Experimental Study of Biogas–Hydrogen Mixtures Combustion in Conventional Natural Gas Systems

Abstract

Biogas is a renewable gas with low heat energy, which makes it extremely difficult to use as fuel in conventional natural gas equipment. Nonetheless, the use of hydrogen as a biogas additive has proven to have a beneficial effect on flame stability and combustion behavior. This study evaluates the biogas–hydrogen combustion in a conventional natural gas burner able to work up to 100 kW. Tests were performed for three different compositions of biogas: BG70 (30% CO2), BG60 (40% CO2), and BG50 (50% CO2). To achieve better flame stability, each biogas was enriched with hydrogen from 5% to 25%. The difficulty of burning biogas in conventional systems was proven, as the burner does not ignite when the biogas composition contains more than 40% of CO2. The best improvements were obtained at 5% hydrogen composition since the exhaust gas temperature and, thus, the enthalpy, rises by 80% for BG70 and 65% for BG60. The stability map reveals that pure biogas combustion is unstable in BG70 and BG60; when the CO2 content is 50%, ignition is inhibited. The properties change slightly when the hydrogen concentrations are more than 20% in the fuel gas and do not necessarily improve.

Numerical Evaluation of the Effect of Fuel Blending with CO2 and H2 on the Very Early Corona-Discharge Behavior in Spark Ignited Engines

“…Simulations were run considering eight different test fuels whose composition was set based on literature findings on biogas composition [17][18][19][20]22] and hydrogen blending [9]. The composition of each fuel is shown in Figure 1: fuel no.…”

“…However, it was detected that the combination of hydrogen fuel and Corona ignition leads to a slight extension of the lean limit of classical ignition systems (φ 0.5 vs. 0.52, respectively) and shorter combustion duration. In light of what described on the effect of Corona discharge on ignitable mixtures including significant amount of hydrogen and carbon dioxide, the characterization of Corona-induced ignition at engine relevant conditions can be crucial also to assess the very early ignition behavior of biogas (CH 4 + CO 2 )-hydrogen blends in SI engines, in which hydrogen play the role of booster of the combustion properties and mixture dilution limit as reported in [13][14][15][16][17][18][19][20].…”

Estudio experimental de la inflamabilidad de mezclas gaseosas de CH4, H2 y CO2 en aire y su potencial energético

“…12 Clasificación de gases inflamables según la temperatura de la superficie……………….. Tabla 1. 13 Influencia de la potencia de la fuente de ignición en los intervalos de explosividad… Tabla 1. 14 Influencia de la presión en los límites de explosividad…………………………………………….…”

“…Sin embargo, el hidrógeno presenta una oportunidad potencial si este se entiende como aditivo de combustibles gaseosos. Esta técnica se aplica actualmente en la industria y en las redes de distribución de gas para mejorar las características de combustión del gas natural, aunque también mejora las características de combustión del biogás [13]. El biogás puede ser entendido como una mezcla de CH 4 y CO 2 por lo que la adición de H 2 tiene considerables implicaciones tanto en las propiedades de combustión como en las características de inflamabilidad [14], [15].…”

“…13. Las regiones inflamables teóricas utilizadas para la determinación experimental se recogen en el Anexo A.…”