Jay Peck

Catalytic Combustion Systems for Microscale Gas Turbine Engines

As part of an ongoing effort to develop a microscale gas turbine engine for power generation and micropropulsion applications, this paper presents the design, modeling, and experimental assessment of a catalytic combustion system. Previous work has indicated that homogenous gas-phase microcombustors are severely limited by chemical reaction timescales. Storable hydrocarbon fuels, such as propane, have been shown to blow out well below the desired mass flow rate per unit volume. Heterogeneous catalytic combustion has been identified as a possible improvement. Surface catalysis can increase hydrocarbon-air reaction rates, improve ignition characteristics, and broaden stability limits. Several radial inflow combustors were micromachined from silicon wafers using deep reactive ion etching and aligned fusion wafer bonding. The 191 mm 3 combustion chambers were filled with platinum-coated foam materials of various porosity and surface area. For near stoichiometric propane-air mixtures, exit gas temperatures of 1100 K were achieved at mass flow rates in excess of 0.35 g/s. This corresponds to a power density of ∼1200 MW/m 3 ; an 8.5-fold increase over the maximum power density achieved for gas-phase propane-air combustion in a similar geometry. Low-order models, including time-scale analyses and a one-dimensional steady-state plug-flow reactor model, were developed to elucidate the underlying physics and to identify important design parameters. High power density catalytic microcombustors were found to be limited by the diffusion of fuel species to the active surface, while substrate porosity and surface area-to-volume ratio were the dominant design variables.

Measurement of pyrolysis products from phenolic polymer thermal decomposition

Batch pyrolysis of phenolic polymer was performed using a step-wise heating procedure in a 50 K increment from room temperature up to 1250 K. A phenolic-polymer sample of 50 mg was loaded in a reactor assembly speci cally designed and built for this study. The mass loss was measured after each 50 K step and the production of gas-phase species was quanti ed using gas-chromatography techniques. The overall mass loss reached about 35%. Water was found to be the dominant product below 800 K. Yields of permanent gases such as hydrogen, methane, carbon monoxide, and carbon dioxide increased with temperature up to 900 K and then decreased at higher temperatures. The yields of light hydrocarbons, such as C2 to C4 hydrocarbons, increased with reaction temperature up to 1000 K and dropped subsequently. Yields of aromatic products, including benzene, toluene, and xylene, were signi cant between 700 and 850 K. The quantitative molar production of species versus temperature is made available for the development of detailed phenolicpolymer pyrolysis models.

Catalytic Combustion Systems for Micro-Scale Gas Turbine Engines

As part of an ongoing effort to develop a micro-scale gas turbine engine for power generation and micropropulsion applications, this paper presents the design, modeling, and experimental assessment of a catalytic combustion system. Previous work has indicated that homogenous gas-phase microcombustors are severely limited by chemical reaction time-scales. Storable hydrocarbon fuels, such as propane, have been shown to blowout well below the desired mass flow rate per unit volume. Heterogeneous catalytic combustion has been identified as a possible improvement. Surface catalysis can increase hydrocarbon-air reaction rates, improve ignition characteristics, and broaden stability limits. Several radial inflow combustors were micromachined from silicon wafers using Deep Reactive Ion Etching (DRIE) and aligned fusion wafer bonding. The 191 mm3 combustion chambers were filled with platinum coated foam materials of various porosity and surface area. For near stoichiometric propane-air mixtures, exit gas temperatures of 1100 K were achieved at mass flow rates in excess of 0.35 g/s. This corresponds to a power density of approximately 1200 MW/m3 ; an 8.5-fold increase over the maximum power density achieved for gas-phase propane-air combustion in a similar geometry. Low order models including time-scale analyses and a one-dimensional steady-state plug-flow reactor model, were developed to elucidate the underlying physics and to identify important design parameters. High power density catalytic microcombustors were found to be limited by the diffusion of fuel species to the active surface, while substrate porosity and surface area-to-volume ratio were the dominant design variables.© 2005 ASME

An algorithm to estimate aircraft cruise black carbon emissions for use in developing a cruise emissions inventory

To provide accurate input parameters to the large-scale global climate simulation models, an algorithm was developed to estimate the black carbon (BC) mass emission index for engines in the commercial fleet at cruise. Using a high-dimensional model representation (HDMR) global sensitivity analysis, relevant engine specification/operation parameters were ranked, and the most important parameters were selected. Simple algebraic formulas were then constructed based on those important parameters. The algorithm takes the cruise power (alternatively, fuel flow rate), altitude, and Mach number as inputs, and calculates BC emission index for a given engine/airframe combination using the engine property parameters, such as the smoke number, available in the International Civil Aviation Organization (ICAO) engine certification databank. The algorithm can be interfaced with state-of-the-art aircraft emissions inventory development tools, and will greatly improve the global climate simulations that currently use a single fleet average value for all airplanes. Implications An algorithm to estimate the cruise condition black carbon emission index for commercial aircraft engines was developed. Using the ICAO certification data, the algorithm can evaluate the black carbon emission at given cruise altitude and speed.

Development of an aerosol mass spectrometer lens system for PM2.5

ABSTRACT The aerodynamic lens system of the Aerodyne Aerosol Mass Spectrometer (AMS) was analyzed using the Aerodynamic Lens Calculator. Using this tool, key loss mechanisms were identified, and a new lens design that can extend the transmission of particulate matter up to 2.5 μm in diameter (PM2.5) was proposed. The new lens was fabricated and experimentally characterized. Test results indicate that this modification to the AMS lens can significantly improve the transmission of large sized particles, successfully achieving a high transmission efficiency up to PM2.5 range.

Quantitative determination of species production from the pyrolysis of the Phenolic Impregnated Carbon Ablator (PICA)

Experiments to quantitatively determine detailed species production from the pyrolysis of Phenolic Impregnated Carbon Ablator (PICA) were performed using a reactor assembly adapted from a previous study on phenol-formaldehyde resin decomposition. A step-wise heating procedure that used a 50 K increment from room temperature up to 1250 K was employed for the experiments. The mass loss was measured after each 50 K step for PICA samples with an initial mass of 100 mg. Species production from the pyrolysis process was quantified using state-of-the-art gas-chromatography techniques. Compared to the more traditional mass spectroscopy techniques, gas chromatography allows to measure all species, from hydrogen to large aromatics. The quantitative molar production of species versus temperature is reported in this work. The species product from PICA pyrolysis are quite different from the species obtained in a previous study on a resole type phenolic resin pyrolysis. This suggests that characterizations need to be carried out for all variations of phenolic-matrix based ablators.

Measurement of naphthalene uptake by combustion soot particles.

In this study, we designed and constructed an experimental laboratory apparatus to measure the uptake of volatile organic compounds (VOCs) by soot particles. Results for the uptake of naphthalene (C10H8) by soot particles typical of those found in the exhaust of an aircraft engine are reported in this paper. The naphthalene concentration in the gas phase and naphthalene attached to the particles were measured simultaneously by a heated flame ionization detector (HFID) and a time-of-flight aerosol mass spectrometer (ToF AMS), respectively. The uptake coefficient for naphthalene on soot of (1.11 ± 0.06) × 10(-5) at 293 K was determined by fitting the HFID and AMS measurements of gaseous and particulate naphthalene to a kinetic model of uptake. When the gaseous concentration of naphthalene is kept below the saturation limit during these experiments, the uptake of naphthalene can be considered the dry mass accommodation coefficient.

Detailed Microphysical Modeling of the Formation of Organic and Sulfuric Acid Coatings on Aircraft Emitted Soot Particles in the Near Field

The development of a detailed microphysical model that describes the complex multicomponent interactions between organic vapors and soot particles emitted from aircraft gas turbine engines is presented. Our model formulation includes both soot surface activation by organic vapors and organic vapor condensation on the activated part of the soot surfaces. To enable this formulation, approaches to estimate chemical and physical properties of aerosols containing complex mixtures of sulfuric acid, water, and organic molecules were developed. Relevant distributions of a list of organic surrogates at the engine exit plane were used to represent complex organic emissions from aircraft engines. A parametric study was performed using this new formulation to understand the effects of ambient conditions, organic emissions levels, and mass accommodation coefficient values on the evolution of near field volatile particulate matter emissions from aircraft engines at ground level. Copyright 2014 American Association for Aerosol Research

Differential photoacoustic spectroscopic (DPAS)-based technique for PM optical absorption measurements in the presence of light absorbing gaseous species

ABSTRACT In this study, we developed an optical monitor to measure light absorption from particulate matter (PM) at 532 nm using a differential photoacoustic absorption spectroscopic (DPAS) technique. The dual-cell system is capable of measuring the photoacoustic signals due to light absorption of total PM and gaseous samples and that of gaseous samples, separately. The resulting differential photoacoustic signal can be used to determine the light absorption purely from the PM species. This measurement method eliminates the interferences from the light-absorbing gaseous species as well as the surrounding low-frequency background acoustic noises. Photoacoustic signals of the DPAS monitor were calibrated with the NO2 gas standards, varying from 100 to 250 parts per billion (ppb). Based on an Allan analysis, a detection sensitivity (2σ) of 0.68 Mm−1 can be achieved in 100 s data acquisition. Using the Jet Burner Test Stand (JBTS) facility at the United Technologies Research Center (UTRC), we measured light absorption by the soot emissions from a representative high-temperature and high-pressure test combustor for aircraft auxiliary power units (APU). The DPAS measurement results at 532 nm, under the high gaseous NO2 conditions, were then compared to the determination of soot mass concentrations from a commercial AVL Micro Soot Sensor (MSS). An excellent linear correlation between the measurements from two instruments was observed. The mass absorption coefficient (MAC) of the soot using the two data sets was 7.4 ± 1.3 m2g−1, in good agreement with the previously reported 8.1 ± 1.7 m2g−1 and the expected value of 7.6 ± 0.6 m2g−1. Copyright

Experimental and Numerical Studies of Sulfate and Organic Condensation on Aircraft Engine Soot

To study the condensation of sulfates and organics on aircraft engine soot, a systematic measurement of particulate matter was performed using a sector rig combustor at various operation conditions and sampling configurations. The condensation of organics increased with increasing soot loading, although the initial vapor phase concentration was lower for the high soot condition. The condensation rate of the organic species is much slower than that of the sulfates, and therefore the availability of the soot surfaces becomes a rate-limiting factor. On the other hand, because the sulfates are nearly completely condensed on soot surfaces even for the low soot conditions, more soot did not significantly increase the condensation of sulfates. The experimental results were explained with a microphysical simulation by using a 6-species surrogate model to represent volatile aircraft emissions. Using the relative composition of the volatile organics based on saturation vapor concentration, and the dry mass accommodation coefficient derived from the correlation to water solubility, the proposed surrogate model was able to match the experimental measurements both qualitatively and quantitatively.Copyright