Hyperpolarized Xenon Magnetic Resonance Imaging of Combustion Processes
There is considerable interest in new methods to probe the chemistry and thermodynamics of enclosed combustion processes. Hyperpolarized xenon gas magnetic resonance imaging enables sensitive and noninvasive analysis of chemical composition and velocity within enclosed and opaque samples. By taking advantage of both the temperature sensitivity of the chemical shift as well as the inertness of xenon-129, temperature and velocity distribution images of an enclosed flame can be acquired. Previous attempts to analyze high-temperature combustion reactions using nuclear magnetic resonance employed two-dimensional exchange spectroscopy of hyperpolarized xenon and proton single-point imaging. In the present study, a homebuilt, water-cooled probe was fabricated, including electronics that are able to withstand high temperatures (approaching 2000 K). Hyperpolarized xenon is premixed with a combustible gas (methane or dimethyl ether) and meets with pure oxygen at an enclosed diffusion flame centered within a 15-mm (diameter) by 25.4-mm (height) insulated coil. A spin echo pulse sequence with velocity and acceleration compensated phase-encodes, is used to generate temperature-weighted, three-dimensional chemical shift images as well as velocity maps of the flame region. This technique can be applied to studying confined combustion processes such as microturbine engines on microelectromechanical systems devices.