Advanced smoke meter development survey and analysis

Ideal smoke meter characteristics are determined to provide a basis for evaluation of candidate systems. Five promising techniques are analyzed in detail to evaluate compilance with the practical smoke meter requirements. Four of the smoke measurement concepts are optical methods: Modulated Transmission (MODTRAN), Cross Beam Absorption Counter (CBAC), Laser Induced Incandescence (LIN), and Photoacoustic Spectroscopy (PAS). A rapid response filter instrument called a Taper Element Oscillating Microbalance (TEOM) is also evaluated. For each technique, the theoretical principles are described, the expected performance is determined, and the advantages and disadvantages are discussed The expected performance is evaluated against each of the smoke meter specifications, and the key questions for further study are given. The most promising smoke meter technique analyzed was MODTRAN, which is a variation on a direct transmission measurement. The soot-laden gas is passed through a transmission cell, and the gas pressure is modulated by a speaker

On the accuracy of aerosol photoacoustic spectrometer calibrations using absorption by ozone

This is the final version of the article. Available from EGU via the DOI in this record.In recent years, photoacoustic spectroscopy has emerged as an invaluable tool for the accurate measurement of light absorption by atmospheric aerosol. Photoacoustic instruments require calibration, which can be achieved by measuring the photoacoustic signal generated by known quantities of gaseous ozone. Recent work has questioned the validity of this approach at short visible wavelengths (404 nm), indicating systematic calibration errors of the order of a factor of 2. We revisit this result and test the validity of the ozone calibration method using a suite of multipass photoacoustic cells operating at wavelengths 405, 514 and 658 nm. Using aerosolised nigrosin with mobility-selected diameters in the range 250-425 nm, we demonstrate excellent agreement between measured and modelled ensemble absorption cross sections at all wavelengths, thus demonstrating the validity of the ozone-based calibration method for aerosol photoacoustic spectroscopy at visible wavelengths.This work was funded by the Met Office. In addition, Nicholas W. Davies was supported by a NERC/Met Office Industrial Case studentship (ref 640052003). Michael I. Cotterell was supported by a Tom West Analytical Chemistry Trust Fund Fellowship. Michael I. Cotterell and Jim M. Haywood were supported by the CLARIFY-2017 Natural Environment Research Council funded proposal (NE/L013797/1)

Diode laser cavity-based techniques for quantification of trace species in laminar sooting flames

Cavity-enhanced absorption spectroscopy (CEAS) has been applied for the first time to in situ measurements of acetylene in sooting flames using a near-infrared diode laser. This is motivated by the role of acetylene as a major precursor in soot formation and the need for accurate measurements of acetylene to understand soot formation (with the eventual goal of reduced emissions). Vertical profiles of acetylene have been investigated in two flat flame burners with some consideration of the effect of radial profiles on the results. This thesis builds on the novel application of continuous-wave cavity ring-down spectroscopy (cw-CRDS) to in situ flame measurements of acetylene: in this work, refinements are made to the technique, which is developed to the point of generating reliable data in standard flames of interest in studies of soot formation. A key advantage of the cw-CRDS approach is that it is an absolute method, not requiring calibration. Nevertheless, the slow data acquisition led to the consideration of alternative approaches. This resulted in research on CEAS, which forms the bulk of this thesis. The advantages of the CEAS technique over cw-CRDS are highlighted, whilst noting the agreement between the two techniques. The CEAS approach allows spectra to be acquired much more rapidly and with better spectral resolution, as well as having a somewhat simpler experimental set-up. This has enabled the acquisition of a large dataset of broad scans over the full scanning range of the diode lasers employed. This thesis also goes on to explore the application of the CEAS technique to flame measurements of OH radical. The recovered profiles of acetylene concentration show good agreement for both techniques and follow the expected trend of higher acetylene concentration with increasing equivalence ratio. They also show a trend of decreasing acetylene concentration with increasing height above the burner surface. This would be consistent with the consumption of acetylene, including in reactions forming polycyclic aromatic hydrocarbons and ultimately soot. However, this is contrary to model predictions also shown in the thesis.Cavity-enhanced absorption spectroscopy (CEAS) has been applied for the first time to in situ measurements of acetylene in sooting flames using a near-infrared diode laser. This is motivated by the role of acetylene as a major precursor in soot formation and the need for accurate measurements of acetylene to understand soot formation (with the eventual goal of reduced emissions). Vertical profiles of acetylene have been investigated in two flat flame burners with some consideration of the effect of radial profiles on the results. This thesis builds on the novel application of continuous-wave cavity ring-down spectroscopy (cw-CRDS) to in situ flame measurements of acetylene: in this work, refinements are made to the technique, which is developed to the point of generating reliable data in standard flames of interest in studies of soot formation. A key advantage of the cw-CRDS approach is that it is an absolute method, not requiring calibration. Nevertheless, the slow data acquisition led to the consideration of alternative approaches. This resulted in research on CEAS, which forms the bulk of this thesis. The advantages of the CEAS technique over cw-CRDS are highlighted, whilst noting the agreement between the two techniques. The CEAS approach allows spectra to be acquired much more rapidly and with better spectral resolution, as well as having a somewhat simpler experimental set-up. This has enabled the acquisition of a large dataset of broad scans over the full scanning range of the diode lasers employed. This thesis also goes on to explore the application of the CEAS technique to flame measurements of OH radical. The recovered profiles of acetylene concentration show good agreement for both techniques and follow the expected trend of higher acetylene concentration with increasing equivalence ratio. They also show a trend of decreasing acetylene concentration with increasing height above the burner surface. This would be consistent with the consumption of acetylene, including in reactions forming polycyclic aromatic hydrocarbons and ultimately soot. However, this is contrary to model predictions also shown in the thesis

NASA's Microgravity Technology Report, 1996: Summary of Activities

This report covers technology development and technology transfer activities within the Microgravity Science Research Programs during FY 1996. It also describes the recent major tasks under the Advanced Technology Development (ATD) Program and identifies current technology requirements. This document is consistent with NASA,s Enteprise for the Human Exploration and development of Space (HEDS) Strategic Plan. This annual update reflects changes in the Microgravity Science Research Program's new technology activities and requirements. Appendix A. FY 1996 Advanced Technology Development. Program and Project Descriptions. Appendix B. Technology Development

The climate impacts of atmospheric aerosols using in-situ measurements, satellite retrievals and global climate model simulations

Aerosols contribute the largest uncertainty to estimates of radiative forcing of the Earth’s atmosphere, which are thought to exert a net negative radiative forcing, offsetting a potentially significant but poorly constrained fraction of the positive radiative forcing associated with greenhouse gases. Aerosols perturb the Earth’s radiative balance directly by absorbing and scattering radiation and indirectly by acting as cloud condensation nuclei, altering cloud albedo and potentially cloud lifetime. One of the major factors governing the uncertainty in estimates of aerosol direct radiative forcing is the poorly constrained aerosol single scattering albedo, which is the ratio of the aerosol scattering to extinction. In this thesis, I describe a new instrument for the measurement of aerosol optical properties using photoacoustic and cavity ring-down spectroscopy. Characterisation is performed by assessing the instrument minimum sensitivity and accuracy as well as verifying the accuracy of its calibration procedure. The instrument and calibration accuracies are assessed by comparing modelled to measured optical properties of well-characterised laboratory-generated aerosol. I then examine biases in traditional, filter-based absorption measurements by comparing to photoacoustic spectrometer absorption measurements for a range of aerosol sources at multiple wavelengths. Filter-based measurements consistently overestimate absorption although the bias magnitude is strongly source-dependent. Biases are consistently lowest when an advanced correction scheme is applied, irrespective of wavelength or aerosol source. Lastly, I assess the sensitivity of the direct radiative effect of biomass burning aerosols to aerosol and cloud optical properties over the Southeast Atlantic Ocean using a combination of offline radiative transfer modelling, satellite observations and global climate model simulations. Although the direct radiative effect depends on aerosol and cloud optical properties in a non-linear way, it appears to be only weakly dependent on sub-grid variability.Natural Environment Research CouncilMet Offic

The evolution of particulates across the sooting limit in turbulent premixed opposed jet flames

Soot formation in combustors is a complex process comprising highly intermittent interactions between physical and chemical processes across a wide range of time-scales. The influence of turbulence on the molecular pathways initiating particulate formation remains unquantified. Controlling soot emissions to the atmosphere will require overcoming large gaps in the understanding of soot formation/oxidation especially in turbulent combustion. The complexities of soot formation in turbulent flames suggests that the use of a flexible compact burner configuration with well–defined boundary conditions and precise control of flow characteristics is of significant advantage. The novel back–to–burnt opposed jet configuration features fractal grid generated turbulence and provides accurate control of flow parameters. The study includes the analyses of the overall flame structure of turbulent premixed ethylene/air flames, the relative concentrations of PAHs associated with soot inception and particle size distributions. The experiments covered a series of sooting flame conditions with variations in the equivalence ratio (1.7 ≤ \phi_{UN} ≤ 2.2), the total rate of strain (255 ≤ a_{T} [s−1] ≤ 610) and burnt gas temperature (1400 ≤ T_{LN} [K] ≤ 1700). The conditions traverse the soot inception limit, e.g. the transition from lightly to heavily sooting flames, with non- intrusive ELS and PAH–PLIF combined probe sampling to quantify gaseous and PAH species using GC–TCD and GC–MS, respectively. The probe sampling features comprehensive sampling steps used to provide accurate concentrations of major gaseous, PAH species and particles with minimum losses. It is shown that the rate of strain exerts a substantial influence on both PAH concentrations and soot formation. Hence, it is likely that soot formation in turbulent flames becomes dominated by contributions from low strain regions. It is also found that the stoichiometry of the mixture controls the concentrations of PAHs associated with soot inception. The results obtained clearly show that benzo(a)pyrene is prevalent in flame structures and that relatively large amounts are condensed onto soot particles. A transition between bimodal and unimodal shapes of the particle size distributions shows strong competitions between oxidation, aggregation and surface growth processes in the turbulent flames.Open Acces

Imaging Fluorescent Combustion Species in Gas Turbine Flame Tubes: On Complexities in Real Systems

Planar laser-induced fluorescence (PLIF) is used to visualize the flame structure via OH, NO, and fuel imaging in kerosene- burning gas turbine combustor flame tubes. When compared to simple gaseous hydrocarbon flames and hydrogen flames, flame tube testing complexities include spectral interferences from large fuel fragments, unknown turbulence interactions, high pressure operation, and the concomitant need for windows and remote operation. Complications of these and other factors as they apply to image analysis are considered. Because both OH and gas turbine engine fuels (commercial and military) can be excited and detected using OH transition lines, a narrowband and a broadband detection scheme are compared and the benefits and drawbacks of each method are examined

A stability and spatial-resolution enhanced laser absorption spectroscopy tomographic sensor for complex combustion flame diagnosis

A novel stable laser absorption spectroscopy (LAS) tomographic sensor with enhanced stability and spatial resolution is developed and applied to complex combustion flame diagnosis. The sensor reduces the need for laser collimation and alignment even in extremely harsh environments and improves the stability of the received laser signal. Furthermore, a new miniaturized laser emission module was designed to achieve multi-degree of freedom adjustment. The full optical paths can be sampled by 8 receivers, with such arrangement, the equipment cost can be greatly reduced, at the same time, the spatial resolution is improved. In fact, 100 emitted laser paths are realized in a limited space of 200mm×200 mm with the highest spatial resolution of 1.67mm×1.67 mm. The stability and penetrating spatial resolution of the LAS tomographic sensor were validated by both simulation and field experiments on the afterburner flames. Tests under two representative experiment states, i.e., the main combustion and the afterburner operation states, were conducted. Results show that the error under the main combustion state was about 4.32% and, 5.38% at the afterburner operation state. It has been proven that this proposed sensor can provide better tomographic measurements for combustion diagnosis, as an effective tool for improving performances of afterburners