To investigate the influences of thermal and pressure loads on the structural deformation of the Liquid Oxygen/Methane rocket engine combustion chamber, a complete thermo-structural analysis scheme including fluid-thermal analysis and structural finite element analysis is developed and then verified to be reasonable. By conducting fluid-thermal analysis, the detailed distribution of the thermal and pressure loads is obtained. These results are utilized as body loads and surface loads in structural finite element analysis. Then, the stress-strain responses of the combustion chamber and the accumulation process of the deformation induced by thermal and pressure loads were studied in detail. The main conclusions are as follows: Under the action of thermal loads alone, the most pronounced residual mechanical strain is at the upstream of the nozzle divergent segment. Reducing the temperature difference between the hot run and the pre-cooling phase can be a feasible improvement measure for this issue. Under the action of the pressure loads alone, the bottom of the cooling channel bends toward the centerline of the combustion chamber. Properly increasing the thickness of the channel bottom near the coolant inlet is deemed to be an effective measure to reduce this bending trend. Under the combined action of thermal and pressure loads, the structural deformation characteristics are determined by the combination of thermal loads and pressure loads, rather than mainly by thermal loads. The accumulation rate of mechanical strain at the channel bottom corner is much rapider than the other positions. Turning the sharp bottom corner of the cooling channel into rounded corner is an alternative method of suppressing strain accumulation.

Nanofluids which act as coolants in various thermal applications have been promising in accomplishing the primary objective of heat transfer. However, the impact of such fluids on flow lines in the form of enhanced friction factor through unacceptable viscosity rise is an issue to be addressed. On the other hand, these fluids are expected to deteriorate the environment when used or disposed. Hence this research focuses on preparing a bionanofluid and investigating on its primary properties, the thermal conductivity and viscosity. The bionanofluid is prepared by dispersing neem (azadirachta indica) assisted zinc oxide nanoparticles in a binary mixture of ethylene glycol-water (50:50 by volume), at volume concentrations of φ=0.05, 0.2 and 0.5%. To compare the properties of these bionanofluids, additional nanofluids were prepared by dispersing combustion derived pure zinc oxide at same volume concentration. By XRD analysis, the average crystallite size of neem assisted ZnO and pure ZnO was found to be 36 nm and 32 nm. Based on the SEM images, the particles were found to be much closely packed in bioparticles than combustion derived ones. The zeta potential of the nanofluids was found to be ±30 mV at pH 6.5, at which the stability is deemed excellent. The thermal conductivity and viscosity of the nanofluids were measured under varying volume concentration and temperature ranging between 20oC and 50oC. Though the thermal conductivity of the conventional ZnO nanofluid is 3.8% higher than the ZnO bionanofluid, the viscosity is 2% lower for the latter than the former, which is highly expected from any nanofluid for an efficient thermal transport.

Indonesia has implemented a policy of using diesel fuel containing 20 percent biofuel (commonly known as B20 biodiesel), as stated in Energy and Mineral Resources Ministerial Decree No. 23/2013. This study investigated the flame-spread characteristics of biodiesel (B20) in a microgravity environment through drop tower facilities. This is due to the difficulty in creating droplet sizes similar to the real liquid sprays in the combustion chamber of diesel engines. The experiment used biodiesel (B20) droplets with a diameter 1 mm. The results show that the biodiesel (B20) droplets have characteristics of a flame–spread limit distance S_BC/d_C0limit = 7. This paper discusses the characteristics of biodiesel (B20) droplets in detail.

The complexity of the actual operation of thermal engineering systems comprises multiphase interfacial phenomena evolving out of equilibrium. Therefore, their generalised formulation can contribute towards better understanding and control of these phenomena, eventually pushing the existing related technologies beyond the state-of-the-art. In this respect, variational principles are significant for a more comprehensive physical representation and for closing the problem, while obtaining relatively simpler mathematical formulations. In this study, a general variational formulation of dissipative two-phase flows based on the minimum entropy production is developed. In particular, this study provides a general expression of the entropy generation rate, which introduces interfacial contributions due to surface tension between different phases, and is used to estimate two-phase flow fraction based on Prigogine's theorem of minimum entropy generation. Subsequently, this formulation is investigated in terms of different assumptions and pressure drop models, and employed to clarify the implementation of Prigogine's theorem to obtain the widely-accepted Zivi's expression of void fraction and the effect of different assumptions on the deviation from his expression. A new expression is finally obtained to cover laminar flow conditions, which are implicitly excluded from the applicability of Zivi’s expression.

Renewable biodegradable butanol blended to diesel fuel was used in an engine that operates on PCCI mode shows excellent combustion characteristics and offer efficient high load performance with minimum exhaust emissions. Its higher octane number prevents engine knock, higher cooling effects have potential to reduce the NO_X emissions and well-mixing ability with air substantially reduces the smoke emission. In the present experimentation, n-butanol and diesel blend B10, B20, B30 and B40 were tested on PCCI mode which was mainly accomplished by DI timing 20 degree CA bTDC and injection pressure 400 bar. For high load operation, B40 blend provided 6.9%, 8.1%, 12.9% and 13.7% higher brake thermal efficiency over B30, B20, B10 and neat diesel respectively at the cost of small increment in brake specific fuel consumptions. Smoke and CO emissions reduction were observed. However, NO and HC emissions produced were higher than the B30, B20, B10 and diesel respectively. Considering the benefits in terms of higher high load efficiency and lower emissions, in addition, delayed CA50 (50% burn at crank angle) than all fuel blends, B40 blend was preferred for higher premixing to attain higher performance.

JIS B 8628, “Air-to-air heat and energy exchanger and ventilators” provides standards for evaluating the performance of the energy recovery ventilators. JIS B 8628 was established in 2000, and revised in 2003. In 2017, JIS B 8628 was revised furthermore to ensure consistency with ISO 16494, which was established in 2014. For that purpose, the two room setup and the ducted setup, which are prescribed in ISO 16494 with specified pressure conditions at inlet and outlet of energy recovery ventilators for the airflow test, the tracer gas test and the thermal performance test, were added in JIS B 8628 (2017). In Japan, either the two room setup or the ducted setup is being used by manufacturers to determine the performance values, which are referred to when the compliance of total building energy performance to the Building Energy Efficiency Act is claimed. However, no studies have yet focused on the difference of the test results between the two room setup and the ducted setup. In this study, authors applied those setups and the test setup prescribed in JIS B 8628 (2003) to four energy recovery ventilators and compared their results. As for the airflow-static pressure characteristics, the curves obtained by the three test setups generally correspond to each other, except for the curves for the air exhaust line obtained by JIS B 8628 (2003). The unit exhaust air transfer ratio values obtained by the ducted setup and JIS B 8628 (2003) tend to be greater than those by the two room setup. As for the thermal performance represented by the total effectiveness, differences among the three test setups can be observed when there is a difference of the unit exhaust air transfer ratio and/or the ratio of the supply airflow rate to the return airflow rate.

This work presents an investigation, both experimentally and numerically, of the similarity of the periodic dynamic behavior of buoyant jet-flames. A single buoyant jet-flame exhibits two well-known types of dynamic behavior, namely, axisymmetric (varicose mode) and asymmetric (sinuous mode) motions, whereas the interaction of two adjacent buoyant flames (twin flames) create an axisymmetric (in-phase mode) and asymmetric (anti-phase mode) motions. Aside from identifying any similarity in the dynamics of the jet-flame systems, this study also aims to provide a proper interpretation for the mode transition of the single buoyant jet-flame, which is generally difficult to control. The thermal boundary layer surrounded by the jet flame was visualized through optical imaging and a three-dimensional numerical prediction. Frequency analysis was executed to determine a global parameter to properly describe the observed dynamic motion and mode transition. Moreover, the critical Reynolds number was discussed as an ideal candidate for characterizing the mode transition having the sinuous meandering behavior for the single-flame and twin-flame systems.

In order to understand turbulent combustion and its combustion characteristics, laminar flame speed is often used. Laminar flame speed plays an important role in turbulent combustion models used in engine combustion simulation. However, there are few reports on laminar flame speed of liquid fuel under high pressure condition simulating the inside of an engine cylinder. In this study, the measuring system using simple compact equipment was developed to obtain laminar flame speed of liquid fuel with the double kernel method under high pressure conditions. In this equipment, as easily ignited at high pressure, laser induced breakdown ignition technique was used. The experiments were conducted on propane-air premixed gas so that it could be easily compared with the reports of other researchers. The experiment was conducted on propane/air premixture so that it could be easily compared with the other reports. A detailed investigation of the time history of the flame separation revealed that the conventional method of calculating the laminar flame speed used in the double kernel method was not suitable for this measuring system. Therefore, a new calculation method for the laminar flame speed was studied, and the pressure dependence of the laminar flame speed of the propane/air premixture was investigated. As a result, it was found that it was in good agreement with other reports. The laminar flame speed measurement system developed in this study is considered to be useful.

The characteristics of the propagation of a detonation from a cylindrical tube of constant cross section into a diverging cone were experimentally investigated using the smoked-foil technique for three explosive gas mixtures: C₂H₂+2.5O₂, 2H₂+O₂+4.5Ar, and C₂H₄+3O₂+0.44N₂. The initial pressure and the cone enlargement angle were varied as governing parameters. The results were summarized in terms of the ratio between the inner diameter of the cylindrical tube through which a detonation initially propagated and the detonation cell width d/λ and of the cone enlargement half angle θ. Four patterns of detonation propagation were observed in the diverging cone: continuous propagation, re-initiation on the cone wall, re-initiation apart from the cone wall, and failure. The obtained results were qualitatively consistent with past experimental results reported by other researchers. However, quantitatively, the obtained results were dependent on the explosive gas mixtures, particularly on the so-called critical tube diameter. Actually, when the critical values of d/λ against detonation failure were normalized by that corresponding to θ = 90°, a single curve unifying all data to some degree was obtained. In addition, some characteristics of the detonation behavior in the diverging cone were explained by simple models.

With the recent miniaturisation of electronic devices, the heat generation density of the devices has increased tremendously, requiring the improvement of the performance of the cooling system. In this study, for the high performance of water cooling devices, we investigated convective heat transfer in a mini-channel where porous media that were manufactured by randomly laminated and sintered fine aluminium wires were inserted as a heat exchanger. We conducted the convective heat transfer experiment by changing the flow state from laminar to turbulent using pure water. We also conducted a numerical analysis using a simple lattice model of porous media with the same wire diameter and porosity as in the experiments by using the software PHOENICS. From both results, we discussed the effect of the structure of the porous media on heat transfer. From the results of the calculated permeability of the porous media using the experimental data of pressure-drop, we confirmed that the flows with the porous media were in a non-Darcy flow state. As heat transfer characteristics, it was shown that the Nu number of the experimental results was larger than that of the computational fluid dynamics (CFD) analysis models. Regarding the effects of wire diameter and porosity, the smaller the wire diameter and porosity, the higher the Nu number. By considering the differences between experimental and analytical results, we proposed two sets of new combination of parameters considering the volume of the fibre of porous media and the surface area, which separately correlated well with relationships of the experimental and analytical results against the Nu number.

The SPICE model of phase change material (PCM) for thermal network transient calculation was investigated. The nonlinear behavior of PCM due to latent heat was modeled by using the voltage dependent current source and the capacitor. A latent heat is stored in the capacitor as electric charges. Corresponding to the PCM phase state, such as solid, liquid and mixed phases, the dependent current source is controlled with PCM temperature and the latent heat quantity of PCM. Since the melting point of PCM has a distribution, the model in which multiple PCM models having different melting points and capacitor capacities were connected in parallel was employed. To validate the numerical simulation model, the aluminum case with PCM sealed inside was prepared. The sample was heated with a rubber heater from the bottom with different heat quantities. The temperature changes of the upper and lower surfaces were measured with thermocouples. The results showed the error between simulated and measured values were below ±4 °C and the calculation time took below real-time. This simulation model can be applied to cooling system optimization and temperature control system.

Conjugate heat transfer analyses of premixed flames propagating toward the insulation or Al alloy wall are performed for C1 to C3 alkanes and H₂ flames at different equivalence ratios of φ = 0.6, 0.8, 1.0 and 1.2 under a high pressure condition of 2MPa in terms of one-dimensional numerical simulations with detailed reaction mechanisms (70 species and 321 reactions for alkanes, 9 species and 19 reactions for H₂). The effects of the equivalence ratio and fuel properties on the heat loss reduction through the wall due to the insulation are investigated in detail. The results show that for all the alkanes and H₂ flames, the temperature at the surface of the insulation wall increases more and faster than that of the Al alloy wall, and the heat loss is reduced due to the insulation. Furthermore, the heat loss reduction rate Λ for the insulation wall to the Al alloy wall becomes higher both with the increase and decrease in the equivalence ratio from the stoichiometric ratio, regardless of the fuel. The value of Λ reaches up to 2.1%. The reason for this tendency of Λ against the equivalence ratio can be explicitly explained by the time variations of gas thermal conductivity and gas temperature gradient in the vicinity of the wall, which control the heat flux through the wall.

The heat and mass transfer in a loop heat pipe evaporator with microgrooves are investigated in a three-dimensional numerical model. The design of the microgroove wick must consider the pressure loss of the vapor. The simulation obtains the detailed pressure distribution of the vapor flow in the grooves. The simulated heat flux distribution in the evaporator revealed that the applied heat flux concentrates along the three-phase contact line (TPCL) within the casing, wick, and grooves. The effect of TPCL length was investigated in three microgroove wicks with circumferential and axial grooves and a classical wick with only axial grooves. The heat-transfer coefficient initially increased with TPCL length increasing, but thereafter decreased because when the TPCL becomes too long, a large pressure loss occurs in the grooves. The developed model was validated experimentally. In both the model and experiment, the heat-transfer coefficient was locally maximized at a certain TPCL length. The proposed method is expected to provide a simple approach for wick design; especially, the wick shape can be optimized merely by varying the TPCL length. The effect of thermal conductivity of the wick material is also discussed.

To effectively utilize renewable biomass resources, gasification technology is being actively developed. Many studies have been performed regarding the gasification of biomass-derived char (i.e., biochar), where the gasification rate varies greatly with experimental device and biomass type, even when the same gasification temperature is used. In addition, the pore development mechanism during gasification i.e., the relation between the gasification reaction rate and interface area, has been rarely studied. Herein, the gasification rate of wooden biochar with H₂O and CO₂ gasifying agents using same experimental apparatus and char samples were investigated. The development of micro- and mesopores in the biochar during gasification with H₂O and CO₂ agents was examined in detail. The results showed that (1) gasification rate constant of biochar was approximately 3–10 times higher under H₂O gasifying agent than under CO₂ agent at 1073–1273 K; (2) this study reported the most typical values of frequency factor A and activation energy E on Arrhenius plot at high temperature region; and (3) the specific surface area of the micro and mesopores increased with proceeding H₂O and CO₂ gasification, and the reaction rate is proportional to the interface area during the gasification process.

Lean combustion is susceptible to combustion instabilities, especially pressure oscillation, and this severely damages the combustor. To prevent this, many studies have attempted to elucidate this phenomenon. However, the physical understanding of the mechanism is still incomplete owing to its complexity. In this study, combustion instability in turbulent spray combustion in lean fuel condition is investigated using Large Eddy Simulation (LES). The combustion chamber has a backward facing step, and kerosene fuel droplets are injected vertically just upstream from the step. The dynamic thickened flame model is used as the turbulent combustion model, and a two-step global reaction model is used for kerosene-air flames. The influence of pressure oscillation on fuel atomization behavior is considered using a model, which predicts the Sauter Mean Diameter of injected the fuel droplets with time. The equivalence ratio is set as 0.6, 0.8, and 1.0. The results show that combustion instability is observed in all cases, and the intensity of combustion instability decreases with a decrease in the equivalence ratio; however a unique phenomenon is observed for the lowest equivalence ratio of 0.6. The unique phenomenon here is the time variation of amplitude of pressure oscillation, whose behavior has been also observed in some other studies. At this condition, while the frequency of pressure oscillation is temporally constant, the frequency of heat release rate varies with time, which is investigated with newly proposed index Time Gap. In addition, the spatial distribution of heat release rate temporally changes with varying frequency. They cause the time variations of correlation between pressure and heat release rate, and finally the amplitude of pressure oscillation temporally varies.