To strengthen energy resiliency, a multi-objective optimization tool was developed, which can calculate optimum amounts to install distributed power generators as private power generation equipment which is available not only during an emergency situation but also during a normal situation. As distributed power generation equipment, cogeneration systems, photovoltaic system, and storage batteries were considered. The tool was developed based on our previous study and two objective functions were applied; one is the expected value of electric power shortage ratio after disasters as an index of the energy-resilience and the other is the total cost as an indicator of economic and environment. Then, case studies were performed considering several sizes and gas-supply pressure type of hospitals. As a result, reasonable Pareto-optimal solutions were obtained. For comparison, a case of an equivalent hospital only installed emergency generators were calculated, and the solution was plotted on the same plane of the objective functions. Therefore, the expected value of the power shortage rate after disasters was 32%. On the other hand, in all the case of the obtained optimal solutions, the expected value could be reduced to less than 20%. In addition, the total cost could also be reduced.

Electric vehicles (EVs) and vehicle-to-home (V2H) technologies are expected to be used as domestic electricity storage systems, thereby promoting the self-consumption of photovoltaic (PV) power. The purpose of this study was to evaluate the profitability of V2H installation, the optimal facility configuration and the energy performance of V2H, while considering a diversity of household types and storage facility options. We optimized the facilities and operation strategy of a residential energy system under many scenarios with different electricity demand profiles, automobile usage patterns and available areas for PV installation. The results showed that a V2H system should generally be installed instead of a stationary battery (SB), but combining a V2H system with a SB is more economical for households with long EV absence times. Additionally, V2H is profitable for households with short EV absence times, large available areas for PV installation and high electricity demand. Furthermore, V2H exhibits superior energy independence and energy-saving effects for households whose annual PV generation exceeds the yearly household electricity demand.

In this study, a multiple-input multiple-output feedforward controller for use with multiple-point fuel injection systems is applied to a diesel engine using an original control-oriented model. The target-tracking performance of this multiple-input multiple-output feedforward controller was then tested in terms of how well the controller adjusts the fuel delivery ratios to the pilot injection, pre-injection, main fuel injection, and the main fuel injection timing, and controls the in-cylinder peak pressure and its timing. Control experiments are conducted at different engine outputs and speeds while changing the targets of the in-cylinder peak pressure and its timing. The controller is able to track the varying targets within an acceptable error included in the original model. The calculation time, which is almost double that of a single-input single-output controller, is sufficiently fast to derive the applicable inputs.

In 2017, the Mistry of Health, Labor, and Welfare in Japan added a requirement for domestic disaster base hospitals to install electric power generation equipment with a generation capacity at least 60% of usual demand for securing business continuity. In this study, we developed a multi-objective optimization tool for assisting the determination of the capacity of distributed generation equipment and contract plans considering energy-resiliency after a disaster. The selected objective functions are a total cost representing economy and environment, and an expected value of power shortage ratio after the catastrophe representing energy-resiliency. As a result, our developed tool could obtain the Pareto-optimal solutions for various size hospitals on the parameter plane of the two objective functions. As well as total costs, for all optimal solutions, the expected value of power shortage ratio under disaster situation resulted in less than 40% suggesting that the national requirement standard is satisfied. Then, the cluster analysis was carried out to grasp the tendency of optimal solutions. From the analysis of average value for each cluster, it is shown that the optimal introductory capacities of gas engine generators and storage batteries couple through the outage probabilities of gas supply. Furthermore, the optimal capacity of photovoltaic is much larger than the one assumed to install on the estimated rooftop area of the hospital building, which suggests that hospital can take an option to introduce more photovoltaics to an adjacent area if possible.

In this study, a hydrogen–air premixed flame in a partially tapered swirl burner in which a stable counterflow of unburned and burned gases is expected to be formed, was investigated. The experimental results indicate the formation of almost steady flames at equivalence ratios of as lean as 0.084, and the resulting ultra-lean flames in the swirling flow had a comet shape. Furthermore, the flame was numerically reproduced, and the mechanisms behind the phenomenon were identified by checking the balance among the chemical enthalpy through diffusion, heat flux by conduction, and transport of these parameters by convection. It was determined that the region around the tip of the flame head was almost dominated only by diffusion and heat conduction similar to a flame ball, but its formation mechanism was found to be essentially different from that of a flame ball because the comet-like flame can be numerically reproduced even without a radiative heat loss, in contrast to a flame ball.

Subsidy and social systems should be designed to effectively promote, for example, the introduction of a mechanical system. For an effective subsidy distribution, developing evidence-based decision-making methodologies is essential. We developed a tool that minimizes an objective function includes economic costs, environmental cost, and disaster risk to determine the amount of energy distributed by the equipment when installing in hospitals against disasters. Open data available on the Internet are used as simulation values herein. This simulation model optimizes six design values using a genetic algorithm based on the values (business site area, demand for heat and electricity, and maximum allowable loss) input by customers for their construction and visualizes the total cost. The tool allows to quantitatively assess the changes in the initial and running costs owing to equipment installation and the avoidable losses related to CO 2 emission reductions and disaster risks. In addition, the net present value (NPV) can be calculated using the obtained values for initial and running costs, thereby allowing to clearly estimate the return on investments after equipment installation. The opportunity profit can be calculated based on the difference between the NPV after 15 years assuming no risk and with disaster risks. A method to set this opportunity profit as a calculated subsidy amount is proposed herein. Decision support can be provided via these simulations to the customers and government subsidy system design engineers.

We propose a new DRG-based mechanism reduction method that considers heat release rate (HRR), transport of species, and reaction rate. In the original DRG method developed by T. Lu and C. K. Law, species importance is evaluated using only the reaction rate, and PSR is used for sampling. However, combustion phenomena are also affected by the transport of species and HRR, and sampling using PSR may be inadequate to produce a skeletal mechanism that can simulate a realistic flame. Therefore, in the proposed transport and heat DRG method, a 1D premixed flame is used for sampling, and species importance is evaluated relative to reaction rate, transport flux, and HRR. The proposed method was evaluated in ethylene/air and n-butane/air 1D premixed flame, and the laminar flame speed and flame structure were obtained using skeletal mechanisms created by three DRG methods, i.e., the original, transport, and transport and heat methods. In the case of the ethylene/air premixed flame, the transport and heat DRG method produced a smaller skeletal mechanism that well-reproduced the result of the detailed mechanism. In the case of n-butane/air premixed flame, smaller skeletal mechanisms were obtained in the region of relative error on laminar flame speed of 0.1–1.0% with the transport and heat DRG method.

<p>Dual fuel engines (DFE) suffer from considerably high total hydrocarbon emissions and low thermal efficiency due to its poor combustion at low loads. Also, further improvement of thermal efficiency is needed at high loads. Therefore, in this study, the effect of double diesel fuel injection on the combustion and exhaust emission characteristics of DFE using town gas 13A (natural gas) was investigated in the experiments and injection strategy was developed. The experiments were conducted using a single-cylinder engine and with a common rail injection system, varying the number of fuel injection and injection timings. In lower loads, the combustion of natural gas was activated by the double injection and both THC emissions and thermal efficiency were improved. By advancing the second injection timing, CA50 was shifted toward the top dead center and hence the thermal efficiency was improved. On the other hand, at higher loads, although the thermal efficiency slightly improved by the double injection, NOx emissions increased. It was suggested that the injection interval of double injection was appropriately selected and the injection timing was retarded so that the NOx emission can be suppressed while keeping the thermal efficiency high.</p>

&lt;p&gt;Hydrogen combustion is attracting attentions because of zero CO&lt;sub&gt;2&lt;/sub&gt; emission. Recently, a gas turbine which uses hydrogen-rich fuel is being developed. In our previous study, we examined the influence of hydrogen-containing ratio on combustion oscillation for fuel mixtures of hydrogen and town gas (13A) experimentally. In the experiment, pressure oscillations were measured by a sensor which is installed at the bottom of the combustor. It is found that two oscillation frequencies near 200 Hz and 400 Hz were simultaneously detected in the case of hydrogen-containing fuels, whereas single oscillation frequency around 350 Hz was observed in the case of only 13A fuel. To understand this difference of oscillating frequencies, we conducted acoustic analysis using one-dimensional different diameter acoustic model. However, this simplest model could not reproduce three types of oscillating frequencies obtained by the experiment. Besides, we used an acoustic impedance of the bottom of the combustion chamber as an acoustic boundary condition. The acoustic impedance is measured experimentally under the noncombustion (cold) condition and corrected by combustion temperature obtained by equilibrium calculation. As a result of applying the corrected acoustic impedance, the three types of oscillating frequencies could be reproduced by acoustic analysis. Furthermore, to express the difference among fuel mixtures, delay times, flame positions, and the mean temperature in the chamber were calculated by the CFD simulation. Consequently, it is found that the acoustic analysis result could reproduced the difference among fuel mixtures; hydrogen makes the oscillating frequencies a little higher, because temperature becomes higher and delay time becomes shorter.&lt;/p&gt;

&lt;p&gt;As a method for mining offshore gas fields, a floating production, storage and offloading (FPSO) system is attracting attention. However, sloshing in the oil-gas separator installed in FPSOs excited by sea waves is expected to cause significant difficulties. To suppress sloshing wave heights, one possibility may be to install perforated plates in a tank. In this study, a method is proposed for the accurate estimation of the first resonant wave height in the horizontal cylindrical tank with a perforated plate under pitching excitation in less time. To accomplish this purpose, the pressure loss due to the perforated plate in the open channel must be estimated accurately. Therefore, the pressure loss is modeled using steady CFD calculations considering the effects of the distribution of the flow velocity and the distribution of the inflow angle. The first order sloshing wave height is calculated in the theoretical analysis by substituting the pressure loss calculated in steady CFD. The wave heights determined using the pressure loss utilized by steady CFD are compared with the experimental value measured with a small-scale model. Using the method proposed in this study, the first resonant wave height of sloshing wave height is calculated accurately in less time.&lt;/p&gt;

Natural gas is relatively clean, and its demand is currently increasing. In most cases, gas fields are located at the bottom of the sea. Therefore, floating production, storage, and offloading (FPSO) systems are now attracting considerable attention. This paper is related to the dynamical design of a FPSO system; in particular, it focuses on the free surface elevation induced by the waves in a horizontal cylindrical and axisymmetric liquid vessel with end caps. In this study, the theory of the wave height and resonant frequency in a horizontal cylinder subjected to pitching via external excitation is developed. Then, a theory taking into account the effect of perforated plates is introduced. A special discussion is made with regard to the number and location of the perforated plates and the effect of a partial opening in a perforated plate on the damping. Finally, the experimental data of resonant wave heights up to the third mode are shown in comparison to the theoretically derived results.

After the 2011 Great East Japan Earthquake, a business continuity planning, i.e., BCP, in a disaster case is attracting attentions in Japan. However, when a customer, i.e. a building owner actually would like to introduce energy generation devices such as a cogeneration equipment, there is no guideline to decide suitable device capacity based on the evaluation of economic efficiency and BCP as well as energy saving performance. This study proposes a method to optimize a plan for installing cogeneration equipment considering BCP under disaster risks simultaneously. We develop a simulation tool to decide an optimized planning of energy-generation equipment configuration. With this simulation tool, we performed case studies for different business cases such as a hospital and a hotel. The simulation results showed that the optimized installing plan can be an over-specification of equipment configuration under the assumption of disaster risks, which is never chosen under conventional definition. Then, we examined the economic performance of an energy generation equipment configuration by calculating a net present value from the viewpoint of BCP. This examination can give judgments of investment-return possibility and suitable subsidy price.

<p>HCCI combustion is effective for improving thermal efficiency of a gas engine, but it has problems such as control of the ignition and combustion. To solve the problem, availabilities of dedicated EGR technique are considered to control its ignition and combustion. Dedicated EGR involves reforming fuel into H₂ or CO by running a single or more cylinder with rich mixture and supplying the exhaust gas directly into other cylinders. In this study, the effect of dedicated EGR on methane HCCI combustion was investigated by experiments. As a result, when equivalence ratio of rich SI combustion or EGR ratios increase, the ignition timing of HCCI advances and combustion becomes steep. The advanced ignition timing is caused by an increase of H₂ mole fraction in the intake gas. In addition, the possibility of controlling the ignition timing, which is strongly concerned with the thermal efficiency of a HCCI engine, by dedicated EGR was discussed. It was shown that the ignition timing linearly depends on H₂ mole fraction in the intake gas.</p>

This paper proposes a scheme, called the disaster-risk-weighted damage inequality, for a customer to perform introductory planning for a distributed generation system considering business continuity planning in a disaster case. To calculate this inequality, the relevant disaster risks are surveyed and system operating simulations for target buildings such as a hotel, a hospital, a large-scale office, and a collective housing building are performed by solving a mixed integer linear programming problem under the assumption that a cogeneration system is installed as a distributed generation system. Next, we determined the probabilities of a disaster occurrence and business interruption due to a disaster, the initial cost of the equipment, the running cost, and the reduction in running cost due to a cogeneration system installation. The cogeneration system was found to effectively reduce the running cost. Finally, the suggested inequality is calculated and determined whether it is satisfied. The result showed that cogeneration system installation very effectively reduces the running cost for a hotel, a hospital, and a large-scale office, compared to the tolerable amount of loss that is preliminarily determined by a customer.

In our previous numerical studies [Nishioka Makihito, Zhenyu Shen, and Akane Uemichi. “Ultra-lean combustion through the backflow of burned gas in rotating counterflow twin premixed flames.” Combustion and Flame 158.11 (2011): 2188–2198. Uemichi Akane, and Makihito Nishioka. “Numerical study on ultra-lean rotating counterflow twin premixed flame of hydrogen–air.” Proceedings of the Combustion Institute 34.1 (2013): 1135–1142]. we found that methane– and hydrogen–air rotating counterflow twin flames (RCTF) can achieve ultralean combustion when backward flow of burned gas occurs due to the centrifugal force created by rotation. In this study, we investigated the mechanisms of ultralean combustion in these flames by the detailed numerical analyses of the convective and diffusive transport of the main species. We found that, under ultralean conditions, the diffusive transport of fuel exceeds its backward convective transport in the flame zone, which is located on the burned-gas side of the stagnation point. In contrast, the relative magnitudes of diffusive and convective transport for oxygen are reversed compared to those for the fuel. The resulting flows for fuel and oxygen lead to what we call a ‘net flux imbalance’. This net flux imbalance increases the flame temperature and concentrations of active radicals. For hydrogen–air RCTF, a very large diffusivity of hydrogen enhances the net flux imbalance, significantly increasing the flame temperature. This behaviour is intrinsic to a very lean premixed flame in which the reaction zone is located in the backflow of its own burned gas.

&lt;p&gt;The effects of elevated-pressure on rotating counterflow twin flame were numerically investigated. The range of pressure is from 1 to 8 atm. We performed numerical simulations with and without radiative heat loss. The loss was evaluated by using an optically thin model, which does not consider reabsorption of radiative energy. Without radiation, the leanest extinction limits reached ultralean conditions; the higher the pressure is, the leaner the extinction limits are. On the other hand, with radiative heat loss, the leanest extinction limits are shifted to richer condition as the pressure becomes higher; above 2 atm, the leanest extinction limits cannot reach ultralean condition. The response curves of the flame temperature to the equivalence ratio are distorted when radiative heat loss is considered. Under high pressure, the flame thickness is thinner and the heat release rate is enhanced mainly because of the increase of gaseous density in the both cases of with and without radiation heat loss. However, the temperature behind the flame zone much decreases due to the radiative heat loss in the high pressure case. This is because of increments of partial pressures of the radiative species and the length of the residence time of fluid in the backflow region of burned gas.&lt;/p&gt;

Rotating counterflow twin premixed flame (RCTF) of hydrogen air was numerically simulated with detailed chemistry to explore the possibility of ultra-lean combustion. As a result, it was found that ultra-lean RCTF of equivalence ratio U = 0.052, which is far leaner than the generally-recognized flammability limit U = 0.10, is realized. It was also found that under ultra-lean conditions the flame temperature of RCTF largely exceeds the adiabatic flame temperature; e.g., at O = 0.06 the former is 1171 K, while the latter is 503 K. This increase of burned gas temperature is attributed to the so-called low Lewis number effect within the flammability limit, but under an ultra-lean condition some other mechanism to increase temperature is dominant. The 'pseudo local equivalence ratio' of burned gas of RCTF differs largely from that of the unburned gas due to the extraordinarily high concentration of H 2O. This suggests the possibility that the local condition at the reaction zone is much richer than the unburned gas, which brings about the large temperature increase. © 2012 The Combustion Institute.

Rotating counterflow twin premixed flames of methane-air were numerically simulated with detailed chemistry based on a similarity solution to explore the leanest extinction limit without preheating and to elucidate the mechanism of " ultra-lean" combustion. We focused on high rotation rate cases in which unrealistic backflow from infinity is allowed to occur since ultra-lean combustion was found to be realized in such a situation. It was found that the reaction zone is in the backflow zone, where the flame's apparent burning velocity is negative, and that the flame zone width is much smaller than that of a 1-D planar premixed flame due to an inversion of the convexity directions of the profiles of temperature and main species concentrations. The decrease of the flame width seems to make the flame less extinguishable. The equivalence ratio of the leanest flame obtained neglecting radiative heat loss is 0.32, while that obtained with an optically thin radiation model is 0.42, which is still much leaner than the ratio of 0.49 for a 1-D planar premixed flame generated using the same radiation model. © 2011 The Combustion Institute.

We experimentally investigated propagation characteristics of the shock wave driven by a gaseous detonation wave emerging from the open end of a cylindrical detonation tube. In the present study, we visualized the shock wave and exhaust flowfields using a shadowgraph optical system and we obtained peak overpressure in the tube axial direction and the continuous shape transformation of shock waves around the tube open end. We also obtained overpressure histories of the shock wave using piezo-pressure transducers within 201 m from the open end of the tube. We normalized and classified these results by four regions using non-dimensional pressure and distance which are independent of variety of mixture and tube diameter. In the vicinity of the open end of the tube, the shock wave is nearly planar and does not significantly attenuate, and the peak overpressure maintains approximately C-J pressure. Subsequently, the shock wave attenuates rapidly, transforming from quasi-spherical to spherical. Farther from the tube open end, the shock wave propagates with approximately sound characteristic so that the peak overpressure decreases proportional to 1/r. Eventually, the shock wave begins to attenuate more rapidly than ideal sound attenuation, which may be due to the viscous effect. © 2010 Springer-Verlag.

The educational hybrid-rocket was successfully launched and it also landed within the predicted area. Aerodynamic characteristics of the rocket designed by students of Tsukuba University were evaluated by the wind tunnel testing with the support of Tokai University. The flight path affected by the environmental condition, especially wind direction and velocity, was simulated with the original calculation program. The altitude of the rocket was measured with the optical equipment and the apex was 123 m although the calculation indicated 198 m. We expected that the insufficient filling or the...

In this study, we focused on a microflow reactor (MFR) as a method to capture the ignition phenomenon occurring in a reciprocating engine and examined a method to easily estimate the ignition delay time. Specifically, we proposed an estimation method that combines ignition position information and ignition delay time using "Livengood - Wu integral." We conducted experiments using a mixed fuel of normal heptane and iso-octane, which is a standard fuel for evaluating knocking in engine. As a result of these experiments, it is possible to obtain an ignition photograph even with very lean premixture in MFR, that is difficult to obtain in other numerical calculations and experiments. This leads that it is possible to estimate the ignition delay time under the super lean burn condition.

© ECOS 2020.All right reserved. This study focuses on the use of Solid Oxide Fuel Cell (SOFC) to large commercial buildings in Japan. This is a novel combined heat and power (CHP) application. SOFC has high power generation efficiency and is expected to be adopted by buildings with relatively smaller heat loads. The effect of CHP is determined by the energy demand of the building, and the energy demand varies not only by the building application but also by region. Therefore, in this study, the adoption of SOFC is analyzed by an optimization model considering energy demand for each region in the case of hospitals, hotels, retail stores and offices as typical commercial buildings. The regional distribution of potential SOFC is also discussed by aggregating them using Geographic Information System (GIS).

&lt;p&gt;Although HCCI combustion has high thermal efficiency, it has difficulties such as controlling its ignition timing and combustion. This study proposed a method to make HCCI combustion in gas engines possible, combining dedicated EGR, SI combustion, and HCCI combustion, i.e. multiple combustion modes engine system. In a DEGR system, one cylinder runs with a premixture of rich fuel and air to reform the part of its exhaust gas into hydrogen and carbon monoxide, which are introduced to other cylinders and promote combustion. In this study, the exhaust gas was introduced through a bypass from rich SI cylinder to HCCI cylinder. In the experiments, conditions of high thermal efficiency and combustion characteristics were investigated. It was revealed that DEGR made HCCI combustion possible on a condition that HCCI combustion was impossible. The more the DEGR rate was, the higher the thermal efficiency was, and the thermal efficiency reached a maximum value when the equivalent ratio of rich SI combustion was adjusted. We proposed the adjustment of premixed gas amount in Rich SI cylinder as a means of improving thermal efficiency, and it was successful.&lt;/p&gt;

<p>Fuel reforming is one of effective methods to control HCCI combustion, and dedicated EGR is an apposite fuel reforming system for engines. In this research, the combustion and exhaust characteristics of methane-fueled rich SI engine were investigated by experiments in order to realize the HCCI engine with dedicated EGR. In the experiments, equivalence ratio and spark timing were the operation parameters, and in-cylinder pressure and exhaust gas composition were measured. As a result, it was proved that dedicated EGR enables the generation of H₂ and CO without decrease of thermal efficiency. On rich SI combustion, an excessive advance of ignition timing causes misfire and instability of the engine. In addition, it was shown that thermal efficiency is one of the main performance indexes of the fuel-reforming cylinder, rather than the mole fraction of H₂ and CO in the exhaust gas.</p>

<p>Dual fuel engines (DFE) suffer from considerably high total hydrocarbon emissions and low thermal efficiency due to its poor combustion at low loads. Also, further improvement of thermal efficiency is needed at high loads. Therefore, in this study, the effect of double diesel fuel injection on the combustion and exhaust emission characteristics of DFE using town gas 13A (natural gas) was investigated in the experiments. The experiments were conducted using a single-cylinder engine and with a common rail injection system, varying the number of fuel injection and injection timings. In lower loads, the combustion was activated by the double injection and both THC emissions and thermal efficiency were improved, especially when the MFB50 was advanced. On the other hand, at higher loads, although the thermal efficiency slightly improved by the double injection, NOx emissions increased. This was because the in-cylinder temperature increased too much as the MFB50 approached top dead center.</p>

Effects of large-amount dilutions of exhaust gas recirculation (EGR) and dedicated-EGR (DEGR) on the ignition characteristics of stoichiometric methane-air premixed air were experimentally studied by using a micro flow reactor. The flames were formed for various EGR/DEGR ratios and equivalence ratios Φ_A in the DEGR cylinder Stable flames and oscillating flames were observed; the combustion characteristics varied because the mixtures were highly diluted with EGR/DEGR gases. Their ignition temperatures were defined by the positions of the flames referred to a measured temperature profile in the quartz tube. Since EGR gas is composed of inert species such as N_2 and CO_2, the ignition temperatures of the premixed gas with EGR gas were higher than that without EGR gas; the EGR gas dilution interferes the ignition timing in reciprocating engines. On the other hand, the ignition temperature of the premixed gas with the dilution of DEGR gas whose equivalence ratios correspond to Φ_A = 1.6 and 1.8 were lower than that with EGR gas. This is because highly-reactive intermediate species such as H_2 and CO. Particularly, the ignition temperatures of the premixed gases highly diluted (40%) with DEGR gas of Φ_A = 1.6 and 1.8 were lower than that without EGR gas or DEGR gas. Therefore, it was found that gases with DEGR have potential for shorting the ignition delay.

Combustion oscillation is investigated experimentally and theoretically in order to predict combustion oscillation for various fuel mixture conditions. To grasp the characteristics of combustion oscillation, combustion experiments were performed in the mockup combustor of micro gas turbine combustor with high swirl number Sw=2.42. Experimental result shows that two types of oscillation were observed: one is piping oscillation whose frequencies are mostly under 100 Hz and the other is combustion oscillation whose frequencies are over 400 Hz. We also found that frequency suddenly shifts to higher frequency about 600 Hz when hydrogen ratio is large. This phenomenon is supposed to be processing vortex core (PVC) because of whirling of vortex core. Since RMS value of pressure due to combustion oscillations obtained by the experiments and calculated laminar flame speed has common characteristics, pressure interaction index was modified due to relationships among laminar flame speed, pressure, density, and heat release rate; the pressure interaction index can be described as a function of laminar flame speed. Then, we proposed the criterion of the growth rate for judgment of combustion oscillation occurrence based on n-z model. This modified criterion could be much successfully judged combustion oscillations than the previous model using the constant value of the pressure interaction index 0.05. However, the criterion is very sensitive about frequency.

Effect of flame stretch on CH_4/air ultra lean co-rotation counter flow premixed flame was investigated by numerical simulation. Counterflow twin flame and co-rotating counterflow twin flame were compared. The result shows that the flame stretch under ultra lean conditions is very small. In the case of ultra lean conditions of co-rotation counterflow twin flames, local burning velocity and radial velocity gradient at the flame front are very small. They are extremely small compared to those of non-rotating counterflow twin flames and ordinary lean co-rotating counterflow twin flames. In addition, the flow velocity at the flame front is also small. We could not determine whether co-rotating counterflow twin flame suffers the effects of flame stretch or not, since the flow fields of these flames are different significantly.

In this study, characteristics of combustion oscillation generated in gas turbine combustor are numerically and experimentally investigated. Numerical analyses are performed with two different methods: Combined EBU method and Comparison PDF Transport method. These numerical results provide important parameters such as delay time. Stability criterion for combustion oscillation is evaluated by the combination of numerical analysis technique and the evaluation formula proposed by Z. M. Ibrahim. Experimental conditions are selected to investigate the condition of combustion oscillation excitation mechanism by changing experimental parameter such as composition of the fuel, equivalence ratios and swirl numbers. As a result, with increasing the rate of hydrogen in fuel or the swirl numbers, combustion oscillation is likely to occur and combustion oscillation occur under the conditions of specific equivalence ratios in the experiment. Finally, experimental results are compared with numerical analyses. A trend of natural frequency to the change of equivalence ratio and the range of equivalence ratios which combustion oscillation occurs by the numerical analysis is in good agreement with those by the experiment.

Counterflow of methane-air premixed gas and burned gas with active radicals are calculated with detailed kinetics. It was found that the effects of addition of radicals on extinction limits and flame structure are not significant. There are small difference between addition and no addition of radicals. Furthermore, due to the strong radial-direction flow, added radicals are transported to radial direction by convection and diminished. Meanwhile, temperature of countering burned gas has a dominant effect on sustaining premixed flames. High-temperature burned gas affects weak flame and its extinction limits are extended. These results agree well with the results of counterflow flames of propane-air premixed gas and burned gas conducted by Darabiha et al. [Darabiha, N., et al., Combust. Sci. Tech., 60 (1988), 267.].

Ultra-lean combustion has been attracting attentions because the emission of CO_2 and NOx would be very low if it realized. We simulated rotating counterflow twin premixed flames and succeeded in forming a further ultra-lean flame of φ=0.32. These flame structures are quite different from general 1-D premixed flame. There are additional stagnation points near the upstream end of the preheat zone due to the backward flow of the burned gas caused by the centrifugal force. In the case of ultra-lean combustion, reactive species of premixed gas are transported by diffusion over the stagnation po...