Albert Ratner

ABSTRACT The current study presents a numerical study of co-firing chunk coal and one kind of light weight biomass, oat hulls, in a stoker boiler. First, a standard combustion model was applied to simulate coal combustion in a real size three dimensional boiler; the results were compared with the temperatures measured at different locations of the stoker boiler to assess the accuracy of heat sink and heat transfer model. Once a good accuracy was achieved, a devolatilization model for oat hulls was derived from experimental data and was matched with this combustion model to simulate combustion in a co-firing stoker boiler. The results showed that light biomass burns in suspension, similar to pulverized coal by following the air flow. Also, the peak temperature inside the furnace inversely varies with the increase of co-firing percentage of oat hulls. This numerical study reveals thermal and economic potential of using unprocessed light weight biomass on the existing combustion facility.

A steady, premixed, rich (phi=1.25), methane/air flat flame at atmospheric pressure with dilution is used to compare LIF and DFWM and evaluate their response to collisional quenching. The dilution is either pure nitrogen or pure carbon dioxide. The dilution is chosen so that the NO levels and temperature are the same for each stoichiometric ratio in the probed zone, while concentrations of quenching species change significantly. Carbon dioxide and nitrogen are, respectively, strong and mild quenchers. In addition, DFWM and LIF signals can be obtained simultaneously ...

ABSTRACT Fuel-air mixing behavior under the influence of imposed acoustic oscillations has been studied by investigating the response of the fuel mixture fraction field. The distribution of local fuel mixture fraction inside the mixing zone, which is expected to evolve into the local equivalence ratio in the flame zone, is closely coupled to unstable and oscillatory flame behavior. The Experiment was performed with an aerodynamically-stabilized non-premixed burner. In this study, acoustic oscillations were imposed at 22, 27, 32, 37, and 55Hz. Phase-resolved acetone PLIF was used to image the flow field of both isothermal and reacting flow cases and this data along with the derived quantities of temporal and spatial unmixedness were employed for analysis. The behavior of the unmixedness factor is compared with the previous measurements of oscillations in the flame zone. This comparison shows that local oscillations (of order millimeters or smaller) in fuel/air mixing are closely related to the oscillatory behavior of the flame. For each driving frequency, the mixture fraction oscillates at that frequency but with a slight phase difference between it and the pressure field/flame intensity, indicating that the fuel mixture fraction oscillation are likely the major reason for oscillatory behaviors of this category of flames and combustor geometry.

ABSTRACT Measurements of fuel mill.wre fraction are made for a jet flame in an acoustic chamber. Acoustic forcing creates a spatially-uniform, temporally-varying pressure field which results in oscillatory behavior in the flame . Forcing is at 22, 27, 32, 37, and 55 Hz. To asses the oscillatory behavior, previous work included chemiluminescence, OH PUF, nitric oxide PUF imaging, and file! mixture fraction measurements by infrared laser absorption. While these results illuminated what was happening to the flame chemistry, they did not provide a complete explanation as to why these things were happening. In this work, the filel mixture fraction is measured through PUF of acetone, which is introduced into the fuel stream as a marker. This technique enables a high degree of spatial resolution of filellair mixture value. Both non-reacting and reacting cases were measured and comparisons are drawn with the results fi'om the previous work. It is found that structure in the mixture fraction oscillations is a major contributor to the magnitude of the flame oscillations. Introduction Combustion instabilities are caused by a coupling between thermo-acoustic and fluid-dynamic conditions present during the combustion processes. Combustion instability is defined here as 'the amplification of acoustic waves' due to the thermo-acoustic coupling between energy release from the combustion process and acoustic waves inside the combustion chamber. The interaction between vortices (mixing), sound (acoustic, or pressure oscillations), and combustion heat release can lead to self-excited oscillations that can cause structural damage. Any unsteadilless in the rate of combustion is a source of sound, generating pressure and velocity fluctuations [2]. Especially, as environmental issues becoming more important, lean premixed combustion schemes are being widely employed, which, while reducing the amount of NOx produced by lowering the flame temperature, have a greater tendency to cause instabilities since the combustion occurs near the lean blow-out limits [3]. A series of theoretical and experimental works [1, 4-6] has been done on this subject in JPC, Caltech . The coupled effects of acoustic forcing with combustion heat release on species concentration was examined by Pun et al. [4,5] with OH-PUF under atmospheric pressure. In figure 1, the flame region is marked as region (1). Phase resolved imaging revealed phase-dependent response of the combustion process under low frequency (22 ~ 55Hz) acoustic excitations. Since this work is closely related to the current work in that both used the same combustion chamber, bumer, and acoustic excitations, it is very interesting and at the same time important to compare the effects of acoustic forcing on the energy release and filellair mixing. Femandez et al. [6] used an infrared laser technique to measure point-wise fuel/air mixing in terms of 'Unmixedness factor' in the same experimental conditions as in the work by Pun et al. Unfortunately, a direct comparison of Pun ' s 311d Femandez's work is not possible because the technique employed by Femandez is time-, but not phase-, resolved. Femandez's did demonstrate that fuel /air mixing within the eductor block is heavily affected by the acoustic excitation . This effort aims to bridge these two studies by producing mixture fraction data that can be directly compared to both Femandez's unmixedness results and to Pun ' s OH PUF results. This work employs single frequency acoustic forcing at five different frequencies, just as the previous efforts, to examine how the local filellair mixing is affected by the imposed acoustic excitation and how this relates to the observed flame behavior. By comparison with earlier work [6], it also becomes possible to understand the evolution of fuel /air mixing. The phase dependence of the mixing process is evaluated by collecting images at random phase values for each frequency . These images are then sorted by phase, with phase defined as a best-fit sinusoid of the acoustic oscillation (as measured by the pressure transducer).

ABSTRACT The Selective Non-Catalytic Reduction (SNCR) of NO emission was investigated for a coal stoker boiler using ANSYS FLUENT. For this purpose, first a combustion model was applied to simulate coal combustion in a three dimensional full scale boiler. In order to assess the accuracy of heat sink and heat transfer model a series of temperature measurements were carried out at different locations of stoker boiler. To verify the model accuracy in predicting pollutants’ emission, the emission of NO was investigated using FLUENT post-processing module and compared to measured data. The post-processing results of NO emission showed good agreement with stack emissions reported to EPA by the University of Iowa Power Plant. Once a good accuracy of comprehensive model was achieved, FLUENT Discrete Phase Modeling (DPM) was considered to simulate urea solution injection into the boiler. For this purpose, several injection rates as well as different injection arrangements and velocities were examined to characterize SNCR process. Results revealed the importance of temperature zone to which urea is injected. A temperature window to have maximum NO reduction while keeping the ammonia slip at its low levels was found to be about 1250-1420 K. It was also found that the nozzles closer to the corners of the wall are more likely to be in this temperature zone and would provide more satisfactory result than injection through middle ones or the innermost. The results showed that injection from higher elevation could provide better result in terms of higher NO reduction and lower ammonia slip by means of more even temperature profile and being closer to the flue gases. It was also found that for the case of injection through middle nozzles and at the elevation of secondary air, urea should have high momentum in order to penetrate into right temperature window and prevent from high amount of ammonia slip. This could be done by means of injecting urea into air pipe and take the advantage of air momentum to carry the urea solution.

ABSTRACT With a global focus on the reduction of fossil fuel consumption and harmful pollutant emissions, new technologies have been raised offering reduced emissions with the combustion of alternative and renewable fuels. Low swirl combustion and the addition of highly reactive fuels into the fuel stream are two methods that have been shown to meet these challenges. In the present study, the thermo-acoustic behavior of a lean premixed low swirl combustor is examined by the variation of several parameters: the equivalence ratio, bulk velocity, chamber pressure, and the addition of hydrogen into the fuel mixture. It is reported that the natural modes of the chamber employed shift upwards for both fuel mixtures examined when increasing the equivalence ratio. As additional heat is dumped into the chamber, the increase in acoustic energy is being pumped through these natural modes. An increase in the bulk velocity is found to have opposite effects on these dominant acoustic modes for the two mixtures investigated. The methane mixture shows negative shifts in frequency when increasing the bulk velocity, whereas the hydrogen-methane mixture displays upward-shifting frequencies. Elevating the chamber pressure results in an increase in the acoustic modes for both mixtures, although the trend is more consistently linear for the hydrogen-methane flames.

... sufficient information from the simulations to allow modeling the local dynamical response of a ... Tube with Planar Heat Source; (b) Sketch of Rijke Tube with Premixed Flame; (c) Sketch ... Theory and experiments match the numerical results, which show that the fundamental mode ...

Various techniques have been employed by investigators to measure the response of flames to unsteady changes, but there has been no systematic study of the relative benefits and drawbacks of these competing techniques. The goal of this work is to characterize the performance of ...

ABSTRACT The majority of modern transportation energy is consumed via combustion of liquid hydrocarbon fuels. Manufactures and consumers are consistently looking for ways to optimize the efficiency of fuel combustion in terms of cost, emissions and consumer safety. Experimental research has shown that the addition of long chained polymers to hydrocarbon fuel imparts non-newtonian characteristics to the emulsified fluid. This results in a suppressed splashing behavior upon spilling over a surface. This has led to a study to not only optimize the emulsion ratio but to characterize the properties of the emulsified fuel (including ignition, extinction and burning rate). This is done to investigate how the modified fuels will impact commercial automotive engines as it relates to their performance and emissions. Experiments are conducted using micro-sized droplets tethered to ceramic fibers. Through a series of synchronous events, droplets are first ignited using electrical hot wire and data is acquired through the use of high speed photography and Schlieren imaging. Time variations regarding droplet diameter are used to characterize the sample size. Residual soot aggregates attached to the support fiber are also collected to be analyzed using SEM technique.

The GAMCIT payload is a Get-Away-Special payload designed to search for high-energy gamma-ray bursts and any associated optical transients. This paper presents details on the design of the GAMCIT payload, in the areas of battery selection, power processing, electronics ...