Analysis of aircraft exhausts with Fourier-transform infrared emission spectroscopy

Optical Diagnostics for Solid Rocket Plumes Characterization: A Review

In recent decades, solid fuel combustion propulsion of spacecraft has become one of the most popular choices for rocket propulsion systems. The reasons for this success are a wide range of applications, lower production costs, simplicity, and safety. The rocket’s plumes leave the nozzle at high temperatures; hence, the knowledge of produced infrared (IR) emissions is a crucial aspect during the design and tests of the rocket motors. Furthermore, rocket plume composition is given by N2, H2, H2O, CO and CO2, while solid rocket motors (SRM) additionally inject some solid particles, given by metal fuel additives in the propellant grain, i.e., aluminum oxide (Al2O3) particles. The main issue is the detection of the particles remaining in the atmosphere due to the exhaust gas of the solid rocket propulsion system that could have effects on ozone depletion. The experimental characterization of SRM plumes in the presence of alumina particles can be conducted using different optical techniques. The present study aims to review the most promising ones with a description of the optics system and their potential applications for SRM plume measurements. The most common measurement techniques are infrared spectroscopy imaging, IR imaging. UV–VIS measurements, shadowgraph, and Schlieren optical methods. The choice of these techniques among many others is due to the ability to study the plume without influencing the physical conditions existing in and around the study object. This paper presents technical results concerning the study of rocket engines plumes with the above-mentioned methods and reveals the feasibility of the measurement techniques applied.

Calculating (14)N(16)O2 spectral line parameters in an infrared range: A comparison of "global" and "local" effective operator methods

Nitrogen dioxide, (14)N(16)O2, line positions and intensities calculated by us based on a "local" effective operator method are compared to the recent results of the "global" calculation. The comparison was made for theoretical absorption coefficients in the spectral range of 600-3700cm(-1) using the measured data taken from the Pacific Northwest National Laboratory. In order to conduct the calculations, empirical parameters of the effective rotational Hamiltonian of the twenty-one vibrational states were applied from the most recent experimental works. The second order parameters of the dipole moment function of (14)N(16)O2 were determined for the first time. The "local" line list in this research consists of one hundred and four bands and includes the line intensities of the v1+v2+v3 band of (14)N(16)O2 that have not yet been investigated in the literature. Among these bands, only eleven bands are included in HITRAN2012. The reasons behind the disagreements between the theoretical and measured absorption coefficients of (14)N(16)O2 are discussed.

Modeling absorption spectra for detection of the combustion products of jet engines by laser remote sensing

The absorption spectra of exhaust gases (H₂O, CO, CO₂, NO, NO₂, and SO₂) and aerosol (soot and Al₂O₃) particles were modeled at different temperatures for the first time and suitable spectral ranges were determined for conducting laser remote sensing of the combustion products of jet engines. The calculations were conducted on the basis of experimental concentrations of the substances and the sizes of the aerosol particles. The temperature and geometric parameters of jet engine exhausts were also taken from the literature. The absorption spectra were obtained via the line-by-line method, making use of the spectral line parameters from the authors' own high-temperature databases (for NO₂ and SO₂ gases) and the HITEMP 2010 database, and taking into account atmospheric transmission. Finally, the theoretical absorption spectra of the exhaust gases were plotted at temperatures of 400, 700, and 1000 K, and the impact of aerosol particles on the total exhaust spectra was estimated in spectral ranges suitable for remote sensing applications.

Aircraft engine exhaust emissions and other airport-related contributions to ambient air pollution: A review

Civil aviation is fast-growing (about +5% every year), mainly driven by the developing economies and globalisation. Its impact on the environment is heavily debated, particularly in relation to climate forcing attributed to emissions at cruising altitudes and the noise and the deterioration of air quality at ground-level due to airport operations. This latter environmental issue is of particular interest to the scientific community and policymakers, especially in relation to the breach of limit and target values for many air pollutants, mainly nitrogen oxides and particulate matter, near the busiest airports and the resulting consequences for public health. Despite the increased attention given to aircraft emissions at ground-level and air pollution in the vicinity of airports, many research gaps remain. Sources relevant to air quality include not only engine exhaust and non-exhaust emissions from aircraft, but also emissions from the units providing power to the aircraft on the ground, the traffic due to the airport ground service, maintenance work, heating facilities, fugitive vapours from refuelling operations, kitchens and restaurants for passengers and operators, intermodal transportation systems, and road traffic for transporting people and goods in and out to the airport. Many of these sources have received inadequate attention, despite their high potential for impact on air quality. This review aims to summarise the state-of-the-art research on aircraft and airport emissions and attempts to synthesise the results of studies that have addressed this issue. It also aims to describe the key characteristics of pollution, the impacts upon global and local air quality and to address the future potential of research by highlighting research needs.

Multipass open-path Fourier-transform infrared measurements for nonintrusive monitoring of gas turbine exhaust composition

The detection limits for NO and NO2 in turbine exhausts by nonintrusive monitoring have to be improved. Multipass mode Fourier-transform infrared (FTIR) absorption spectrometry and use of a White mirror system were found from a sensitivity study with spectra simulations in the mid-infrared to be essential for the retrieval of NO2 abundances. A new White mirror system with a parallel infrared beam was developed and tested successfully with a commercial FTIR spectrometer in different turbine test beds. The minimum detection limits for a typical turbine plume of 50 cm in diameter are approximately 6 parts per million (ppm) for NO and 9 ppm for NO2 (as well 100 ppm for CO2 and 4 ppm for CO).

Modeling of gas absorption cross sections by use of principal-component-analysis model parameters

Monitoring the amount of gaseous species in the atmosphere and exhaust gases by remote infrared spectroscopic methods calls for the use of a compilation of spectral data, which can be used to match spectra measured in a practical application. Model spectra are based on time-consuming line-by-line calculations of absorption cross sections in databases by use of temperature as input combined with path length and partial and total pressure. It is demonstrated that principal component analysis (PCA) can be used to compress the spectrum of absorption cross sections, which depend strongly on temperature, into a reduced representation of score values and loading vectors. The temperature range from 300 to 1000 K is studied. This range is divided into two subranges (300-650 K and 650-1000K), and separate PCA models are constructed for each. The relationship between the scores and the temperature values is highly nonlinear. It is shown, however, that because the score-temperature relationships are smooth and continuous, they can be modeled by polynomials of varying degrees. The accuracy of the data compression method is validated with line-by-line-calculated absorption data of carbon monoxide and water vapor. Relative deviations between the absorption cross sections reconstructed from the PCA model parameters and the line-by-line-calculated values are found to be smaller than 0.15% for cross sections exceeding 1.27 x 10(-21) cm(-1) atm(-1) (CO) and 0.20% for cross sections exceeding 4.03 x 10(-21) cm(-1) atm(-1) (H2O). The computing time is reduced by a factor of 10(4).

Nonintrusive optical measurements of aircraft engine exhaust emissions and comparison with standard intrusive techniques

Nonintrusive systems for the measurement on test rigs of aeroengine exhaust emissions required for engine certification (CO, NO(x), total unburned hydrocarbon, and smoke), together with CO(2) and temperature have been developed. These results have been compared with current certified intrusive measurements on an engine test. A spectroscopic database and data-analysis software has been developed to enable Fourier-transform Infrared measurement of concentrations of molecular species. CO(2), CO, and NO data showed agreement with intrusive techniques of approximately ?30%. A narrow-band spectroscopic device was used to measure CO(2) (with deviations of less than ?10% from the intrusive measurement), whereas laser-induced incandescence was used to measure particles. Future improvements to allow for the commercial use of the nonintrusive systems have been identified and the methods are applicable to any measurement of combustion emissions.