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Franck-Condon factors in radiative, excitation and ionization molecular transitions of oxygen, carbon monoxide, nitric oxide, etc
Comparison of the new generation of air quality monitoring instruments with some more traditional methods. The first generation of air quality measurement instruments, based on the use of oxidant coulometric cells, nitrogen oxide colorimetry, carbon monoxide infrared analyzers, and other types of detectors, is compared with new techniques now coming into wide use in the air monitoring field and involving the use of chemiluminescent reactions, optical absorption detectors, a refinement of the carbon monoxide infrared analyzer, electrochemical cells based on solid electrolytes, and laser detectors.
A model which predicts nitric oxide and carbon monoxide emissions from a swirl can modular combustor is discussed. A detailed analysis of the turbulent fuel-air mixing process in the swirl can module wake region is reviewed. Hot wire anemometry was employed, and gas sampling analysis of fuel combustion emissions were performed.
The exhaust emission test was designed to measure hydrocarbons, carbon monoxide, and oxides of nitrogen concentrations and determine mass emissions through calculations during a simulated aircraft landing-takeoff cycle. The calculations required to convert exhaust emission concentrations (raw emission measurements) into mass emissions were emphasized.
To accomplish simultaneous reduction of unburned hydrocarbons, carbon monoxide, and oxides of nitrogen, required major modifications to the combustor. The modification most commonly used was a staged combustion technique. While these designs are more complicated than production combustors, no insurmountable operational difficulties were encountered in either high pressure rig or engine tests which could not be resolved with additional normal development. The emission reduction results indicate that reductions in unburned hydrocarbons were sufficient to satisfy both near and far-termed EPA requirements. Although substantial reductions were observed, the success in achieving the CO and NOx standards was mixed and depended heavily on the engine/engine cycle on which it was employed. Technology for near term CO reduction was satisfactory or marginally satisfactory. Considerable doubt exists if this technology will satisfy all far-term requirements.
Six headplate modules in a flame-tube combustor were evaluated. Unburned hydrocarbons, carbon monoxide, and oxides of nitrogen were measured for three types of fuel injectors both with and without a mixing venturi. Tests were conducted using jet A fuel at an inlet pressure of 0.69 megapascal, an inlet temperature of 478 K, and an isothermal static pressure drop of 3 percent. Oxides of nitrogen were reduced by over 50 percent with a mixing venturi with no performance penalties in either other gaseous emissions or pressure drop.
Test were conducted to determine the effect of primary-zone equivalence ratio on the formation of smoke and other gaseous pollutants in an experimental can combustor. Several fuel injection techniques were examined at primary-zone equivalence ratios from 0.8 to 2.0. The main emphasis was on reducing fuel-rich-combustion smoke levels. Two of the four fuel injection configurations studied produced smoke levels below a smoke number of 20 at a primary-zone equivalence ratio of about 1.7. As the fuel mixing and atomization were recorded at primary-zone equivalence ratios as high as 2.0. The gaseous emissions of unburned hydrocarbons, carbon monoxide, and oxides of nitrogen were quite sensitive to the fuel injection configuration as well as to the primary-zone equilvalence ratio.
A multigas correlation interferometer, based on the previously developed and tested COPE instrument, has been designed and fabricated and is presently undergoing laboratory testing. The CIMATS instrument has the capability to remotely measure densities of selected gaseous atmospheric species in the spectral range 2 to 2.5 and 4 to 10 microns. The sensor has been designed for both nadir viewing and earth limb viewing. As presently configured the sensor is capable of measuring ammonia, nitrous oxide, and carbon monoxide in the nonthermal infrared spectral region and carbon monoxide and sulfur dioxide in the thermal infrared. Other gaseous species can be measured by inclusion of additional narrow band filters.
A series of fundamental problems related to jet engine air pollution and combustion were examined. These include soot formation and oxidation, nitric oxide and carbon monoxide emissions mechanisms, pollutant dispension, flow and combustion characteristics of the NASA swirl can combustor, fuel atomization and fuel-air mixing processes, fuel spray drop velocity and size measurement, ignition and blowout. A summary of this work, and a bibliography of 41 theses and publications which describe this work, with abstracts, is included.
Experimental tests were conducted to develop a combustion system for a 40 atmosphere pressure, 2480 K exhaust gas temperature, turbine cooling facility. The tests were conducted in an existing facility with a maximum pressure capability of 10 atmospheres and where inlet air temperatures as high as 894 K could be attained. Exhaust gas temperatures were as high as 2365 K. Combustion efficiences were about 100 percent over a fuel air ratio range of 0.016 to 0.056. Combustion efficiency decreased at leaner and richer ratios when the inlet air temperature was 589 K. Data are presented that show the effect of fuel air ratio and inlet air temperature on liner metal temperature. Isothermal system pressure loss as a function of diffuser inlet Mach number is also presented. Data included exhaust gas pattern factors; unburned hydrocarbon, carbon monoxide, and oxides of nitrogen emission index values; and smoke numbers.
Gas turbine engine inlet parameters reflect changes in local atmospheric conditions. The pollutant emissions for the engine reflects these changes. In attempting to model the effect of the changing ambient conditions on the emissions it was found that these emissions exhibit an extreme sensitivity to some of the details of the combustion process such as the local fuel-air ratio and the size of the drops in the fuel spray. Fuel-air ratios have been mapped under nonburning conditions using a single JT8D-17 combustion can at simulated idle conditions, and significant variations in the local values have been found. Modelling of the combustor employs a combination of perfectly stirred and plug flow reactors including a finite rate vaporization treatment of the fuel spray. Results show that a small increase in the mean drop size can lead to a large increase in hydrocarbon emissions and decreasing the value of the CO-OH rate constant can lead to large increases in the carbon monoxide emissions. These emissions may also be affected by the spray characteristics with larger drops retarding the combustion process. Hydrocarbon, carbon monoxide, and oxides of nitrogen emissions calculated using the model accurately reflect measured emission variations caused by changing engine inlet conditions.
The results of an investigation of the effect of operating conditions and fuel properties on emission for the two-stage combustion of fuels with significant organic nitrogen content are presented. The way in which the emissions of nitrogen oxides and carbon monoxide are affected by the decreased hydrogen content and the increased organic nitrogen content of coal-derived fuels is discussed. Limited measurements of smoke from the rich-lean combustion of simulated syncrude fuels indicate relatively high smoke emissions in spite of the very lean second-stage burning. This fact, together with the high observed carbon monoxide emissions, suggests that trade-offs will be necessary between the conditions that minimize NOx and those that control CO and smoke emissions.
Applications of the Differential Absorption Lidar (DIAL) technique to the remote sensing of pollutant gases are surveyed. In the DIAl technique, the differential absorption of two laser beams reflected back to a receiver from a target determines the concentration of the gas being studied. The types of instruments available are considered in detail: dye lidar (to measure nitrogen dioxide, sulfur dioxide, and ozone); carbon dioxide laser (for ozone, ethylene, ammonia, and hydrazine), helium-neon laser (for methane); hydrogen fluoride laser (for HF); and tunable diode laser (for nitric oxide and carbon monoxide). DIAL instruments are compared with other optical remote sensors such as Fourier-transform infrared spectrometers, correlation spectrometers (COSPEC and GASPEC), and grating spectrometers; and criteria for the selection of an appropriate gas measuring system are suggested. Laser and other optical remote sensors are found to be cost effective in many cases, despite the fact that they are more costly than point-monitoring systems.
Samples of 1% Pt/SnO2 catalyst were exposed to a stoichiometric gas mixture of 1% CO and 1.2% O2 in helium over a range of flowrates from 5 to 15 sccm and temperatures from 338 to 394 Kelvin. Reaction rate constants for the catalytic oxidation of carbon monoxide and their temperature dependence were determined and compared with previous literature values.
Platinum on tin oxide (Pt/SnO2) good catalyst for oxidation of carbon monoxide at or near room temperature. Catalytic activity peaks at about 17 weight percent Pt. Catalysts with platinum loadings as high as 46 percent fabricated by technique developed at Langley Research Center. Work conducted to determine optimum platinum loading for this type of catalyst. Major application is removal of unwanted CO and O2 in CO2 lasers.
One of the unqualified successes of the earth observation program is NASA's continuing monitoring of the ozone layer from space. This activity began in the early 70's with research instruments and continues to this day with the TOMS instrument series and the Upper Atmosphere Research Satellite. In the near future, NASA will be launching the EOS Aura spacecraft (launch mid-2003) which will continue our study of the chemical processes that produce stratospheric ozone depletion. In addition, Aura will begin the first global study of lower atmospheric air pollution including urban ozone, aerosols, nitrogen oxides and carbon monoxide. Atmospheric air pollution measurements from earth orbit involve the development of very high precision spectrometer technologies that have never been flown in space. Farther into the future, lower atmospheric ozone and aerosols may be monitored by space based lidars in low earth orbit, by sensors in geostationary orbit and by continuous limb observations instrument from the Lagrange point L2.
Biomass burning generates hydrocarbons, nitrogen oxides and carbon monoxide that lead to tropospheric ozone pollution. Other combustion products form soot and various aerosol particles that make up smoke. Since early 1997 smoke and tropospheric ozone have been monitored in real-time from TOMS (Total Ozone Mapping Spectrometer) at toms.gsfc.nasa.gov (smoke aerosol) and metosrv2.umd.edu/-tropo (tropospheric ozone). The striking increase in smoke and tropospheric ozone observed during the 1997 Indonesian fires was the first extreme episode observed. During the August-November period, plumes of excess ozone and smoke coincided at times but were decoupled at other times, a phenomenon followed with trajectories. Thus, trans-boundary evolution of smoke and ozone differed greatly. The second discovery of the 1997 TOMS record was a dynamical interaction of ozone with the strong El Nino Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) that led to a jump in tropospheric ozone in March 1997 over the entire Indian Ocean, well ahead of the intense burning period. A climatology of smoke and tropospheric ozone from a 1980's TOMS instrument shows offsets in the timing of these pollutants - further evidence that factors other than biomass burning exert a strong influence on tropical tropospheric ozone.
Aircraft future aircraft jet engines will run at higher pressures to obtain greater fuel efficiency and performance. This will require new combustor designs to keep the nitrogen oxide and carbon monoxide emissions at environmentally acceptable levels. The actual pressures and temperatures found in gas turbine combustors must be duplicated in a laboratory to verify the emissions characteristics of gas turbine engines. Recognizing this, the U.S. aircraft gas turbine industry identified a need for a national facility that could duplicate the severe inlet conditions of future combustors. Because of our expertise in combustion emissions reduction research and in the design and operation of high-pressure test facilities, the NASA Lewis Research Center was seen as the natural location for such a facility. As a national laboratory, Lewis could provide these facilities to all U.S. gas turbine engine manufacturers while protecting their proprietary interests. Called the Advanced Subsonic Combustion Rig, the facility will provide up to 60-atm pressures at inlet temperatures up to 1300 F and air flow rates up to 38 lb/sec. Furthermore, it will offer state-of-the-art diagnostic methods for characterizing advanced combustor concepts. Aeronautical combustion research at Lewis provided several significant accomplishments recently in support of both the High Speed Research (HSR) and Advanced Subsonic Technology (AST) programs. For example, in the High Speed Research Program, NO_x reductions of up to 90 percent were achieved in prototype combustor hardware. Advanced computational analysis, gas sampling, and laser diagnostic techniques were critical to this success. Working closely with the gas turbine industry, we have successfully transferred this low-emissions combustor technology into engine prototype hardware. This hardware is now being tested at the engine manufacturers facilities. Complementary tests in Lewis currently available 30-atm test facilities are also underway, taking advantage of Lewis unique diagnostic capabilities. By utilizing test facilities belonging to both NASA and its industry partners, we have tested multiple combustor concepts in a shorter period of time.