Biogas is considered to be an excellent fuel which burns without smoke. The main constituent of biogas is :

Biogas is a renewable fuel produced through the anaerobic digestion of organic matter such as animal manure, food waste, and sewage [1]. It is considered an excellent fuel because it burns without smoke and has a higher thermal efficiency compared to traditional fuels like kerosene or dung cakes [1]. The main constituent of biogas is methane (CH4), which typically accounts for 50% to 80% of its volume [3]. Methane is the primary combustible component and the source of the gas's energy content. Other constituents include carbon dioxide (20% to 50%), and trace amounts of hydrogen, hydrogen sulphide, and nitrogen [1]. Because methane is the primary ingredient, biogas can be purified into biomethane and used similarly to natural gas for heating, electricity generation, or as a vehicle fuel [3][4].

Sources

1. [1] NCERT. (2022). Contemporary India II: Textbook in Geography for Class X (Revised ed.). NCERT. > Chapter 5: Print Culture and the Modern World > Biogas > p. 117
2. [3] https://www.sciencedirect.com/topics/engineering/biogas
3. [4] https://www.epa.gov/agstar/how-does-anaerobic-digestion-work