In the present study, tests are conducted on the Kirloskar TV-1 four stroke single cylinder water cooled diesel engine. In the first phase of investigation, study optimized the 230 bar as a best injector opening pressure, 26 degrees bTDC as a best injection timing, 18 as best a compression ratio, 5 holes nozzle as a best nozzle and re-entrant toroidal piston bowl geometry as a best piston bowl geometry when the engine is operated single fuel (B20). In the second phase of investigation, study optimized the 0.48 kg/h Bio-CNG flow rate as a best flow rate, 29 degrees bTDC as a best injection timing, CR 18 as a best compression ratio and Venturi-type carburetor as the best carburetor when the engine is operated with dual fuel (B20+Bio-CNG). In the third phase of investigation, existing baseline diesel engine is modified with all above optimized engine parameters and test results are compared with baseline engine. The experimental study revealed that modified engine has shown the improved performance, combustion and emission characteristics than the baseline engine when it is operated with dual fuel (B20+Bio-CNG). Thus, dairy scum biodiesel and Bio-CNG can be used as alternative fuels in the CI engines with slight modification. (C) 2019 Elsevier Ltd. All rights reserved.