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.

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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.

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This paper describes the numerical and experimental approaches that were applied to study swirl nozzles that are widely used in direct-injection gasoline engines. As the numerical approach, the fuel and air flow inside a nozzle was first analyzed by using a two-phase flow analysis method employing a volume of fluid (VOF) model. Spray droplet formation was then analyzed with a discrete droplet model (DDM). As the experimental approach, particle image velocimetry (PIV) was used to measure the spray velocity distribution. These approaches were applied to test nozzles having a tapered tip geometry at the nozzle exit. The spray shapes produced by the nozzles were skewed to the tapered side. Additionally, the cone angle of the spray on the skewed side did not change very much even under a condition of high ambient pressure. The analysis results suggest that the skewed spray shapes are influenced mainly by the spray cone angle and circumferential fuel mass distribution at the nozzle exit.

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Ambient air velocity distributions in and around a D. I. gasoline spray were measured using a combination of LIF and PIV techniques. A rhodamine and water solution was injected into ambient air to disperse the fine fluorescent liquid particles used as tracers. A fuel spray was injected into the fluorescent tracer cloud and was illuminated by an Nd: YAG laser light sheet (532nm). The scattered light from the spray droplets and tracers was cut off by a high-pass filter (>560nm). As the fluorescence (>600nm) was transmitted through the high-pass filter, the tracer images were captured using a CCD camera and the ambient air velocity distribution could be obtained by PIV based on the images. This technique was applied to a D. I. gasoline spray. The ambient air flowed up around the spray and entered into the tail of the spray. Furthermore, the relative velocity between the spray and ambient air was investigated.

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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 NO_x 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.

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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.

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The CFD simulations were performed integrating the low-temperature oxidation reaction. Analyses were made with respect to the first auto-ignition location in the case of a premixed-charge compression auto-ignition in a laminar flow field and in the case of the auto-ignition in an end gas during an S. I. Engine combustion process. In the latter simulation, the spatially-filtered transport equations were solved to express fluctuating temperatures in a turbulent flow in consideration of strong non-linearity to temperature in the reaction equations. It is suggested that the first auto-ignition location does not always occur at higher-temperature locations and that the difference in the locations of the first auto-ignition depends on the time period during which the local end gas temperature passes through the region of shorter ignition delay, including the NTC region.

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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.

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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.

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A homogeneous charge compression ignition (HCCI) engine is known to have high thermal efficiency and low nitrogen oxide emission. However, the control of ignition timing and its combustion period over a wide range of engine speeds and loads is one of the barriers to the realization of the engine. On the lean side of the equivalence ratio, control of ignition is difficult due to its long delay of ignition, and there is knocklike problem under high load. In both computations and experiments of HCCI engine operated on dimethyl ether, the operable range (the possible range of fuel input from just ignitable to knock-occurring state) shifted to the rich side with decreasing intake temperature and amount of mixing of carbon dioxide. The range of fuel input was reduced at low intake temperatures, because the hot flame onset angle advanced more quickly than it did at high intake temperatures. However, the mixing of CO₂ caused the operable range to shift to the rich side while retaining the same range. The results of this study indicated the possibility of high-load operation or extension of the load range by exhaust gas recirculation.

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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.

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The stratified charge combustion system has been widely studied due to the significant potentials for low fuel consumption rate and low exhaust gas emissions. The fuel-air mixture formation process in a direct-injection stratified charge engine is influenced by various parameters, such as atomization, evaporation, and in-cylinder gas motion at high temperature and high pressure conditions. It is difficult to observe the in-cylinder phenomena in such conditions and also challenging to analyze the following stratified charge combustion. Therefore, the combustion phenomena in simplified stratified charge conditions aiming to analyze the fundamental stratified charge combustion are examined. That is, an experimental apparatus which can control the mixture distribution and the gas motion at ignition timing was developed, and the effects of turbulence intensity, mixture concentration distribution, and mixture composition on stratified charge combustion were examined. As a result, the effects of fuel, charge stratification, and turbulence on combustion characteristics were clarified.

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In our previous works, the mean local burning velocity turned out to be changed from the original laminar burning velocity due to the preferential diffusion effect and it was found to be an important factor as dominating the turbulent burning velocity. In the present study, an attempt is made to investigate directly the local propagation characteristics of methane and propane premixed turbulent flames in the wrinkled laminar flame region. A laser tomography technique is used to obtain the local flame configuration and movement, and quantitative analyses are performed. As a result, the estimated local flame displacement velocities are found to be distributed over a wide range and to be dependent on the local curvature of the turbulent flame. In addition, its mean value of the methane mixture has a tendency to become larger as decreasing its equivalence ratio, whereas that of the propane mixture becomes smaller.

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Recent experimental studies have shown that with split injection strategy, the soot and NO_x 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.

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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 structures clearly remain. The paper details the microscopic structure of the heterogeneity in diesel sprays, and it demonstrates availability of the entropy method.

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Pilot injection in DI Diesel Engines is a very effective method reducing nitrogen oxides and noise. However the injection behavior of small quantities of pilot fuel is unstable, and the cylinder-to-cylinder deviations in injection mass and spray development occur in multi-cylinder direct injection diesel engines. This study investigates the correlation between cylinder-to-cylinder deviations in spray development and combustion and emissions when the pilot injection was applied at idling. It was found that the cylinder-to-cylinder deviations in spray behavior are not the sole reason for the deviations in combustion and emission, but that peculiar conditions to a cylinder such as air movement and in-cylinder carbon deposits also play a role. In this study the HC components in the exhaust gas with and without pilot injection was investigated, and it is shown that deviations in combustion with pilot injection result in deviations in low carbon component emissions and in the rate of pressure rise which is responsible for exhaust odor and engine noise.

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In order to reduce NO_x and smoke simultaneously and also to improve markedly the trade-off between smoke and NO_x 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-NO_x 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.

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The chemical gas-phase reduction process used to reduce nitric oxide (NO) in diesel engine exhaust has been applied to a high-speed, light-duty diesel engine. The chemical gas-phase reduction process involves adding methylamine (CH₃NH₂) in water solution to the exhaust gas as an NO reduction agent. In this study, an experimental selective noncatalytic NO reduction system designed to be used with a diesel engine was applied to evaluate this technique for practical use. The NO_x reduction ratio (R_NOx) of methylamine processes with and without the installation of a particulate filter was investigated. Two different mixing chambers with different volumes and residence times (0.1s and 0.17s) were also tested. Longer residence times were required to achieve a given level of NO_x reduction in unfiltered exhaust, suggesting that the presence of particulate matter inhibits NO reduction. For the standard residence time (0.1s), the process achieved 64% NO reduction in unfiltered diesel exhaust, which increased to 80% NO reduction when a particle filter was fitted to the system.

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In this study, we proposed a new method to calculate the fractal dimension in order to evaluate the change of the eddy structure of tumbling flow. The procedure of our method is 1) Carrying out wavelet transform of the turbulence and obtaining the information of the turbulence about both time and frequency. 2) Calculating the fractal dimension at each time from the wavelet transform of the turbulence. 3) Evaluating change of the eddy structure in the turbulence by using the fractal dimension obtained. As a result, the fractal dimension first decreases a little at the time of the tumbling flow broken down and then the fractal dimension increases near TDC. that is, the eddies that are generated by the tumbling flow which has broken down have larger scale and transmit the energy to the small eddies in the compression stroke.

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The most popular conventional combustion models are the “Eddy-Break-Up Model” by Spalding and “Eddy Dissipation Model” by Magnussen, both of which are accepted as applicable to premixed flames. However, these models have not simulated all the premixed combustion phenomena. In this paper we assess four combustion models; (1) “Eddy Dissipation Model”: “Magnussen Model”; (2) premixed combustion model of the “Katsuki Model” which controls the reaction rate by the Damköhler number; (3) the “Kido Model”, which predicts turbulent burning velocity by laminar burning velocity and turbulent characteristics and (4) the “Modified Katsuki Model”, in which the fluctuations of concentrations and temperature are solved by the transport equation. In present work, the Kido model is newly presented as computational code based on the flame cell concept and the modified Katsuki model is also developed for application to multi-fuel systems. Our study showed that the “Modified Katsuki Model” could predict the premixed combustion phenomena sufficiently and could trace the changes of the frame front.

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This study presents the unsteady fluctuation measurements of impeller discharge flow for a centrifugal compressor in unstable operating region. The characteristics of the blade-to-blade flow under rotating stall were investigated by measuring unsteady velocity fluctuations at several different diffuser axial distances using a hot wire anemometer and high frequency pressure transducers mounted on the shroud wall. The flow characteristics in terms of the radial and tangential velocity components and turbulence intensity at the impeller exit were analyzed by using double phase-locked ensemble averaging techniques. During one stall period, a deep wake core was observed on the suction surface near the hub for the maximum radial velocity instant. On the other hand, large wake region existed in the middle of the passage near the shroud side. For the radial velocity increasing instant a quite strong core flow was generated at the pressure side, however, for the decreasing instant comparatively strong core flow was developed near the suction side.

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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.

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Flow injection is being used in steam turbines for some combined or geothermal plants in order to increase its total thermal efficiency. It can be easily imagined, however, that such a flow injection is accompanied by additional aerodynamic loss due to the flow mixing or the change in local flow angle. Preliminary three-dimensional steady numerical simulations are conducted for the flow field inside the chamber from which the secondary flow is injected. The results showed a small variation of the flow velocity at the injection slot and provided useful information concerning the magnitude of the pitchwise variation of the injection angle. Further numerical simulations in a turbine stage were then performed by prescribing different injection angle distribution at the injection slot. The turbine stage computations revealed the existence of a high loss region generated from the interaction of the injected flow and the passage vortex near the tip of the nozzle vanes. It was found that injection angles orientated to the suction side of the stator provided lower loss values, while cases where flow was injected to the pressure side minimized the flow angle deviation.

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A twist-type rubber-tube pump, consisting of a tube with one side fixed and the other connected to a motor axis, has been developed. Liquid inside the tube is discharged according to the twist angle of the tube. Discharge volume ΔV of the pump is therefore approximated by the formula ΔV=[1-L₀{L₀²+r_e²(θ-α)²}-¹/²]S₀L₀, where S₀ is the cross-sectional area of the tube, L₀ is tube length, θ is twist angle, r_e is typical tube radius, and α is the delay angle of discharge. A prototype “twist pump” (tube inside diameter: 4mm; outside diameter: 8mm; length: 50mm) was evaluated by continuous pump tests. These tests showed that the prototype discharges 50µL of liquid at a maximum twist angle of 270° and has a long life; that is, the discharge pattern changes little after two million repetitions of the pump cycle.

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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.

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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.

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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 8.1), 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 NO_x and CO₂. Conditionally, before the NO_x 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 NO_x absorption rate into the alkaline seawater. Because NO_x 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.

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