Measurement of Temperature and H2O Concentration in Premixed CH4/Air Flame Using Two Partially Overlapped H2O Absorption Signals in the Near Infrared Region

It is important to monitor the temperature and H2O concentration in a large combustion environment in order to improve combustion (and thermal) efficiency and reduce harmful combustion emissions. However, it is difficult to simultaneously measure both internal temperature and gas concentration in a large combustion system because of the harsh environment with rapid flow. In regard, tunable diode laser absorption spectroscopy, which has the advantages of non-intrusive, high-speed response, and in situ measurement, is highly attractive for measuring the concentration of a specific gas species in the combustion environment. In this study, two partially overlapped H2O absorption signals were used in the tunable diode laser absorption spectroscopy (TDLAS) to measure the temperature and H2O concentration in a premixed CH4/air flame due to the wide selection of wavelengths with high temperature sensitivity and advantages where high frequency modulation can be applied. The wavelength regions of the two partially overlapped H2O absorptions were 1.3492 and 1.34927 μm. The measured signals separated the multi-peak Voigt fitting. As a result, the temperature measured by TDLAS based on multi-peak Voigt fitting in the premixed CH4/air flame was the highest at 1385.80 K for an equivalence ratio of 1.00. It also showed a similarity to those tendencies to the temperature measured by the corrected R-type T/C. In addition, the H2O concentrations measured by TDLAS based on the total integrated absorbance area for various equivalent ratios were consistent with those calculated by the chemical equilibrium simulation. Additionally, the H2O concentration measured at an equivalence ratio of 1.15 was the highest at 18.92%.

Diffraction line broadening from nanocrystals under large hydrostatic pressures

Atomistic copper nanocrystals were investigated via Molecular Dynamics (MD) under hydrostatic pressure to probe the relationship between applied load and structure deformation. The corresponding X-ray powder diffraction patterns were generated from the atomic coordinates. The analysis followed both the traditional Williamson-Hall approach based on pseudo-Voigt fitting and an alternative, more accurate method able to derive the integral breadths without applying a fitting. The Williamson-Hall results show discrepancies not fully associated with an issue of fitting.

Residual Stress Error Introduced by Truncated Patterns: Prediction and Correction

The truncation of diffraction patterns in residual stress determination is often observed for broadened peaks when the 2θ acquisition range is not wide enough. The loss of information effects induced can either be traduced by a bad estimation of the background line, for the methods including a background subtraction, or a restriction of the analysis area for the others. In that borderline case, the results obtained by all methods with theirs specific parameters, developed to estimate the peak localisation are rather distributed in a wide range of stress values. In this paper we propose to review and to test some of the most common methods for stress evaluation (parabola, middle of chord, centred centroïd, asymmetrical pseudo-Voigt fitting). A separate study is made concerning error introduced on the 2θ peak position and on the final stress value estimated. For the parabola method, an analytical expression including some approximations such as the peak shape and its full width at half maximum is then given for the prediction and the correction of these errors. This study is sponsored by PSA PEUGEOT-CITROËN, RENAULT and SNECMA.