Mitsuaki Tanabe

• PhD
• Professor (Full) at Nihon University

div class="section abstract"> Although methane number is widely used to predict knocking occurrence and its intensity, it does not determine a fuel composition uniquely, that means, the knocking intensity by the different composition fuel must show difference even if the same methane number fuels are employed. To establish a novel index, the knocki...

Combustion oscillation in a rocket combustor was analyzed using a Variational Auto-Encoder (VAE). Dimension reductions were conducted on various physical quantities (p′, ˙q′, etc.) in the combustor. Orthogonal modes were obtained using proper orthogonal decomposition for the output of VAE. Pumping and damping regions in the combustor were identifie...

Cool flame oscillation of a fuel droplet array in high-temperature air was numerically simulated by using a droplet vaporization/spontaneous ignition numerical model. The time series data of temperature and chemical species spatial distributions were obtained. The data were used to train a Variational Auto-Encoder (VAE) that reduces the dimension o...

A microgravity experiment is going to be held in 2022 by using sounding rocket to clarify a cool flame dynamics of multiple n-decane droplets such as ignition delay time, ignition location, cool flame propagation, and so on. To predict the cool flame dynamics near ignition limit, 2D axisymmetric unsteady numerical calculation was carried out. A sin...

A technique using deep neural network (DNN) is introduced for the analysis of combustion dynamics recently. The functionality of the conventional machine learning, proper orthogonal decomposition (POD), technique, is summarized; and how it can be implemented by DNN is explained from mathematical viewpoint. Deep auto-encoder (DAE) consist of an enco...

Deep auto-encoder (DAE) is applied to the decomposition analysis on the transition process of intrinsic combustion oscillation. Two dimensional URANS simulation reproduced combustion oscillation in CVRC (continuously variable resonance combustor) including the dynamics of the stable-to-unstable and unstable-to-stable transition. The transition proc...

Oscillation mode of the triple flame in standing acoustic field was investigated by POD (Proper Orthogonal Decomposition) method for cross-sectional images of them. In order to capture the shape of the triple flame cross section, the chemiluminescence of acetone mixed in the burner flow was visualized by PLIF (Planar Laser Induced Fluorescence). Th...

The similarity between POD (Proper Orthogonal Analysis) and NN (Neural Network) is explained and an example of NN to perform reduced dimension analysis on a combustion oscillation problem is presented. The dimension reduction procedure by Snapshot-POD is shown to be expressed by a three layer AE (Auto-Encoder). Based on this, a DAE (Deep Auto-Encod...

div class="section abstract"> This study focused on a non-equilibrium plasma discharge as a means of assisting HCCI combustion.Experiments were conducted with a four-stroke single-cylinder engine fitted with a spark electrode in the top of the combustion chamber for continuously generating non-equilibrium plasma from the intake stroke to the exhaus...

Preliminary studies have been done in a framework of the “Symbolic Project of College of Science and Technology, Nihon University” on the new technologies potentially capable of improving energy conversion efficiency. New concepts for thermal engine, solar and nuclear energy utilization, and for their associated numerical simulation were proposed....

The flame curvature and the lift-off height of a triple flame under acoustic oscillations are investigated. The multi-slot burner, which can make uniform streamwise flow velocity and stabilize the triple flame two-dimensionally is employed. The triple flame is formed at the anti-node of velocity oscillations. The flame curvature and the lift-off he...

End-gas compression by propagating flame in super-lean SI engines was simulated by a RCM to uncover the spontaneous ignition process of the end-gas in in-cylinder under highly turbulent conditions. Lean n-heptane-air mixture of 0.5 and 0.7 in equivalence ratio was employed. In-cylinder turbulence was generated by a perforated plate set in the cylin...

Self-excited combustion oscillations in a model rocket combustor is investigated experimentally. A unique dump combustor, CVRC (Continuously Variable Resonance Combustor), is employed to realize a well-controlled self-excitation. The combustor has a coaxial injector whose oxidizer post has a choked inlet that is variable in length allowing for a de...

div class="section abstract"> It is difficult to control the ignition timing of Homogeneous Charge Compression Ignition (HCCI) engines because they lack a physical means of igniting the mixture. Another issue of HCCI engines is their narrow operating range owing to the occurrence of misfiring at low loads and abnormal combustion at high loads. As a...

This study investigated the effect of streamer discharge on lean-combustion in an internal combustion engine. A continuous streamer discharge was generated in the wall-side of the combustion chamber of a 2-stroke optically accessible engine that allowed visualization of the entire bore area. The experimental results showed that the weak flame was i...

This study investigated the effect of streamer discharge on autoignition and combustion in a Homogeneous Charge Compression Ignition (HCCI) engine. A continuous streamer discharge was generated in the center of the combustion chamber of a 2-stroke optically accessible engine that allowed visualization of the entire bore area. The experimental resul...

Lift-off height and flame curvature of a triple flame formed with methane-air and propane-air mixture are investigated experimentally in various fuel concentration gradients and sound pressures. Burning velocity of the triple flame has strong correlation with fuel concentration gradient, and lift-off height is determined by balanced position betwee...

Prediction of combustion instability is essential in reducing development costs of large scale rocket engines. Recently, high fidelity CFD models have shown some ability to represent the stability characteristics of sub-scale experimental combustors. A challenge remains in acquiring experimental measurements of critical combusting flow properties,...

The flame stabilization method using thermo-acoustic oscillation was demonstrated and the effectiveness of the sound for the flame stabilization was validated by investigation of the lift-off height change in a standing acoustic field which is a simple acoustic system. The insight of stabilization mechanism, focused on the variation of temperature,...

In this study, we generated the uniform diameter micro-bubbles using a piezo-vibration assisted capillary nozzle for apply the nano/micro bubbles device use. The capillary nozzle (diameter: 35 μm) was fabricated by FIB technique, and attached with piezo-device as micro bubbles generator. The fabricated piezo-nozzle showed inflective movement, whose...

Combustion experiments were conducted with an optically accessible engine that allowed the entire bore area to be visualized for the purpose of making clear the characteristics that induce extremely rapid HCCI combustion and knocking accompanied by cylinder pressure oscillations. The HCCI combustion regime was investigated in detail by high-speed i...

There are strong demands today to further improve the thermal efficiency of internal combustion engines against a backdrop of various environmental issues, including rising carbon dioxide (CO_2) emissions and global warming. One factor that impedes efforts to improve the thermal efficiency of spark ignition engines is the occurrence of knocking. Th...

Knocking intensity under the in-cylinder flow field was investigated by using a rapid compression machine (RCM). The nitrogen diluted and non-diluted fuel-air mixtures were employed for the examination of the combustion characteristics under the in-cylinder flow field. The behaviors of flame propagation and the spontaneous ignition in end gas were...

Ignition delay times and combustion times of iso-octane/air mixture and nitrogendiluted/ non-diluted gasoline/air mixture were measured by using a rapid compression machine under the conditions equivalent to practical engines. The dilution ratios were 0, 20 and 50% by external percentage. For the case of iso-octane, the pressure range is 1.77 to 2....

A method of flame stabilization using thermo-acoustic self-excited sound oscillation is demonstrated and the flame stabilization mechanism is investigated by a simplified standing acoustic fields generated by two loud speakers and a resonance tube. V-shaped flame which is formed in low flow velocity fields is employed for the mechanism investigatio...

Ammonium nitrate (AN) composite propellants are environmentally friendly, chlorine-free propellants. To improve the burning rate of composite propellant, aluminum particles are added as an extra energy ingredient for many composite propellants. However, the effects of agglomerate and ignition of aluminum particles on the temperature profile in the...

Knocking characteristics for various flame propagation velocity was investigated by changing turbulence in the combustion chamber. The use of the super rapid compression machine (SRCM) provides an opportunity to investigate the behavior of intense knocking. The behavior of flame propagation and spontaneous ignition of end gas were observed and flam...

Hydrazine monopropellant thrusters are used as propulsion system for trajectory corrections and other operations of satellites or unmanned spacecrafts. But hydrazine is difficult to handle, therefore the design and the synthesis of next generation monopropellants that could be able to supersede hydrazine is currently studied by scientists around th...

Characteristics of secondary flow caused by local heating/cooling in standing acoustic fields were predicted by numerical simulations and verified by microgravity experiments. As a result of both the simulations and the experiments, at the middle of a velocity node and the neighboring velocity anti-node, the heated air was blown toward the node and...

Wrinkled and corrugated flames were observed at velocity anti-node in the standing acoustic field. It is thought that the deformation is cased by baroclinic torque. The detailed influence of the baroclinic torque on the structure of the flame front remains to be unclarified. In this study, numerical investigation has been carried out on the roles o...

Knocking characteristics for various flame propagation velocity was investigated by changing turbulence in the combustion chamber. The use of the super rapid compression machine (SRCM) [1, 2] provides an opportunity to investigate the behavior of intense knocking. The behavior of flame propagation and spontaneous ignition of end gas were observed a...

Behaviors of shock waves in knocking phenomena were observed in detail and influences of low temperature reaction on the flame and spontaneous ignition of end gas were investigated through experiments using high-speed direct and schlieren photography. As a result, it was found that light emission of shock waves, that is an indicator of pressure, ro...

Homogeneous Charge Compression Ignition combustion in homogenized temperature fields was investigated experimentally using a super rapid compression machine. Temperature fields before a blue flame occurs are thought to control the burning process. The time of blue flame occurrence, burn rate and ignition delay time were measured. Temperature homoge...

Ducted rockets are one kind of ramjet engines which are air-breathing propulsion system suited for supersonic flight. Fuel components used for ducted rockets are fuel-rich propellant. To obtain high specific impulse, it is desired that the fuel materials evolve high combustion heat per unit mass in the air. Boron is the most suitable material of th...

In this study, we evaluated effect of Aluminum (Al) particles for combustion mechanism of Ammonium Nitrate (AN) composite propellant. In the result of the combustion experiments, the burning rate of AN composite propellants increased with increasing concentration of Al particles. Aluminum particles do not ignite and combust at solid phase including...

Many liquid monopropellant thrusters have been used hydrazine. The hydrazine is toxic and hazard to handle. Next generation monopropellant needs to be used in place of the hydrazine, therefore the next generation monopropellant supersedes hydrazine has been studied all over the world. The GAP is stable substance at ordinary temperatures and pressur...

The combustion behavior of the aluminum particles near the burning surface of the aluminized composite propellant was studied. The combustion of the strand in the strand burner and the computational fluid dynamics (CFD) around the burning aluminum particle were performed. The temperature histories from combustion experiments and the temperature dis...

From the microgravity experiments on single fuel droplet combustion and on spark-ignited premixed flame in acoustic field, that have been done in this decade, secondary flow has been confirmed. The flow occurs only when combustion occurs and always in the direction to the neighboring node of velocity oscillation in standing acoustic field. This flo...

To design a rocket motor, thrust and burning rate of propellant are important factors. The combustion efficiency of a rocket motor is determined by combustion of aluminum (Al). It is needed to ignite aluminum particles near the burning surface of propellant. The temperature in the reaction zone increases with increasing the distance from burning su...

Secondary flow is a flow which is caused by the interference between standing acoustic fields and local density change. The behavior of the secondary flow depends on the location of the given local density change in the standing acoustic fields. When the density change is given at the middle of a velocity node and the neighboring velocity anti-node...

The influence of an acoustic field on premixed flame propagation was examined by numerical simulation and experiment. The influence was evaluated from the two points of view. One is the diffusive transport and the other is convective transport. The particle oscillation by sound is considered to increase diffusivity in the acoustic field like turbul...

Combustion efficiency of characteristic velocity is important factor that shows reaction situation in combustion chamber. And if a propellant burned completely in combustion chamber, C * combustion efficiency is 100%. However, metal particles are mixed in the propellant and metal particles are hard to completely burn. Therefore, there is a possibil...

To design the rocket motor, thrust and burning rate of propellant are important factors. The large range of burning rate makes the design criteria increase. The range of burning rate is expanded with catalyst or changing the size of oxidizers, however the range of burning rate of ammonium perchlorate composite propellants is small. Black powder has...

Interference between an acoustic field and premixed flame is investigated. Two kinds of transport processes are considered to cause combustion promotion in the acoustic field. One is diffusive transport. It has long been considered that the acoustic oscillation promotes diffusion, like turbulence does. The other is convective transport. Acousticall...

For ignition of boron (B) in the dncted roeket, it is neeessary to search the ignition distance and the flame area of the fuel rich hot gas (FRHG). The ignition temperature of B is over 1000 K and the flame temperature of the FRHG is higher than 1500 K. To improve the ignition characteristic of the FRHG, the propellant is included the metal particl...

We had improved RCM and developed a Super Rapid Compression Machine (SRCM) that realizes an extremely rapid compression compared with the conventional RCM. In this study, the performance of the developed SRCM was evaluated. The SRCM was used to investigate on the effects of equivalence ratio on HCCI of n-heptane and iso-octane fuel/air mixture. Exp...

Improvement on thermal efficiency in spark ignition engines requires high compression ratio, lean burn, reduction of cooling loss and soon. High compression ratio is the most promising way to improve the thermal efficiency, while engine knock becomes critical problem. High-speed Knocking is difficult to test since it gives mechanical damages to the...

Ramjet induced compressed air to a secondary combustor and mixed with fuel. High thrust was needed to overcome air drug, therefore the diameter of nozzle throat must be large. The flow speed in the secondary combustor was higher than 200 m/s. The residue time in the secondary combustor was shorter than 10 ms, and the mixture gas burned at very shor...

It is important to control the spontaneous ignition and the succeeding combustion to achieve the expansion of the Homogeneous Charge Compression Ignition (HCCI) engine's operation region and the suppression of the knocking in SI engines. However, the most frequenty used tool that is the Rapid Compression Machine (RCM), can not simulate the ignition...

Boron has been considered most attractive fuel for ducted rockets because of its high combustion heat with oxygen. However, boron was found to be impractical as the fuel because of its poor combustion efficiency due to the meager ignition characteristics. Boron had to be ignited and combusted forcibly in the residence time of the recirculation zone...

The mechanism of the streaming caused by local heating in standing sound waves is investigated through experiments and numerical simulations. The prediction of combustion oscillation occurrence requires knowledge on the interference of acoustic oscillation and combustion. The research on the phenomenon had discovered a new thermal convection. When...

The jet flame characteristics at the fuel gas injector in the secondary combustor were evaluated to obtain optimum design parameters of the gas generator. Mixed gas of air and fuel gas temperature in the secondary combustor was an important factor to make the jet flame. Self-burning solid propellants were used for gas generator, and it needed to ta...

Ducted rockets take full advantage in supersonic. Therefore, they need powerful thrust to overcome large drag. Using boron particles as fuel is effective approach to improve thrust. However, it is difficult to ignite and burn boron particles in the combustor. To burn boron particles for short time in the combustor, a propellant contained high-energ...

Ducted rockets, one kind of ramjets, are superior to the typical solid rocket motors in specific fuel consumption. Ducted rockets need large thrust since they are operated in supersonic Using boron as fuel is effective approach to improve thrust Boron has a so high heat of combustion that it is possible improve thrust However it is difficult to ign...

Interaction between droplet combustion and acoustic oscillation is clarified. As the simplest model, an isolated fuel droplet is combusted in a standing sound wave. Apart from the conventional idea that oscillatory component of flow influences heat and mass transfer and promotes combustion, a new model that a secondary flow dominates combustion pro...

Combustion and ignition characteristics of pyrolant containing sulfur were investigated. Burning rate and ignition delay time were measured using black powder, which was one of the pyrolants containing sulfur. Burning rate increases with increasing sulfur content (ξ), and reaches the maximum at ξ=0.25. The maximum value is 7.5 times larger than tha...

A new convection in micro-gravity was discovered that occurs when droplet burns off a node and an anti-node of standing sound waves experimentally. The convection is named "thermo-acoustic streaming". It has found that the thermo-acoustic streaming promotes a burning rate. The situations around the streaming are not investigated yet. Detailed distr...

Combustion in standing sound wave induces a new type of convection that is named as thermo-acoustic streaming. The mechanism of the streaming is analyzed and experimental investigations are made to evaluate its influence on burning rate of a droplet. Since natural convection has characteristics very similar to the streaming, microgravity conditions...

Combustion of an isolated fuel droplet in acoustic fields is investigated by microgravity experiments. The influence of standing sound wave is examined by varying amplitude of velocity fluctuation, frequency of sound and location of droplet. Variation of flame shape and burning rate is determined. As a result, spreading flame to one direction as we...

Combustion characteristics of mono-sized particle group were investigated in supercritical environments, to find the relation between actual spray and the results on a droplet and droplet array. Mono-sized octadecanol particles of 35μm, 55μm and 135 μm in Sauter mean diameter were prepared in advance by filtering sprayed droplets. The flame propaga...

High pressure single droplet combustion in standing acoustic field was examined to clarify the relation between density of ambient gas and strength of thermo-acoustic streaming. Ambient pressure of 0.1,0.2,0.5MPa are tested in this experiment. Acoustic pressure, acoustic frequency and relative droplet position to standing acoustic fields were varie...

Thermo-acoustic streaming is a newly observed convection that occurs when droplets burn in standing sound wave. The convection promotes heat and mass transfer that lead to combustion enhancement. Theoretical analysis predicts that the non-dimensional excess burning rate (k/k0)-1 is proportional to the square or quadratic root of acoustic Grashof nu...

Catalytic combustion of propane-air mixture was investigated. Platinum catalysts over a flat stainless steel with γ-alumina washcoat were employed. The employed burner has three catalysts set parallel to the mixture flow, spaced at an interval of 5, 10 and 15 mm. Both experiment and numerical simulation were made at inlet temperature of 553 K, inle...

The influence of acoustic fields on combustion of a single fuel droplet has been investigated using microgravity. The natural convection-free conditions allow the role of sound alone to be established by avoiding the coupling of sound-induced alternating convection and natural convection. Experiments were done with n-decane single droplets of about...

The experiment was carried out in homogeneous propane-air mixture and in several concentration gradient of mixture. Igniter is put on the upper side of the combustion chamber. In concentration gradient experiment, mixture was ignited from lean side. An experimental study was conducted in a combustion chamber. The combustion chamber has glass window...

Spontaneous ignition of isolated single fuel droplets in air is investigated. Special attention is given to the transient behavior of chemical reactions. Single-stage and two-stage ignition or cool flame behavior is investigated. A fuel droplet of n-heptane, n-dodecane, or iso-octane is suddenly exposed in a high-temperature, high-pressure air to i...

For the first time, spherical diffusion flames of n-decane, n-heptane, and methanol established around fuel-drenched porous spheres were investigated by applying the two-dimensional laser-induced predissociation fluorescence method to measure the OH radical under microgravity conditions. Focus of this work was laid on the development of a UV-laser...

Experimental and theoretical studies on the spontaneous ignition process of isolated fuel droplets were carried out. Time dependent temperature fields around the igniting droplets were observed by interferometry so that two step temperature rise can be detected. Some experiments are performed under microgravity to obtain reference data. Induction t...

The effects of natural convection on two-stage spontaneous ignition of a fuel droplet were studied experimentally. A suspended n-dodecane droplet of 0.7 mm in its initial diameter was employed. Ignition phenomena were observed by a fine thermocouple (0.025 mm) and by an interferometer so as to detect an invisible cool flame. A direct photographic m...

The evaporation of fuel droplets under high ambient pressure and temperature in normal gravity and microgravity has been investigated experimentally. For subcritical ambient conditions, droplet evaporation after a heat-up period follows the d2-law. For all data the evaporation constant increases as the ambient temperature increases. At identical am...

Natural convection is suppressed in space environment due to the weightlessness. Only centrifugal force is utilized currently to drive gas-phase thermal convection in space. This paper presents an alternative way to drive thermal convection. From the investigation of combustion oscillation in rocket motors, a new thermal convection had been found i...

The self-ignition process of single n-heptane droplets in the two-stage ignition regime (600-1100 K, 0.3-1 MPa) was numerically investigated with a detailed 62-step chemical model for n-heptane (437 elementary reactions, 92 species) where special attention has been paid on the low temperature branch. This detailed numerical simulations presents res...