Browsing by Subject "wave rotor combustor"

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    Design of Optical Diagnostic System for Wave Rotor Constant Volume Combustor
    (Office of the Vice Chancellor for Research, 2014-04-11) Baharuddin, Fatin; Yong, Zhen Wei; Chow, Kok Hwang
    The recent energy price hike brings the urge to produce a more efficient power generation engines, which could result in lower fuel consumption, higher efficiency and less pollutants. Such a new approach is being developed at IUPUI with the participation of global engine maker Rolls Royce, utilizing an alternate thermodynamic cycle (Humphrey cycle) and a novel pulsed combustor for gas turbine engines, called a Wave Rotor Combustor (WRC). The proposed wave rotor ignition test rig consists of two combustion chambers (a rotating pre-chamber and a stationary main chamber), electrical and ignition systems and data acquisition system. Experiments and numerical studies have been conducted to study the ignition and flame propagation process using different hydrocarbon fuels (methane, ethylene and propane). Currently, hydrogen cannot be used for experiments because it does not produce soot; consequently, the flame propagation process cannot be visualized with the images captured using high speed camera. Therefore, the objective of the present research is to design an optical system to visualize the flame propagation process in a WRC for all fuels including hydrogen. Among various optical techniques available for flow visualization, Schlieren photography is commonly used for flows with sharp density gradients. Based on the configuration there are different types of Schlieren imaging system such as Z-type, parallel beam system and single mirror system. From our present research we have identified that Z-type Schlieren system meets all our requirements; suitable for present study, low cost, easy to set-up. All the components required to design the Z-type Schlieren system have been finalized, ordered and all the components have been received. Initially, Schlieren system is being tested using a simple combustion light source such as candle flame. Later, experiments will be conducted using different fuels to visualize the flame propagation process inside the wave rotor combustor.
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    Experimental investigation of hot-jet ignition of methane-hydrogen mixtures in a constant-volume combustor
    (2016-12) Paik, Kyong-Yup; Nalim, M. Razi; Zhu, Likun; Yu, Whitney
    Investigations of a constant-volume combustor ignited by a penetrating transient jet (a puff) of hot reactive gas have been conducted in order to provide vital data for designing wave rotor combustors. In a wave rotor combustor, a cylindrical drum with an array of channels arranged around the axis spins at a high rpm to generate high-temperature and high-pressure product gas. The hot-gas jet ignition method has been employed to initiate combustion in the channels. This study aims at experimentally investigating the ignition delay time of a premixed combustible mixture in a rectangular, constant-volume chamber, representing one channel of the wave rotor drum. The ignition process may be influenced by the multiple factors: the equivalence ratio, temperature, and the composition of the fuel mixture, the temperature and composition of the jet gas, and the peak mass flow rate of the jet (which depends on diaphragm rupture pressure). In this study, the main mixture is at room temperature. The jet composition and temperature are determined by its source in a pre-chamber with a hydrogen-methane mixture with an equivalent ratio of 1.1, and a fuel mixture ratio of 50:50 (CH4:H2 by volume). The rupture pressure of a diaphragm in the pre-chamber, which is related to the mass flow rate and temperature of the hot jet, can be controlled by varying the number of indentations in the diaphragm. The main chamber composition is varied, with the use of four equivalence ratios (1.0, 0.8, 0.6, and 0.4) and two fuel mixture ratios (50:50, and 30:70 of CH4:H2 by volume). The sudden start of the jet upon rupture of the diaphragm causes a shock wave that precedes the jet and travels along the channel and back after reflection. The shock strength has an important role in fast ignition since the pressure and the temperature are increased after the shock. The reflected shock pressure was examined in order to check the variation of the shock strength. However, it is revealed that the shock strength becomes attenuated compared with the theoretical pressure of the reflected shock. The gap between theoretical and measured pressures increases with the increase of the Mach number of the initial shock. Ignition delay times are obtained using pressure records from two dynamic pressure transducers installed on the main chamber, as well as high-speed videography using flame incandescence and Schileren imaging. The ignition delay time is defined in this research as the time interval from the diaphragm rupture moment to the ignition moment of the air/fuel mixture in the main chamber. Previous researchers used the averaged ignition delay time because the diaphragm rupture moment is elusive considering the structure of the chamber. In this research, the diaphragm rupture moment is estimated based on the initial shock speed and the longitudinal length of the main chamber, and validated with the high-speed video images such that the error between the estimation time and the measured time is within 0.5%. Ignition delay times decrease with an increase in the amount of hydrogen in the fuel mixture, the amount of mass of the hot-jet gases from the pre-chamber, and with a decrease in the equivalence ratio. A Schlieren system has been established to visualize the characteristics of the shock wave, and the flame front. Schlieren photography shows the density gradient of a subject with sharp contrast, including steep density gradients, such as the flame edge and the shock wave. The flame propagation, gas oscillation, and the shock wave speed are measured using the Schlieren system. An image processing code using MATLAB has been developed for measuring the flame front movement from Schlieren images. The trend of the maximum pressure in the main chamber with respect to the equivalence ratio and the fuel mixture ratio describes that the equivalence ratio 0.8 shows the highest maximum pressure, and the fuel ratio 50:50 condition reveals lower maximum pressure in the main chamber than the 30:70 condition. After the combustion occurs, the frequency of the pressure oscillation by the traversing pressure wave increases compared to the frequency before ignition, showing a similar trend with the maximum pressure in the chamber. The frequency is the fastest at the equivalence ratio of 0.8, and the slowest at a ratio of 0.4. The fuel ratio 30:70 cases show slightly faster frequencies than 50:50 cases. Two different combustion behaviors, fast and slow combustion, are observed, and respective characteristics are discussed. The frequency of the flame front oscillation well matches with that of the pressure oscillation, and it seems that the pressure waves drive the flame fronts considering the pressure oscillation frequency is somewhat faster. Lastly, a feedback mechanism between the shock and the flame is suggested to explain the fast combustion in a constant volume chamber with the shock-flame interactions.