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[en] An experimental study using the combustor with branch tube was conducted in order to model the industry combustor with FGR (flue gas recirculation) system and to study a thermo-acoustic instability generated by a branch tube. The branch tube is a structure used to modify a system geometry and then to change its pressure field, and the thermo-acoustic instability, usually occurs in a confined geometry, can result in serious problems on industrial combustors. Thus understanding of the instability created by modifying geometry of combustor is necessary to design and operate combustor with FGR system. Pressure fluctuation in the combustion chamber was observed according to diameter and length of branch and it was compared with the solution of 1-D wave equation. It was found that branch tube affects the pressure field in the combustion chamber, and the pressure fluctuation in the combustion chamber was reduced to almost zero when phase difference between an incipient wave in the combustion chamber and a reflected wave in the branch tube is π at the branch point. Also, the reduction of pressure fluctuation is irrespective of the installed height of branch tube if it is below h* =0.9 in the close-open tube and open-open tube
[en] Complete text of publication follows. Requirements for the Thellier and Thellier (1959) double heating palaeointensity determination technique are equality of blocking temperatures of partial natural remanent magnetisation (NRM) and thermoremanent magnetisation and linear field dependence of TRM. While the equality of blocking temperatures is tested during the experimental procedure by partial TRM checks and tail checks, the field dependence is in general not checked. However, two palaeointensity determination experiments can be derived from both aforementioned requirements: 1. the temperature is changed and the field is kept constant, i.e. the classical Thellier-Thellier technique and 2. the temperature is kept constant and the magnetising field is varied. We applied both techniques to promising baked limestone samples from a Roman limestone kiln at Tournai (Belgium) and from a pottery kiln of the same period from Bruyelle (Belgium) in order to test if both independent methods yield the same results. The studied limestone samples were taken inside the combustion chamber wall at two distances from the fire exposed surface, i.e. at 0 to 2.2 cm and at 4.8 to 7 cm. The alteration checks made during palaeointensity experiments fall generally inside the error envelope of the fitted slope. This indicates the absence of thermo-chemical alteration during the experiment and is apparently independent from the distance of the sample to the fire, although a colour gradient from white to black is observed at increasing distance from the fire. Somewhat different palaeointensities are systematically obtained with both palaeointensity determination methods. At 0 to 2.2 cm distance, the value is about 55 μT while at a 4.8 to 7 cm distance the value is about 72 μT. As the latter value is closer to known values for the same time period, the values obtained close to the fire are probably untrustworthy. Possibly, a low-temperature thermo-chemical disequilibrium, due to post-baking weathering, causes alteration below the first heating step (i.e. below 150 deg C) and being equalised by heating at 150 deg C. In this case, newly-formed magnetic grains would contribute only to the laboratory remanence. Consequently, TRM values are increased, implicating a flatter slope and eventually lower palaeointensity. The interior of the limestone slab, i.e. at 4.8 to 7 cm distance would not have been affected by weathering, and yields thus correct values. Palaeointensity determinations from the baked clay sample taken from the combustion chamber of the Roman pottery kiln at Bruyelle were not successful at distances close to the fire due to thermo-chemical magnetic mineral alteration. However, in samples taken between 6.5 and 8 cm from the fire exposed surface, the alteration is negligible and both palaeointensity determination methods yield very similar results of 73 and 76 μT. The good consistency of the results applying both techniques encourages us to use the variable field technique for further investigations, because the thermal stress during the experimental procedure is lower compared to the Thellier-Thellier technique, as one heats only to a constant temperature. However, preliminary alteration tests should be carried out in order to detect low temperature alteration and to choose the optimal heating temperature.
[en] The turbopump is a pressurizing system that supplies liquid propellants to the combustion chamber of a rocket engine at high pressure. As an integral component of a high-speed pumping system, the inducer used in a turbopump is forward-attached to an impeller to improve suction performance. This paper describes an experimental investigation on the flow instabilities of a two-bladed axial inducer due to cavitation. Cavitation development and its instabilities were analyzed. Asymmetric cavitation and cavitation surge were observed, and characterized by measuring the inlet pressure fluctuation for various cavitation numbers and flow coefficients. As flow coefficient decreases, the increased intensity of asymmetric cavitation was observed with an increased inception number of asymmetric cavitation. The frequency of the detected cavitation surge in the 4-10Hz range varied depending on the cavitation number. The instantaneous transition to cavitation surge appeared at the end of asymmetric cavitation as the cavitation number decreased. However, a further decrease in cavitation number resulted in the stable operation of the inducer with low values of pressure fluctuation. Finally, an intensive cavitation surge appeared after a significant amount of head loss
[en] This paper is the first investigation of the steady flow characteristics of an SI engine with a semi-wedge combustion chamber as a function of the port shape. For this purpose, the planar velocity profiles were measured at the 1.75B position by particle image velocimetry. The flow patterns were examined with both a straight and a helical port. Two swirls were observed up to 4 mm valve lift with the straight port and up to 2 mm with the helical one; however, only one swirl was present after these lifts. The flow characteristics changed suddenly between 4 and 5 mm lift in the straight port; on the other hand, the change with lift was gradual with the helical port – the transition points between flow regimes were different with the port shapes. In addition, the centers of the swirls were relatively far from the cylinder center so that the effect of eccentricity may not be negligible at 1.75B, regardless the shape. The eccentricity values with the straight port were especially high – over 0.5 for all lifts. Finally, real velocities were found to be much lower than those predicted by the assumption of ISM evaluation, with the profiles differing qualitatively as well.
[en] In a liquid rocket engine, acoustic damping induced by gas-liquid scheme injectors is studied experimentally for combustion stability by adopting linear acoustic test. In the previous work, it has been found that gas-liquid scheme injector can play a significant role in acoustic damping or absorption when it is tuned finely. Based on this finding, acoustic-damping characteristics of multi-injectors are intensively investigated. From the experimental data, it is found that acoustic oscillations are almost damped out by multi-injectors when they have the tuning length proposed in the previous study. The length corresponds to a half wavelength of the first longitudinal overtone mode traveling inside the injector with the acoustic frequency intended for damping in the chamber. But, new injector-coupled acoustic modes show up in the chamber with the injectors of the tuning length although the target mode is nearly damped out. And, appreciable frequency shift is always observed except for the case of the worst tuned injector. Accordingly, it is proposed that the tuning length is adjusted to have the shorter length than a half wavelength when these phenomena are considered
[en] This study is the second investigation on the steady flow characteristics of an SI engine with a semi-edge combustion chamber as a function of the port shape with varying evaluation positions. For this purpose, the planar velocity profiles were measured from 1.75B, 1.75 times of bore position apart from the bottom of head, to 6.00B positions using particle – image velocimetry. The flow patterns were examined with both a straight and a helical port. The velocity profiles, streamlines, and centers of swirl were almost the same at the same valve lift regardless of the measuring position, which is quite different from the case of the pent-roof combustion chamber. All the eccentricity values of the straight port were out of distortion criterion 0.15 through the lifts and the position. However, the values of the helical port exceeded the distortion criterion by up to 4 mm lift, but decreased rapidly above the 3.00B position and the 5 mm lift. There always existed a relative offset effect in the evaluation of the swirl coefficient using the PIV method due to the difference of the ideal impulse swirl meter velocity profile assumption, except for the cylinder-center-base estimation that was below 4 mm of the straight port. Finally, it was concluded that taking the center as an evaluation basis and the assumption about the axial velocity profile did not have any qualitative effect on swirl evaluation, but affected the value owing to the detailed profile.
[en] Investigations on combustion chambers have shown that the entrainment of the ambient fluid can be greatly enhanced by imparting swirl to the emanating jet. Hence, it is expected that buoyant jets with swirl will also cause faster mixing with the ambient fluid and dilute the pollutants very rapidly. Though swirling buoyant jets discharging vertically into stagnant homogeneous environment have been investigated to a limited extent, no information seems to exist on the behaviour of a swirling buoyant jet discharging horizontally or at some angle of inclination. This report presents a theoretical model and the resulting solutions
[en] Tests with nozzles of different types are conducted in a segment of a combustion chamber. The nozzle associated with the most efficient fuel combustion is identified. Tests of a complete combustion chamber in a gas-turbine engine are recommended.
[en] The evaporative gas turbine cycle is a new high efficiency power cycle that has reached the pilot plant testing stage. The latest configuration proposed for this cycle is known as part flow evaporative gas turbine cycle (PEvGT) in which humidification is combined with steam injection. Having advantages of both steam injected and humid air cycles, it is regarded as a very desirable plant for future. In this paper the exergy equations have been added to the mathematical model. Then exergy analysis and optimization of the PEvGT cycles: PEvGT and PEvGT-IC have been done. This study show that the maximum exergy destruction rate related to combustion chamber in both cycles. The exergetic optimization shows, the maximum first and second efficiency occur in the highest values of part-flow humidification rate. (author)
[en] Low signature combustion chambers are often wrought with combustion instability. Acoustic waves are generated owing to interaction of chamber flow field with the combustion flame-front, causing pressure fluctuations in the chamber. This paper demonstrates the feasibility of certain PU composites that may be applied to dampen prescribed chamber acoustic perturbation and thus promote combustion stability. This is achieved by the absorption of acoustic energy and its dissipation into heat within the composite matrix. Signal Attenuation data relative to 10 mm untreated steel plate unequivocally confirm that the performance is intricately linked to the dynamic modulus of the material, which may be tailored to suit the incident frequency. Vibration analysis is employed to determine modulus sensitivity to imposed frequency. A piezoelectric transducer is driven by a pulsar-receiver unit to perform acoustic characterization of the materials employing the pulse-echo mode in the 1-100 kHz frequency range. (author)