Showing papers on "Combustion published in 1999"

Fuel oil quality of biomass pyrolysis oils-state of the art for the end users

Abstract: Biomass pyrolysis oils have potential to be used as a fuel oil substitute. Combustion tests have shown that the oils burn efficiently in standard or slightly modified boilers and engines with rates similar to those for commercial fuels. However, these tests also identified several challenges in bio-oils applications resulting from their properties. The oils have heating values of only 40−50% of that for hydrocarbon fuels. They have a high water content that is detrimental for ignition. Organic acids in the oils are corrosive to common construction materials. Solids (char) can block injectors or erode turbine blades. Over time, reactivity of some components in the oils leads to formation of larger molecules that results in high viscosity and in slower combustion. This paper discusses physical and chemical characteristics of bio-oils relevant to fuel applications as well as some low-cost methods for improvement of these properties. It also provides bio-oil specifications proposed by some industrial users an...

Construction of a 1° × 1° fossil fuel emission data set for carbonaceous aerosol and implementation and radiative impact in the ECHAM4 model

Abstract: Global-scale emissions of carbonaceous aerosol from fossil fuel usage have been calculated with a resolution of 1° × 1°. Emission factors for black and organic carbon have been gathered from the literature and applied to domestic, transport, and industrial combustion of various fuel types. In addition, allowance has been made for the level of development when calculating emissions from a country. Emissions have been calculated for 185 countries for the domestic, industrial, and transport sectors using a fuel usage database published by the United Nations [1993]. Some inconsistencies were found for a small number of countries with regard to the distribution of fuel usage between the industrial and domestic sectors. Care has been taken to correct for this using data from the fuel use database for the period 1970–1990. Emissions based on total particulate matter (TPM) and submicron emission factors have been calculated. Global emissions for 1984 of black carbon total 6.4 TgC yr−1 and organic carbon emissions of 10.1 TgC yr−1 were found using bulk aerosol emission factors, while global black carbon emissions of 5.1 TgC yr−1 and organic carbon emissions of 7.0 TgC yr−1 were found using submicron emission factors. Use of the database is quite flexible and can be easily updated as emission factor data are updated. There is at least a factor of 2 uncertainty in the derived emissions due to the lack of exactly appropriate emission data. The emission fields have been introduced into the ECHAM4 atmospheric general circulation model and run for 5 model years. Monthly mean model results are compared to measurements in regions influenced by anthropogenic fossil fuel emissions. The resultant aerosol fields have been used to calculate the instantaneous solar radiative forcing at the top of the troposphere due to an external mixture of fossil fuel derived black carbon and organic carbon aerosol. Column burdens of 0.143 mgBC m−2 and 0.170 mgOC m−2 were calculated. Because of secondary production of organic carbon aerosol, it is recommended that the burden of organic carbon aerosol be doubled to 0.341 mgOC m−2. The resultant forcing when clouds are included is +0.173 W m−2 for black carbon and −0.024 W m−2 for organic carbon (×2) as a global annual average. The results are compared to previous works, and the differences are discussed.

A twin fluid-bed reactor for removal of CO2 from combustion processes

Abstract: A new process is proposed for CO2 removal from flue gas using the reaction CaO + CO2 ↔ CaCO3. This process consists of two fluidized bed reactors connected by solid transportation lines. In one reactor (absorber), CO2 in the flue gas is captured by CaO at 873 K and the produced CaCO3 is transported to another reactor (regenerator), in which CaCO3 is decomposed to CaO at 1223 K. The produced CaO is transported to the absorber again. The heat of decomposition in the regenerator is supplied by feeding coal and pure oxygen, thus the flue gas from the regenerator is high purity CO2 (>95%, dry base). In this work, a conceptual study is conducted for material balance, heat balance, power generation, and power consumption for O2 production and CO2 liquefaction (compression). Also, a kinetic study of CaO+CO2 → CaCO3 was conducted to design the absorber. The required bed height of the absorber was calculated by use of a bubbling fluidized bed model. The bed height was found to be determined not by the chemical reaction rate but by the arrangement of heat transfer tubes for heat recovery.

Premixed charge compression ignition engine with optimal combustion control

Abstract: A premixed charge compression ignition engine, and a control system, is provided which effectively initiates combustion by compression ignition and maintains stable combustion while achieving extremely low nitrous oxide emissions, good overall efficiency and acceptable combustion noise and cylinder pressures. The present engine and control system effectively controls the combustion history, that is, the time at which combustion occurs, the rate of combustion, the duration of combustion and/or the completeness of combustion, by controlling the operation of certain control variables providing temperature control, pressure control, control of the mixture's autoignition properties and equivalence ratio control. The combustion control system provides active feedback control of the combustion event and includes a sensor, e.g. pressure sensor, for detecting an engine operating condition indicative of the combustion history, e.g. the start of combustion, and generating an associated engine operating condition signal. A processor receives the signal and generates control signals based on the engine operating condition signal for controlling various engine components to control the temperature, pressure, equivalence ratio and/or autoignition properties so as to variably control the combustion history of future combustion events to achieve stable, low emission combustion in each cylinder and combustion balancing between the cylinders.

Hydrocarbon combustion power generation system with co2 sequestration

Abstract: A low or no pollution engine is provided for delivering power for vehicles or other power applications. The engine has an air inlet which collects air from a surrounding environment. At least a portion of the nitrogen in the air is removed using a technique such as liquefaction, pressure swing adsorption or membrane based air separation. The remaining gas is primarily oxygen, which is then compressed and routed to a gas generator. The gas generator has an igniter and inputs for the high pressure oxygen and a high pressure hydrogen-containing fuel, such as hydrogen, methane or a light alcohol. The fuel and oxygen are combusted within the gas generator, forming water and carbon dioxide with carbon containing fuels. Water is also delivered into the gas generator to control the temperature of the combustion products. The combustion products are then expanded through a power generating device, such as a turbine or piston expander to deliver output power for operation of a vehicle or other power uses. The combustion products, steam and, with carbon containing fuels, carbon dioxide, are then passed through a condenser where the steam is condensed and the carbon dioxide is collected or discharged. A portion of the water is collected for further processing and use and the remainder is routed back to the gas generator. The carbon dioxide is compressed and cooled so that it is in a liquid phase or super critical state. The dense phase carbon dioxide is then further pressurized to a pressure matching a pressure, less hydrostatic head, existing deep within a porous geological formation, a deep aquifer, a deep ocean location or other terrestrial formation from which return of the CO2 into the atmosphere is inhibited.

Diesel combustion: an integrated view combining laser diagnostics, chemical kinetics, and empirical validation

Abstract: This paper proposes a structure for the diesel combustion process based on a combination of previously published and new results Processes are analyzed with proven chemical kinetic models and validated with data from production-like direct injection diesel engines The analysis provides new insight into the ignition and particulate formation processes, which combined with laser diagnostics, delineates the two-stage nature of combustion in diesel engines Data are presented to quantify events occurring during the ignition and initial combustion processes that form soot precursors A framework is also proposed for understanding the heat release and emission formation processes

A kinematic model of a ducted flame

Abstract: A premixed ducted flame, burning in the wake of a bluff-body flame-holder, is considered. For such a flame, interaction between acoustic waves and unsteady combustion can lead to self-excited oscillations. The concept of a time-invariant turbulent flame speed is used to develop a kinematic model of the response of the flame to flow disturbances. Variations in the oncoming flow velocity at the flame-holder drive perturbations in the flame initiation surface and hence in the instantaneous rate of heat release. For linear fluctuations, the transfer function between heat release and velocity can be determined analytically from the model and is in good agreement with experiment across a wide frequency range. For nonlinear fluctuations, the model reproduces the flame surface distortions seen in schlieren films.Coupling this kinematic flame model with an analysis of the acoustic waves generated in the duct by the unsteady combustion enables the time evolution of disturbances to be calculated. Self-excited oscillations occur above a critical fuel–air ratio. The frequency and amplitude of the resulting limit cycles are in satisfactory agreement with experiment. Flow reversal is predicted to occur during part of the limit-cycle oscillation and the flame then moves upstream of the flame-holder, just as in experimental visualizations. The main nonlinearity is identified in the rate of heat release, which essentially ‘saturates’ once the amplitude of the velocity fluctuation exceeds its mean. We show that, for this type of nonlinearity, describing function analysis can be used to give a good estimate of the limit-cycle frequency and amplitude from a quasi-nonlinear theory.

Release of Inorganic Constituents from Leached Biomass during Thermal Conversion

Abstract: Leaching of inorganic materials has recently been shown to substantially improve the combustion properties of biomass fuels, especially straw but including other herbaceous and woody fuels. Leaching with water removes large fractions of alkali metals (typically >80% of potassium and sodium) and chlorine (>90%). Smaller fractions of sulfur and phosphorus are also removed. Alkali metals are heavily involved in ash fouling and slagging in combustion and thermal gasification systems. Chlorine is a facilitator of alkali volatilization, and contributes to corrosion and air pollution. The presence of these elements has reduced or eliminated the use of certain biomass fuels in many combustion applications, even where such use might provide significant environmental benefits. Leaching could mitigate the undesirable effects of biomass ash in thermal systems. Reported here for the first time are comparative studies of volatile inorganic species evolving from leached and unleached biomass fuels during thermal convers...

SiC Recession Caused by SiO2 Scale Volatility under Combustion Conditions: I, Experimental Results and Empirical Model

Abstract: A high-pressure burner rig was developed to evaluate the response of chemical-vapor-deposited SiC material during exposure to simulated gas turbine combustor conditions. Linear weight loss and surface recession rates of SiC were observed in both fuel-lean and fuel-rich gas mixtures. This response was shown to result from SiO2 scale volatility. Arrhenius-type temperature dependence was demonstrated. In addition, the effects of pressure and gas velocity were defined in terms of a gaseous-diffusion-controlled process for volatile reaction products (such as SiO, Si(OH)4, and iO(OH)x). Accordingly, multiple linear regression was used to develop empirical recession relationships of the form exp(-DeltaQ/RT)Pxvyfor both lean and rich combustion conditions. Part II of this paper discusses the thermodynamics and gaseous-diffusion model of this recession. The empirical models discussed here enable prediction of SiC recession for any combination of T, P, and vin turbine environments. For typical combustion conditions, recession of 0.2-2 µm/h was predicted at 1200°-1400°C. Thus, long-term, high-temperature, high-velocity exposure may degrade silicon-based or SiO2-forming material by recession in combustion gas environments.

Development of a Novel Chemical-Looping Combustion: Synthesis of a Solid Looping Material of NiO/NiAl2O4

Abstract: A new kind of solid looping material, NiO/NiAl2O4, was synthesized based on integration of NiO, as solid reactant, with a composite metal oxide of NiAl2O4, as a binder, for applying it to chemical-looping combustion. The chemical looping combustion including reduction (fuel with metal) and oxidation (air with the reduced metal oxide) could make a breakthrough in simultaneous contribution to both energy and environmental issues. The reactivity of the reduction and oxidation was investigated by TGA (thermogravimetrical analysis). The results obtained here indicated that the new looping material, NiO/NiAl2O4, might significantly improve reaction rate, conversion, and regenerability in cyclic reaction, compared with the other materials. In addition, the carbon deposition can be completely avoided by addition of water vapor at a ratio of H2O/CH4 = 2.0. These results suggest that this new looping material of NiO/NiAl2O4 may play a vital role in developing chemical-looping combustion.

System for nox reduction in exhaust gases

Abstract: A system for NOx reduction in combustion gases, especially from diesel engines, incorporates an oxidation catalyst to convert at least a portion of NO to NO2, a particulate filter, a source of reductant such as NH3, and an SCR catalyst. Considerable improvements in NOx conversion are observed.

Design and Simulation of Four-Stroke Engines

Abstract: This book provides design assistance with the actual mechanical design of an engine in which the gas dynamics, fluid mechanics, thermodynamics, and combustion have been optimized so as to provide the required performance characteristics such as power, torque, fuel consumption, or noise emission.

Method and system for supplying hydrogen for use in fuel cells

Abstract: The present invention provides a method and system for efficiently producing hydrogen that can be supplied to a fuel cell (52). The method and system of the present invention produces hydrogen in a reforming reactor (12) using a hydrocarbon stream (21) and water vapor stream (25) as reactants. The hydrogen produced is purified in a hydrogen separating membrane (14) to form a retentate stream (42) and purified hydrogen stream (40). The purified hydrogen can then be fed to a fuel cell (52) where electrical energy is produced and a fuel cell exhaust stream (76) containing water vapor and oxygen-depleted air is emitted. In one embodiment of the present invention, a means and method are provided for recycling a portion of the retentate stream (42) to the reforming reactor (12) for increased hydrogen yields. In another embodiment, a combustor (94) is provided for combusting a second portion (48) of the retentate stream (42) to provide heat to the reforming reaction or other reactants. In a preferred embodiment, the combustion is carried out in the presence of at least a portion (92) of the oxygen-depleted air stream (76) from the fuel cell (52). Thus, the system and method of the present invention advantageously uses products generated from the system to enhance the overall efficiency of the system.

Global emissions of hydrogen chloride and chloromethane from coal combustion, incineration and industrial activities: Reactive Chlorine Emissions Inventory

Abstract: Much if not all of the chlorine present in fossil fuels is released into the atmosphere as hydrogen chloride (HCl) and chloromethane (CH3Cl, methyl chloride). The chlorine content of oil-based fuels is so low that these sources can be neglected, but coal combustion provides significant releases. On the basis of national statistics for the quantity and quality of coal burned during 1990 in power and heat generation, industrial conversion and residential and commercial heating, coupled with information on the chlorine contents of coals, a global inventory of national HCl emissions from this source has been constructed. This was combined with an estimate of the national emissions of HCl from waste combustion (both large-scale incineration and trash burning) which was based on an estimate of the global quantity released from this source expressed per head of population. Account was taken of reduced emissions where flue gases were processed, for example to remove sulphur dioxide. The HCl emitted in 1990, comprising 4.6 ± 4.3 Tg Cl from fossil fuel and 2 ± 1.9 Tg Cl from waste burning, was spatially distributed using available information on point sources such as power generation utilities and population density by default. Also associated with these combustion sources are chloromethane emissions, calculated to be 0.075 ± 0.07 Tg as Cl (equivalent) from fossil fuels and 0.032 ± 0.023 Tg Cl (equivalent) from waste combustion. These were distributed spatially exactly as the HCl emissions, and a further 0.007 Tg Cl in chloromethane from industrial process activity was distributed by point sources.

A Study of the Homogeneous Charge Compression Ignition Combustion Process by Chemiluminescence Imaging

Abstract: An experimental study of the Homogeneous Charge Compression Ignition (HCCI) combustion process has been conducted by using chemiluminescence imaging. The major intent was to characterize the flame structure and its transient behavior. To achieve this, time resolved images of the naturally emitted light were taken. Emitted light was studied by recording its spectral content and applying different filters to isolate species like OH and CH.Imaging was enabled by a truck-sized engine modified for optical access. An intensified digital camera was used for the imaging. Some imaging was done using a streak-camera, capable of taking eight arbitrarily spaced pictures during a single cycle, thus visualizing the progress of the combustion process. All imaging was done with similar operating conditions and a mixture of n-heptane and iso-octane was used as fuel.Some 20 crank angles before Top Dead Center (TDC), cool flames were found to exist. They appear with a faint structure, evenly distributed throughout the combustion chamber. There was no luminosity recorded between the end of cool flames and the start of the main heat release. Around TDC the main heat release starts. Looking at a macro scale, we find that the charge starts to burn simultaneously at arbitrary points throughout the charge. Since the thermal boundary layer is colder than the bulk of the charge, the local heat release is delayed close to the walls. As a result, the total heat release is slowed down. Ensemble averaged1 images show this wall boundary effect clearly when plotted against CAD. The peak intensity at the main combustion event is one order of magnitude greater than that of the cool flame and the structure is a lot more protruding.Since spontaneous emission imaging is a line-of-sight integration, the flame structure appears a bit smeared. The micro scale structure is very similar from one cycle to another, but there are large variations between cycles on the macro scale. (Less)