Showing papers on "Combustion published in 2001"

Measurement of emissions from air pollution sources. 3. C1-C29 organic compounds from fireplace combustion of wood.

Abstract: Organic compound emission rates for volatile organic compounds (VOC), gas-phase semivolatile organic compounds, and particle-phase organic compounds are measured from residential fireplace combustion of wood. Firewood from a conifer tree (pine) and from two deciduous trees (oak and eucalyptus) is burned to determine organic compound emissions profiles for each wood type including the distribution of the alkanes, alkenes, aromatics, polycyclic aromatic hydrocarbons (PAH), phenol and substituted phenols, guaiacol and substituted guaiacols, syringol and substituted syringols, carbonyls, alkanoic acids, resin acids, and levoglucosan. Levoglucosan is the major constituent in the fine particulate emissions from all three wood types, contributing 18−30% of the fine particulate organic compound emissions. Guaiacol (2-methoxyphenol), and guaiacols with additional substituents at position 4 on the molecule, and resin acids are emitted in significant quantities from pine wood combustion. Syringol (2,6-dimethoxyphenol) and syringols with additional substituents at position 4 on the molecule are emitted in large amounts from oak and eucalyptus firewood combustion, but these compounds are not detected in the emissions from pine wood combustion. Syringol and most of the substituted syringols are found to be semivolatile compounds that are present in both the gas and particle phases, but two substituted syringols that have not been previously quantified in wood smoke emissions, propionylsyringol and butyrylsyringol, are found exclusively in the particle phase and can be used to help trace hardwood smoke particles in the atmosphere. Benzene, ethene, and acetylene are often used as tracers for motor vehicle exhaust in the urban atmosphere. The contribution of wood smoke to the ambient concentrations of benzene, ethene, and acetylene could lead to an overestimate of the contribution of motor vehicle tailpipe exhaust to atmospheric VOC concentrations.

Chemical Characterization of Fine Particle Emissions from Fireplace Combustion of Woods Grown in the Northeastern United States

Abstract: The fireplace combustion of wood is a significant and largely unregulated source of fine particle pollution in the United States. Source apportionment techniques that use particulate organic compounds as tracers have been successful in determining the contribution of wood smoke to ambient fine particle levels in specific areas in California. To apply these techniques to the rest of the United States, the differences in emissions profiles between different wood smoke sources and fuel types should be resolved. To this end, a series of fireplace source tests was conducted on six fuel wood species found in the Southern United States to determine fine particulate emission factors for total mass, ionic and elemental species, elemental and organic carbon, and over 250 individual organic compounds. The wood species tested, chosen for their high abundance and availability in the Southern U.S. region, were yellow poplar, white ash, sweetgum, mockernut hickory, loblolly pine, and slash pine. The differences in the emissions of compounds such as substituted phenols and resin acids help to distinguish between the smoke from hardwood and softwood combustion. Levoglucosan, a cellulose pyrolysis product which may serve as a tracer for wood smoke in general, was quantified in the emissions from all the wood species burned. The furofuran lignan, yangambin, which was emitted in significant quantities from yellow poplar combustion and not detected in any of the other North American wood smokes, is a potential species-specific molecular tracer which may be useful in qualitatively identifying particulate emissions from a specific geographical area where yellow poplar is being burned.

Automobile exhaust catalysts

Abstract: It has now been over 25 years since the introduction of the catalytic converter to reduce emissions from the internal combustion engine. It is considered one of the greatest environmental successes of the 20th century, however, new emission control technologies are still being developed to meet ever more stringent mobile source (gasoline and diesel) emissions. This short review will discuss the basis for improvements and highlight technology area, which will require further improvements in emissions and fuel economy. Some of the issues related to fuel cells which some believe may replace the internal combustion engines for automobile applications is also be briefly discussed.

Onboard fuel conversion for hydrogen-fuel-cell-driven vehicles

Abstract: Increasingly stringent legislation controls emissions from internal combustion engines to the point where alternative power sources for vehicles are necessary. The hydrogen fuel cell is one promising option, but the nature of the gas is such that the conversion of other fuels to hydrogen on board the vehicle is necessary. The conversion of methanol, methane, propane, and octane to hydrogen is reviewed. A combination of oxidation and steam reforming (indirect partial oxidation) or direct partial oxidation are the most promising processes. Indirect partial oxidation involves combustion of part of the fuel to produce sufficient heat to drive the endothermic steam reforming reaction. Direct partial oxidation is favored only at high temperatures and short residence times but is highly selective. However, indirect partial oxidation is shown to be the preferred process for all fuels. The product gases can be taken through a water–gas shift reactor, but still retain ∼2% carbon monoxide, which poisons fuel-cell ca...

Review: reaction synthesis processing of Ni–Al intermetallic materials

Abstract: Nickel aluminide intermetallic compounds possess attractive properties that make them good candidates for high temperature structural applications. The production of these materials in short processing times and low energy via reaction synthesis routes has been reviewed in this article including most recent novel reactive methods applied to Ni–Al intermetallics (e.g. microwave combustion synthesis and hot extrusion reaction synthesis). Future directions in this field have been suggested.

A Mechanism of Combustion Instability in Lean Premixed Gas Turbine Combustors

Abstract: There has been increased demand in recent years for gas turbines that operate in a lean, premixed (LP) mode of combustion in an effort to meet stringent emissions goals. Unfortunately, detrimental combustion instabilities are often excited within the combustor when it operates under lean conditions, degrading performance and reducing combustor life. To eliminate the onset of these instabilities and develop effective approaches for their control, the mechanisms responsible for their occurrence must be understood. This paper describes the results of an investigation of the mechanisms responsible for these instabilities. These studies found that combustors operating in a LP mode of combustion are highly sensitive to variations in the equivalence ratio (O) of the mixture that enters the combustor. Furthermore, it was found that such O variations can be induced by interactions of the pressure and flow oscillations with the reactant supply rates. The O perturbations formed in the inlet duct (near the fuel injector) are convected by the mean flow to the combustor where they produce large amplitude heat release oscillations that drive combustor pressure oscillations. It is shown that the dominant characteristic time associated with this mechanism is the convective time from the point of formation of the reactive mixture at the fuel injector to the point where it is consumed at the flame. Instabilities occur when the ratio of this convective time and the period of the oscillations equals a specific constant, whose magnitude depends upon the combustor design, Significantly, these predictions are in good agreement with available experimental data, strongly suggesting that the proposed mechanism properly accounts for the essential physics of the problem. The predictions of this study also indicate, however, that simple design changes (i.e., passive control approaches) may not, in general, provide a viable means for controlling these instabilities, due to the multiple number of modes that may be excited by the combustion process.

Modeling of Complex Premixed Burner Systems by Using

Abstract: The numerical modeling of realistic burner systems puts a very high demand on computational resources. The computational cost of combustion simulations can be reduced by techniques that simplify the chemical kinetics. In this paper, the recently introduced flamelet-generated manifold method for premixed combustion systems is applied to laminar flames. In this method, the reduced mechanism is created by using solutions of one-dimensional flamelet equations as steady-state relations. For a methane/air mixture a manifold is constructed with two controlling variables: one progress variable and the enthalpy to account for energy losses. This manifold is used for the computation of a two-dimensional burner-stabilized flame and the results are compared with results of detailed computations. The results show that these two controlling variables are sufficient to reproduce the results of detailed computations. The influence of flame stretch on the accuracy of the method is investigated by simulating strained flames in stagnation-point flows. The computation time can be reduced by a factor of 20 when a flamelet-generated manifold is applied. The reduction in computation time enables us to perform simulations of combustion in more complex combustion systems. To show that the method can be used to give accurate predictions, a semi-practical furnace is modeled and the results are compared with temperature measurements. The experimental setup consists of a cylindrical radiating furnace with a ceramic-foam surface burner in the top disc. Radial profiles of temperature have been measured at two different heights in the furnace. The measurements agree quite well with the results of the numerical simulation using a flamelet-generated manifold. © 2001 by The Combustion

Closed-Loop Control of an HCCI Engine

Abstract: This paper presents a strategy for closed-loop control of a multi-cylinder turbocharged Homogeneous Charge Compression Ignition (HCCI) engine. A dual fuel port injection system allows control of combustion timing and load individually for each cylinder. The two fuels used are isooctane and n-heptane, which provides a wide range of autoignition properties. Cylinder pressure sensors provide feedback and information regarding combustion. The angle of 50% heat release is calculated in real time for each cycle and used for timing feedback. Inlet air preheating is used at low loads to maintain a high combustion efficiency.

Ten residual biomass fuels for circulating fluidized-bed gasification

Abstract: In co-operation with a Dutch company (NV Afvalzorg) and the Dutch agency for energy and environment (Novem), ECN has successfully tested 10 different biomass residues in its 500 kW th circulating fluidized-bed gasification facility. Among the fuels used are demolition wood (both pure and mixed with sewage sludge and paper sludge), verge grass, railroad ties, cacao shells and different woody fuels. Railroad ties turn out to contain very little (heavy) metals. Initially, fuel feeding problems often impeded smooth operation. Contrary to feeding systems, the circulating fluidized-bed gasification process itself seems very flexible concerning the conversion of different kinds of biomass fuels. The fuel moisture content is one of the most important fuel characteristics. More moisture means that more air is needed to maintain the process temperature resulting in better carbon conversion and lower tar emission but also lower product gas heating value and lower cold gas efficiency. So, for a good comparison of the gasification behaviour of different fuels, the moisture content should be similar. However, the moisture content should be defined on an ash-free basis rather than on total mass (the usual way). Some of the ashes produced and retained in the second cyclone were analysed both for elemental composition and leaching behaviour. It turned out that the leaching rate of Mo and Br, elements only present in small concentrations, are preventing the ash to be considered as inert material according to the Dutch legislation for dumping on landfill sites.

Complex Chemistry Modeling of Diesel Spray Combustion

Abstract: The thesis illustrates the application of computational fluid dynamics (CFD) to turbulent reactive two-phase flows in piston engines. The focus of the thesis lies on numerical simulations of spray combustion phenomena with an emphasis on the modeling of turbulence/chemistry interaction effects using a detailed chemistry approach. The turbulence/chemistry interaction model accounts for the effects of turbulent micro-mixing on the chemical reaction rates. The models have been implemented in the {\bf KIVA3-V} code and successfully applied to spray combustion analysis in a constant volume and a DI Diesel engine. The limitations and difficulties of representing the spray in a Lagrangian fashion are also adressed. Three different liquid fuels have been used in the simulations: n-heptane, methanol and dimethyl ether (DME). Detailed and reduced chemical mechanisms have been developed and validated for all these fuels and reasonable agreement between experimental data and numerical simulations has been obtained.

Supersonic Combustion Experiments with a Cavity-Based Fuel Injector

Abstract: Recent results from combustion experimentsin a direct-connectsupersoniccombustorarepresented. Successful ignition and sustained combustion of gaseous ethylene have been achieved using an injector/e ameholder concept with low-angle, e ush-wall fuel injection upstream of a wall cavity. Two interchangeable facility nozzles (Mach 1.8 and 2.2) were used to obtain combustor inlet e ow properties that simulate e ight conditions between Mach 4 and 6 at a dynamic pressure of 47.9 kPa. Mainstream combustion was achieved at equivalence ratios between 0.25 and 0.75 using only a spark plug and no other external ignition aids. Delta-force levels between 667 and 1779 N were measured, with corresponding combustor pressure ratios between 3.1 and 4.0. Video records of the e ame zone show an intensely active combustion zone with rapid e ame spreading. One-dimensional performance analysis of the test data indicates a combustion efe ciency around 80% with an average combustor skin friction coefe cient of 0.0028.

Progress in Thermochemical Biomass Conversion

Abstract: Combustion: Co-combustion of coal and biomass wastes in fluidised bed Development of catalytic wood fired boiler The mathematical modelling of biomass pyrolysis in a fixed bed and experimental verification Operating parameters for the circulating fluidised bed (CFB) processing of biomass Combustion properties of a fuel bed - Experimental and modelling study Summary of recent parametric studies of small-scale domestic biomass combustion Combustion processes in a biomass fuel bed - Experimental results of the influence of airflow and of particle size and density Influence of the ash composition in slagging and defluidisation in a biomass fired commercial CFB boiler A new type of a boiler plant for dry and wet biofuel Gasification: Modern technologies of biomass conversion Redox process for the production of clean hydrogen from biomass Dynamic Modelling of Char Gasification in a Fixed-Bed A two stage pyrolysis/gasification process for herbaceous waste biomass from agriculture Fundamental fluid-dynamic investigations in a scaled cold model for biomass-steam gasification Biomass Power Generation: Sugar Cane Bagasse and Trash Biomass and waste to energy conversion in the Netherlands by means of (in) direct co-combustion: Status, projects and future applications in the Dutch utility sector Gasification study of biomass mixed with plastic wastes The development of methanol synthesis with biomass gasification Final report: Varnamo demonstration programme Design of a moving bed granular filter for biomass gasification Pyrolysis: Bagasse pyrolysis in a wire mesh reactor BCO/Diesel oil emulsification: Main achievements of the emulsification process and preliminary results of tests on diesel engine Overview of fast pyrolysis Production of hydrogen from biomass-derived liquids Levoglucosenone - A product of catalytic fast pyrolysis of cellulose Pyrolysis and gasification of black liquors from alkaline pulping of straw in a fixed bed reactor Thermal efficiency of the HTU process for biomass liquefaction Low-temperature pyrolysis as a possible technique for the disposal of CCA treated wood waste Mathematical modelling of the flash-pyrolysis process for wood particles Flash pyrolysis of biomass in a conical spouted bed. Kinetic study in the 400-500C range Scale up effect on plastics waste pyrolysis Research on the rotating cone reactor for sawdust flash pyrolysis Thermal desorption technology: Low temperature carbonisation of the biomass for manufacturing of activated carbon Scaling-up and operation of a flash-pyrolysis system for bio-oil production and applications on basis of the rotating cone technology Systems: Utilisation of bagasse residues in power production Barriers for the introduction of biomass in the Netherlands Assessment of the techno-economic viability of a bioelectricity demonstration plant in Spain Innovative components for decentralised combined heat and power generation from biomass gasification A role of bioenergy utilization technologies considering bioenergy supply potential and energy systems using a global energy and land use model

Detailed surface reaction mechanism in a three-way catalyst

Abstract: Monolithic three-way catalysts are applied to reduce the emission of combustion engines. The design of such a catalytic converter is a complex process involving the optimization of different physical and chemical parameters (in the simplest case, e.g., length, cell densities or metal coverage of the catalyst). Numerical simulation can be used as an effective tool for the investigation of the catalytic properties of a catalytic converter and for the prediction of the performance of the catalyst. To attain this goal, a two-dimensional flow-field description is coupled with a detailed surface reaction model (gas-phase reactions can be neglected in three-way catalysts). This surface reaction mechanism (with C3H6 taken as representative of unburnt hydrocarbons) was developed using sub-mechanisms recently developed for hydrogen, carbon monoxide and methane oxidation, literature values for C3H6 oxidation, and estimates for the remaining unknown reactions. Results of the simulation of a monolithic single channel are used to validate the surface reaction mechanism. The performance of the catalyst was simulated under lean, nearly stoichiometric and rich conditions. For these characteristic conditions, the oxidation of propene and carbon monoxide and the reduction of NO on a typical Pt/Rh coated three-way catalyst were simulated as a function of temperature. The numerically predicted conversion data are compared with experimentally measured data. The simulation further reveals the coupling between chemical reactions and transport processes within the monolithic channel.

Multi-Zone DI Diesel Spray Combustion Model for Cycle Simulation Studies of Engine Performance and Emissions

Abstract: A quasi -dimensional, multi-zone, direct injection (DI) diesel combustion model has been developed and implemented in a full cycle simulation of a turbocharged engine. The combustion model accounts for transient fuel spray evolution, fuel-air mixing, ignition, combustion and NO and soot pollutant formation. In the model, the fuel spray is divided into a number of zones, which are treated as open systems. While mass and energy equations are solved for each zone, a simplified momentum conservation equation is used to ca lculate the amount of air entrained into each zone. Details of the DI spray, combustion model and its implementation into the cycle simulation of Assanis and Heywood [1] are described in this paper. The model is validated with experimental data obtained in a constant volume chamber and engines. First, predictions of spray penetration and spray angle are validated against measurements in a pressurized constant volume chamber. Subsequently, predictions of heat release rate, as well as NO and soot emissions are compared with experimental data obtained from representative heavy-duty, turbocharged diesel engines. It is demonstrated that the model can predict the rate of heat release and engine performance with high fidelity. However, additional effort is require d to enhance the fidelity of NO and soot predictions across a wide range of operating conditions.