STUDY ON A LOWER HEAT LOSS MICRO GAS TURBINE COMBUSTOR WITH POROUS INLET

A micro gas turbine combustor with a sintered porous chamber wall as inlet was tested and simulated. When burning methane in the 2.14 cm(3) chamber volume combustor, its maximum power density reached 336 M W/m(3). The combustion efficiency was above 90% when producing 850-1100 K exit gas. The pressure drop ratio of the porous inlet was below 5 kPa with 6 L/min premixed gas flow rate at hot condition. Compared with a conventional solid-wall micro combustor with heat recovery channel, the outside wall temperature of the porous-wall micro combustor decreased 150-200 K, and the heat loss ratio reduced from 40-80% to 20-40%. Direct numerical simulation based on the skeletal chemical kinetics model was used to elucidate the flame structure and heat loss reducing mechanism of the porous-wall micro combustor

Evaporation and Combustion Characteristics of Kerosene Droplets in Localized Stratified Vortex-tube Combustor: A Numerical Investigation

The combustion of AC(10)H(20)droplets was investigated to explore the combustion performance of liquid fuels in localized stratified vortex-tube combustor (LSVC). The evaporation ratio, flame structure, stability limit, heat loss, and combustion efficiency in the LSVC were investigated under various equivalence ratios and fuel mass fluxes numerically. Results corroborate that the LSVC exhibits a large heat release with uniform flame front, large stability limit, low heat loss, high evaporation rate, and good combustion efficiency under lean operating conditions, indicating good potential to deal with liquid fuels directly. Then, the evaporation and stabilization mechanisms are analyzed. As for the former, the evaporation ratio in LSVC increases sharply along the axial direction toward the outlet, indicating a high evaporation rate, which is optimized through the heat produced by itself efficiently. Viz., the vortex currents can entrain the AC(10)H(20)droplets to interior high-temperature region and then promote the evaporation of liquid fuels. As for the latter, the localized stratified distribution of species in the LSVC results in an edge flame structure, which differs from that in the traditional vortex-tube combustors. The local equivalence ratio increases along the radial direction toward the center. The increased local equivalence ratio of the interior is crucial for stabilization and the decreased local equivalence ratio of exterior enables the heat loss to be reduced. In the end, the edge flame structure and the low heat loss yields a large heat release in the LSVC, which can increase the flame speed, thereby ensuring the stabilization and the high burn-off rate

Numerical investigation on ignition intensification of n-butane with tert-butyl hydroperoxide (TBHP) addition

Aimed to intensify the ignition and combustion process of n-butane fuel in micro internal combustion (IC) engines, ignition delay characteristics of n-butane/air mixtures with tert-butyl hydroperoxide (TBHP) addition ratios below 10% were investigated numerically by CHEMKIN-PRO software. Results show that ignition delay times of n-butane can be shortened nonlinearly with TBHP addition at initial temperatures of 650 K to 1000 K, namely, the reduction rate of ignition delay times rises slowly as the TBHP addition ratio increases. In addition, the negative temperature coefficient (NTC) behavior can be weakened significantly with TBHP addition at 650 K to 1000 K. Especially, the ignition delay time of n-butane can be reduced about 32 times with 10% TBHP addition at 750 K. However, the ignition intensification effect of TBHP addition is slight when the initial temperature is above 1000 K. The acting mechanism of TBHP addition was investigated in detail by the rate of production and consumption (ROP), sensitivity, and reaction pathway analysis. The ROP analysis shows that the released and quickly consumed OH radicals with TBHP addition play an important role in promoting n-butane ignition at the lower initial temperature. However, the relatively slow consumption rate of OH radicals at higher temperature weakens the intensification effect. Furthermore, the sensitivity analysis and reaction pathway analysis indicate that the dominated elemental reactions and reaction pathway vary significantly with TBHP addition at lower initial temperature

Study of UV Rayleigh scattering thermometry for flame temperature field measurement

This paper explores Rayleigh scattering thermometry via a wavelength of 355 nm through a unique measurement scheme. In this context, the p-polarization and s-polarization Rayleigh scattering of flame and air (as the temperature calibration reference) are measured. Subtraction of p-polarization Rayleigh scattering intensity from that of s-polarization is proposed to eliminate the background noise and fluorescence interference influence to reduce the temperature measurement uncertainties. To validate this method, the temperature field of CH4/N-2/O-2 premixed flame at phi = 0.78 on a McKenna burner is detected by this Rayleigh scattering thermometry, and the axial temperature profile is validated with the literature data. Within the region of interest domain (-5 mm to 5 mm in the radial direction), an overall temperature measurement system precision of +/- 46.5 K is reported. The influence of both p-polarization Rayleigh scattering and laser sheet inhomogeneity on the temperature measurement is further quantitatively studied. The measurement uncertainties relevant to laser energy variation and flame Rayleigh scattering cross-section variation due to temperature increase are specified as 1.4% and 2%-8%, respectively. Eventually, temperature measurements of single-shot images are attempted, and the large signal dynamic range (100-1000 [a.u.]) indicates a promising potential for temperature field interpretation of turbulence combustion. (C) 2019 Optical Society of Americ

The Deposition and Burning Characteristics During Slagging Co-Firing Coal and Wood: Modeling and Numerical Simulation

Numerical analysis was used to study the deposition and burning characteristics of combining co-combustion with slagging combustion technologies in this paper. The pyrolysis and burning kinetic models of different fuels were implanted into the WBSF-PCC2 (wall burning and slag flow in pulverized co-combustion) computation code, and then the slagging and co-combustion characteristicsespecially the wall burning mechanism of different solid fuels and their effects on the whole burning behavior in the cylindrical combustor at different mixing ratios under the condition of keeping the heat input samewere simulated numerically. The results showed that adding wood powder at 25% mass fraction can increase the temperature at the initial stage of combustion, which is helpful to utilize the front space of the combustor. Adding wood powder at a 25% mass fraction can increase the reaction rate at the initial combustion stage; also, the coal ignitability is improved, and the burnout efficiency is enhanced by about 5% of suspension and deposition particles, which is helpful for coal particles to burn entirely and for combustion devices to minimize their dimensions or sizes. The results also showed that adding wood powder at a proper ratio is helpful to keep the combustion stability, not only because of the enhancement for the burning characteristics, but also because the running slag layer structure can be changed more continuously, which is very important for avoiding the abnormal slag accumulation in the slagging combustor. The theoretic analysis in this paper proves that unification of co-combustion and slagging combustion technologies is feasible, though more comprehensive and rigorous research is needed

Improved Two-Color Method for Temperature Measurement of Soot Flames

An improved two-color method, which originates from an approximate emissivity ratio model based on the empirical emissivity formula by Hottel and Broughton, was developed to measure the temperature field of soot flames generated on a McKenna burner in the present study. In conjunction with the onion-peeling method and Tikhonov regularization, the reconstructed temperature fields of rich C2H4/air soot flames under varied equivalence ratios were obtained by calculating the 550 and 650 nm spontaneous emission signal images, which were recorded by an intensified charge coupled device, respectively. At the same time, an autoscanning R-type thermocouple was used to measure flame temperature for validating the reconstructed data. The results show that the reconstructed temperature distributions agreed well with the measured data by thermocouple, and the reconstructed temperature is more precise by the present improved two-color method than by the classic two-color method based on a constant emissivity assumption

Quantitative gaseous temperature and mole concentration measurements in spray generated mixture by p-xylene-PLIF imaging

The current study originally presents a detailed approach to implement the p-xylene based two-color PLIF for measuring gaseous mixture temperature and mole concentration field simultaneously. An 80 * 0.8mm(2) laser sheet at 266nm is employed to excite homogenous p-xylene/nitrogen steady mixture flow in a calibration cell, where the known p-xylene mole concentration and temperature are adjustable. Doing so, the full band/spectral (centered at 289nm) fluorescence intensity are respectively captured by ICCD camera that allows establishments of temperature-fluorescence ratio database. Concomitantly, the full band fluorescence intensity correlation with temperature and mole concentration is rightly created as well. Utilizing the identical laser sheet and detection channel, the quantitative temperature and mole concentration field in a far-field developed-spray region could be inferred by terms of full band/spectral fluorescence imaging through previous calibration database. The error propagation issue of temperature and mole concentration measurement by this approach are discussed. As a result, it is found that the relative temperature and mole concentration uncertainties are in the range of 5.4 similar to 7.3% and 8 similar to 9.3% (or 12.3 similar to 18.7% by bottom-up approach), respectively, within studied temperature range of 423 similar to 573K. Therefore, the suitability and capability of p-xylene as the tracer for spatio-temporal temperature and mole concentration measurements are preliminarily validated, which offers an alternative tracer option for gasoline/its surrogate spray studies. It is noted that replacing the p-xylene by other suitable fluorescence tracer, i.e.,1-methylnaphthalene, this approach could be rightly performed for studies of Diesel engine, or even gas turbine

Cellular instabilities of n-butane/air flat flames probing by PLIF-OH and PLIF-CH2O laser diagnosis

The structure and instability characteristics of non-adiabatic fuel-rich n-butane/air cellular flames on McKenna burner were experimentally investigated at atmospheric pressure. Planar Laser Induced Fluorescence (PLIF-OH and PLIF-CH2O) flame diagnosis technology was utilized to probe the flame structure under varied equivalence ratio and inflow mixture velocity respectively. Results show that, the equivalence ratio plays an important role in forming cellular flames. The flat, wrinkled and cellular flames appear in turn when increasing equivalence ratio and inflow velocity. Differed to the separated cells of cellular flames appeared in direct Digital camera images and PLIF-OH images, the PLIF-CH2O images clearly display that all cellular flames are connected. In the PLIF-OH images of cellular flames, the OH radical fluorescence signal intensity is higher in the convex region toward unburned mixture than in the concave region, but in PLIF-CH2O images, the fluorescence signal intensity is nearly unchanged in both convex and concave regions. Quantitative stand-off distance and amplitude data probed by PLIF-OH and PLIF-CH2O diagnosis together reveal that the onset of non-adiabatic n-butane/air cellular flames on flat flame burner is dominantly governed by diffusive-thermal mechanism