomena gained by application of these diagnostic techniques, combined with equally advanced numerical simulation of the process, has been instrumental in designing modern combustion devices with efficient performance and reduced pollutant emission. Also, similar diagnostic techniques are now employed to develop sensors for process control in combustion. This article intends to give a perspective on the potential of combustion diagnostics by highlighting selected application examples and by guiding the reader to recent literature. In particular, techniques are emphasized, which permit measurement of important features of the chemical composition, sometimes in conjunction with flow field parameters. Although a complete image of present research and applications in combustion diagnostics and control is beyond the scope of this article, this overview may be a starting place where ideas may be found to solve specific combustion problems with the aid of diagnostics. (Less)

Journal ArticleDOI
TL;DR: In this paper, a critical requirement for the implementation of diesel particulate filters on diesel-powered vehicles is having a low "break-even temperature" (BET), defined as the temperature at which particulate deposition on the filter is balanced by particulate oxidation.
Abstract: A critical requirement for the implementation of diesel particulate filters on diesel-powered vehicles is having a low “break-even temperature” (BET), which is defined as the temperature at which particulate deposition on the filter is balanced by particulate oxidation on the filter. This balance point needs to occur at sufficiently low temperatures, either to fit within the exhaust temperature range of the typical duty cycle for a diesel vehicle or to require a minimum of active regeneration. Catalytic coating on the diesel particulate filter, the use of a fuel-borne catalyst, and oxidation catalysts placed upstream of the particulate filter can all reduce the BET. Another important factor in reducing the BET is the sulfur content of the fuel, because the sulfur dioxide generated during combustion can poison catalyst activity. However, fuel formulation factors other than sulfur content can also have significant effects on the BET. Considered in this work were low sulfur diesel fuel (LSD, 325 ppm sulfur),...

Journal ArticleDOI
TL;DR: In this paper, a vitiated coflow flame consisting of a lifted jet flame formed by a fuel jet issuing from a central nozzle into a large coaxial flow of hot combustion products from a lean premixed H 2 /air flame is presented and compared to numerical results from probability density function (PDF) calculations incorporating various mixing models.

Journal ArticleDOI
01 Jan 2005
TL;DR: In this article, a detailed kinetic model describing the formation and consumption of polycyclic aromatic hydrocarbons (PAH) and soot in fuel-rich hydrocarbon combustion has been developed.
Abstract: Combustion-generated polycyclic aromatic hydrocarbons (PAH) and soot particles are of significant environmental concern whereas controlled combustion is of increasing interest for the synthesis of carbonaceous nanostructures such as fullerenic material. Improved understanding of chemical and physical processes involved in PAH and soot formation is required to correlate operating conditions with emission characteristics. A detailed kinetic model describing the formation and consumption of PAH and soot in fuel-rich hydrocarbon combustion has been developed. Using a sectional approach, large PAH and carbonaceous particles with diameters of up to ≈70 nm are defined as classes (BINs) covering given mass ranges. Numbers of carbon and hydrogen atoms corresponding to their average masses are assigned to each BIN, accounting for a decrease in H/C ratios with increasing particle size. The model has been successfully tested for a rich premixed benzene/oxygen/argon flame ( ϕ = 2.4, 10% argon, v = 25 cm s −1 , 5.33 kPa). Model predictions are compared with published experimental data including mole fraction profiles of individual PAH and concentration as well as number density profiles of soot. Reactions of PAH radicals with PAH and between PAH radicals were found to be the dominant pathway to soot nuclei. Surface growth contributes ≈75% to the final particle mass, and reaction of acetylene with particle radicals is the major growth pathway. Surface growth reactions are involved in PAH depletion in the postflame zone. Particle coagulation involving BINs and BIN radicals significantly contributes to the formation of progressively larger particles whereas oxidation by OH plays a non-negligible role in their depletion.

Journal ArticleDOI
01 Jan 2005
TL;DR: In this paper, a spiral counterflow "Swiss roll" burner was evaluated with and without a bare-metal Pt catalyst and a wide range of Reynolds numbers (Re ) were tested using propane-air mixtures.
Abstract: An experimental study of a spiral counterflow “Swiss roll” burner was conducted, with emphasis on the determination of extinction limits and comparison of results with and without bare-metal Pt catalyst. A wide range of Reynolds numbers ( Re ) were tested using propane–air mixtures. Both lean and rich extinction limits were extended with the catalyst, though rich limits were extended much further. With the catalyst, combustion could be sustained at Re as low as 1.2 with peak temperatures as low as 350 K. A heat transfer parameter characterizing the thermal performance of both gas-phase and catalytic combustion at all Re was identified. At low Re , the “lean” extinction limit was actually rich of stoichiometric, and rich-limit had equivalence ratios exceeded 40 in some cases. No corresponding behavior was observed without the catalyst. Gas-phase combustion, in general, occurred in a “flameless” mode near the burner center. With or without catalyst, for sufficiently robust conditions (high Re , near-stoichiometric) not requiring heat recirculation, a visible flame would propagate out of the center, but this flame could only be re-centered if the catalyst were present. Gas chromatography indicated that at low Re , even in extremely rich mixtures, CO and non-propane hydrocarbons did not form. For higher Re , where both gas-phase and catalytic combustion could occur, catalytic limits were slightly broader but had much lower limit temperatures. At sufficiently high Re , catalytic and gas-phase limits merged. It is concluded that combustion at low Re in heat-recirculating burners greatly benefits from catalytic combustion with the proper choice of mixtures that are different from those preferred for gas-phase combustion. In particular, the importance of providing a reducing environment for the catalyst to enhance O 2 desorption, especially at low Re where heat losses are severe thus peak temperatures are low, is noted.

Journal ArticleDOI
TL;DR: In this paper, combustion velocities were experimentally determined for nanocomposite thermite powders composed of aluminum (Al) fuel and molybdenum trioxide (MoO3) oxidizer under well-confined conditions.
Abstract: Combustion velocities were experimentally determined for nanocomposite thermite powders composed of aluminum (Al) fuel and molybdenum trioxide (MoO3) oxidizer under well-confined conditions Pressures were also measured to provide detailed information about the reaction mechanism Samples of three different fuel particle sizes (44, 80, and 121nm) were analyzed to determine the influence of particle size on combustion velocity Bulk powder density was varied from approximately 5% to 10% of the theoretical maximum density (TMD) The combustion velocities ranged from approximately 600 to 1000m∕s Results indicate that combustion velocities increase with decreasing particle size Pressure measurements indicate that strong convective mechanisms are integral in flame propagation

Journal ArticleDOI
01 Jan 2005-Carbon
TL;DR: In this article, carbon-supported catalysts were held at elevated temperatures under dry air conditions, and the carbon support was evaluated with a first-order kinetic model to describe the results.

Journal ArticleDOI
TL;DR: In this article, a general semidetailed kinetic scheme of hydrocarbon oxidation to heavy fuels is presented, where a lumped approach is applied to n-decane, n-dodecane, and n-hexadecane.
Abstract: The main goal of this paper is the extension of a general semidetailed kinetic scheme of hydrocarbon oxidation to heavy fuels. Taking previous n-pentane and n-heptane kinetic modeling experience a step further, a lumped approach was systematically applied to n-decane, n-dodecane, and n-hexadecane. These semidetailed submodels for higher n-alkanes are directly derived from the complete set of primary propagation reactions, automatically generated by the MAMOX++ program on the basis of a small set of reference kinetic parameters. This proposed approach and lumped model are supported by a wide range of comparisons with a large variety of experimental measurements relating to stirred and flow reactors, premixed and diffusion flames, and fuel droplet combustion under microgravity conditions. The general agreement obtained in the overall range of conditions further confirms and supports the soundness of the small set of kinetic parameters used as reference values for the different classes of the primary propaga...

Journal ArticleDOI
TL;DR: In this article, a series of platinum-loaded carbons with two different carbon supports are aged ex situ in an isothermal oven and in situ using a 1.2-V fuel cell accelerated test.
Abstract: We explore ex situ and in situ fuel cell catalyst degradation test methods and the impact of catalyst degradation on fuel cell performance. A series of platinum-loaded carbons with two different carbon supports are aged ex situ in an isothermal oven and in situ using a 1.2-V fuel cell accelerated test. The ex situ combustion test and in situ 1.2 V accelerated fuel cell test both show that the rate and extent of carbon combustion for samples with the same platinum loading increases as the surface area of the carbon increases, presumably because platinum deposits as smaller particles, covering more of the carbon surface. In addition, the rate of reaction/loss of carbon is shown to increase significantly if humidity is introduced into the environment, a concern for long-term polymer electrolyte membrane fuel cell (PEMFC) operation because PEMFCs operate in a hot, humidified, oxygenated environment. Finally, graphitized carbon black supports with the same surface area and platinum loading as ungraphitized supports show much greater stability in both the ex situ and in situ tests, suggesting that carbon surface chemistry plays a strong role in oxidative stability under fuel cell conditions.

Journal ArticleDOI
TL;DR: In this paper, the characteristics of small Swiss-roll combustors were investigated experimentally in detail, and the effects of design parameters on the performance of these combustors are examined. But the results of these experiments were limited to a single combustion room and double spiral-shaped channels.

Journal ArticleDOI
TL;DR: In this paper, a detailed chemistry-based CFD model was developed to simulate the diesel spray combustion and emission process, where a reaction mechanism of n-heptane was coupled with a reduced NOx mechanism to simulate diesel fuel oxidation and NOx formation.
Abstract: A detailed chemistry-based CFD model was developed to simulate the diesel spray combustion and emission process. A reaction mechanism of n-heptane is coupled with a reduced NOx mechanism to simulate diesel fuel oxidation and NOx formation. The soot emission process is simulated by a phenomenological soot model that uses a competing formation and oxidation rate formulation. The model is applied to predict the diesel spray lift-off length and its sooting tendency under high temperature and pressure conditions with good agreement with experiments of Sandia. Various nozzle diameters and chamber conditions were investigated. The model successfully predicts that the sooting tendency is reduced as the nozzle diameter is reduced and/or the initial chamber gas temperature is decreased, as observed by the experiments. The model is also applied to simulate diesel engine combustion under PCCI-like conditions. Trends of heat release rate, NOx and soot emissions with respect to EGR levels and start-of-injection timings are also well predicted. Both experiments and models reveal that soot emissions peak when the start of injection occurs close to TDC. The model indicates that low soot emission at early SOI is due to better oxidation while low soot emission at late SOI is due to less formation. Since NOx emissions decrease monotonically with injection retardation, a late injection scheme can be utilized for simultaneous soot and NOx reduction for the engine conditions investigated in this study.Copyright © 2005 by ASME

Journal ArticleDOI
TL;DR: In this article, the fundamental concepts that control aluminum combustion are discussed, starting from a discussion of the D − n − 1 − 2 - 1.8 -approximation of the law, and the effect of the ambient medium on the burning time is considered.
Abstract: Characteristics of aluminum combustion are summarized in an overview of the subject, focusing on the burning time of individual particles. Combustion data from over ten different sources with almost 400 datum points have been cataloged and correlated. Available models have also been used to evaluate combustion trends with key environmental parameters. The fundamental concepts that control aluminum combustion are discussed, starting from a discussion of the D n law. The exponent in the D n law is shown to be lower than two, with nominal values of ≈1.5 to 1.8 being typical. The effect of the ambient medium on the burning time is considered, oxygen as an oxidizer being twice as effective as water and about five times more effective than carbon dioxide. The effect of pressure and initial temperature is minor.

Journal ArticleDOI
TL;DR: In this article, the authors explored the diesel injection and combustion processes in an effort to better understand the differences in NOx emissions between biodiesel, Fischer−Tropsch (FT) diesel, and their blends with a conventional diesel fuel.
Abstract: This study explores the diesel injection and combustion processes in an effort to better understand the differences in NOx emissions between biodiesel, Fischer−Tropsch (FT) diesel, and their blends with a conventional diesel fuel. Emissions studies were performed with each fuel at a variety of static fuel injection timing conditions in a single-cylinder DI diesel engine with a mechanically controlled, in-line, pump-line-nozzle fuel injection system. The dynamic start of injection (SOI) timing correlated well with bulk modulus measurements made on the fuel blends. The high bulk modulus of soy-derived biodiesel blends produced an advance in SOI timing compared to conventional diesel fuel of up to 1.1 crank angle degrees, and the lower bulk modulus of the FT diesel produced a delay in SOI timing of up to 2.4 crank angle degrees. Compared to conventional diesel fuel at high load, biodiesel fuel blends produced increases in NOx emissions of 6−9% while FT fuels caused NOx emissions to decrease 21−22%. Shifts in...

Proceedings ArticleDOI
TL;DR: In this paper, the potential of in-cylinder thermal stratification for reducing the pressure-rise rate in HCCI engines was investigated, and the coupling between thermal stratifications and combustion-phasing retard was investigated.
Abstract: This work investigates the potential of in-cylinder thermal stratification for reducing the pressure-rise rate in HCCI engines, and the coupling between thermal stratification and combustion-phasing retard A combination of computational and experimental results is employed The computations were conducted using both a custom multi-zone version and the standard single-zone version of the Senkin application of the CHEMKIN III kinetics-rate code, and kinetic mechanisms for iso-octane This study shows that the potential for extending the high-load operating limit by adjusting the thermal stratification is very large With appropriate stratification, even a stoichiometric charge can be combusted with low pressure-rise rates, giving an output of 16 bar IMEPg for naturally aspirated operation For more typical HCCI fueling rates (Φ = 038 - 045), the optimal charge-temperature distribution is found to depend on both the amount of fuel and the combustion phasing For combustion phasing in the range of 7 - 10°CA after TDC, a linear thermal distribution is optimal since it produces a near-linear pressure rise For other combustion phasings, non-linear distributions are required to achieve a linear pressure rise Also, the total thermal width must be greater at higher fueling rates to avoid excessive pressure-rise rates The study also shows that increasing the natural thermal width of the charge by 50% would allow the equivalence ratio to be increased from 044 to 060, with an associated increase of the IMEPg from 524 to 695 kPa for naturally aspirated operation It was also found that the naturally occurring thermal stratification plays a major role in producing the experimentally observed benefit of combustion-timing retard for slowing the combustion rate Reduced chemical-kinetic rates with combustion retard are found to play a lesser role