Laser-induced incandescence (LII) is a promising new diagnostic for measuring the volume fraction of elemental carbon in engine exhaust. The technique is considerably more precise and sensitive than conventional measurement procedures, and can be applied either with or without dilution. However, LII has been slow to gain acceptance because of presumed complexity of use and high initial cost. In this paper we demonstrate a prototype LII system that offers turn-key operation and long-term cost that is highly competitive with other techniques because of very low labor costs. The LII system ran unattended for 7.5 weeks, logging 1078 heavy-duty diesel engine tests during 24/7 operation of a dilution tunnel facility. Among the tests logged were 363 FTP steady-state mode tests and 250 FTP transient tests for which gravimetric measurements of total particulate matter (PM) were obtained. Of these tests, removal of the filter-based volatile matter using supercritical fluid extraction was performed on 142 and 147 of the tests, respectively. The correlation between the time-integrated LII signals and the dry gravimetric measurements for the steady-state mode tests is used to calibrate the LII measurements in mass units. This calibration is then used to evaluate the correlation between the LII and dry gravimetric measurements for the transient tests. Finally, time-resolved LII measurements for the steady-state mode tests are presented to illustrate three forms of unsteadiness that would seem undesirable.
Particulate matter (PM) emission exhausted from diesel engine should be reduced to keep the clean air environment. PM emission was considered that it consisted of coarse and aggregate particles, and nuclei-mode particles of which diameter was less than 50nm. However the detail characteristics about these particles of the PM were still unknown and they were needed for more physically accurate measurement and more effective reduction of exhaust PM emission. In this study, the size distributions of solid particles in PM emission were reported. PMs in the tail-pipe emission were sampled from three type diesel engines. Sampled PM was chemically treated to separate the solid carbon fraction from other fractions such as soluble organic fraction (SOF). The electron microscopic and optical-manual size measurement procedures were used to determine the size distribution of primary particles those were formed through coagulation process from nuclei-mode particles and consisted in aggregate particles. The centrifugal sedimentation method was applied to measure the Stokes diameter of dry-soot. Aerodynamic diameters of nano and aggregate particles were measured with scanning mobility particle sizer (SMPS). The peak aggregate diameters detected by SMPS were fallen in the same size regime as the Stokes diameter of dry-soot. Both of primary and Stokes diameters of dry-soot decreased with increases of engine speed and excess air ratio. Also, the effects of fuel properties and engine types on primary and aggregate particle diameters were discussed.
Heavy-duty diesel engines have adopted numerous technologies for clean emissions and low fuel consumption. Some are direct fuel injection combined with high injection pressure and adequate in-cylinder air motion, turbo-intercooler systems, and strong steel pistons. Using these technologies, diesel engines have achieved an extremely low CO2 emission as a prime mover. However, heavy-duty diesel engines with even lower NOx and PM emission levels are anticipated. This study achieved high-boost and lean diesel combustion using a single cylinder engine that provides good engine performance and clean exhaust emission. The experiment was done under conditions of intake air quantity up to five times that of a naturally aspirated (NA) engine and 200MPa injection pressure. The adopted pressure booster is an external supercharger that can control intake air temperature. In this engine, the maximum cylinder pressure was increased and new technologies were adopted, including a monotherm piston for endurance of Pmax =30MPa. Moreover, every engine part is newly designed. As the boost pressure increases, the rate of heat release resembles the injection rate and becomes sharper. The combustion and brake thermal efficiency are improved. This high boost and lean diesel combustion creates little smoke; ISCO and ISTHC without the ISNOx increase. It also yields good thermal efficiency.
A parametric study of automotive diesel combustion in a low-temperature, late-injection combustion regime is described. Injection pressure was varied from 600-1200 bar, swirl ratio from 1.44-7.12, and intake temperature from 30-110°C. In-cylinder pressure records, heat release analysis, spatially-integrated soot luminosity, and images of the spatial distribution of combustion luminosity are employed to study the influence of these parameters on the combustion and soot formation/oxidation processes. Load points of 3 and 6 bar gross IMEP at 1500RPM and an O2 concentration of 0.15 are considered. Increased injection pressure is found to enhance the early mixture formation process, resulting in increased peak apparent heat release, generally decreased soot luminosity, and modestly increased light-load soot oxidation rates. At lower injection pressures, more soot luminosity is observed from the squish volume. In contrast, variation of flow swirl impacts the latter half of the combustion process, and affects the initial combustion only slightly. An optimum Ricardo swirl ratio of roughly 3 is found for best moderate-load efficiency and soot oxidation. A marked reduction in early heat release rates and peak soot luminosity is observed with decreased intake temperature. Nevertheless, significant in-cylinder soot luminosity is observed even at the lowest intake temperatures, indicating that complete suppression of in-cylinder soot formation is difficult with the fuel injection and combustion system characteristics employed.
In diesel combustion it is commonly known that NOx emissions increase when the fuel injection velocity increases. On the other hand, increased fuel velocity reduces NOx in steady jet flames due to a decreased residence time in the flame region. To answer this contradiction, the authors have made variety of experiment and numerical simulation. The results indicated that the large NOx formation in diesel engine is due to the weak mixing intensity in the spray tip region, where the flow and turbulence structure is quite different from the continuous jet flames. The fact indicates that there is a possibility of reducing NOx from diesel engines by enhancing mixing intensity at the spray tip region to the level of continuous jet flame. As one of the attempts to make the velocity profile of diesel spray similar to the steady jet, an inert gas was injected prior to the fuel injection in a model apparatus in atmospheric pressure condition. The result showed that the flame apparently became less luminous by the pre-injection of nitrogen, and the NOx emission index was two-thirds of the non pre-injection case. Numerical simulation also showed the effect of pre-injection for the reduction of NOx. The paper presents the experimental and numerical simulation results together with photographic analysis of enhanced mixing of spray tip region when water was injected as the pre-injection for increasing mixing.
In this paper, three soot models previously proposed for diesel combustion and soot formation studies are briefly reviewed and compared. The three models are (1) two-step empirical soot model, (2) eight-step phenomenological soot model, and (3) complex-chemistry coupled phenomenological soot model. All three models have been implemented into the KIVA-3V simulation code. For comparison, a heavy-duty DI diesel engine case with fuel injection typical of standard DI diesel operating conditions was studied. Flame structures of a single diesel spray predicted using these three models were compared, and the results offer our perspective on the application of these three models to soot modeling in diesel engines.
Visualization plays an effective role in the establishment of a new combustion concept by helping to find the optimal results quickly among many different parameters and contributing to a shorter development period. Laser-induced fluorescence, Raman scattering and infrared absorption were used to measure the air/fuel ratio quantitatively in a third-generation direct-injection gasoline (DIG) engine with a spray-guided mixture formation process and comparisons were made with the mixture formation concepts of the first- and second-generation DIG engines. The optimum combination of fuel spray, gas flow and combustion chamber configuration was found to be different for the three generations of DIG engines. The characteristics of the stable combustion region for obtaining higher thermal efficiency and cleaner exhaust emissions differed among the three mixture formation concepts.
The effect of split injection on the mixture characteristics of DISI (Direct Injection Spark Ignition) engines was investigated firstly by the Laser Absorption Scattering (LAS) technique. Through splitting the fuel injection process, two possible benefits were found: 1) High density liquid droplets piling up at the leading edge of the spray can be circumvented, subsequently the reduction of the spray tip penetration; 2) The quantity of “over lean” (φv<0.7, φv: equivalence ratio of vapor) mixture in the spray can be significantly reduced. These are believed to contribute to the reduction of the engine-out smoke and HC emissions. In order to clarify the mechanism behind the effect of the split injection, the spray-induced ambient air motion was investigated by the LIF-PIV technique. The strong ambient air entrainment into the tail region of the spray and a counter-vortex structure were found in both the single and split injections. In the case of the single injection, the spray develops in extending its length, subsequently a larger volume results and thus it is diluted to “over lean” by the ambient air entrainment. In contrast, in the case of split injection, the second spray is injected into the tail region of the first spray and its evaporation is promoted by the ambient air motion induced by the first spray. Hence the replenishment of the liquid fuel into the leading edge of the first spray is reduced. As a consequence, the high density liquid droplets piling up at the leading edge is avoided. Furthermore, a more compact spray results so that the ambient air motion plays a positive role on evaporating the spray into “more combustible” (0.7<φv<1.3). This is especially true in the tail region of the spray and the region where the counter-vortex motion is occurring.
Knock phenomenon in SI engines is regarded as an auto-ignition of unburned end-gas, and it has been widely examined by using rapid compression machines (RCM), shock-tubes or test engines. Recent researches point out the importance of the low temperature chemical reaction and the negative temperature coefficient (NTC). To investigate the effects, analyses of instantaneous local gas temperature, flow visualization and gaseous pressure were conducted in this study. As measurements using real engines are too difficult to analyze, the authors aimed to make measurements using a constant volume vessel under knock conditions where propagating flame exists during the induction time of auto-ignition. Adopting the two-wire thermocouple method enabled us to measure the instantaneous local gas temperature until the moment when the flame front passes by. High-speed images inside the unburned region were also recorded simultaneously using an endoscope. As a result, it was found that when knock occurs, the auto-ignition initiation time seems slightly early compared to the results without knock. This causes a higher volume ratio of unburned mixture and existence of many hot spots and stochastically leads to an initiation of knock.
This paper presents simultaneous laser based measurements of formaldehyde and OH-radical distributions in a 0.5 liter optical HCCI engine with direct injection. Formaldehyde is formed as an intermediate species when combusting hydrocarbons. The formation occurs through low temperature reactions in an early phase of the combustion process. Later in the process formaldehyde is being consumed. Formaldehyde is, therefore, used as indicator of the first stage of combustion and a marker of zones with low-temperature reactions. The OH radical is formed as an intermediate during the high temperature reactions, and is used as a marker of zones where the combustion is ongoing. The purpose of the investigation was to study how the combustion process is affected by the change in homogeneity that arises from early and late injection, respectively. The measurement technique used was planar laser-induced fluorescence where formaldehyde was excited at 355nm and OH at 283nm.
By employing a direct-injection diesel engine equipped with a common-rail type of injection system, by adding formaldehyde (CH2O) to the intake air, and by changing the fuel-injection timing, the compression ratio and the intake-air temperature, a mechanism for CH2O as a fuel additive to affect auto-ignition was discussed. Unlike an HCCI type of engine, the diesel engine can expose an air-fuel mixture only to a limited range of the in-cylinder temperature before the ignition, and can separate low- and high-temperature parts of the mechanism. When low-temperature oxidation starts at a temperature above 900K, there are cases that the CH2O advances the ignition timing. Below 900K, to the contrary, it always retards the timing. It is because, above 900K, a part of the CH2O changes into CO together with H2O2 as an ignition promoter. Below 900K, on the other hand, the CH2O itself acts as an OH radical scavenger against cool-flame reaction, from the beginning of low-temperature oxidation. Then, the engine was modified for its extraordinary function as a gasoline-knocking generator, in order that an effect of CH2O on knocking could be discussed. The CH2O retards the onset of auto-ignition of an end gas. Judging from a large degree of the retardation, the ignition is probably triggered below 900K.
For numerically predicting the combustion processes in homogeneous charge compression ignition (HCCI) engines, practical chemical kinetic models have been explored. A genetic algorithm (GA) has been applied to the optimization of the rate constants in detailed chemical kinetic models, and a detailed kinetic model (592 reactions) for gasoline reference fuels with arbitrary octane number between 60 and 100 has been obtained from the detailed reaction schemes for iso-octane and n-heptane proposed by Golovitchev. The ignition timing in a gasoline HCCI engine has been predicted reasonably well by zero-dimensional simulation using the CHEMKIN code with this detailed kinetic model. An original reduced reaction scheme (45 reactions) for dimethyl ether (DME) has been derived from Curran’s detailed scheme, and the combustion process in a DME HCCI engine has been predicted reasonably well in a practical computation time by three-dimensional simulation using the authors’ GTT code, which has been linked to the CHEMKIN subroutines with the proposed reaction scheme and also has adopted a modified eddy dissipation combustion model.
In this research, the influence on natural gas combustion of H2 and CO was investigated by numerical calculations with elementary reactions. The investigation was carried out using the following procedures: 1. To research basic oxidation characteristics of CH4/H2/CO mixed fuel, parametric calculations for initial temperature were carried out. 2. For investigation of the effect of H2 and CO on CH4 combustion, the calculations with H2 and CO initial mole fraction variation was carried out. As a result, it was clarified that the oxidation temperature of CO was higher than that of CH4 and H2, the increase of H2 initial fraction has the effect to advance CH4 ignition timing, and increase of the CO fraction, under the condition that only CO was added, has the opposite effect of H2 addition.
The interfacial phenomena of magnetic fluids subjected to a normal magnetic field are studied experimentally. To begin with, the effect of the shape and the dimension of the transparent containers on the interfacial phenomena is examined for two kinds of magnetic fluids, ferricolloid W-40 and ferricolloid HC-50. The cross-sectional shape of the container is made to be circular, square and hexagon. The dimension of the container is set to 55mm, 70mm and 85mm. The critical magnetic induction values Bc calculated on the basis of the present expriment are compared with those obtained from the theoretical analysis by Cowley & Rosensweig, where at these values of Bc the interfacial phenomena begin to be built up. Finally, on the hysteresis in generating the transition between three kinds of deformation modes on the interface, the present observation results are compared with those obtained from the analysis by A. Gailitis. It was concluded that the shape and the dimension of the containers had no effect on the interfacial phenomena, and the critical value Bc caluculated by measured data agreed with that of the theoretical analysis. And also, the mechanism of the hysteresis was clarified mathematically in the manner of the analysis by Gailits.
The differences in turbulence statistics between compressible and incompressible turbulent channel flows are investigated at low-Reynolds numbers using semi-local scaling. DNS of the compressible turbulent channel flow between isothermal walls at low-Mach numbers and DNS of the incompressible flow are performed. It is revealed that the reduction in the pressure-strain correlation term is due to the reductions in RMS velocity-derivative fluctuations and in the absolute correlations between pressure and velocity-derivative fluctuations in the compressible turbulent channel flow at low-Mach and Reynolds numbers.
This study attempts to prepare Ni nano-magnetic fluid using the developed submerged arc nanoparticle synthesis system (SANSS). Using optimized process parameters, Ni nanoparticles having average diameter of 10 nm were be fabricated, and these Ni nanoparticles prepared by the SANSS has strong magnetic features. When the surfactant PVP-K30 is added to the prepared nanofluid, molecules of the surfactant adhere to the surface of the nanoparticles, enabling the nanoparticles to remain in steady suspension and good dispersion. The nanofluid thus obtained was magnetic and had good flow property. In contrast, Ni particles in nanofluid without surfactant added cannot maintain good dispersion and there is no interdependent motion between the particles and the fluid. Traditional magnetic fluids containing non-nanoscaled particles are non-Newtonian fluids with viscosity higher than that of pure fluids without particles, whereas magnetic fluids with well dispersed nanoparticles more closely resemble Newtonian fluids. The Ni nanoparticles fabricated by the SANSS has no residual magnetization or coercive force, thus showing superparamagnetism. Under the magnetic field effect, Ni nanoparticles will move in the direction of the magnetic field. Nanoparticles can resume steady suspension in the carrying liquid when the magnetic field is removed.
Viscous fingering in non-Newtonian fluids in a rectangular Hele-Shaw cell was investigated. The cell was filled with a 0.5 or 1.0wt% aqueous solution of carboxymethylcellulose (CMC), a shear-thinning fluid. Air was injected into the cell and the growth of viscous fingers was observed. The velocity of finger tip was characterized by the pressure gradient. A modified Darcy law was able to describe the characteristics of the tip velocity that the growth rate of the tip velocity increased with increasing pressure gradient in the CMC solutions. The prediction of tip velocity with the modified Darcy law indicated that an effective pressure gradient near the tip was larger than the average pressure gradient between the finger tip and the cell exit and that the rate of increase depended on the cell gap width.
The effect of angle and length of the inlet guide vane on the performance of the cross-flow fan was examined. By installing guide vane of one sheet in tongue division side in the suction region, the performance of the cross-flow fan becomes more high pressure and high efficient than the case without the guide vane. The prerotation of the inlet flow which is counter directional with the rotation of the rotor is generated by the guide vane. In the high flow region, the high pressure and high efficiency are obtained since the suction cascade work increases by the prerotation of the flow, and since the leading edge separation of the suction cascade is more avoided to high flow. Moreover, in the low flow region, it is possible to suppress the circulating flow in scroll side in the rotor suction inlet. Therefore, the high efficiency is obtained in the low power compared to the result without the guide vane.
A Micro-Electrohydrodynamic (EHD) pump is tested experimentally. The EHD pump examined in this paper is fabricated with two cylindrical copper electrodes of the inner diameter 3mm. The distance between electrodes was changed from 0.6mm to 1.2mm. In order to simplify the characterization of the pressure capacity of the EHD pump, the uniform electric field added in the gap between the cylindrical electrodes using aluminum disc electrodes (40mm outer diameter). The static pressure and the mean velocity in a closed fluidic circuit were measured with Dibutyl sebacate as working fluid. The liquid has a dielectric constant, ε /ε0=4.8 and a low electric conductivity, σ=4.7× 10-10 (S/m). The static pressure results are compared with the theoretical results. The theoretical model is based on the unipolar conduction which generates the space charge in the liquid. In this model, the Coulomb force can contribute to the EHD motion. The static pressure results show a linear relationship with the square of the electric filed. This linear relationship supports the assumption that the unipolar conduction generates the pressure driving force. The estimation of the EHD pump efficiency based on the theoretical model is 18% with the electrode gap of 1.2mm between the electrodes and 5% with the one of 0.6mm.
The acoustic scattering by a submerged spherical rigid obstacle near an acoustically hard concave corner, which is insonified by plane waves at arbitrary angles of incidence, is studied. The formulation utilizes the appropriate wave-harmonic field expansions and the classical method of images in combination with the translational addition theorems for spherical wave functions to develop a closed-form solution in form of infinite series. The analytical results are illustrated by numerical examples where the spherical object is located near the rigid boundary of a fluid-filled quarterspace and is insonified by plane waves at oblique angles of incidence. Subsequently, the basic acoustic field quantities such as the form function amplitude, the scattered far-field pressure, and the scattered acoustic intensity are evaluated for representative values of the parameters characterizing the system. The limiting case involving a spherical object submerged in an acoustic halfspace is considered and good agreement with a well-known solution is established.
The purpose of this investigation is to explore the possibility of using artificial mechanical means for excitation of shear layers with application in swirling jet mixing enhancement. For this purpose, a novel mechanical device for excitation of the helical instabilities of swirling jets is designed, fabricated, and used in these experiments. The device consists of a rotating cylinder with internal lobes of small height to induce small perturbations. The number of lobes and the direction of rotation can be varied to induce helical waves at azimuthal wave numbers of m=+0, ±1, ±2, ±3, and ±4. The m=+0 denotes the plane-wave excitation, m=±1 identifies the first helical mode with one lobe, m=±2 is the second helical wave with two lobes and so on. The positive and negative signs imply helical perturbation waves that spin in the same or opposite direction to the swirl direction, respectively. Swirl is induced in the airflow by a 45° vane-type swirl generator. Time mean axial velocity and turbulence measurements of the swirling jet, with and without excitation, are measured by hot-wire anemometer. The results are compared with the baseline (plane-wave excitation) at various helical modes. The acquired data is presented in 3D mesh plots and 2D contour plots. It is observed that new device is effective in excitation of the helical instability waves and in mixing enhancement of the swirling jet.
This paper describes the optimization of blade sweep in a transonic axial compressor rotor. The shape optimization has been performed using response surface method and the three-dimensional Navier-Stokes analysis. Two shape variables of the rotor blade, which are used to define the rotor sweep, are introduced to increase the adiabatic efficiency of the axial compressor. Blade sweep has been used in the transonic compressor design with the intent of reducing shock losses. Throughout the optimization, optimal shape having a backward sweep is obtained. Adiabatic efficiency, which is the objective function of the present optimization, is successfully increased by 1.25 percent. Separation line due to the interference between a shock and surface boundary layer on the blade suction surface is moved downstream for the optimized blade compared to the reference one. It is noted that the increase in adiabatic efficiency for the optimized blade is caused by moving the separation line to the downstream on the blade suction surface.
Monte Carlo simulations have been carried out for the clathrate hydrate of CO2 hydrates. In this study, we investigate the structure and statistical thermodynamic property of CO2 hydrates at temperatures ranging from 150 to 288[K] and at a pressure of up to 50[MPa] under constant temperature and pressure conditions. We have found that the hydrate structure can be maintained at approximately 283[K]. The thermodynamic property of density reflects the cage occupancy of the guest molecules and enthalpy increases with increasing temperature. Through our MC simulations, we also clarified hydrate and nonhydrate dividing lines by comparing them with other researchers’ experimental results.
In the present study, new experimental data on the heat transfer characteristics and the performance of a spirally coiled heat exchanger under sensible cooling conditions is presented. The spiral-coil heat exchanger consists of a steel shell and a spirally coiled tube unit. The spiral-coil unit consists of six layers of concentric spirally coiled tubes. Each tube is fabricated by bending a 9.27mm diameter straight copper tube into a spiral-coil of five turns. The innermost and outermost diameters of each spiral-coil are 67.7 and 227.6mm, respectively. Air and water are used as working fluids in shell side and tube side, respectively. A mathematical model based on the conservation of energy is developed to determine the heat transfer characteristics. There is a reasonable agreement between the results obtained from the experiment and those obtained from the model and a good agreement for the high air mass flow rate region. The results obtained from the parametric study are also discussed.
This study investigates the behavior of blast wave by employing the finite volume method to solve the associated three-dimensional, time-dependent, inviscous flow Euler equations. The numerical results are shown to be in good agreement with the experimental results obtained from shock tube flow studies. The results also identify the complex phenomena of flow structures, pressure distributions, and different types of reflected waves for closed-ended and open-ended bomb shelters.
The flow field in swirl-type tubular flame burners was measured using a Particle Imaging Velocimetry (PIV) system with an easily controlled kerosene droplet tracer generator. Through characterization of the flow field in two burners with different swirl numbers, it was found that the flow is an axisymmetric vortex flow. The tangential component of the velocity is zero at the tube center, and increases proportionally with radius at first, and then falls slowly in a radial direction. The gradient of the tangential component near the vortex center depends significantly on the swirl number and the flow rate. The vortex center oscillates around the tube center in a roughly circular area, and this precession is significantly sensitive to the swirl number. The radius of the precession area shrinks as the swirl number increases. The radial distributions of the axial velocity take a plateau-shape for the weak swirl burner (swirl number S=0.21), whereas they take an “M” shape for the strong swirl burner (S=0.78) with reverse flow in the vicinity of the burner axis. The occurrence of the axial reverse flow is dominated by the swirl number, and is affected by the flow rate as well. Finally, a comparison was made between the swirl numbers calculated with the measured velocity profiles in a cross section and those calculated from the input angular momentum.
The effect of oxygen concentration on the soot deposition process from a diffusion flame to a solid wall was investigated in a microgravity environment to attain in-situ observations of the process. An ethylene (C2H4) diffusion flame was formed around a cylindrical rod burner in oxygen concentrations of O2=21, 35, and 50%with a surrounding air and wall temperatures of 300K. Laser extinction was adopted to determine the soot volume fraction distribution between the flame and burner wall. The experimental results show that the soot particle distribution region moves closer to the surface of the wall and that more deposition occurs with increasing surrounding oxygen concentrations. The experiments determined the trace of the maximum soot concentration position, defined as the “soot line”, and it was comparable to that established with numerical calculations. A numerical simulation was also performed to understand the motion of soot particles in the flame and the characteristics of the soot deposition to the wall. The results successfully predicted the differences in the motion of soot particles by different oxygen concentrations near the burner surface and are in good agreement with observed soot behavior, ie the “soot line”, in microgravity. A comparison of the calculations and experimental results led to the conclusion that a consideration of the thermophoretic effect is essential to understand the soot deposition on walls.
Laminar counterflow nonpremixed flames with local extinction caused by nonuniform inflows are numerically investigated in two-dimensions in a system governed by Lewis numbers of unity and assuming a single-step, irreversible, finite-rate reaction. A numerical method based on the SIMPLE algorithm is used. Edge flame structures are investigated through the introduction of a new progress variable defined as the normalized integral of the mass fraction of a product in the mixture fraction Z space and which expresses the progress of the chemical reaction. Calculation results reveal that the edge flame structure can be classified into three regions; fully burning flame, weakened flame with a low reaction rate, and a non-reacting preheat region. Under these conditions, and in terms of the energy balance, the edge flame structure is dependent on the Z-directional heat diffusion transport, heat consumption (given by the progress variable), and heat production by chemical reaction. It is found that each type of flame structure can be well characterized by three parameters; the mixture fraction, the stoichiometric scalar dissipation rate, and the progress variable. These three parameters are identified as important factors affecting the edge flame structure of nonpremixed flames with local extinction.
This paper describes the atomization performance of a newly designed atomizer with internal impinging mechanisms inside the atomizer. The spray drop size distribution was measured by a Malvern RT-Sizer. Results show that the Sauter mean diameter below 10µm has been achieved with GLR of 0.14. The minimum mean drop size can be lowered to 4.0µm under a test condition of the liquid pressure and gas pressure of 2.5bar and 3.5bar, respectively. This test suggests that extra fine atomization on the liquid phase can be achieved under low pressure conditions using this particular atomizer. Such performance cannot be easily achieved with the conventional nozzle design. Results also show that better atomization performance can be achieved by increasing the internal impinging angle and the orifice diameter. An empirical formula of SMD, in terms of operating conditions and nozzle length scale is also presented in this paper.
The thermal response of electronic assemblies during forced convection-infrared reflow soldering is studied numerically. Soldering for attaching electronic components to printed circuit boards is performed in a process oven that is equipped with porous panel heaters, through which air is injected in order to dampen temperature fluctuations in the oven. Forced convection-infrared reflow soldering process with air injection is simulated using a two-dimensional numerical model. The multimode heat transfer within the reflow oven as well as within the electronic assembly is simulated. Parametric study is also performed to study the effects of various conditions such as conveyor speed, air injection velocity, and electronic assembly emissivity on the thermal response of electronic assemblies. The results of this study can be used in the process oven design and selecting the oven operating conditions to ensure proper solder melting and solidification.
The research was conducted to evaluate conversion characteristics of three-way catalyst(TWC) with a double-layer washcoat to improve the light-off temperature and the thermal durability. The evaluations considered factors such as the PM loading ratio and loading quantity of the tri-metal catalyst for Rh-Pd-Pt configuration, the washcoat composition, and the cell density. The higher cell density of TWC can improve the light-off temperature because of the lower heat capacity of the substrate and the increase of the surface area. Loading quantity and ratio of precious metals has appropriate value to light-off performance in each cell density of substrate. A proper selection of the bottom layer washcoat loaded with Pd can promote thermal stability and the upper layer washcoat with an excellent ability of oxygen storage can improve the light-off performance and the durability of the double-layer TWC. The best TWC with double-layer was 9Hy(0.6x11x3) with 140cell/cm2 substrate.