Chamber Core Research Articles

Study the Effect of Acoustical Fuel Enhancement on the Flame Characteristics

Abstract This work presents a 2D numerical simulation of the nonpremixed combustion of natural gas in an axisymmetric cylindrical chamber, focusing on the effect of adding acoustical excitation to inlet fuel velocity on temperature, exhaust pollutants, and combustion products velocity. Pulsation combustion generates vortices and enhances mixing, which in turn increases combustion efficiency and reduces emissions so it is used in many industrial applications like dryers and boilers. The turbulence is solved using detached eddy simulation model, which is a hybrid modeling between large eddy simulation and realizable k–e model. The chemical reactions are described by the eddy dissipation model. The radiative intensity transport equations are solved using P-1 radiation model. The numerical model achieved a great agreement with experimental data on temperature and species mass fraction. The main outcome of the work is the demonstration of a significant decrease in a volume of pulsed flame compared to a nonpulsed flame with 18% reduction in the flame length. Increasing the Strouhal number enhances the temperature homogenization along the combustion chamber and the flame does not concentrate in the chamber core and toward the chamber exhaust. Changing the fuel velocity from the stoichiometric ratio due to the fuel pulsation cools the chamber and reduces the average temperature from 2000 to 1750 K. There was a reduction in the mass fraction of carbon monoxide, nitrogen monoxide and soot by 50, 28, and 285%, respectively. Increasing fuel frequency increases maximum velocity by 66% axially and 14% radially.

Abstract LB-37: A patient-derived in vitro model of colorectal cancer: a perfusion culture system that recapitulates patient tumor composition and structure in 3-dimensions

Abstract Cancer medicine would benefit greatly from a practical technology that accurately predicts the sensitivity of individual patient tumors to drugs. Previously developed in vitro chemosensitivity models have generally failed to do this because they do not incorporate key aspects of the tumor microenvironment (TME), which clearly plays a role in drug resistance. There has been significant interest in patient-derived xenograft (PDX) chemosensitivity testing as an alternative to in vitro models, but the applicability of this approach is limited by engraftment percentages and growth rates. We have developed an in vitro technology that is designed to recapitulate the 3D tissue architecture of patient-derived colorectal tumors including accessory (endothelial and immune) cells, starting with freshly excised tumor specimens. The system incorporates: 1) low-sheer, tangential flow of nutrient medium above and below an open, synthetic 3D cell scaffold; and 2) exchange of metabolic gasses via permeable membranes which separate the culture chamber core from gassing chambers located above and below the nutrient flow compartments. This design allows establishment of gas and nutrient gradients across the cell scaffold that closely mimic conditions in vivo. Aliquots of mechanically and enzymatically dissociated, freshly excised, primary human colorectal adenocarcinomas were introduced into the 3D culture system and maintained for up to 3 weeks. Routine maintenance of the cultures involved partial medium exchanges as needed based on glucose concentrations in the circulating medium. The proportions and arrangement of key cell types (e.g., normal muscularis, tumor epithelium, stromal fibroblasts, endothelial cells, and immune cells) in the cultured explants were compared to those of the original tumor by standard histological techniques. Results revealed good agreement between the histology of the original tumor and that of the in vitro model. These results suggest that this model technology could be applied to individual patient drug selection as well as studies of colorectal cancer biology that are not feasible or practical in vivo. Citation Format: William P. Pfund, Paul A. Neeb. A patient-derived in vitro model of colorectal cancer: a perfusion culture system that recapitulates patient tumor composition and structure in 3-dimensions. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-37. doi:10.1158/1538-7445.AM2014-LB-37

Study of dimethyl ether homogeneous charge compression ignition combustion process using a multi-dimensional computational fluid dynamics model

A multi-dimensional Computational Fluid Dynamics (CFD) model is adopted to investigate the Dimethyl Ether (DME) Homogeneous Charge Compression Ignition (HCCI) combustion and emissions processes. A reduced chemical mechanism is coupled with a CFD code in the multi-dimensional CFD model. The pressure profiles predicted by the multi-dimensional CFD model are more accurate than the single-zone model, because the wall heat transfer and in-cylinder turbulence flow are considered. During the combustion process the in-cylinder temperature distribution undergoes a process from inhomogeneity to homogeneity. Both low and high temperature reactions don't occur simultaneously throughout the cylinder. The low temperature reactions are initiated near the piston surface and squish region, and the high temperature reactions are initiated in the combustion chamber core zone and squish region. Emission analysis indicates that unburned fuel and CH 2O account for the majority of unburned hydrocarbon (HC). The unburned fuel, CH 2O and CO emission mainly resides in the bottom, middle and upper part of the piston-ring crevice region, respectively. With the decrease of DME equivalence ratio, unburned fuel and CO increases. However, when the DME equivalence ratio is too small, CO emission decreases.

Chamber Core Structures for Fairing Acoustic Mitigation

Abstract : The U.S. Air Force Research Laboratory is pursuing an innovative composite structure design called chamber core for constructing launch vehicle payload fairings. A composite chamber core fairing consists of many axial tubes sandwiched between face sheets, tubes that can be used as acoustic dampers to reduce low-frequency interior noise with virtually no added mass. This paper presents the results of experimental studies of noise transmission through a 1.51 m diameter x 1.42 m tall chamber core cylinder. It was tested in a semireverberant acoustics laboratory using band-limited random noise at sound pressure levels up to 110 dB. The bare cylinder provided approximately 12.7 dB of attenuation over the 0-500 Hz bandwidth and 15.3 dB over 0-2000 Hz. The noise reduction increased to over 18 dB for both bandwidths with the axial tubes acting as acoustic dampers. Narrowband reductions in excess of 15 dB were measured around specific acoustic resonances. This was accomplished with virtually no added mass to the composite cylinder. Results were compared with the performance provided by a 2.5 cm acoustic blanket treatment. The acoustic dampers were as effective as the acoustic blanket at low frequency, but not at higher frequencies. The acoustic dampers were better able to couple with and damp the low-frequency acoustic modes. Together, the acoustic blanket and dampers provided over 10 dB more noise reduction over the 2000 Hz bandwidth than the bare cylinder.

Fairing Noise Control Using Tube-Shaped Resonators

Abstract : The potential for noise mitigation in composite Chamber Core fairings is investigated by using the walls of the fairing structure itself as acoustic resonators. This is the first documented application of long cylindrical tube-shaped resonators for fairing noise control. The theory and modeling of tube-shaped resonators for controlling fairing acoustic resonances is presented. The potential for noise mitigation in composite Chamber Core fairing using the walls of the fairing structure itself as acoustic resonators is investigated. Design criteria such as geometry damping, spatial coupling, and robustness are considered for a variety of tube resonators. The results showed that a small number of tube resonators reduced the amplitude of low-frequency acoustic resonances by 10-12 dB in the test system and provided nearly 6 dB of reduction over the bandwidth from 0 to 400 Hz.

On the noise transmission and control for a cylindrical chamber core composite structure

The vibroacoustic properties, sound transmission behavior, and noise transmission control of a novel chamber core composite cylinder are studied. An approximate uniform shell model of the sandwich cylindrical chamber core structure is developed to aid in the calculation of the ring frequency and external critical frequency. Acoustic modal parameters are analytically and experimentally obtained. The structural modal parameters are identified from measured data. The coupling between structural and acoustic modes is investigated. The sound transmission into the cylindrical chamber core is experimentally characterized, where the stiffness-, cavity resonance-, mass-, and coincidence-controlled zones are identified. Finally, the addition of fills to the wall chambers of the chamber core is investigated as a part of passive control study, which also serves to corroborate the model development.

Prediction of temperature front in a gas turbine combustion chamber

Numerical computation has been applied to investigate the temperature field in a gas turbine combustion chamber. The simulation assumed that pressure imbalance conditions of air flow between primary and secondary inlets occur. The combustion chamber under study is part of a 70 MW gas turbine from an operating combined cycle power plant. The combustion was simulated with normal fuel–air flow rate assuming stoichiometric conditions. Under these conditions characteristic temperature and pressure fields were obtained provided equity of boundary conditions at air inlets applies. However, with pressure distribution imbalances of the order of 3 kPa between primary and secondary air inlets, excessive heating in regions other than the combustion chamber core were obtained. Over heating in these regions helped to explain what was observed to produce permanent damage to auxiliary equipment surrounding the combustion chamber core, like the cross flame pipes. It is observed that high temperatures which normally develop in the central region of the combustion chamber may reach other surrounding upstream regions by modifying slightly the air pressure. Microscope scanning of the damaged pipes confirmed that the material was exposed to high temperatures such as predicted through the numerical computation.

Helmholtz design for noise transmission attenuation on a chamber core composite cylinder

This work explores the feasibility of using Helmholtz resonators to attenuate a subscale ChamberCore cylinder noise transmission. The ChamberCore cylindrical composite is an innovative new sandwich-type structure. It consists of an outer skin, an inner skin, and linking ribs. There are wedge-cross-section chambers along the axis direction between the outer and inner skins. These chambers provide a potential for the acoustic Helmholtz resonator design in order to reduce the noise transmission, which is dominated by the internal acoustic cavity. In this experimental work, the sound transmission behavior of the ChamberCore fairing is investigated and divided into four interesting frequency regions: the stiffness-controlled zone, cavity resonance-controlled zone, coincidence-controlled zone, and mass-controlled zone. It is found that the noise transmission in the low-frequency band is controlled by the structural stiffness and cavity resonances, where the acoustic Helmholtz design method has the potential to improve the noise transmission.

Investigation of the sound transmission behavior of a chamber core cylinder

Several kinds of novel composite structures, such as advanced grid stiffened (AGS) and chamber core (CC) structures have been designed, fabricated, and investigated for both civil and military applications. The chamber core composite is a novel advanced sandwich-type structure that is created by filament winding an inner shell onto a cylindrical mandrel, arranging previously fabricated U-shaped channels around the perimeter of this shell to form the inner chamber walls, and filament winding an outer shell followed by a co-cure process. In this study, the structural/acoustic behavior of a normal composite chamber core cylinder is investigated both theoretically and experimentally. Lightly coupled structural and acoustic modal parameters are identified using experimental modal analysis techniques. The properties of sound transmission loss (TL) of the cylinder are also investigated experimentally. The effect of the structural/acoustic natural frequencies and the damping on the sound transmission loss is analyzed. Finally, passive control strategies are discussed, and several passive control materials for improving the sound transmission loss (0–500 Hz) of the cylinder are experimentally evaluated. [Work sponsored by the Air Force Research Laboratory Space Vehicles Directorate (AFRL/VS), POC Dr. Steven Lane, (505) 846-9944.]

Modelling gas motion in a rapid-compression machine

In this paper, a model which describes the behaviour of the pressure, density and temperature of a gas mixture in a rapid compression machine is developed and analyzed. The model consists of a coupled system of nonlinear partial differential equations, and both formal asymptotic and numerical solutions are presented. Using asymptotic techniques, a simple discrete algorithm which tracks the time evolution of the pressure, temperature and density of the gas in the chamber core is derived. The results which this algorithm predict are in good agreement with experimental data.