This document is about conducting a comparative study of using different alternative fuels in a CI engine. It discusses biogas as an alternative fuel, how biogas is made through anaerobic digestion of organic waste, and the working principle of biogas in an engine. Experimental results showed heavy carbon deposition and corrosion from sulfur dioxide during combustion when using biogas. Advantages of biogas include being renewable, non-polluting, and reducing landfills. Disadvantages include needing more technological advancements and containing impurities. The conclusion is that biogas can be used as a primary fuel in CI engines without much modification and up to 80-90% of diesel can be replaced by biogas.