http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2013 , Hindawi Publishing Corporation . All rights reserved. Thu, 23 May 2013 08:34:52 +0000 http://www.hindawi.com/journals/jc/2013/267631/ The heat release process in a free volume combustion chamber and in porous reactors has been analyzed under Diesel engine-like conditions. The process has been investigated in a wide range of initial pressures and temperatures simulating engine conditions at the moment when fuel injection starts. The resulting pressure history in both porous reactors and in free volumes significantly depends on the initial pressure and temperature. At lower initial temperatures, the process in porous reactors is accelerated. Combustion in a porous reactor is characterized by heat accumulation in the solid phase of the porous structure and results in reduced pressure peaks and lowered combustion temperature. This depends on reactor heat capacity, pore density, specific surface area, pore structure, and heat transport properties. Characteristic modes of a heat release process in a two-dimensional field of initial pressure and temperature have been selected. There are three characteristic regions represented by a single- and multistep oxidation process (with two or three slopes in the reaction curve) and characteristic delay time distribution has been selected in five characteristic ranges. There is a clear qualitative similarity of characteristic modes of the heat release process in a free volume and in porous reactors. A quantitative influence of porous reactor features (heat capacity, pore density, pore structure, specific surface area, and fuel distribution in the reactor volume) has been clearly indicated. M. Weclas and J. Cypris Copyright © 2013 M. Weclas and J. Cypris. All rights reserved. Tue, 21 May 2013 10:03:11 +0000 http://www.hindawi.com/journals/jc/2013/749321/ Experiments on cofiring dried sewage sludge, wet sewage sludge with coal and polyethylene (PE) were carried out on a pilot scale 0.15MWt circulating fluidized bed combustion (CFBC) plant, and the influence of furnace temperatures, cofiring rates on N2O and NO emissions was investigated. Temperature is an effective parameter influencing N2O emission, and higher temperature leads to significant N2O reduction and decrease of conversion ratio of fuel-N to N2O. Increasing in cofiring rates leads to higher nitrogen content in the mixed fuel, which could result in higher NO and N2O emissions from combustion. With more sewage sludge addition, higher NO but lower N2O emissions are observed. N2O emission from cofiring wet sewage sludge with coal is higher than that from cofiring dried sewage sludge with coal and PE, and fuel-N conversion ratio to N2O and NO is much higher in cofiring wet sewage sludge with coal than that in cofiring dried sewage sludge with coal and PE. Zhiwei Li and Hongzhou He Copyright © 2013 Zhiwei Li and Hongzhou He. All rights reserved. Tue, 23 Apr 2013 15:52:08 +0000 http://www.hindawi.com/journals/jc/2013/790672/ Carbon combustion in the forward stagnation flowfield has been examined through experimental comparisons, by conducting aerothermochemical analyses, with the surface C-O2 and C-CO2 reactions and the gas-phase CO-O2 reaction taken into account. By virtue of the generalized species-enthalpy coupling functions, close coupling of those reactions has been elucidated. Explicit combustion-rate expressions by use of the transfer number in terms of the natural logarithmic term, just like that for droplet combustion, have further been obtained for the combustion response in the limiting situations. It has been confirmed that before the establishment of CO flame, the combustion rate can fairly be represented by the expression in the frozen mode, that after its establishment by the expression in the flame-attached or flame-detached modes, and that the critical condition derived by the asymptotics can fairly predict the surface temperature for its establishment. The formulation has further been extended to include the surface C-H2O and gas-phase H2-O2 reactions additionally, so as to evaluate the combustion rate in humid airflow. Since those expressions are explicit and have fair accuracy, they are anticipated to make various contributions not only for qualitative/quantitative studies, but also for various aerospace applications, including propulsion with high-energy-density fuels. Atsushi Makino, Masahiro Hojo, and Masahito Shintomi Copyright © 2013 Atsushi Makino et al. All rights reserved. Tue, 12 Feb 2013 11:56:22 +0000 http://www.hindawi.com/journals/jc/2013/154202/ Reduced-gravity experiments were performed on combustion of droplets composed of n-heptane mixed with methanol or ethanol. The initial alcohol mass fraction in a droplet was 0% (pure heptane) or 5%. The experiments were performed at 0.1 MPa and 25°C with air or with ambients of oxygen and helium with oxygen mole fractions of 0.3 or 0.4. Initial droplet diameters were in the range 0.67 mm to 0.92 mm. After considering measurement uncertainties, burning rates decreased appreciably as the initial droplet diameter increased for combustion in air but not for combustion in the oxygen/helium environments. It was also found that addition of either methanol or ethanol did not influence burning rates appreciably and that burning rates were larger for the oxygen/helium environments than for air if initial droplet diameter dependences were accounted for. I. Aharon, V. K. Tam, and B. D. Shaw Copyright © 2013 I. Aharon et al. All rights reserved. Thu, 06 Dec 2012 07:51:03 +0000 http://www.hindawi.com/journals/jc/2012/353257/ A direct numerical simulation (DNS) database of freely propagating statistically planar turbulent premixed flames with a range of different turbulent Reynolds numbers has been used to assess the performance of algebraic flame surface density (FSD) models based on a fractal representation of the flame wrinkling factor. The turbulent Reynolds number Ret has been varied by modifying the Karlovitz number Ka and the Damköhler number Da independently of each other in such a way that the flames remain within the thin reaction zones regime. It has been found that the turbulent Reynolds number and the Karlovitz number both have a significant influence on the fractal dimension, which is found to increase with increasing Ret and Ka before reaching an asymptotic value for large values of Ret and Ka. A parameterisation of the fractal dimension is presented in which the effects of the Reynolds and the Karlovitz numbers are explicitly taken into account. By contrast, the inner cut-off scale normalised by the Zel’dovich flame thickness does not exhibit any significant dependence on Ret for the cases considered here. The performance of several algebraic FSD models has been assessed based on various criteria. Most of the algebraic models show a deterioration in performance with increasing the LES filter width. Mohit Katragadda, Nilanjan Chakraborty, and R. S. Cant Copyright © 2012 Mohit Katragadda et al. All rights reserved. Mon, 26 Nov 2012 08:43:52 +0000 http://www.hindawi.com/journals/jc/2012/918754/ This paper presents process simulation of moving bed gasifier using low rank, subbituminous Usibelli coal from Alaska. All the processes occurring in a moving bed gasifier, drying, devolatilization, gasification, and combustion, are included in this model. The model, developed in Aspen Plus, is used to predict the effect of various operating parameters including pressure, oxygen to coal, and steam to coal ratio on the product gas composition. The results obtained from the simulation were compared with experimental data in the literature. The predicted composition of the product gas was in general agreement with the established results. Carbon conversion increased with increasing oxygen-coal ratio and decreased with increasing steam-coal ratio. Steam to coal ratio and oxygen to coal ratios impacted produced syngas composition, while pressure did not have a large impact on the product syngas composition. A nonslagging moving bed gasifier would have to be limited to an oxygen-coal ratio of 0.26 to operate below the ash softening temperature. Slagging moving bed gasifiers, not limited by operating temperature, could achieve carbon conversion efficiency of 99.5% at oxygen-coal ratio of 0.33. The model is useful for predicting performance of the Usibelli coal in a moving bed gasifier using different operating parameters. Mandar Kulkarni and Rajive Ganguli Copyright © 2012 Mandar Kulkarni and Rajive Ganguli. All rights reserved. Mon, 19 Nov 2012 15:33:24 +0000 http://www.hindawi.com/journals/jc/2012/716050/ Many practical combustion systems such as residential gas burners contain dense groupings or clusters of jet flames with sufficiently small spacing between them, which causes flame interaction. The interaction effect, due in part to Oxygen deficiency in the interstitial space between the flames, causes the spreading of flames, which may merge together to form larger group flames. This interactive effect is studied analytically by revisiting the laminar isolated flame theory for 2D jets, for which similarity solutions are readily available in compressible form, and symmetrical interaction zones can be observed. Flame characteristics were studied by obtaining analytical expressions for flame specific parameters such as height and width, lift-off height and blow-off velocity, air entrainment and mixing layer growth. The theory for multiple interacting jets describes an approximate criterion for interburner spacing at which flame interaction and group flame formation are first observed. The analytical framework presented in this paper presented in this paper produced results which were compared with experimental measurements. The experimental apparatus allowed the interburner spacing to be varied from 7.87 mm to 50.8 mm, and measurements of flame height, width, lift-off height and group-flame formation under interactive modes. Images of the evolving flow field were taken and Schlieren images of the multiple 2D jets were also recorded using a digital camera. S. T. Tillman, S. Kuchibhatla, K. Annamalai, J. A. Caton, and D. Ranjan Copyright © 2012 S. T. Tillman et al. All rights reserved. Wed, 14 Nov 2012 15:48:11 +0000 http://www.hindawi.com/journals/jc/2012/837019/ A two-dimensional numerical model of opposed flow flame spread over thin solid fuel is formulated and modeled to study the effect of gas phase heat sink (a wire mesh placed parallel to the fuel surface) on the flame-spread rate and flame extinction. The work focuses on the performance of the wire mesh in microgravity environment at an oxygen concentration 21%. The simulations were carried out for various mesh parameters (wire diameter, “” and number of wires per unit length, “”) and mesh distance perpendicular to fuel surface “”. Simulations show that wire mesh is effective in reducing flame-spread rate when placed at distance less than flame width (which is about 1 cm). Mesh wire diameter is determined not to have major influence on heat transfer. However, smaller wire diameter is preferred for better aerodynamics and for increasing heat transfer surface area (here prescribed by parameter “”). Flame suppression exhibits stronger dependence on number of wires per unit length; however, it is relatively insensitive to number of wires per unit length beyond certain value (here 20 cm−1). Vinayak Malhotra, Chenthil Kumar, and Amit Kumar Copyright © 2012 Vinayak Malhotra et al. All rights reserved. Wed, 07 Nov 2012 14:15:47 +0000 http://www.hindawi.com/journals/jc/2012/915482/ A simplified chemistry based three-dimensional Direct Numerical Simulation (DNS) database of freely propagating statistically planar turbulent premixed flames with a range of different values of turbulent Reynolds number has been used for the a priori modelling of the curvature term of the generalised Flame Surface Density (FSD) transport equation in the context of Large Eddy Simulation (LES). The curvature term has been split into the contributions arising due to the reaction and normal diffusion components of displacement speed and the term originating from the tangential diffusion component of displacement speed. Subsequently, these contributions of the curvature term have been split into the resolved and subgrid contributions. New models have been proposed for the subgrid curvature terms arising from the combined reaction and normal diffusion components and the tangential diffusion component of displacement speed. The performances of the new model and the existing models for the subgrid curvature term have been compared with the corresponding quantity extracted from the explicitly filtered DNS data. The new model for the subgrid curvature term is shown to perform satisfactorily in all cases considered in the current study, accounting for wide variations in LES filter size. Mohit Katragadda and Nilanjan Chakraborty Copyright © 2012 Mohit Katragadda and Nilanjan Chakraborty. All rights reserved. Wed, 31 Oct 2012 16:04:25 +0000 http://www.hindawi.com/journals/jc/2012/738940/ This paper discusses the effect of ignition delay time in diesel engines on the formation of particulate matter, using fuel formulations with different sulfur concentrations from various sources. Our findings indicate that the cetane number has a significant influence on particulate matter emissions, especially in engines with mechanical fuel injection. The maximum pressure in the combustion chamber increases as the cetane number increases, favoring the increase in the cracking reactions of high molecular weight fractions remaining in the liquid state and thus increasing the production of particulate matter. In certain conditions, this increase in pressure has a beneficial effect on the thermal efficiency of the cycle. Higher temperatures in the combustion chamber augment the speed of oxidation, reducing unburned hydrocarbon emissions. The ignition delay time of fuel has a strong effect on the formation of particulate matter and on the emission of unburned hydrocarbons. Renato Cataluña and Rosangela da Silva Copyright © 2012 Renato Cataluña and Rosangela da Silva. All rights reserved. Sun, 21 Oct 2012 08:45:09 +0000 http://www.hindawi.com/journals/jc/2012/137653/ Two-dimensional kinetic simulation has been carried out to investigate the effects of repetition rate and pulse width of nanosecond repetitively pulsed discharges on stabilizing premixed lean methane-air combustion. The repetition rate and pulse width are varied from 10 kHz to 50 kHz and from 9 ns to 2 ns while the total power is kept constant. The lower repetition rates provide larger amounts of radicals such as O, H, and OH. However, the effect on stabilization is found to be the same for all of the tested repetition rates. The shorter pulse width is found to favor the production of species in higher electronic states, but the varying effects on stabilization are also found to be small. Our results indicate that the total deposited power is the critical element that determines the extent of stabilization over this range of discharge properties studied. Moon Soo Bak and Mark A. Cappelli Copyright © 2012 Moon Soo Bak and Mark A. Cappelli. All rights reserved. Thu, 11 Oct 2012 17:05:42 +0000 http://www.hindawi.com/journals/jc/2012/374089/ The work presents the assessment of a low emissions premixer/swirl burner configuration utilizing lean stratified fuel preparation. An axisymmetric, single- or double-cavity premixer, formed along one, two, or three concentric disks promotes propane-air premixing and supplies the combustion zone at the afterbody disk recirculation with a radial equivalence ratio gradient. The burner assemblies are operated with a swirl co-flow to study the interaction of the recirculating stratified flame with the surrounding swirl. A number of lean and ultra-lean flames operated either with a plane disk stabilizer or with one or two premixing cavity arrangements were evaluated over a range of inlet mixture conditions. The influence of the variation of the imposed swirl was studied for constant fuel injections. Measurements of turbulent velocities, temperatures, OH* chemiluminescence and gas analysis provided information on the performance of each burner set up. Comparisons with Large Eddy Simulations, performed with an 11-step global chemistry, illustrated the flame front interaction with the vortex formation region under the influence of the variable inlet mixture stratifications. The combined effort contributed to the identification of optimum configurations in terms of fuel consumption and pollutants emissions and to the delineation of important controlling parameters and limiting fuel-air mixing conditions. P. Koutmos, G. Paterakis, E. Dogkas, and Ch. Karagiannaki Copyright © 2012 P. Koutmos et al. All rights reserved. Thu, 06 Sep 2012 14:43:29 +0000 http://www.hindawi.com/journals/jc/2012/794671/ The performance of algebraic flame surface density (FSD) models has been assessed for flames with nonunity Lewis number (Le) in the thin reaction zones regime, using a direct numerical simulation (DNS) database of freely propagating turbulent premixed flames with Le ranging from 0.34 to 1.2. The focus is on algebraic FSD models based on a power-law approach, and the effects of Lewis number on the fractal dimension D and inner cut-off scale 𝜂𝑖 have been studied in detail. It has been found that D is strongly affected by Lewis number and increases significantly with decreasing Le. By contrast, 𝜂𝑖 remains close to the laminar flame thermal thickness for all values of Le considered here. A parameterisation of D is proposed such that the effects of Lewis number are explicitly accounted for. The new parameterisation is used to propose a new algebraic model for FSD. The performance of the new model is assessed with respect to results for the generalised FSD obtained from explicitly LES-filtered DNS data. It has been found that the performance of the most existing models deteriorates with decreasing Lewis number, while the newly proposed model is found to perform as well or better than the most existing algebraic models for FSD. Mohit Katragadda, Nilanjan Chakraborty, and R. S. Cant Copyright © 2012 Mohit Katragadda et al. All rights reserved. Thu, 06 Sep 2012 13:24:57 +0000 http://www.hindawi.com/journals/jc/2012/282851/ This work aims at demonstrating the feasibility of replacing Indonesian coal (INC) with hydrothermally treated municipal solid waste (MSWH) in cocombustion with high ash Indian coal (IC). The combustion efficiencies and emissions (CO, NO) of MSWH, INC and their blends with IC for a series of tests performed under a range of temperatures and air conditions were tested in a drop-tube reactor (DTR). The results showed the following. The combustion efficiency of IC was increased by blending both MSWH and INC and CO emission was reduced with increasing temperature. For NO emission, the blending of MSWH led to the increase of NO concentration whereas the effects of INC depended on the temperature. The combustion behaviors of IC-MSWH blend were comparable to those of the IC-INC blend indicating it is possible for MSWH to become a good substitute for INC supporting IC combustion. Moreover, the CO emission fell while the NO emission rose with increasing excess air for IC-MSWH blend at 900°C and the highest combustion efficiency was obtained at the excess air of 1.9. The existence of moisture in the cocombustion system of IC-MSWH blend could slightly improve the combustion efficiency, reduce CO, and increase NO. Liang Lu, Yuqi Jin, Masato R. Nakamura, Marco J. Castaldi, and Kunio Yoshikawa Copyright © 2012 Liang Lu et al. All rights reserved. Tue, 21 Aug 2012 16:19:53 +0000 http://www.hindawi.com/journals/jc/2012/927081/ A microwave-assisted spark plug was used to extend the lean operating limit (lean limit) and reduce emissions of an engine burning methane-air. In-cylinder pressure data were collected at normalized air-fuel ratios of 𝜆=1.46, 𝜆=1.51, 𝜆=1.57, 𝜆=1.68, and 𝜆=1.75. For each 𝜆, microwave energy (power supplied to the magnetron per engine cycle) was varied from 0 mJ (spark discharge alone) to 1600 mJ. At lean conditions, the results showed adding microwave energy to a standard spark plug discharge increased the number of complete combustion cycles, improving engine stability as compared to spark-only operation. Addition of microwave energy also increased the indicated thermal efficiency by 4% at 𝜆=1.68. At 𝜆=1.75, the spark discharge alone was unable to consistently ignite the air-fuel mixture, resulting in frequent misfires. Although microwave energy produced more consistent ignition than spark discharge alone at 𝜆=1.75, 59% of the cycles only partially burned. Overall, the microwave-assisted spark plug increased engine performance under lean operating conditions (𝜆=1.68) but did not affect operation at conditions closer to stoichiometric. Vi H. Rapp, Anthony DeFilippo, Samveg Saxena, Jyh-Yuan Chen, Robert W. Dibble, Atsushi Nishiyama, Ahsa Moon, and Yuji Ikeda Copyright © 2012 Vi H. Rapp et al. All rights reserved. Tue, 07 Aug 2012 12:25:51 +0000 http://www.hindawi.com/journals/jc/2012/496460/ We present a new combustion simulation technique based on a lookup table approach. In the proposed technique, a flow solver extracts the reaction rates from the look-up table using the mixture fraction, progress variable, and reaction time. Look-up table building and combustion simulation are carried out simultaneously. The reaction rates of the chemical species are recorded in the look-up table according to the mixture fraction, progress variable, and time scale of the reaction. Once the reaction rates are recorded, a direct integration to solve the chemical equations becomes unnecessary; thus, the time for computing the reaction rates is shortened. The proposed technique is applied to an eddy dissipation concept (EDC) model and it is validated through a simulation of a CO-H2-air nonpremixed flame. The results obtained by using the proposed technique are compared with experimental and computational data obtained by using the EDC model with direct integration. Good agreement between our method and the EDC model and the experimental data was found. Moreover, the computation time for the proposed technique is approximately 99.2% lower than that of the EDC model with direct integration. Kazui Fukumoto and Yoshifumi Ogami Copyright © 2012 Kazui Fukumoto and Yoshifumi Ogami. All rights reserved. Tue, 31 Jul 2012 14:01:49 +0000 http://www.hindawi.com/journals/jc/2012/564621/ Over the past years, the use of a presumed probability density function (PDF) for combustion progress variable or/and mixture fraction has been becoming more and more popular approach to average reaction rates in premixed and partially premixed turbulent flames. Commonly invoked for this purpose is a beta-function PDF or a combination of Dirac delta functions, with the parameters of the two PDFs being determined based on the values of their first and second moments computed by integrating proper balance equations. Because the choice of any of the above PDFs appears to be totally arbitrary as far as underlying physics of turbulent combustion is concerned, the use of such PDFs implies weak sensitivity of the key averaged quantities to the PDF shape. The present work is aimed at testing this implicit assumption by comparing mean heat release rates, burning velocities, and so forth, averaged by invoking the aforementioned PDFs, with all other things being equal. Results calculated in the premixed case show substantial sensitivity of the mean heat release rate to the shape of presumed combustion-progress-variable PDF, thus, putting the approach into question. To the contrary, the use of a presumed mixture-fraction PDF appears to be a sufficiently reasonable simplification for modeling the influence of fluctuations in the mixture fraction on the mean burning velocity provided that the mixture composition varies within flammability limits. Chen Huang and Andrei N. Lipatnikov Copyright © 2012 Chen Huang and Andrei N. Lipatnikov. All rights reserved. Tue, 24 Jul 2012 11:21:05 +0000 http://www.hindawi.com/journals/jc/2012/912581/ This work presents the experimental results of lard combustion with diesel for heating. The work is divided into two parts, the first of which deals with the identification of lard as fuels and characterization of diesel, as well as determining the chemical and thermodynamic properties of mixtures of both components. The second part studies the optimum combustion point of lard and oil mixtures in a conventional plant, varying the percentage of lard in mixing, air flow, and injection pressure. J. F. San José Alonso, S. Alonso Miñambres, and I. Gobernado Arribas Copyright © 2012 J. F. San José Alonso et al. All rights reserved. Tue, 03 Jul 2012 09:04:41 +0000 http://www.hindawi.com/journals/jc/2012/176037/ Biomass, in form of residues and waste, can be used to produce energy with low environmental impact. It is important to use the feedstock close to the places where waste are available, and with the shortest conversion pathway, to maximize the process efficiency. In particular waste vegetable oil and the organic fraction of municipal solid waste represent a good source for fuel production in urban areas. Dual fuel engines could be taken into consideration for an efficient management of these wastes. In fact, the dual fuel technology can achieve overall efficiencies typical of diesel engines with a cleaner exhaust emission. In this paper the feasibility of a cogeneration system fuelled with waste vegetable oil and biogas is discussed and the evaluation of performance and emissions is reported on the base of experimental activities on dual fuel heavy duty engine in comparison with diesel and spark ignition engines. The ratio of biogas potential from MSW and biodiesel potential from waste vegetable oil was estimated and it results suitable for dual fuel fuelling. An electric power installation of 70 kW every 10,000 people could be achieved. L. De Simio, M. Gambino, and S. Iannaccone Copyright © 2012 L. De Simio et al. All rights reserved. Sun, 01 Jul 2012 18:38:07 +0000 http://www.hindawi.com/journals/jc/2012/241587/ Combustion and gasification properties of pulverized coal and char have been investigated experimentally under the conditions of high temperature gradient of order 200°C·s−1 by a CO2 gas laser beam and CO2-rich atmospheres with 5% and 10% O2. The laser heating makes a more ideal experimental condition compared with previous studies with a TG-DTA, because it is able to minimize effects of coal oxidation and combustion by rapid heating process like radiative heat transfer condition. The experimental results indicated that coal weight reduction ratio to gases followed the Arrhenius equation with increasing coal temperature; further which were increased around 5% with adding H2O in CO2-rich atmosphere. In addition, coal-water mixtures with different water/coal mass ratio were used in order to investigate roles of water vapor in the process of coal gasification and combustion. Furthermore, char-water mixtures with different water/char mass ratio were also measured in order to discuss the generation ratio of CO/CO2, and specified that the source of Hydrocarbons is volatile matter from coal. Moreover, it was confirmed that generations of CO and Hydrocarbons gases are mainly dependent on coal temperature and O2 concentration, and they are stimulated at temperature over 1000°C in the CO2-rich atmosphere. Zhigang Li, Xiaoming Zhang, Yuichi Sugai, Jiren Wang, and Kyuro Sasaki Copyright © 2012 Zhigang Li et al. All rights reserved. Mon, 28 May 2012 11:11:13 +0000 http://www.hindawi.com/journals/jc/2012/218916/ The stability limits of a jet flame can play an important role in the design of burners and combustors. This study details an experiment conducted to determine the liftoff and blowout velocities of oblique-angle methane jet flames under various air coflow velocities. A nozzle was mounted on a telescoping boom to allow for an adjustable burner angle relative to a vertical coflow. Twenty-four flow configurations were established using six burner nozzle angles and four coflow velocities. Measurements of the fuel supply velocity during liftoff and blowout were compared against two parameters: nozzle angle and coflow velocity. The resulting correlations indicated that flames at more oblique angles have a greater upper stability limit and were more resistant to changes in coflow velocity. This behavior occurs due to a lower effective coflow velocity at angles more oblique to the coflow direction. Additionally, stability limits were determined for flames in crossflow and mild counterflow configurations, and a relationship between the liftoff and blowout velocities was observed. For flames in crossflow and counterflow, the stability limits are higher. Further studies may include more angle and coflow combinations, as well as the effect of diluents or different fuel types. Jonathan N. Gomes, James D. Kribs, and Kevin M. Lyons Copyright © 2012 Jonathan N. Gomes et al. All rights reserved. Sun, 27 May 2012 13:34:42 +0000 http://www.hindawi.com/journals/jc/2012/927345/ This work investigates the active control of an unstable Rijke tube using robust output model predictive control (RMPC). As internal model a polytopic linear system with constraints is assumed to account for uncertainties. For guaranteed stability, a linear state feedback controller is designed using linear matrix inequalities and used within a feedback formulation of the model predictive controller. For state estimation a robust gain-scheduled observer is developed. It is shown that the proposed RMPC ensures robust stability under constraints over the considered operating range. Fabian Jarmolowitz, Christopher Groß-Weege, Thomas Lammersen, and Dirk Abel Copyright © 2012 Fabian Jarmolowitz et al. All rights reserved. Thu, 17 May 2012 08:37:45 +0000 http://www.hindawi.com/journals/jc/2012/138619/ The quasi-steady model of the combustion of a fuel droplet has been modified. The approach involved the modification of the quasi-steady model to reflect the difference in constant properties across the flame front. New methods for accurately estimating gas constants and for estimating Lewis number are presented. The proposed theoretical model provides results that correlate favorably with published experimental results. The proposed theoretical model also eliminates the need for unguided adjustment of thermal constants or the complex analysis of the variation of thermal properties with temperature and can serve as a basis for analysis of other combustion conditions like droplets cloud and convective and high-pressure conditions. Etim S. Udoetok Copyright © 2012 Etim S. Udoetok. All rights reserved. Wed, 16 May 2012 08:23:15 +0000 http://www.hindawi.com/journals/jc/2012/587987/ Reduced and normal gravity combustion experiments were performed with fiber-supported methanol droplets with initial diameters in the 1 mm size range. Experiments were performed with air-diluent mixtures at about 0.101 MPa and 298 K, where carbon dioxide, helium, or xenon was separately used as the diluent gas. Results indicate that ambient gas transport properties play an important role in determining flammability and combustion behaviors including burning rates and radiant heat output histories of the droplets. Droplets would burn with significantly higher mole fractions of xenon than helium or carbon dioxide. In reduced gravity, droplets would burn steadily with a xenon mole fraction of 0.50 but would not burn steadily if helium or carbon dioxide mole fractions were 0.50. Comparison with previous experimental data shows that ignitability and combustion characteristics of droplets are influenced by the fuel type and also the gravitational level. Burning rates were about 40% to 70% higher in normal gravity than in reduced gravity. Methanol droplets also had burning rates that were typically larger than 1-propanol burning rates by about 20% in reduced gravity. In normal gravity, however, burning rate differences between the two fuels were significantly smaller. Benjamin Shaw and Jingbin Wei Copyright © 2012 Benjamin Shaw and Jingbin Wei. All rights reserved. Tue, 15 May 2012 09:04:25 +0000 http://www.hindawi.com/journals/jc/2012/854393/ A Dynamic model of Homogeneous Charge Compression Ignition (HCCI), based on chemical kinetics principles and artificial intelligence, is developed. The model can rapidly predict the combustion probability, thermochemistry properties, and exact timing of the Start of Combustion (SOC). A realization function is developed on the basis of the Sandia National Laboratory chemical kinetics model, and GRI3.0 methane chemical mechanism. The inlet conditions are optimized by Genetic Algorithm (GA), so that combustion initiates and SOC timing posits in the desired crank angle. The best SOC timing to achieve higher performance and efficiency in HCCI engines is between 5 and 15 degrees crank angle (CAD) after top dead center (TDC). To achieve this SOC timing, in the first case, the inlet temperature and equivalence ratio are optimized simultaneously and in the second case, compression ratio is optimized by GA. The model’s results are validated with previous works. The SOC timing can be predicted in less than 0.01 second and the CPU time savings are encouraging. This model can successfully be used for real engine control applications. AbdoulAhad Validi, Jyh-Yuan Chen, and Akbar Ghafourian Copyright © 2012 AbdoulAhad Validi et al. All rights reserved. Tue, 24 Apr 2012 08:31:35 +0000 http://www.hindawi.com/journals/jc/2012/786920/ The impact of particle size distribution (PSD) of pulverized, low rank high volatile content Alaska coal on combustion related power plant performance was studied in a series of field scale tests. Performance was gauged through efficiency (ratio of megawatt generated to energy consumed as coal), emissions (SO2, NO𝑥, CO), and carbon content of ash (fly ash and bottom ash). The study revealed that the tested coal could be burned at a grind as coarse as 50% passing 76 microns, with no deleterious impact on power generation and emissions. The PSD’s tested in this study were in the range of 41 to 81 percent passing 76 microns. There was negligible correlation between PSD and the followings factors: efficiency, SO2, NO𝑥, and CO. Additionally, two tests where stack mercury (Hg) data was collected, did not demonstrate any real difference in Hg emissions with PSD. The results from the field tests positively impacts pulverized coal power plants that burn low rank high volatile content coals (such as Powder River Basin coal). These plants can potentially reduce in-plant load by grinding the coal less (without impacting plant performance on emissions and efficiency) and thereby, increasing their marketability. Rajive Ganguli and Sukumar Bandopadhyay Copyright © 2012 Rajive Ganguli and Sukumar Bandopadhyay. All rights reserved. Sun, 22 Apr 2012 13:55:21 +0000 http://www.hindawi.com/journals/jc/2012/153410/ The production of biodiesel has notably increased over the past decade. Currently, plant oil is the main feedstock for biodiesel production, but, due to concerns related to the competition with food production, alternative oil feedstocks have to be found. Oleaginous yeasts are known to produce high amounts of lipids, but no integrated process from microbial fermentation to final biodiesel production has reached commercial realization yet due to economic constraints. Therefore, growth and lipid production of red yeast Rhodotorula glutinis was tested on low-cost substrates, namely, wastewaters from potato, fruit juice, and lettuce processing. Additionally, the production of carotenoids as high-value by-products was examined. All evaluated wastewaters met the general criteria for microbial lipid production. However, no significant increase in lipid content was observed, probably due to lack of available carbon in wastewaters from fruit juice and lettuce processing, and excess of available nitrogen in potato processing wastewater, respectively. During growth on wastewaters from fruit juice and lettuce processing the carotenoid content increased significantly in the first 48 hours. The relations between carbon content, nitrogen content, and carotenoid production need to be further assessed. For economic viability, lipid and carotenoid production needs to be increased significantly. The screening of feedstocks should be extended to other wastewaters. Teresa Schneider, Simone Graeff-Hönninger, William Todd French, Rafael Hernandez, Wilhelm Claupein, William E. Holmes, and Nikolaus Merkt Copyright © 2012 Teresa Schneider et al. All rights reserved. Thu, 19 Apr 2012 14:44:44 +0000 http://www.hindawi.com/journals/jc/2012/781659/ In Korea, municipal solid waste (MSW) treatment is conducted by converting wastes into energy resources using the mechanical-biological treatment (MBT). The small size MSW to be separated from raw MSW by mechanical treatment (MT) is generally treated by biological treatment that consists of high composition of food residue and paper and so forth. In this research, the hydrothermal treatment was applied to treat the surrogate MT residue composed of paper and/or kimchi. It was shown that the hydrothermal treatment increased the calorific value of the surrogate MT residue due to increasing fixed carbon content and decreasing oxygen content and enhanced the dehydration and drying performances of kimchi. Comparing the results of paper and kimchi samples, the calorific value of the treated product from paper was increased more effectively due to its high content of cellulose. Furthermore, the change of the calorific value before and after the hydrothermal treatment of the mixture of paper and kimchi can be well predicted by this change of paper and kimchi only. The hydrothermal treatment can be expected to effectively convert high moisture MT residue into a uniform solid fuel. Daegi Kim, Pandji Prawisudha, and Kunio Yoshikawa Copyright © 2012 Daegi Kim et al. All rights reserved. Mon, 09 Apr 2012 09:43:30 +0000 http://www.hindawi.com/journals/jc/2012/285185/ First test flights using blends with algae oil are already carried out and expectations by the aviation and other industries are high. On the other hand technical data about performance of cultivation systems, downstream processing, and suitability of algae oil as fuel are still limited. The existing microalgae growing industry mainly produces for the food and feed market. Energy efficiency is so far out of scope but needs to be taken into account if the product changes to biofuel. Energy and CO2 balances are used to estimate the potential of algae oil to fulfil the EU sustainability criteria for biofuels. The analysis is supported by lab tests as well as data gained by a pilot scale demonstrator combined with published data for well-known established processes. The algae oil composition is indicator of suitability as fuel as well as for economic viability. Approaches attaining high value fractions are therefore of great importance and will be discussed in order to determine the most intended market. Pascal Schlagermann, Gerold Göttlicher, Robert Dillschneider, Rosa Rosello-Sastre, and Clemens Posten Copyright © 2012 Pascal Schlagermann et al. All rights reserved. Thu, 15 Mar 2012 16:24:07 +0000 http://www.hindawi.com/journals/jc/2012/780370/ The potential of a progress variable formulation for predicting autoignition and subsequent kernel development in a nonpremixed jet flame is explored in the LES (Large Eddy Simulation) context. The chemistry is tabulated as a function of mixture fraction and a composite progress variable, which is defined as a combination of an intermediate and a product species. Transport equations are solved for mixture fraction and progress variable. The filtered mean source term for the progress variable is closed using a probability density function of presumed shape for the mixture fraction. Subgrid fluctuations of the progress variable conditioned on the mixture fraction are neglected. A diluted hydrogen jet issuing into a turbulent coflow of preheated air is chosen as a test case. The model predicts ignition lengths and subsequent kernel growth in good agreement with experiment without any adjustment of model parameters. The autoignition length predicted by the model depends noticeably on the chemical mechanism which the tabulated chemistry is based on. Compared to models using detailed chemistry, significant reduction in computational costs can be realized with the progress variable formulation. Rohit Kulkarni and Wolfgang Polifke Copyright © 2012 Rohit Kulkarni and Wolfgang Polifke. All rights reserved.