David K. Benson

Method and apparatus for thermal management of vehicle exhaust systems

A catalytic converter is surrounded by variable conductance insulation for maintaining the operating temperature of the catalytic converter at an optimum level, for inhibiting heat loss when raising catalytic converter temperature to light-off temperature, for storing excess heat to maintain or accelerate reaching light-off temperature, and for conducting excess heat away from the catalytic converter after reaching light-off temperature. The variable conductance insulation includes vacuum gas control and metal-to-metal thermal shunt mechanisms. Radial and axial shielding inhibits radiation and convection heat loss. Thermal storage media includes phase change material, and heat exchanger chambers and fluids carry heat to and from the catalytic converter.

The use of the counterflow diffusion flame in studies of inhibition effectiveness of gaseous and powdered agents

The problem of laboratory assessment of the relative effectiveness of gaseous and powdered agents in chemically inhibiting real fires is approached by use of the recently developed counterflow diffusion flame. The regions of stability of such flames are presumed to correlate with the chemically controlled reaction rate in inhibited flames. A scaled-down version of the flame system developed by Tsuji and Yamaoka is described, together with the provisions made to add gaseous and powdered agents in known amounts. The effect of addition of gases such as CF3Br, CF2ClBr, CH3Br, CO2, Ar, and N2 to the air and fuel side of methane-air, propane-air, and n-butane-air flames is shown. The results are consistent with expectations based on other techniques. The counterflow flame technique works equally well with powdered agents, apart from the only partially solved problems inherent in achieving steady powder loading of the air stream. A comparison of three commercial powdered agents added to the air stream of a CH4-air flame is shown. The powders are more effective on a weight basis than CF3Br.

Mechanisms of fatigue in mill-annealed Ti-6Al-4V at room temperature and 600°F

The mechanisms of the fatigue of mill-annealed Ti-6A1-4V were studied at 600°F and room temperature. Early crack initiationN0/Nf< 0.14) was found to occur in hcpα-grains by a slip-band mechanism under all but the least severe conditions of cyclic stress. Under cyclic stresses near the fatigue limit at room temperature, fatigue cracks began much laterN0/Nf ∼ 0.4) at the interface between hcpα and bccβ grains without detectable slip. Under all conditions, Stage I fatigue crack growth occupied 50 to 80 pct of the total life. Although mechanical twins were produced in profusion near the growing Stage II fatigue cracks, they appeared to play no role in crack initiation or Stage I crack growth; nor did they facilitate Stage II growth. None of the observations could be interpreted as evidence for a metallurgical instability or strain-induced phase transformation which might be harmful to the fatigue resistance of the alloy.