Dynamics of premixed methane/air mixtures in a heated microchannel with different wall temperature gradients

The unsteady flame propagation mode (FREI) is affected by the wall temperature gradient. As the temperature gradient approaches zero, the mixture ignites at its auto-ignition temperature, frequency decreases and this leads to extinction of FREI mode.

Molecular ion sources for low energy semiconductor ion implantation (invited)

Smaller semiconductors require shallow, low energy ion implantation, resulting space charge effects, which reduced beam currents and production rates. To increase production rates, molecular ions are used. Boron and phosphorous (or arsenic) implantation is needed for P-type and N-type semiconductors, respectively. Carborane, which is the most stable molecular boron ion leaves unacceptable carbon residue on extraction grids. A self-cleaning carborane acid compound (C4H12B10O4) was synthesized and utilized in the ITEP Bernas ion source resulting in large carborane ion output, without carbon residue. Pure gaseous processes are desired to enable rapid switch among ion species. Molecular phosphorous was generated by introducing phosphine in dissociators via 4PH3 = P4 + 6H2; generated molecular phosphorous in a pure gaseous process was then injected into the HCEI Calutron-Bernas ion source, from which P4(+) ion beams were extracted. Results from devices and some additional concepts are described.

Investigations on flame dynamics of premixed H2–air mixtures in microscale tubes

The flame propagation is affected by flame shape angle and wall heat transfer coeff. A minimum flame propagation speed is observed for planar flames with nearly zero flame shape angle for 580 h⁻² K⁻¹ wall heat transfer coeff. range.

Numerical investigations of unsteady flame propagation in stepped microtubes

Flame dynamics near the contraction is governed by flame stretching. Change in fuel–air mass-flux entering flame plays a crucial role in accelerating the propagating flames at certain thermal boundary conditions as flame reaches the contraction.

Pattern formation of flames in radial microchannels with lean methane-air mixtures

Premixed methane-air mixture is introduced at the center of two parallel circular quartz plates separated by a millimeter scale distance (<or= 5mm). Two plates are heated with an external heater to create a positive temperature gradient condition along the flow direction. The combustion characteristics of lean methane-air mixtures are investigated at phi=0.67 and phi=0.85 in the laminar flow regime (Re approximately 500-1800). Contrary to the general perception of a stable premixed flame front at a radial location, a large variety of unstable and dynamic flame front patterns are observed at phi=0.67. At phi=0.85, stable flame propagation mode dominated the regime diagram and unstable flame propagation modes are observed under limited conditions. In these unstable flame propagation modes, single and multiple flame fronts rotate around the center at a rate of 15-50 Hz.