Combustion resistance of the¹²⁹Xe hyperpolarized nuclear spin state

Abstract

Using a methane-xenon mixture for spin exchange optical pumping, MRI of combustion was enabled. The (129)Xe hyperpolarized nuclear spin state was found to sufficiently survive the complete passage through the harsh environment of the reaction zone. A velocity profile (V(z)(z)) of a flame was recorded to demonstrate the feasibility of MRI velocimetry of transport processes in combustors.

Continuous flow production of concentrated hyperpolarized xenon gas from a dilute xenon gas mixture by buffer gas condensation

“…In terms of the reactivity of hydrocarbon gases coexisting with highly reactive Rb in the SEOP cell, Rb does not seem to readily react with saturated hydrocarbon gases such as methane 21 , 32 , ethane 32 and butane 33 . Any reaction also seems to be very slow for the unsaturated hydrocarbon isobutene used here.…”

Hyperpolarised xenon MRI and time-resolved X-ray computed tomography studies of structure-transport relationships in hierarchical porous media

“…Experiments could potentially be conducted at elevated temperatures. A number of studies expose hyperpolarized noble gases to high temperature reaction zones, for example for the study of catalytic hydrogenation [21], for MRI of the gas dynamics in combustion zones [19,49], and during catalytic hydrogen combustion for the purification of the hp noble gases during the production of these MRI contrast agents [18]. These types of experiments are possible because hp 129 Xe, produced through the laser pumping process, has extremely low spin temperature around 10 -2 K that is preserved in thermal environments with 5 order of magnitude higher temperatures as long as the T1 relaxation time is longer as the transport processes involved.…”

“…The high NMR signal intensity associated with hyperpolarized (hp) noble gases [15], [16] enables MRI of the gas phase at conditions of the low density Knudson regime [17]. The hyperpolarized spin state survives brief passage through a high temperature reactions zone, thus enabling in-situ hp 129 Xe NMR spectroscopy [18] and in situ hp 129 Xe MRI [19] of a combustion process that is unfathomable through conventional, thermally polarized magnetic resonance methods [20]. Furthermore, the chemical shift of 129 Xe in a porous medium is strongly temperature dependent; an effect that has been used as a probe of the start-up phase of a hydrogenation reaction [21].…”

Perspectives of hyperpolarized noble gas MRI beyond 3He

“…This has been demonstrated in SEOP of CH 4 –Xe mixtures that served as fuel for hp 129 Xe MRI of combustion [37]. Methane as a saturated hydrocarbon compound shows little affinity to react with rubidium under SEOP conditions.…”

“…A novel example is the measurement of gas flow within a flame using a continuous flow of a CH 4 –hp 129 Xe fuel mixture. MRI of the entire flame region is possible due to the combustion resistance of the 129 Xe hyperpolarized state [37]. Velocimetric measurements in lungs are also feasible but are experimentally demanding since they cannot be performed in a continuous flow mode.…”