Biogas Cleaning.

Biogas is made up of about 50-75% Methane(CH₄) and 50-25% Carbon Dioxide(CO₂) and small amounts of Nitrogen(N₂), Hydrogen(H₂), Hydrogen Sulfide(H₂S) and Oxygen(O₂).

In some fire extinguishers they put Carbon Dioxide(CO₂). 

Trying to burn Biogas with a high CO₂  contents will be counter productive.

In order to get a bright and warm flame from the biogas it will have to be cleaned first.

Another disadvantage of Biogas is the Hydrogen Sulfide in it, which will corrode the internal parts of an engine.

Before Biogas can be used efficiently and without harm to your engine it should be scrubbed or cleaned. The easiest and cheapest way of doing this is to simply bubble the gas through water. The carbon dioxide molecules will bond with the water and leave you with clean Methane. More complex and expensive ways of removing Carbon dioxide from biogas include washing it under a high pressure spay.