Showing papers in "Journal of Combustion Science and Technology in 2004"

Mobility of Arsenic in Coal Fly Ash of Different Particle Size

Abstract: Coal, slag and fly ashes were sampled from a 300 MW utility boiler at the rated load The arsenic contents of those samples were analysed and the distribution of arsenic in combustion product was investigated The influence of particle size on the arsenic concentration were also studied The result shows that Arsenic quantity in fly ash to total combustion products is about 518% and arsenic was highly enriched in the smallest ash particle The mobility of arsenic of fly ash was investigated using sequential extraction procedures The results for four fly ashes are fairly simila that the content of arsenic bound in differat forms of occurronce in the fly ash studied increase in the order residuecarbonate-bound, surface oxide-bound ionsreadily exchangeable ionswater-extractable However, the arsenic in small particles was more active and harmful

Analysis of Combustion Characteristics of RDF by Thermogravimetry

Abstract: Combustion characteristics of refuse derived fuel (RDF) prepared from combustible components (plastics, plants, fabric and their mixtures) were analyzed by means of thermogravimetry. The combustion activation energy and frequency factor were obtained by Doyle method. The results showed: RDF of plants had two ignition points; RDF of fabric, plastics and their mixtures had only one ignition point of fixed carbon; RDF of fabric was the most prone to ignition and have the most dramatic combustion and the least duration period; RDF of plastics had the longest duration period; RDF of their mixture have stable combustion and long duration period. Thus stable incineration can be guaranteed. Combustion reaction of RDF can be described by several first level reaction: the degree of difficulty of combustion reaction can by describe by the apparent activation energy;combustion characteristics of mixture RDF can not be describe by simple accumulation of combustion characteristics of every components of the mixture.

Effect of Combustion Parameters on Diesel Engine Smoke Opacity Under Constant Speed and Increasing Torque Transient Operating Condition

Abstract: The air-fuel ratio, smoke opacity and in-cylinder pressure of a TCA diesel engine under constant speed and increasing torque transient operating conditions were tested by a home-made control and measurement system. The conclusions can be drawn that with the rise of the torque increasing rate the air-fuel ratio decreased rapidly,the combustion start point delayed,the combustion duration prolonged, and the premixed combustion rate reduced. All the factors mentioned above make the diesel engine smoke opacity increased with the torque increasing rate.

Emission Characteristics of Turbo-Charge Diesel Engine with Bio-Diesel Fuel

Abstract: comparative tests were made on a turbo-charge diesel engine fueled by bio-diesel and ordinary diesel separately in terms of the output power, fuel consumption and emission characteristics. The results show that the influenc of bio-diesel fuel on the engine output power is less than 5% when the injection pump is the same without change. The diesel engine exhaust smoke ,PT, CO and HC emission could be reduced greatly when bio-diesel fuel is burnt, but the NO_x emission could be increased. The shortcoming of the bio-diesel fuel could be overcome through a proper delay of the injecting timing. The bio-diesel fuel is an ideal recycling clean fuel.

Effect of Residence Time on Tar Catalytic Cracking Behavior with Calcium Oxide

Abstract: The effect of residence time on the catalytic behavior of calcium oxide in tar cracking at different temperatures in the freeboard of a fluidized bed was investigated in order to decrease the amount of tar produced by coal pyrolysis and simultaneously to make coal gas have high quality . There exist almost no bubbles in the freeboard,so the calcium oxide well contacted with the tar, which is of benefit to improving the effect of calcium oxide on tar cracking. The results show that the yield of tar is reduced apparently by the addition of calcium oxide and the effect of calcium oxide on the yield of tar increases quickly as residence time rises, but at 750 ℃ the effect of calcium oxide begins to decrease when residence time is above 3 s. The addition of calcium oxide also increases the yields of H_2, CO, aliphatic hydrocarbons and the thermal value of gas.

Experimental Investigation on the Oxidation Rules of Pyridine

Abstract: The oxidation rules of pyridine which is nitrogen-containing model compound were investigated over the temperature range of 600—1 400 ℃The major products were measured with Fourier transform infrared radiation analyzer(Ft-Ir) and QUINTOX KM9106 analyzer The results showed that the main resultants of the reaction were NO,NO_2,N_2O,CO and CO_2 The maximum emission of N_2O appears between 750 ℃ and 900 ℃The amount of NO_x increases with the growth of temperature And the maximum CO appears at 650 ℃ when the oxygen exceed or are equal to 76% of the theoretical (amount) of oxygen The product includes a great deal of CO when the oxygen are equal to 59%, which prevents the formation of NO_x

Trace Pollutant in MSW Incinerator Fly Ash: Heavy Metals and Dioxins

Abstract: Municipal solid waste incinerator (MSWI)fly ash contains leachable heavy metals and toxic equivalents (TEQ) dioxins of high level, and is usually classified as a hazardous waste Thus further detoxification and stabilization treatment must be applied to MSWI fly ash before disposing The trace pollutants such as heavy metal and dioxins of MSWI fly ash have an important influence on selection of treatment technology Dioxin and heavy metal in fly ashes collected from several MSW incinerators in China and France were studied in detail A comparative analysis with previous studies is performed The results show that the content of each heavy metal is different The contents of Cu, Pb and Zn are usually more than thoses of Cr, Ni and Cd in fly ash The content of dioxins varies in the range of 136～3154 ng/g The results indicate that trace pollutant(such as heavy metal and dioxins) in MSWI fly ash is significantly affected by raw material, tape of furnace, incineration temperature and residence time

Optimization of Diesel Chamber by Advanced Combustion Simulation

Abstract: A calculation of thermodynamic cycle and combustion of a six-cylinder diesel by thermodynamic simulation tool BOOST and CFD simulation tool FIRE which was implanted advanced moving-meshes technology is presented in this paper. The mathematical models in the simulation of fuel spray and breakup, mixture formation and combustion of a diesel are described.Based on detailed insight into the governing processes provided by the 3D simulation results, various aspects of the interaction of spray propagation and combustion with chamber geometry, turbine intensity and the number of injection holes are discussed. Finally, some optimized configurations which took into account all of the factors mentioned above have been proposed in this paper.

Gasification of Petroleum Coke with Additional Coal Ash

Abstract: The steam gasification experiments of petroleum coke with additional coal ash were carried out in 60% steam by using a thermobalance. The results show that steam gasification rate increases when coal ash is present. And the more the content of coal ash is, the higher the steam gasification rate increases. The effect of change of the coal ash content on gasification rate becomes smaller when the content increases. Gasification activation energy decreases when coal ash is present.

Cylinder Pressure and Combustion Noise of Internal Combustion Engine

Abstract: The time-frequency and spectrum analysis information is gained from the measurement of cylinder pressure and noise by the method of wavelet packet analysis. The characters of the cylinder pressure and noise are studied by the time-frequency and spectrum analysis. The situation of the piston slapping noise and combustion noise in each frequency range of the measured noise is discussed. The cylinder pressure and combustion noise' energy in each frequency range is also calculated and analyzed. The results demonstrate that the high-frequency oscillation pressure has an important effect on combustion noise. Analyzing the cylinder pressure and noise by the time-frequency and spectrum analysis method can gain more information about the combustion noise and the piston slapping noise, and provide technical support for separating combustion noise and its principle research.

Effects of Micropore Structure and Surface Properties on the SO_2 Removal in Flue Gas by Active Coke

Abstract: Two active cokes with similar specific surface area but from different origins were used to remove SO_2 in simulated flue gas. The active cokes were characterized by N_2 adsorption at 77 K, and analyzed by BET equation to obtain BET surface area, by t-plot method to obtain micropore volume and micropore area, by Horvath-Kawazoe equation and Dubinin-Astakhov equation to obtain micropore distribution from different profiles, and by density functional theory to get pore size distribution. The surface functional groups were determined by X-ray photoelectron spectroscopy and the surface basicity is detected by the adsorption of benzoic acid. The results show that there is almost no connection between the desulphurization activity of the active cokes and their BET surface areas, pore volume , but certain relationship exists between the pore size and the pore size distribution. Within the five kinds of functional groups detected, the density of ether and carbonyl exhibits the consistence with the desulphurization activity and is correlated with values of the adsorption of benzoic acid. It can be concluded that the surface basicity is mainly related to the ether and carbonyl functional groups and determines the capacity of carbon sorbent.

Experimental Study on Static Pressure Distribution Properties of Gas-Solid Injector Under Pressure

Abstract: On the testing equipment of a pressurized pneumatic conveying system, a detailed investigation of an important parameter, the location of driving nozzle, which can affect the conveying characteristics of the convergent gas-solid injector was performed The experimental results indicate that the location of the driving nozzle and the convergent section angle has an obvious influence on the maximal mass flow rate of the conveyed material, and this effect has relation to the back pressure of the pneumatic conveying system In addition, the location of the driving nozzle and the convergent section angle still affect on the static pressure distribution in the convergent gas-solid injector

A Study on the Mechanism of New Conceptual Mixture Formation of Lean Diffusion Combustion in the Bump Combustion Chamber of a Diesel Engine

Abstract: Based on a self-made optical experimental facility and a CFD numerical analysis code, experimental investigations and numerical simulations of the mixing process of an impinging diesel fuel spray were carried out The computed results were in good agreement with the experimental ones obtained by planar laser-induced fluorescence (PLIF) method by comparison Both measured and computed results with a plane or an actual combustion chamber wall indicated that the wall-impingement jet would stripped off the wall and formed a secondary space jet when it met with the bump on the wall This resulted in the rises of space mixing volume and mixing rate of the wall-impingement jet with the surrounding air, and a "flash mixing" phenomenon appeared with rapid mixing of diesel fuel and air And the amount of fuel accumulated on the wall was reduced The computational results also showed that the bump on the chamber wall changed the flow field structure of in-cylinder gas motion, and that the counter-flow "two-vortex-structure" near the BUMP significantly enhanced entrainment of the secondary jet to the surrounding air and thus promoted the mixing of fuel with air And it was the key to the formation of lean mixture and lean diffusion combustion in the bump combustion chamber

An Electronic Control System Development of Reducing NO_x Emission in a Quasi-Homogeneous Lean Burn Gasoline Engine

Abstract: For the special requirements from NO_x adsorber-reduction catalyst, an electronic control system was developed. The system can set different A/F and time interval. In the rich oxygen burn condition, the system controls the engine to operate lean burn running.In the reduction condition, the system reduces the opening of throttle and advances ignition timing automatically in order to obtain constant output power. The system was experimented on Toyota 8A-FE16 valves EFI lean burn gasoline engine, and the results showed that the system meet the requirements of NO_x adsorber-reduction catalyst operation.

Three-Dimensional Simulation for Helical Intake Port of 4BTAA Diesel Engine

Abstract: The three-dimensional flow field in an un-simplified helical intake port was numerically simulated using CFD software for a practical engine.The calculation results of the port quality evaluation,flow coefficient and torque show good (agreement) with the flow test results.The simulated flow field provides a detailed insight into the processes governing air flow under port bench conditions.The developed port has been manufactured for the 4BTAA diesel engine which has come up to the Europe Ⅱ emission standard.The good agreement indicates that CFD simulation is reliable for use by the engine developer to provide directions for port design.

Experimental Research on Combustion of Petroleum Coke Mixed with Coal Powder

Abstract: On the basis of combustion characteristic of soft coal and petroleum coke and mixed-grinding characteristic, the combustion characteristic of petroleum coke mixed with coal powder was experimented on the equipment in which the quantity of burning-coke powder is 200 kg/h The results show that the pyrolysis characteristic of petroleum coke is similar to that of anthracite and its combustion characteristic to that of deficient coal In the storage-style and steel ball-grinding system, when the mixed quantity of petroleum coke is controlled within 30~0_0, the material does not adhibit the abrader and in the process of transportation, coal powder and coke powder are rarely separated Thus it takes on favorable grinding characteristic In the experimental condition, when petroleum coke burns with coal powder, the ignition characteristic rarely changes, but with the increase of the mixed quantity of coke, the mechanical loss because of incomplete-burning (it is mainly carbon-content of ash) increases, which directly influences the combustion efficiency

Influence of Injection Parameters on the Local Crank Angle Resolved Heat Flux on the Piston Wall

Abstract: This paper presents an investigation of the effects of different injection parameters and engine operational conditions on the combustion, local crank angle resolved temperature and heat flux in a single cylinder heavy duty DI diesel research engine with a displacement of 2.02 I. The investigated injection parameters and engine conditions were: Start of Injection (SOl), Needle Opening Pressure (NOP), injection duration, Exhaust Gas Recirculation (EGR), engine load and engine speed. The local crank angle resolved surface temperature was measured at nine different positions along the spray axis and between two sprays at the piston wall. The instantaneous heat flux was calculated from the measured temperature traces by solving the one-dimensional unsteady heat conduction equation.

Model and Experiment for Three-Dimensional Temperature Measurement Based on Flame Image

Abstract: The three-dimensional temperature measurement is very important for the operation and the control in the power industry This paper presents a method for measuring the three-dimensional temperature based on the flame images, making use of the optical model of the camera and the radiative transfer equation The algebraic reconstruction technique (ART) is used to solve the equation sets The experimental results show the good perspective in the further research

Flamelet Modeling of Turbulent Non-Premixed Flame Based on Detailed Chemical Reaction Mechanisms

Abstract: The stretched laminar diffusion flamelet structures under different strain rates were numerically calculated based on a set of detailed chemical reaction mechanism GRI-Mech 3.0 for methane oxidation. From the calculation, flamelet library consisting of a series of stretched laminar flamelet structures is generated.These laminar flamelet structures were compared with the piloted turbulent diffusion flame (Flame D)of the mean turbulent flame structures of Sandia National Laboratory. It is found that the mean flame structures of the considered turbulent flame at different locations almost all fall into the area covered by the series of laminar flamelet structures, which indicates the validity of the flamelet model. Then, by using the flamelet model, numerical simulations of Flame D were performed and the modeling accuracy and depth of flamelet model are investigated.

Resistance Properties for Horizontal Pipe in Dense Phase Pneumatic Conveying of Pulverized Coal Under High Pressures

Abstract: This paper investigated the pressure drops for horizontal pipes in dense-phase pneumatic conveying of pulverized coal under high pressures through experiments and theoretic calculation. Based on Barth's pneumatic conveying theory, Stegmaier's empirical equation of the additional pressure drop coefficient is introduced and applied in the calculation.It is found that the unit pressure drops in the stabilized conveying section of a horizontal pipe increase despite apparent velocity of the conveying air is decreased. Distinctly, a key factor affecting the pressure drops for horizontal pipe is the concentration of conveyed pulverized coal, though the pressure drops caused by the conveying air can't be ignored under high pressures.With the comparison between the calculated results and the experimental data, it is shown that the calculated results agreed fairly well with the experimental data. This illuminated that the additional pressure drops method based on Barth's pneumatic conveying theory has a better adjustability to the prediction of the resistance characteristics for the dense phase pneumatic conveying of pulverized coal under higher pressure.

Tumble Motion in the Cylinder of the 4-Valve Spark Ignition Engines

Abstract: The prediction of the tumble speed in the cylinder of a spark ignition engine is discussed.Based on the experiment results from the steady state flow rig and the flow field measurement in the cylinder of a motored engine by laser doppler anemometer (LDA) system,a model for the physical process of the tumble formation is proposed.That is:during the early stage of induction and before the piston reaches a critical crank angle,the tumble can′t be formed effectively.This critical piston position of crank angle should correspond to the time when the in-cylinder tumble has to be distorted and destroyed by the upward moving piston during the late stage of the compression stroke.A model for predicting the tumble speed is derived and verified by the steady flow rig and the in-cylinder flow measurement results by a LDA system.

Combustion and Emission Characteristics of a DI Diesel Engine Fueled by Diesel-Methanol Blends

Abstract: The economy and power performances, combustion and emission characteristics of diesel-methanol blended fuels with different blend proportions (0, 15%, 20%) in a DI diesel engine have been studied. The various characteristics of blended fuels are recorded and compared with neat diesel fuel in order to study the influence of different quantities of methanol. The tests were carried out using the method of equal excess air coefficient. The results show that under the conditions of same engine speed and equal excess air coefficient,the brake thermal efficiency of diesel-methanol blended fuels is higher than that of neat diesel fuel due to the improvement of combustion caused by the properties of diesel-methanol blended fuels . Smoke emissions decrease dramatically and CO emissions reduce too with the increase of methanol content. NOx emissions, however, increase and reach the maximum value at a 10%～15% content of methanol.

Experimental Investigation on the Combustion Characteristics of Using Diesohol for the Turbocharged Diesel Engine with Intercooler

Abstract: Without any change of the configuration for the turbocharged diesel engine with intercooler ,the diesel and three kinds of diesohol fuels (E10,E15 and E20) are analyzed for combustion characteristics at four kinds of engine modes .The results show that the parameters of the combustion characteristics such as periods of ignition delay , maximum value of heat release and combustion duration are changed as the ethanol volume concentration of diesohol fuel is changed . The advantages of ethanol fuel has a great effect on the combustion process at the high load of high speed, and the disadvantages of ethanol fuel play important roles at the low load of low speed.

Effect of Hydrogen and Vapor on Laminar Flame Speeds of Methane/Air Mixtures

Abstract: Hydrogen can improve the combustion of fuel with an addition of water. To obtain a better view on the effect of hydrogen and vapor on flame propagation, by using CHEMKIN-Ⅱ software, laminar flame speeds of methane/air mixtures with and without hydrogen and vapor were calculated and analyzed. The results show that hydrogen can increase flame speed, and even more when the initial temperature becomes higher; the addition of vapor will decrease the laminar flame speeds of methane/air mixtures, and vapor will also weaken the ability of hydrogen in increasing flame speed.

Modeling Atomization and Evaporation Processes of Hollow-Cone Fuel Sprays for GDI Engine

Abstract: A sheet spray model is proposed to simulate the atomization processes of pressure-swirl hollow-cone fuel sprays which are widely used in gasoline direct injection (GDI) engines these days Breakup of the liquid sheets is modeled by using the surface wave breakup theory Improved Spalding-type evaporation and drop drag models are used to calculate drop evaporation and drop dynamic drag, and an initial spray slug module is introduced into calculation All models are implemented in a multidimensional computer code KIVA3 and used to study hollow-cone fuel sprays for different injection conditions in a constant pressure chamber Detailed comparisons of computed and experimental spray characteristics such as spray contour structures, spray tip penetrations, drop sizes(SMD) are made A single droplet evaporation processes are also simulated The computational result from these models coincides with the experimental one very well

Numerical Analysis of Reduction in Mixture Concentration and Soot Emissions in a Diesel Engine by Swirl

Abstract: In order to reveal the effects of swirl on mixture formation and soot emissions in a diesel engine, numerical simulations of mixture concentration, velocity vector field, fuel droplet spatial distribution and spray characteristics of a diesel spray under different swirl ratios in the combustion chamber of an automotive diesel engine were performed, using a CFD three-dimensional numerical analysis code and experimentally-validated models of spray and turbulence. The simulated results indicate that, with the increase of swirl ratios from 0 to 5.0, the fuel-air equivalence ratios of the local richest area decrease gradually in the vertical plane which passes through an injector hole axis,while they first decrease and then increase in the plane which passes through the same injector hole axis and is perpendicular to the vertical one. It is essential to choose a correct section. The plane which passes through the injector hole axis and is perpendicular to the vertical one is selected for the purpose of exactly assessing the effects of swirl on mixture concentration and soot formation region distribution. Attention nust be paid to both the swirl in the horizontal plane which is perpendicular to the cylinder axis and the turbulence or tumble in the vertical plane which passes through the cylinder axis when air flow in the combustion chamber is organized. If the swirl ratio is too high, and the turbulence or tumble in the vertical plane is too weak, the entrainment of the spray jet to the air at the bottom of the combustion chamber will be impaired, and the air utilization ratio will be reduced. With the swirl ratio increased, the jet camber along the swirl direction becomes heavy, jets of different injector holes interfere with each other, and a local richest mixture region appears in the vicinity of the cylinder center. This is not beneficial to reduction in soot emissions. So it is imperative that swirl should be reasonably matched with a specific combustion chamber geometry and fuel injection system.

Gasification Reactivity of Petroleum Coke with Steam and Carbon Dioxide

Abstract: Gasification reactivity of three petroleum cokes from different plants was investigated using thermobalance and the effects of agent,temperature and steam partial pressure to gasification were studied.The experimental results show that petroleum coke has good gasification reactivity with steam,but poor with carbon dioxide.And at the same experimental condition,the reaction rate of C-H_2O is more than ten times higher than that of C-CO_2.With 60% steam,the increase of the average reaction rate is linear to temperature,1 time per 50 ℃.At 1 000 ℃,the effect of steam partial pressure on the average reaction rate is not well-proportioned.The reaction rate show a maximum value at some carbon conversion,which is affected by agent instead of by temperature and steam partial pressure.And the instantaneous reactivity grows continuously during the gasification of petroleum coke.Based on experimental data,a correlation equation for reaction rate to temperature,steam partial pressure and carbon conversion in steam was derived.

Simulation of Turbulent Non-Premixed Flames Influenced by Buoyancy

Abstract: The buoyancy-modified k-e model and the eddy-dissipation-concept (EDC) turbulent combustion model are employed to numerically simulate the methane turbulent non-premixed flames with low fuel/air initial momentum in a swirl combustor. Two cases of the calculated results of time-averaged gas velocities, temperature and species concentrations, root-mean-square of fluctuating gas velocity and other quantities are obtained. They are compared with the measured test data.General agreement between them is achieved. At the same time, the calculated results are also compared with those obtained by the standard k-e model.With these comparisons, the influence of buoyancy on the turbulent non-premixed flame with low initial momentum is delineated.

Progress in Numerical Simulation of Turbulent Reacting Rate of NO Formation in Turbulent Combustion

Abstract: As a method of optimum design in reducing pollutant emission of combustion,the numerical simulation of NO formation in turbulent combustion is playing more and more important role.One of the key problems is to establish reasonable and economic mathematical model.Based on resent research results reported by different researchers, the chemical reacting mechanism and current status of mathematical model of NO formation in turbulent combustion is reviewed from thermal NO and fuel NO, and computational results are analyzed. The detailed model equations and algebraic formulas of NO formulation are also given for later reference.

Experimental Study on the Effects of EGR on HCCI Combustion Process and Emissions of DME/CNG Dual Fuel

Abstract: Experimental study of effects of cooled exhaust gas recirculation(EGR) on homogenous charge compression ignition(HCCI) combustion process and emission characteristics was carried out on a single-cylinder direct injection diesel engine fueled with dimethyl ether(DME)/compressed natural gas(CNG) dual fuel. The results indicate that with the increased EGR rate, the ignition time delayed, the heat release rate decreased, and the combustion duration extended. While the proportion of DME increased, the ignition time advanced, the peak heat release rate increased, and the combustion duration decreased. Although the proportions of DME of misfire and knock both increased with EGR rate increased, the proportion range of DME between misfire and knocking was enlarged. So EGR can extend the operating range of HCCI engine. For each EGR rate, there is a proportion range of DME in which higher thermal efficiency can be obtained. HC and CO (emissions) both ascended with the increased EGR rate, and decreased with the proportion of DME increased. NO_x emission remained at a very low level except that knocking occurred. The control of the proportion of DME and EGR rate is the key technique to control the combustion process, performance and emissions of HCCI engine fueled with DME/CNG dual fuel.