Showing papers in "Jsme International Journal Series B-fluids and Thermal Engineering in 2003"
TL;DR: In this article, the authors investigated the characteristics of autoignition and combustion of natural gas in a 4-stroke HCCI engine and also clarified the influence of n-butane on auto-ignition.
Abstract: Homogeneous charge compression ignition (HCCI) is regarded as the next generation combustion regime in terms of high thermal efficiency and low emissions. It is difficult to control autoignition timing and combustion duration because they are controlled primarily by the chemical kinetics of fuel-air mixture. In this study, it was investigated the characteristics of autoignition and combustion of natural gas in a 4 stroke HCCI engine. And also, to clarify the influence of n-butane on autoignition and combustion of natural gas, it was changed the blend ratio of n-butane from 0mol% to 10mol% in methane/n-butane/air mixtures. Autoignition strongly depends on in-cylinder gas temperature. Autoignition of natural gas occurs when in-cylinder gas temperature reaches in a range of 1000±100K under this experimental condition. To realize high thermal efficiency and low CO emissions, it is necessary to prepare operation conditions that maximum cycle temperature is over 1500K. Autoignition temperature is 25K lower by increasing n-butane blend ratio of 10%. As the blend ratio of n-butane increases, the maximum cycle temperature increases, and THC, CO emissions reduce.
48 citations
TL;DR: In this article, a genetic algorithm was used for shape optimization of airship hulls, which is a particular artificial intelligence technique for large spaces, striking a remarkable balance between exploration and exploitation of search space, and it was found that GA is a powerful method for such multi-dimensional, multi-modal and nonlinear objective function.
Abstract: A special and effective aerodynamics calculation method has been applied for the flow field around a body of revolution to find the drag coefficient for a wide range of Reynolds numbers. The body profile is described by a first order continuous axial singularity distribution. The solution of the direct problem then gives the radius and inviscid velocity distribution. Viscous effects are considered by means of an integral boundary layer procedure, and for determination of the transition location the forced transition criterion is applied. By avoiding those profiles, which result in the separation of the boundary layer, the drag can be calculated at the end of the body by using Young's formula. In this study, a powerful optimization procedure known as a Genetic Algorithms (GA) is used for the first time in the shape optimization of airship hulls. GA represents a particular artificial intelligence technique for large spaces, striking a remarkable balance between exploration and exploitation of search space. This method could reach to minimum objective function through a better path, and also could minimize the drag coefficient faster for different Reynolds number regimes. It was found that GA is a powerful method for such multi-dimensional, multi-modal and nonlinear objective function.
42 citations
TL;DR: In this paper, a new engine concept consisting of HCCI combustion for low and midrange loads and spark ignition combustion for high loads was introduced, and the timing of the intake valve closing was adjusted to alter the negative valve overlap and effective compression ratio.
Abstract: A new engine concept consisting of HCCI combustion for low and midrange loads and spark ignition combustion for high loads was introduced. The timing of the intake valve closing was adjusted to alter the negative valve overlap and effective compression ratio to provide suitable HCCI conditions. The effect of mixture formation on auto-ignition was also investigated using a direct injection engine. As a result, HCCI combustion was achieved with a relatively low compression ratio when the intake air was heated by internal EGR. The resulting combustion was at a high thermal efficiency, comparable to that of modern diesel engines, and produced almost no NOx emissions or smoke. The mixture stratification increased the local A/F concentration, resulting in higher reactivity. A wide range of combustible A/F ratios was used to control the compression ignition timing. Photographs showed that the flame filled the entire chamber during combustion, reducing both emissions and fuel consumption.
39 citations
TL;DR: In this paper, a refined two-zone heat release model for combustion diagnostics in spark-ignition (SI) engines was developed and assessed, where a more general complex-variable formulation of Newton's convection law was applied for modeling the instantaneous surface-averaged heat flux so as to take the unsteadiness of gaswall temperature difference into account.
Abstract: A refined two-zone heat release model for combustion diagnostics in spark-ignition (SI) engines was developed and assessed. The novelty of the model includes the following improvements. A more general complex-variable formulation of Newton's convection law was applied for modeling the instantaneous surface-averaged heat flux so as to take the unsteadiness of gas-wall temperature difference into account. A CAD procedure was introduced to estimate the heat-transfer wall areas of the burned- and unburned-zone for assigned geometric features of the flame front. The energy conservation law was applied to the unburned-gas zone instead of the isentropic law that is commonly used to evaluate the temperature of the unburned gas. The calibration of the cumulative mass-fraction burned at the end of the flame propagation process was carried out through an overall energy balance of the whole cylinder charge during combustion. The unreleased energy predicted at the end of the flame propagation was related to the combustion efficiency stemming from the exhaust-gas composition. The new heat release model was shown to be an accurate means of combustion diagnostics for SI engines through its application to the analysis of combustion in a multivalve engine fueled by either natural gas or gasoline under a significant sample of operating conditions.
37 citations
TL;DR: In this paper, the trade-off between smoke and NOx without deteriorating fuel consumption was investigated in a four cylinder naturally-aspirated DI diesel engine, where natural gas was charged homogeneously into the intake air and was burned igniting by a small amount of gas oil injection.
Abstract: In order to reduce NOx and smoke simultaneously and also to improve markedly the trade-off between smoke and NOx without deteriorating fuel consumption, natural gas was charged homogeneously into the intake air and was burned igniting by a small amount of gas oil injection in a four cylinder naturally-aspirated DI diesel engine. Combustion tests were carried out by changing the ratio of the amount of natural gas and the amount of gas oil first, secondarily the intake preheating temperature, and thirdly the EGR rate respectively. Effects of the respective parameter on the ignition and the burning rate of natural gas, exhaust emissions and specific fuel consumption were clarified experimentally. It is found that significant improvement of smoke-NOx trade-off can be obtained without deteriorating fuel consumption by the suitable combination between the natural gas charge rate, the intake preheating temperature and the EGR rate for each engine load condition.
30 citations
TL;DR: In this paper, the three-dimensional vortical flow structures and velocity fluctuation near the rotor tip in an axial flow fan having two different tip clearances have been investigated using a rotating hot wire probe and a numerical simulation.
Abstract: Three-dimensional vortical flow structures and velocity fluctuation near the rotor tip in an axial flow fan having two different tip clearances have been investigated by experimental analysis using a rotating hot wire probe and a numerical simulation. It is found that a tip leakage vortex is observed in the blade passage, which has a major role near the rotor tip. The tip leakage vortex formed close to the leading edge of the blade tip on suction side grows in the streamwise direction, and forms a local recirculation region resulting from a vortex breakdown inside the blade passage. The recirculation region is enlarged by increasing the tip clearance. The larger recirculation region induces the acceleration of the through flow, thus resulting in the increase of the broadband noise. High velocity fluctuation is observed at the interference region between the tip leakage vortex and the through flow in the flow field where the tip leakage vortex is tightly rolled up without its breakdown. Near the casing wall, a discrete frequency is formed between tip leakage vortex core and rotor trailing edge.
28 citations
TL;DR: In this paper, the design methods for thermal systems with predominant radiation are given, followed by applications of these methods to idealized but practical engineering systems, and two general techniques are discussed: regularization methods, which remove or ameliorate the ill-conditioned portion of the problem at the expense of some degree of accuracy, and optimization methods which replace the illconditioned problem with a well-posed problem that must be solved repetitively through a systematic approach to a useful solution.
Abstract: Design methods for thermal systems with predominant radiation are given, followed by applications of these methods to idealized but practical engineering systems It is argued that such designs in general present inverse mathematical problems, in that an outcome (the desired output of the systems) is prescribed, and the necessary inputs (geometry, heater placement, heater power distribution) are to be found that will achieve the desired output Such inverse problems require some methods for handling their ill-conditioned nature Two general techniques are discussed: Regularization methods, which remove or ameliorate the ill-conditioned portion of the problem at the expense of some degree of accuracy ; and optimization methods, which replace the ill-conditioned problem with a well-posed problem that must be solved repetitively through a systematic approach to a useful solution Applications of both methods to a variety of radiative transfer problems are discussed and demonstrated, including problems in which heater power is determined, problems in which the geometry of the enclosure must be determined, and problems with a prescribed transient power distribution on the processed material that must be provided by the heaters Problems with conduction and/or convection in addition to radiation are also discussed, as are problems with specularly reflecting surfaces, participating media between the heaters and the processed materials, and enclosures with complex geometries
27 citations
TL;DR: In this article, the emissions of CO2, SO2, NOx, CO, CH4, NMHC, N2O, Dust (SPM), Ni, As, Cd, Cr, Hg, Pb, Zn, and Zn per kWh of electricity generated were estimated for the systems using a combined method of process analysis and input-output analysis.
Abstract: The life cycle inventory (LCI) of the electric power generation plays a vital role on LCIs of the industrial products. However there are no formal life cycle assessment (LCA) studies in Indonesia so far due to limited number of LCA expertise and lack of sufficient databases relevant to domestic conditions. The objective of this study is to introduce life cycle assessment (LCA) method for Indonesian electric power generation systems and to establish LCI for electricity grid mix of Indonesia. In this paper, the emissions of CO2, SO2, NOx, CO, CH4, NMHC, N2O, Dust (SPM), Ni, As, Cd, Cr, Hg, Pb, Zn per kWh of electricity generated were estimated for the systems using a combined method of process analysis and input-output analysis. Additional analyses on the impacts of emerging and future technologies as well as the influences of changes of various assumptions are helpful for a better understanding. As the result, the LCA evaluations are discussed for further ecological improvement.
26 citations
TL;DR: In this paper, the use of seawater and its electrolysis for the exhaust emission control in marine diesel engines was introduced, where seawater was used to remove PMs through direct contact with the sprayed seawater droplets.
Abstract: It is the purpose of this paper to introduce the usage of seawater and its electrolysis for the exhaust emission control in marine diesel engines First, with using only seawater that is naturally alkaline (pH typically around 81), the SO2 and SO3 are absorbed by relatively high solubility compared to other components of exhaust pollutants, and PMs (Particulate Matter) are removed through direct contact with the sprayed seawater droplets Besides, the electrolyzed alkaline seawater by electrolysis, which contains mainly NaOH together with alkali metal ions (i e Na+, Mg2+, Ca2+), is used as the absorption medium of NOx and CO2 Conditionally, before the NOx absorption treatment with using the alkaline seawater, nitric oxide (NO) must be adequately oxidized to nitrogen dioxide (NO2) by the acidic seawater in order to increase NOx absorption rate into the alkaline seawater Because NOx absorption is the most suited to conditions when both volume fractions (NO: NO2 ratio) are of equal portions Finally, this research would also plan to treat the effluent by applying electro-dialysis and electro-flotation techniques in the future The way to reduce emissions from the marine diesel engines is to make it attractive from an operating perspective, as well as an environmental perspective
24 citations
TL;DR: In this article, an RSM optimization was performed to demonstrate the emission reduction capability of the combined effects of high injection pressure, boost pressure, and cooled EGR on a HSDI diesel engine equipped with a common rail injection system.
Abstract: In previous work, an RSM optimization was performed to demonstrate the emission reduction capability of the combined effects of high injection pressure, boost pressure, and cooled EGR on a HSDI diesel engine equipped with a common rail injection system. The RSM optimization led optimum operating parameters to low-temperature and premixed combustion characteristics, i. e., the MK combustion region, resulting in simultaneous reductions in NOx and PM emissions without sacrificing BSFC. However, further retardation of injection timing and increase of EGR rate from the optimum point resulted in significant deterioration of the engine stability with misfire. In the present work, further RSM optimization was conducted to investigate the effect of intake boost pressure on MK combustion. It was found that the increase of intake boost pressure shortened ignition delay, which was not favorable for MK combustion. However it allowed the use of heavier EGR and later injection timings, which intensified the characteristics of MK combustion, i. e., lower-temperature and more thoroughly premixed combustion characteristics. Compared to the previous optimum point, the NOx emission level of the new optimum point was improved by 48%, and it was possible to improve PM emissions further by 71%, while retaining BSFC at the same level. At the new optimum point NOx and PM emissions were 0.54 and 0.092g/kW-hr, respectively, which met the EPA Tier II 2004 automotive diesel mandates.
24 citations
TL;DR: In this paper, a review of recent advances in enhancing boiling heat transfer from electronic components immersed in dielectric liquids by use of surface microstructures is presented, which includes rough surfaces produced by sanding, vapor blasting hard particles, sputtering of SiO 2 followed by wet etching of the surface, chemical vapor deposition of siO 2 film etc., laser-drilled cavities, a brush-like structure (dendritic structure), reentrant and micro-reentrant cavities.
Abstract: This paper reviews recent advances in enhancing boiling heat transfer from electronic components immersed in dielectric liquids by use of surface microstructures. The microstructures developed include rough surfaces produced by sanding, vapor blasting hard particles, sputtering of SiO 2 followed by wet etching of the surface, chemical vapor deposition of SiO 2 film etc., laser-drilled cavities, a brush-like structure (dendritic structure), reentrant and micro-reentrant cavities, microfins, and porous structures fabricated by alumina particle spraying and painting of silver flakes, diamond particles, aluminum particles and copper particles. Heat sink studs with drilled holes, microfins, multi-layered micro-channels and pores, and pin fins with and without microporous coating have also been developed. The height of microstructure ranges from 0 to 12 mm. The primary issues discussed are the mitigation of temperature overshoot at boiling incipience, enhancement of nucleate boiling heat transfer and increasing the critical heat flux
TL;DR: In this article, the hydrodynamic characteristics of two-phase flow influenced by the change in gravity were analyzed using data of flow patterns, void fraction, frictional pressure drop associated with its characteristics were obtained at normal gravity and in microgravity and hyper-gravity (2g) conditions aboard MU-300 aircraft capable of parabolic trajectory flying.
Abstract: Reliable design of space thermal management systems requires a through understanding of the hydrodynamic characteristics of two-phase flow influenced by the change in gravity. The data of flow patterns, void fraction, frictional pressure drop associated with its characteristics were obtained at normal gravity and in microgravity and hyper-gravity (2g) conditions aboard MU-300 aircraft capable of parabolic trajectory flying. Some experiments were performed for an air-water two-phase flow through 10mm diameter adiabatic test section with 600mm length of transparent acrylic resin horizontal tube. The results obtained at three gravity levels (µg, 1g and 2g) are compared with some of the existing flow pattern transition, void fraction and frictional pressure drop models and correlations. The gravity dependency of flow patterns was more clearly appeared with the decrease in gas and liquid flow rates. The effect of gravity on two-phase flow was insignificant for the turbulent flow regions.
TL;DR: In this paper, the authors describe the spray characteristics of the slit nozzle and show that the spray penetration increases with increasing the slit thickness, and the effect of the thickness on spray drop size is small.
Abstract: Direct injection gasoline engines have been developed for the improvement of fuel economy and exhaust emissions. Recently, a new concept of stratified charge combustion has been proposed. A slit nozzle was adopted to realize the new concept. The nozzle has a rectangular orifice and forms a thin fan-shaped spray. This paper describes the spray characteristics of the slit nozzle. The following results were obtained. (1) The spray penetration increases with increasing the slit thickness. (2) The effect of the slit thickness on spray drop size is small. (3) The features of the slit nozzle are high spray penetration, widely diffuse spray and fine atomization compared with the swirl nozzle.
TL;DR: In this paper, a dual-wavelength laser absorption-scattering technique (LAS) was developed by using the 2nd harmonic (532nm) and the 4th harmonic (266nm) of an Nd: YAG laser and using dimethylnaphthalene as a test fuel.
Abstract: Recent experimental studies have shown that with split injection strategy, the soot and NOx emissions from a diesel engine can be reduced significantly in comparison with a conventional non-split injection. To understand the mechanism of emissions reduction, it is essential to clarify the process of mixture formation in the diesel spray. For characterizing the droplets and vapor concentration distributions inside a fuel spray, a dual-wavelength laser absorption-scattering technique (LAS) was developed by using the 2nd harmonic (532nm) and the 4th harmonic (266nm) of an Nd: YAG laser and using dimethylnaphthalene as a test fuel. By applying the ultraviolet-visible LAS imaging technique, the distributions of droplets and vapor concentrations in the spray, which was injected into a high-temperature and high-pressure nitrogen ambient in a constant volume vessel by a common-rail diesel injection system, were measured and quantitatively analyzed. The effect of injection mass ratio of double-pulse injections on distributions of equivalence ratios of vapor and droplets in the sprays was examined.
TL;DR: In this paper, a model of alkaline water electrolysis was established, which can express void fraction and current density profiles along electrodes, and show the existence of the optimum condition.
Abstract: There is an optimum condition on water electrolysis efficiency due to the effects of generated bubbles between electrodes. In this paper, in order to explain the existence of the optimum condition, a model of alkaline water electrolysis was established. The model can express void fraction and current density profiles along electrodes, and show the existence of the optimum condition. For verification of this model, rising velocity, diameter distribution of bubbles between electrodes and current density profiles along electrodes were measured during water electrolysis of KOH solution. Two-phase flows between electrodes were observed by a still camera and a digital video camera. The results showed that bubble rising velocity ranges from 4 - 24 cm/s and becomes larger as current density increases. Bubble diameter ranges from 0.01-0.8mm, where average diameter becomes large as current density increases. Obtained results showed the sound validity of present model.
TL;DR: In this article, the authors studied the vortex shedding in an oscillatory incoming flow at Reynolds numbers of 80, 100 and 200 by numerical solutions and found that the time-averaged mean recirculation region in the oscillatory flow is smaller than that for the steady flow and is inversely proportional to the forcing amplitude or Reynolds number.
Abstract: Vortex shedding behind a square cylinder in an oscillatory incoming flow is studied at Reynolds numbers of 80, 100 and 200 by numerical solutions. The forcing frequencies investigated for the oscillatory incoming flow are ff/fso=0.4∼4.0 and the forcing amplitudes normalized by the mean incoming velocity are 0.1, 0.2 and 0.4, where fso is the vortex shedding frequency under steady incoming flow and ff is the forcing frequency of the oscillatory incoming flow. In the lock-on region, the flow is in a periodic state and there is a strong regularity between the drag and lift forces. The different phase diagram between the drag and lift forces is brought on by the different lift mode. The phase difference between the incoming velocity and the drag is nearly the same magnitude of 65∼70 degrees in the lock-on region. The time-averaged mean recirculation region in the oscillatory incoming flow is smaller than that for the steady one and is inversely proportional to the forcing amplitude or the Reynolds number. The time-averaged streamwise mean velocity in the oscillatory incoming flow recovers more quickly than that in the steady incoming flow.
TL;DR: In this article, the combustion mechanism of the homogeneous charge compression-ignition (HCCI) engine in order to control ignition and combustion as well as to reduce HC and CO emissions and to maintain high combustion efficiency by calculating the chemical kinetics of elementary reactions.
Abstract: The present study focuses on clarifying the combustion mechanism of the homogeneous-charge compression-ignition (HCCI) engine in order to control ignition and combustion as well as to reduce HC and CO emissions and to maintain high combustion efficiency by calculating the chemical kinetics of elementary reactions. For the calculations, n-butane was selected as fuel since it is a fuel with the smallest carbon number in the alkane family that shows two-stage autoignition (heat release with low-temperature reaction (LTR) and with high-temperature reaction (HTR)) similarly to higher hydrocarbons such as gasoline. The CHEMKIN code was used for the calculations assuming zero dimensions in the combustion chamber and adiabatic change. The results reveal the heat release mechanism of the LTR and HTR, the control factor of ignition timing and combustion speed, and the condition need to reduce HC and CO emissions and to maintain high combustion efficiency.
TL;DR: In this article, a planar jet shedding past a square cylinder was numerically studied, and it was shown that the ratio of jet velocity to uniform inlet velocity significantly affects the overall flow structures and thus scalar transport downstream of the cylinder.
Abstract: In this investigation, confined vortex shedding past a square cylinder with a planar jet is numerically studied. Flow and scalar-transport simulations are presented for various cases including both laminar and turbulent flow situations. It is shown that the ratio of jet velocity to uniform inlet velocity significantly affects the overall flow structures and thus scalar transport downstream of the cylinder. Especially, when the ratio is large enough, the jet penetrates the main vortices shed from the cylinder, resulting in significant changes in the flow and scalar fields. In the case of laminar flow, regions of intense scalar are formed along the streamlines from the jet exit, and the oscillation of the force on the cylinder eventually disappears as the jet velocity is close to the inlet velocity. Large Eddy Simulation of turbulent flow also reveals complex flow structures and intense mixing depending on the velocity ratio; regions of intense scalar coincide with those of high turbulence intensity. The results obtained exhibit fuel-air mixing characteristics observed in a planar combustor where the square cylinder plays the role of a flame-holder.
TL;DR: In this paper, a diagnosis technique for temperature and microstructure of real surfaces on a basis of the hardware performance of a wide-spectral-range high-speed spectrophotometer system was proposed.
Abstract: Surface microstates of real surfaces of solid materials change in industrial environments, or they are changed in industrial surface processes positively A real time diagnosis technique for the surface microstates should be developed for the process control We propose a diagnosis technique for temperature and microstructure of real surfaces on a basis of the hardware performance of our wide-spectral-range high-speed spectrophotometer system With respect to the temperature, an active spectral pyrometer technique is adopted, in which the reflection of the surface is measured as well as the self-emission With respect to the microstructure, an attention is paid to the interference and diffraction of radiation in a new real surface model An experiment is made on a metal surface in a high-temperature oxidation process to verify the performance of this technique Spectra of emission and reflection energy of radiation in a near-infrared through infrared region are measured at every 2s, and analyzed Time transition of the surface temperature of an order of 1100K is estimated within an inaccuracy of 10K The average thickness d and rms roughness σI of the surface film are estimated to be in regions of d=008∼38µm and σI=001∼071µm, respectively
TL;DR: In this paper, both tubular flame temperature and Bunsen flame temperature have been measured for lean methane, hydrogen and propane/air mixtures, and numerical simulation has been conducted to examine radiation effect.
Abstract: Both tubular flame temperature and Bunsen flame temperature have been measured for lean methane, hydrogen and propane/air mixtures. These temperatures have been compared with the adiabatic flame temperature, which is the typical temperature with no stretch. Results show that, the temperature of the tubular flame is almost the same as the adiabatic flame temperature for a lean methane/air mixture, considerably higher for a lean hydrogen/air mixture, and lower for a lean propane/air mixture. For the temperature around the Bunsen flame tip, this response is opposite to that of the tubular flame. To examine radiation effect, numerical simulation has been conducted. It is found that the radiative heat loss only reduces the flame temperature by 30 to 80°C. Thus, the different dependency of flame temperature on the mixtures is explained by stretch effect with the Lewis number considerations, and the response of these flames exhibits opposite behavior.
TL;DR: In this paper, the authors investigated local diffusion phenomena in diesel sprays with focusing on scales of fuel cloud and eddies based on a newly developed entropy method, and they showed that the diffusion intensity is the highest in the vicinity of the nozzle exit, and the heterogeneity scale is the smallest here.
Abstract: Rapid mixing of fuel and air is an essential factor in improving combustion and emissions of diesel engines, and it is important to know the relationship between the microscopic structure of the heterogeneous distribution of fuel clouds and the local turbulence structure. This paper investigates local diffusion phenomena in sprays with focusing on scales of fuel cloud and eddies based on a newly developed entropy method. The results show that the diffusion intensity is the highest in the vicinity of the nozzle exit, and the heterogeneity scale is the smallest here. The heterogeneity scale increases gradually along the spray axis towards the downstream, with smaller size scales in the large clouds. In the downstream region, small-scale structures diffuse and become unclear, while large scale struclures clearly remain. The paper details the microscopic structure of the heterogeneity in diesel sprays, and it demonstrates availability of the entropy method.
TL;DR: In this article, the effect of a preferential diffusion in relation to the flame curvature under the negative stretch regime is discussed, and the maximum flame temperature cannot be rationalized by the local stretch rate, and changes over a wide range depending on the preferential diffusion.
Abstract: Numerical analysis is performed on the H2/N2-air laminar counterflow diffusion flames affected by positive or negative stretch rate induced by locally sucking flow from fuel and air sides. Adjusting the suction velocity leads to the formation of three typical flame shapes, flat, or with concave or convex curvature. Numerical computations taking into account detailed chemical kinetics and multicomponent diffusion clarify the effects of negative stretch rate on the flame structure and characteristics. In addition, the effect of a preferential diffusion in relation to the flame curvature under the negative stretch regime is discussed. The results show that (1) Temperature increases with decreasing the stretch rate, and the tendency remains even in the regime of negative stretch rate. (2) H2 concentration due to the preferential diffusion and excess enthalpy due to the non-unity Lewis number effect become relatively significant with decreasing stretch rate. This is one of the reasons for (1). (3) Temperature increase due to the negative stretch rate depends on the flame curvature. (4) The maximum flame temperature cannot be rationalized by the local stretch rate, and changes over a wide range depending on the preferential diffusion in relation to flame curvature.
TL;DR: In this article, the effects of flame stretch on an outwardly propagating flame are considered experimentally for both laminar and turbulent flames, and the underlying mechanisms in consideration of interaction between flame stretch and the Lewis number are discussed.
Abstract: The effects of flame stretch on an outwardly propagating flame are considered experimentally for both laminar and turbulent flames. Although the thermo-diffusive mechanism caused by the flame/stretch interaction is well known for laminar flames or for weakly stretched flames, recent studies have shown that it influences the local and global flame structures of turbulent premixed flames which consist of strongly stretched flamelets. In this study, outwardly propagating flames of methane and propane mixtures, which are representative of light and heavy hydrocarbons, respectively, over a wide range of equivalence ratio, are used in the application to engine combustion. The primary objective of the present study is to investigate both laminar and turbulent burning velocities experimentally and to discuss the underlying mechanisms in consideration of interaction between flame stretch and the Lewis number.
TL;DR: For numerically predicting the mixture formation and combustion processes in premixed compression ignition engines, fuel spray submodels (the authors' modified wave breakup model, etc.), an ignition submodel (Livengood Wu's model or Schreiber's reduced kinetic model) and a combustion sub model (Reitz's model) were incorporated into the authors' GTT code.
Abstract: For numerically predicting the mixture formation and combustion processes in premixed compression ignition engines, fuel spray submodels (the authors' modified wave breakup model, etc.), an ignition submodel (Livengood Wu's model or Schreiber's reduced kinetic model) and a combustion submodel (Reitz's model) were incorporated into the authors' GTT code. The combustion processes in the two types of premixed compression ignition engines (side-injection and central injection engines) were numerically analyzed using this code. These submodels were validated by comparing the calculated results of heat release rate with experimental ones.The calculated amount of NO production using the extended Zeldovich mechanism nearly agreed with the experimental one.
TL;DR: In this paper, a super-adiabatic combustion engine was proposed with high thermal efficiency of 57.5% over a wide range of operation conditions. But the performance of the proposed engine was limited to a concentration of 1.58 vol% methane in air.
Abstract: Super-adiabatic combustion engine proposed here has a high thermal efficiency of 57.5% over a wide range of operation conditions. The engine consists of a displacer piston, a power piston and a porous medium in a cylinder. These create reciprocating motions with a phase relation angle. After scavenging, a mixture introduced is compressed by the displacer piston and preheated by the porous medium, and then, ignited in the vicinity of the downstream end of the porous medium. The main reaction occurs in the power piston side cylinder. By the heat recirculation from the residual combustion-gas enthalpy to the enthalpy increase in the mixture, the maximum temperature becomes higher than the theoretical (adiabatic) flame temperature. As a result, the system has such a high thermal efficiency and extends the flammability limit to a concentration of 1.58 vol.% methane in air.
TL;DR: In this article, a wavelet transform is introduced to analyze frequency characteristics of the fluctuating pressure on rotor blade in a propeller fan, which is mainly generated due to the unsteady behavior of the vortical flow, such as the tip vortex and the leading edge separation vortex.
Abstract: A wavelet transform is introduced to analyze frequency characteristics of the fluctuating pressure on rotor blade in a propeller fan. The fluctuating pressure on the rotor blade is obtained by using the results of a large eddy simulation. The frequencies having high spectral peaks of the fluctuating pressure are determined by taking the time average of the local absolute modulus of the wavelet. The dominant frequency of the real-time pressure selected at the high pressure fluctuation region corresponds well to that of the fluctuating rotor torque and the experimental result of fan noise. It is mainly generated due to the unsteady behavior of the vortical flow, such as the tip vortex and the leading edge separation vortex, in the propeller fan. A frequency in the separation bubble region on the suction surface is higher than that of the dominant frequency caused by the vortical flow.
TL;DR: In this paper, a direct injection gasoline engine employing a new stratified combustion system has been developed, where a fan-shaped fuel spray and a shell-shaped piston cavity achieved the combustion strategy.
Abstract: A direct injection gasoline engine employing a new stratified combustion system has been developed. A fan-shaped fuel spray and a shell-shaped piston cavity achieved the combustion strategy. The process of stratified mixture formation and consequent stratified combustion is affected by the fuel spray characteristics, therefore numerical analysis (CFD) was applied to understand the phenomena of mixture formation process. From the results of CFD, it was clarified that the vaporization characteristic is important in realizing a suitable stratified mixture formation, in addition to the spray liquid characteristics, and CFD enables prediction and analysis of actual phenomena.
TL;DR: In this article, the authors investigated the dependence of CO poisoning on types of catalyst using Pt and Pt-Ru alloy and found that if the FC was operated at a high CO concentration, no significant improvement could be expected when using increased pressure, and further the effects of the operating temperature is almost the same for the two types of catalysts.
Abstract: This paper covers our investigation into a decline in FC performance resulting from hydrogen fuel containing CO. Several investigations were conducted into the dependence of CO poisoning on types of catalyst using Pt and Pt-Ru alloy. The investigations are summarized as follows: 1) The poisoning prediction formulas and the poisoning estimation coefficient to predict and estimate the performance were derived theoretically. 2) The actual process of CO poisoning was scrutinized by focusing on adsorption of CO and desorption of CO2 molecules, and changes of several polarizations caused by CO poisoning were estimated. 3) Investigations into the relationship between the CO concentration, operating pressure, operating temperature and the CO poisoning were carried out. If the FC was operated at a high CO concentration, no significant improvement could be expected when using increased pressure, and further, the effects of the operating temperature is almost the same for the two types of catalyst.
TL;DR: In this article, two-phase flow pattern data during horizontal in-tube flow boiling are presented for pure and mixed refrigerants of R134a and R123, where the flow pattern is observed through tubular sight glasses located at inlet and outlet of the test section, which is made of a stainless steel tube.
Abstract: Two-phase flow pattern data during horizontal in-tube flow boiling are presented for pure and mixed refrigerants of R134a and R123. The flow pattern is observed through tubular sight glasses located.at inlet and outlet of the test section, which is made of a stainless steel tube, 2 m long with 10 mm I.D., 1.5 mm wall thickness. The obtained results are compared to the available various correlations for flow pattern. The flow pattern map of Hashizume was very well agreement with the present data except the region of low mass velocity. Weisman flow pattern map was also known to satisfactorily predict data for refrigerants in the region of annular flow. In order to establish the transition quality to annular flow in this study, flow pattern are simply classified into two groups ; stratified (including intermittent, stratified and stratified-wavy) flow and unstratified (annular) flow. The transition quality from stratified to unstratified flow was obtained by modifying the liquid Froude number.
TL;DR: In this paper, the authors developed a method utilizing an experimental-numerical method for the estimation of the thermal contact resistance between the fin collar and tube surface and evaluated the factors affecting the thermalcontact resistance in a fin-tube heat exchanger.
Abstract: The contact between fin collar and tube surface of a fin-tube heat exchanger is secured through mechanical expansion of tubes. However, the characteristics of heat transfer through the interfaces between the tubes and fins have not been clearly understood because the interfaces consist partially of metal-to-metal contact and partially of air. The objective of the present study is to develop a new method utilizing an experimental-numerical method for the estimation of the thermal contact resistance between the fin collar and tube surface and to evaluate the factors affecting the thermal contact resistance in a fin-tube heat exchanger. In this study, heat transfer characteristics of actual heat exchanger assemblies have been tested in a vacuum chamber using water as an internal fluid, and a finite difference numerical scheme has been employed to reduce the experimental data for the evaluation of the thermal contact conductance. The present study has been conducted for fin-tube heat exchangers of tube diameter of 7mm with different tube expansion ratios, fin spacings, and fin types. The results show, with an appropriate error analysis, that these parameters as well as hydrophilic fin coating affect notably the thermal contact conductance. It has been found out that the thermal contact resistance takes fairly large portion of the total thermal resistance in a fin-tube heat exchanger and it turns out that careful consideration is needed in a manufacturing process of heat exchangers to reduce the thermal contact resistance.