Impact of Gaseous Chemistry in H₂–O₂–N₂ Combustion over Platinum at Fuel-Lean Stoichiometries and Pressures of 1.0–3.5 bar

Abstract

The catalytic and gas-phase combustion of fuel-lean H2–O2–N2 premixtures was investigated in a channel coated with platinum at pressures 1.0–3.5 bar, a range encompassing microreactors in portable power generation systems and passive hydrogen recombiners in nuclear power plants. One-dimensional Raman spectroscopy assessed the progress of catalytic hydrogen combustion, while planar laser-induced fluorescence (LIF) of the hydroxyl radical monitored gaseous combustion. Simulations were performed using a 2-D code with detailed catalytic and gas-phase reaction mechanisms and realistic transport. Both LIF measurements and simulations revealed that homogeneous combustion was vigorously sustained below ∼2.5 bar, while it was effectively suppressed at higher pressures. This was due to the intricate pressure dependency of the hydrogen gaseous ignition chemistry and the competition between catalytic and gaseous chemical reactions for hydrogen consumption. Parametric simulations determined the smallest critical channel heights allowing for appreciable gaseous combustion and their dependency on pressure, wall temperature, and inlet velocity. It was shown that for the narrower channels of catalytic microreactors homogeneous combustion was relevant only for wall temperatures above 1300 K, whereas for the wider hydrogen recombiner channels it could be relevant for wall temperatures down to 1100 K. Furthermore, at 1100 K the critical channel heights were nonmonotonic functions of pressure, reaching their peaks at 2.0–2.5 bar.

Preparation of Highly Active and Thermally Conductive Platinum Nanoparticle/Ce–Zr–Y Mixed Oxide/AAO Washcoat Catalyst for Catalytic Hydrogen Combustion Technologies

“…Despite the common opinion that hydrogen autoignition initiates at 585 °C (literature reflecting value for gaseous ignition of hydrogen/air mixtures at 1 bar), different temperatures have been experimentally discovered for hydrogen autoignition over Pt-based catalyst. − It was stated that there are four routes between the heterogeneous (catalytic combustion) and homogeneous (gas-phase combustion) reaction pathways: (i) promotion of homogeneous ignition due to the exothermicity of the catalytic pathway that heats up the reactor walls and consequently the flowing gas; (ii) catalytic combustion promoted by the near-wall depletion of the deficient reactant (hydrogen fuel); (iii) promotion of one of the pathways via the major species produced by the catalytic pathway over the gaseous induction zone (for example, water generated during CHC chemically inhibits homogeneous ignition in hydrogen/air mixtures while it promotes homogeneous ignition in methane/air mixtures); and (iv) catalytic adsorption/desorption reactions of radical species . For example, it has been demonstrated that homogeneous ignition of hydrogen/air mixtures requires the temperature of the reactor wall to be at least 927 °C at atmospheric pressure. , In a study by Sui et al, the autoignition of hydrogen was possible only at the reactor wall temperature of 827 °C.…”

“…For example, it has been demonstrated that homogeneous ignition of hydrogen/air mixtures requires the temperature of the reactor wall to be at least 927 °C at atmospheric pressure. , In a study by Sui et al, the autoignition of hydrogen was possible only at the reactor wall temperature of 827 °C. Also, the authors stated that safe recombiner operation is in the pressure range of 2.0–2.5 bar …”

“…Also, the authors stated that safe recombiner operation is in the pressure range of 2.0−2.5 bar. 8 Currently, there are four types of catalytic sections used in PARs: (i) cartridges filled with ceramic spherical-shaped Pdcoated pellets, (ii) stainless-steel (SS) plates washcoated with a noble metal/γ-Al 2 O 3 layer, (iii) metallic plates coated with catalyst powder, and (iv) ceramic rods coated with noble metals. 9 A suitable catalyst for PAR application should fulfill a range of requirements to ensure safe PAR operation.…”

Lattice Boltzmann model with generalized wall boundary conditions for arbitrary catalytic reactivity

“…It is further noted that straight channels are not a convenient idealization, but are used in both laboratory and industrial catalytic systems (see Refs. [23,[32][33][34]37,38]).…”

“…There are considerably fewer literature investigations on heterogeneous reactions by LBM, even though this topic is of main interest in many practical systems such as automotive exhaust gas treatment, fuel processing, synthesis of chemicals, power generation, geochemical applications [21,22], hydrogen recombiners in nuclear power plants [23], etc. Kang et al [14] advanced the nonthermal multicomponent model with the catalytic reactive boundary condition from Arcidiacono et al [13] to account for large temperature differences.…”