Experimental investigation of hydrogen-enriched biogas deflagration characteristics within a constant volume cylindrical vessel

Abstract

Experimental investigations of hydrogenated biogas deflagration, considering varying carbon dioxide percentages (0%, 10%, 20%, and 30%) and the addition of hydrogen at two different percentages (5% and 10%), were carried out within a constant cylindrical combustion chamber, across three equivalence ratio (ER = 0.8, 1, 1.2). The aim was to explore the potential for recycling CO2 in biogas applications. Analysis of the experimentally recorded pressure profile allowed the calculation of crucial parameters, including the net heat release rate (NHRR) and the deflagration index (KG). The study's results highlight the effect of CO2 concentration in biogas on combustion efficiency compared to CH4/air combustion. It was found that an increase in the CO2 volume fraction in biogas leads to a reduction in the net heat release rate (NHRR), especially in stoichiometric and rich mixtures. This finding is significant as it provides insights into the combustion dynamics of biogas with varying CO2 levels, contributing to the understanding of biogas combustion efficiency under different conditions. Under lean conditions (Φ = 0.8), combustion tests were unsuccessful. However, the injection of 5% H2 proved sufficient to enhance the reactivity of lean mixtures and promote flame propagation. The findings indicate superior performance of biogas-hydrogenated mixtures compared to stoichiometric and rich mixtures of CH4/air combustion. Nonetheless, the addition of hydrogen increased the deflagration index, an important parameter for managing explosion risks. This nuanced understanding contributes valuable insights into optimizing the removal of CO2 from biogas and combustion processes involving hydrogenated biogas, with implications for both efficiency and safety considerations.