This paper reports experimental data on flashback and lean blowout characteristics of H2/CO/CH4 mixtures. Data were obtained over a range of fuel compositions at fixed approach or burned flow velocity, reactant temperature, and combustor pressure at several conditions up to 4.4 atm and 470 K inlet reactants temperature. Consistent with prior studies, these results indicate that the percentage of H2 in the fuel dominates the mixture blowout characteristics. These blowout characteristics can be captured with classical Damko¨hler number scalings to predict blowoff equivalence ratios to within 10%. Counter-intuitively, the percentage of hydrogen had far less effect on flashback characteristics, at least for fuels with hydrogen mole fractions less than 60%. This is due to the fact that two mechanisms of “flashback” were noted: rapid flashback into the premixer, presumably through the boundary layer, and movement of the static flame position upstream along the centerbody. The former and latter mechanisms were observed at high and low hydrogen concentrations. In the latter mechanism, flame temperature, not flame speed, appears to be the key parameter describing flashback tendencies. We suggest that this is due to an alteration of the vortex breakdown location by the adverse pressure gradient upstream of the flame, similar to the mechanism proposed by Sattelmayer and co-workers [1]. As such, a key conclusion here is that classical flashback scalings derived from, e.g., Bunsen flames, may not be relevant for many parameter regimes found in swirling flames.

The spectral sensitivity of the visual system varies markedly between the fovea and surrounding periphery owing in part to the rapid fall in macular pigment density with eccentricity. We examined how colour appearance changes between the fovea and near periphery (8°) by measuring achromatic loci and the loci of unique and binary hues. Chosen colours remained much more similar at the two locations than predicted by the change in spectral sensitivity. Compensation for white may reflect long-term gain changes within the cones that equate sensitivity for the local average stimulus in the fovea and periphery. However, adjusting only to the average stimulus cannot correct for all of the effects of a spectral sensitivity change, and predicts differences in colour percepts between the fovea and periphery that were not observed. The similarities in hue percepts at 0 and 8° thus suggest that additional processes help compensate colour appearance to maintain constancy in the near periphery. We model the results of previous studies to show that similar adjustments are implied by age-related changes in lens pigment, and to show that these adjustments are consistent with previous measurements of peripheral colour appearance based on hue cancellation.

The increasing demand for total hip arthroplasty (THA) in relatively young, high-demand patients has led to the use of hard-on-hard bearing surfaces. Adverse local tissue reaction/pseudotumor and elevated serum metal ion levels are commonly reported complications encountered in metal-on-metal THA, while audible articulation and rim fracture are reported in ceramic-on-ceramic THA. For this reason, ceramic-on-metal THA was implemented as an ideal hard-on-hard bearing combination. In this report, we describe a case of bilateral simultaneous ceramic-on-metal THA in a 69-year-old woman who presented 7 years postoperatively with unilateral hip pain associated with underlying pseudotumor and elevated serum cobalt and chromium ion levels. Pre-revision workup, intraoperative findings, and postoperative evaluation are included and suggest acetabular malposition as a potential source for complication.

This paper describes measurements of the dependence of lean blowout limits upon fuel composition for H2/CO/CH4 mixtures. Blowout limits were obtained at fixed approach flow velocity, reactant temperature, and combustor pressure at several conditions up to 4.4 atm and 470 K inlet reactants temperature. Consistent with prior studies, these results indicate that the percentage of H2 in the fuel dominates the mixture blowoff characteristics. That is, flames can be stabilized at lower equivalence ratios, adiabatic flame temperatures, and laminar flame speeds with increasing H2 percentage. Various methods of correlating these data were evaluated, using combinations of Lewis number (Lemix), adiabatic flame temperature (Tad), flame speed (SL), and chemical time (τchem). These correlations clearly indicate the significance of the mixture diffusivity, heat content, and flame propagation speed upon blowout characteristics across a wide fuel spectrum. Two basic models of flame stabilization discussed in the literature were evaluated — a well-stirred reactor based approach that considers the ratio of chemical and flow times, and a propagative mechanism that considers the ratio of flame and flow speed. Both mechanisms were able to correlate some, but not all segments of the data set.

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