Can hydrogen enriched biogas be used as domestic fuel? - Part I – Thermal Characteristics of Blended Biogas/H2 Impinging Flames

Biogas is a renewable energy source widely produced by breakdowns of organic matters in natural environment and industry. However, it is not yet an ideal replacement of fossil fuels because its high CO2 content would deteriorate its thermal performance. To upgrade biogas for possible domestic application, hydrogen enrichment is proposed by adding high-grade hydrogen (H2) to biogas in order to improve its flammability and heating value, and reduce pollutant emission. However, most previous studies on blended Biogas/H2 focus on analysing the effects of H2 fraction and nozzle-to-plate distance on the heat flux profile and flame temperature. No comprehensive study has ever demonstrated the influence of the Reynolds number and equivalence ratio under a wide operating range. In this study, a test rig was built to investigate the effects of the Reynolds number and equivalence ratio on heat flux and thermal efficiency of blended biogas/H2 impinging flame. The blended biogas/H2 consisted of 80% biogas and 20% H2 addition in volume. Biogas was artificially made by 60% CH4 and 40% CO2 (BG60). The Reynolds number ranges from 300 to 1500 and equivalence ratio ranges from 1 to 3. A comparative study was also conducted between pure biogas (BG60) and biogas with 20% H2 enrichment.

Impact of Hydrogen Addition on the Thermoacoustic Instability and Precessing Vortex Core Dynamics in a CH4/H2/air Technically Premixed Combustor

We study the impact of H2 enrichment on the unsteady flow dynamics and thermoacoustic instability in the single nozzle PRECCINSTA swirl combustor. We analyze data from two operating modes, premixed (PM) and technically premixed (TPM). The experiments were performed at atmospheric conditions with H2/CH4 fuel mixtures at a global equivalence ratio of 0.65 while maintaining a constant thermal power of 20 kW. We examine the effect of H2 addition on the flow dynamics by analyzing cases with three fuel compositions: 0% H2, 20% H2 and 50% H2 in both operating modes. A new multi resolution modal decomposition method, using a combination of wavelet transforms and proper orthogonal decomposition (WPOD) of the experimental time resolved high speed flow velocity and OH-PLIF measurements is performed. Thermoacoustic oscillations are observed in the TPM operating mode alone. WPOD results for the 0% H2 TPM operating mode case reveals intermittent helical PVC oscillations along with axi-symmetric hydrodynamic flow oscillations due to the thermoacoustic oscillation. These oscillations cause local flame extinction near the nozzle centrebody resulting in liftoff. A precessing vortex core (PVC) oscillation develops in the flow that enables intermittent flame reattachment and results in intermittent thermoacoustic oscillations in this case. In the 0% H2 PM case, the flame remains lifted off of the centrebody despite the presence of PVC oscillations in this case as well. H2 enrichment results in the suppression of flame lift-off and the PVC in both operating modes. We show from flow strain rate statistics and extinction strain rate calculations that the increase of the latter with H2 addition, allows the flame to stabilize in the region near the centrebody where the pure CH4 cases show lift off. The lack of thermoacoustic oscillations in the PM operating mode shows that the primary heat release driving mechanism is due to fuel-air ratio oscillation that the thermoacoustic oscillation generates. The time averaged flow fields and the emergence of the PVC when the flame is lifted off, together suggest that PVC oscillations are caused by the separation between the vortex breakdown bubble and the wake behind the centrebody, as suggested by prior computational studies.

Pd-based bimetallic catalysts for parahydrogen-induced polarization in heterogeneous hydrogenations

Production of hyperpolarized catalyst-free gases and liquids by heterogeneous hydrogenation with parahydrogen can be useful for various technical as well as biomedical applications, including in vivo studies, investigations of mechanisms of industrially important catalytic processes, enrichment of nuclear spin isomers of polyatomic gases, and more. In this regard, the wide systematic search for heterogeneous catalysts effective in pairwise H2 addition required for the observation of parahydrogen-induced polarization (PHIP) effects is crucial. Here in this work we demonstrate the competitive advantage of Pd-based bimetallic catalysts for PHIP in heterogeneous hydrogenations (HET-PHIP). The dilution of catalytically active Pd with less active Ag or In atoms provides the formation of atomically dispersed Pd1 sites on the surface of Pd-based bimetallic catalysts, which are significantly more selective toward pairwise H2 addition compared to the monometallic Pd. Furthermore, the choice of the dilution metal (Ag or In) has a pronounced effect on the efficiency of bimetallic catalysts in HET-PHIP, as revealed by comparing Pd-Ag and Pd-In bimetallic catalysts.

Pd-based bimetallic catalysts for HET-PHIP

Production of hyperpolarized catalyst-free gases and liquids by heterogeneous hydrogenation with parahydrogen (HET-PHIP) can be useful for various technical as well as biomedical applications, including in vivo studies, investigations of mechanisms of industrially important catalytic processes, enrichment of nuclear spin isomers of polyatomic gases, and more. In this regard, the wide systematic search for heterogeneous catalysts effective in pairwise H2 addition required for the observation of PHIP effects is crucial. Here in this work we demonstrate the competitive advantage of Pd-based bimetallic catalysts for HET-PHIP. The dilution of catalytically active Pd with less active Ag or In atoms provides the formation of atomically dispersed Pd1 sites on the surface of Pd-based bimetallic catalysts, which are significantly more selective toward pairwise H2 addition compared to the monometallic Pd. Furthermore, the choice of the dilution metal (Ag or In) has a pronounced effect on the efficiency of bimetallic catalysts in HET-PHIP, as revealed by comparing Pd-Ag and Pd-In bimetallic catalysts.