This manuscript describes the development of an ultrafast (i.e., femtosecond), mid-infrared, laser-absorption diagnostic and its initial application to measuring temperature, CO, and CH 4 in flames. The diagnostic employs a Ti:Sapphire oscillator emitting 55-fs pulses near 800 nm which were amplified and converted into the mid-infrared (mid-IR) though optical parametric amplification (OPA) at a repetition rate of 5 kHz. The pulses were directed through the test gas and into a high-speed midinfrared spectrograph to image spectra across a ≈30 nm bandwidth with a spectral resolution of ≈0.3 nm. Gas properties were determined by least-squares fitting a spectroscopic model to measured single-shot absorbance spectra. The diagnostic was validated with measurements of temperature, CO, and CH 4 in a static-gas cell with an accuracy of 0.7% to 1.8% of known values. Single-shot, 5 kHz measurements of temperature and CO were acquired near 4.9 µm in a laser-ignited HMX (i.e., 1,3,5,7tetranitro-1,3,5,7-tetrazoctane) flame and exhibited a 1-σ precision of 0.4% at ≈2700 K. Further, CH 4 and temperature measurements were acquired near 3.3 µm in a partially premixed CH 4 -air flame produced by a Hencken burner and exhibited a precision of 0.3% at ≈1000 K. laser-absorption spectroscopy, ultrafast spectroscopy, mid-wave infrared spectroscopy, broadband absorption spectroscopy

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Experiments have been performed on fully premixing multiport burners closely representative of those used in modern domestic heating systems to study the ways in which the detail design of the burner head affects the incidence of unwanted thermoacoustic oscillations in practical installations. The effects of changes in the spacing of the flame ports, the velocity profile of the mean flow within the ports and the topography of the firing surface on the acoustic impedance of the burner and the transfer function of the flame array are analysed separately. In some of the experiments diagnostic changes have also been made to the fuel:air ratio of the mixture burned. The results confirm practical experience that small changes to the head design can have very major influences on the stability of complete systems but show also that the effects of these design changes are not well represented by simple models.

The total, state-selective and angular-differential cross sections for single electron capture in He + -He collisions are investigated by using the two-center atomic orbital close-coupling method in the energy range 0.2-650 keV/u. The angular-differential cross sections for electron capture to the ground state of He are calculated at collision energies of 0.625, 1.25, 7.5, 25, 60, and 150 keV/u within the eikonal approximation for the scattering amplitude. Both total and differential cross sections are compared with the available experimental and theoretical data. The calculated differential cross sections exhibit oscillatory structures with exponentially decreasing amplitude and frequency decreasing with increasing the collision energy. They show good agreement with the experimental data for scattering angles , 0 q q < where 0 q decreases with increasing the collision energy ( 0.2 deg 0 q » for E=0.625 keV/u, 0.006 deg 0 q » for E=150 keV/u). We found out that for a given collision energy, the oscillatory structure of angular-differential cross section is strongly correlated with the oscillatory structure of the impact parameter dependence of electron capture probability.