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Papathakos, L. C.

Publications and source records attributed to Papathakos, L. C..

11 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Aircraft sampling of the sulfate layer near the tropopause following the eruption of Mount St. Helens

Twenty filter sampling flights of the NASA Lewis F-106 aircraft were conducted in the Great Lakes region between June 4 and August 8, 1980, following the major eruption of Mount St. Helens, Washington on May 18. The IPC-1478 filters were exposed over an altitude range spanning the local tropopause. Quarter sections were analyzed for sulfate and nitrate by ion chromatography and selected samples were analyzed for chloride by selective ion electrode. Trace elements were searched by X-ray fluorescence analysis. A filter sample taken above the tropopause on June 5 indicated a sulfate level of 50 times the baseline measurements. Subsequent measurements over a period of 2 months showed an initial dropoff and formation of a persistent layer of sulfate above the tropopause with a concentration of 10 to 18 times previously measured background-levels. Concentrations of nitrate above the tropopause exhibited considerable variability and some enhancement compared with previously measured concentration levels. It is suggested that the source of the nitrate may also be volcanic as evidenced by its temporal relationship to the sulfate concentration changes. Based on the null results of X-ray fluorescence measurements, there is no evidence of ash particle concentrations greater than 3.4 microns g/cubic m persisting in the layer above the tropopause after the second transit of the cloud.

Lezberg, E. A.↗
NASA NTRS1982

Aircraft sampling of the sulfate layer near the tropopause following the eruption of Mount St. Helens

Twenty-three filter sampling flights of the NASA Lewis F-106 aircraft, were conducted in the Great Lakes region between June 4 and Dec. 23, 1980, following the major eruption of Mount St. Helens on May 18. The IPC-1478 filters were exposed over an altitude range spanning the local tropopause. A filter sample exposed above the tropopause on June 5 indicated a sulfate level 50 times the baseline measurements, which is consistent with the trajectory predictions of the leading edge of the cloud on its second transit around the earth. Subsequent measurements over a period of 7 months revealed the existence of a layer of sulfate above the tropopause that decayed to a level of about 4 times previously measured background levels by the beginning of August. Concentration of nitrate above the tropopause exhibited considerable variability and showed some enhancement compared with previously measured concentration levels. On the basis of the null results of X ray fluorescence measurements, there is no evidence of ash particle concentrations of greater than 3.4 microns/cu m persisting in the layer above the tropopause following the second transit of the cloud.

Lezberg, E. A.↗
NASA NTRS1978

Global sensing of gaseous and aerosol trace species using automated instrumentation on 747 airliners

The Global Atmospheric Sampling Program (GASP) is collecting and analyzing data on gaseous and aerosol trace contaminants in the upper troposphere and lower stratosphere. Measurements are obtained from automated systems installed on four 747 airliners flying global air routes. Improved instruments and analysis techniques are providing an expanding data base for trace species including ozone, carbon monoxide, water vapor, condensation nuclei, and mass concentration of sulfates and nitrates. Simultaneous measurements of several trace species obtained frequently can be used to identify the source of the air mass as being typically tropospheric or stratospheric.

Perkins, P. J.↗
NASA NTRS1977

Preliminary studies of autoignition and flashback in a premixing-prevaporizing flame tube using Jet-A fuel at lean equivalence ratios

Lean equivalence ratios from 0.3 to 0.7 were observed. Combustor inlet air pressures were varied from 0.54 to 2.5 MPa, combustor inlet air temperatures from 550 to 700 K, and reference velocities from 8 to 35 meters per second. Autoignition delay times ranged from 15 to 100 milliseconds and varied inversely with pressure. The Arrhenius activation energy was 41,840 joules per mole. Temperature rise data were obtained in a long premixing-prevaporizing tube at a pressure of 0.56 MPa. Preflame temperature rise data were a function of equivalence ratio, inlet air temperature, and tube residence time. Significant temperature rise occurred above temperatures of 760 K, with autoignition occurring at 775 K for equivalence ratios greater than 0.47. The reactions were similar to cool-flame phenomena. Flashback velocities were measured at temperatures of 610 and 700 K, pressure of 0.56 MPa, and equivalence ratios from 0.6 to 1. Flashback velocities varied from 30 to 65 meters per second.

Marek, C. J.↗
NASA NTRS1977

Global sensing of gaseous and aerosol trace species using automated instrumentation on 747 airliners

The Global Atmospheric Sampling Program (GASP) by NASA is collecting and analyzing data on gaseous and aerosol trace species in the upper troposphere and lower stratosphere. Measurements are obtained from automated systems installed on four 747 airliners flying global air routes. Advances were made in airborne sampling instrumentation. Improved instruments and analysis techniques are providing an expanding data base for trace species including ozone, carbon monoxide, water vapor, condensation nuclei and mass concentrations of sulfates and nitrates. Simultaneous measurements of several trace species obtained frequently can be used to uniquely identify the source of the air mass as being typically tropospheric or stratospheric. A quantitative understanding of the tropospheric-stratospheric exchange processes leads to better knowledge of the atmospheric impact of pollution through the development of improved simulation models of the atmosphere.

Perkins, P. J.↗
NASA NTRS1976

Exhaust emissions from a premixing, prevaporizing flame tube using liquid jet A fuel

Emissions of nitrogen oxides, carbon monoxide, and unburned hydrocarbons were measured in a burner where liquid Jet A fuel was sprayed into the heated air stream and vaporized upstream of a perforated plate flameholder. The burner was tested at inlet air temperatures at 640, 800, and 833 K, an inlet pressure of 5.6 X 100,000 N/m squared, a reference velocity of 25 m/sec, and equivalence ratios from lean blowout to 0.7. Nitrogen oxide levels of below 1.0 g NO2/kg fuel were obtained at combustion efficiencies greater than 99 percent. The measured emission levels for the liquid fuel agreed well with previously reported premixed gaseous propane data and agreed with well stirred reactor predictions. Autoignition of the premixed fuel air mixture was a problem at inlet temperatures above 650 K with 104 msec premixing time.

Marek, C. J.↗
NASA NTRS1973

Use of an air-assisted fuel nozzle to reduce idle emissions of a jt8d engine combustor

Tests were performed at typical engine idle conditions on a single-can JT8D combustor installed in a 24 centimeter (9.45 in.) housing to evaluate the effect of an air-assist nozzle on reducing exhaust emissions. By injecting high-pressure air through the secondary-flow passage of a standard duplex fuel nozzle, it was possible to reduce hydrocarbon emissions from 840 parts per million to 95 parts per million and carbon monoxide emissions from 873 parts per million to 258 parts per million. NOX emissions increased slightly from 18 parts per million to 22 parts per million. An air-assist differential pressure of only 20.1 newtons per square centimeter (29.1 psi) and an airflow rate of only 0.22 percent of the total combustor airflow was required.

Papathakos, L. C.↗