Enhancement of biogas/air combustion by hydrogen addition at elevated temperatures

Abstract

Summary In this study, combustion characteristics of various biogas/air mixtures with hydrogen addition at elevated temperatures were experimentally investigated using bunsen burner method. Methane, CH4, was diluted with different concentrations of carbon dioxide, CO2, 30 to 40% by volume, to prepare the biogas for testing. It is followed by the hydrogen, H2, enrichment within the range of 0 to 40% by volume and the temperature elevation of unburned gas till 440 K. Blowoff velocities were measured by lowering the jet velocity until a premixed flame could be stabilized at the nozzle exit, while laminar burning velocities were calculated by analyzing the shape of the directly captured premixed bunsen flames. The results showed that hydrogen had a positive effect on the blowoff velocity for all three fuel samples. Nonlinear growth of the blowoff velocity with hydrogen addition was associated to the dominance of methane‐inhibited hydrogen combustion process. It was also observed that the increase in the initial temperature of the unburned mixture led to a linear increase of the blowoff velocity. Moreover, specific changes in flame structure such as flame height, standoff distance, and the existence of tip opening were attributed to the change in the blowoff velocity. The effect of CO2 content in the mixture was examined with regards to laminar burning velocity for all compositions. The outcome of the experiment showed that the biogas mixture with higher content of CO2 possessed lower values of laminar burning velocity over the wide range of equivalence ratios. A reduced GRI‐Mech 3.0 was used to simulate the combustion of biogas/air mixtures with different compositions using ANSYS Fluent. The numerically simulated stable conical flames were compared with the experimental flames, in terms of flame structure, showing that the reduced GRI‐Mech 3.0 was suitable for modeling the combustion of biogas/air mixtures.

Laminar Burning Velocity of Biogas-Containing Mixtures. A Literature Review

“…Other studies revealed the effect of additives (N 2 , Ar, H 2 O or CO 2 ) on CH 4 /air, CH 4 /CO 2 /air and CH 4 /O 2 /H 2 /inert flames [35][36][37][38][39][40][41]. The attention of other researchers has been directed towards the combustion characteristics of biogas under hydrogen-enriched conditions [24,[42][43][44][45][46][47][48][49]. In some experiments, realised in a spark ignition engine, small H 2 amounts were added to biogas to enhance engine performance and reduce pollutant emissions [16,[50][51][52][53].…”

Catalytic Hydrogen Combustion for Domestic and Safety Applications: A Critical Review of Catalyst Materials and Technologies

“…The effect hereof is characterized by two factors: the curvature of the flame tip and the disproportion of molecular diffusion of the components of the mixture. However, the effect is more apparent at higher concentrations of hydrogen [108].…”

“…This can, however, be expected, considering the increased flame speed of hydrogen when compared to natural gas [40]. In a study by Nurmukan et al, combustion characteristics, such as the occurrence of blow-offs (high fuel flow velocity that extinguishes the flame) and burning velocities, were examined for biogas/hydrogen mixtures [108]. Figure 4 presents the images of the biogas/hydrogen flames with hydrogen concentrations in the range of 0-40 vol% at the same inlet velocity (top) and the images of the flames at various inlet velocities before blow-off (bottom).…”

“…Figure 4. Photographs of premixed flames with hydrogen additions (0-40 vol%) (top) at the same inlet velocity and the flames at various inlet velocities before blow-off (bottom) (adapted from[108] with permission from John Wiley and Sons).…”

Advantages of hydrogen addition in a passive pre‐chamber ignited SI engine for passenger car applications

“…Although there are multiple breakthroughs in the understanding of combustion characteristics of hydrogen enriched flames in multiple research devices, the applicability of this knowledge is still in its early stage. While there are plenty of research works related to constantvolume chambers, 26,27 scaled burners, 28 or rapid compression machines 29 ; the state-of-the-art in H 2 ICE is more limited and mostly focused on developing engines fueled by pure hydrogen. 30 Nonetheless, this approach is still difficult to implement for commercial transportation in passenger cars due to severe economic constraints.…”