The present study aims to investigate emission characteristics with the B20 blend level of first, second and third generation biodiesels. The engine, a naturally aspirated, single cylinder, diesel engine, was operated at 1500 rpm engine speed and at different engine loads with intervals of 25%. Also, the engine is analyzed by Diesel RK mathematical tool and emission characteristics such as smoke, carbon dioxides (CO2), particulate matter (PM), nitric oxide (NO) and summary of emission (SE) were obtained. Numerical simulation is performed using pure diesel (D100), first, second and third generation B20 (80% diesel + 20% biodiesel). Results of reduction in emissions for biodiesel blend were found to be lower than diesel fuel as smoke (BSN) by 54.68% for jojoba, PM by 4.8% for coconut, 52.0% for jojoba and 7.1% for fish oil, NO by 38.2% for jatropha curcas, and SE by 8.8% for soybean, 12.9% for jatropha curcas and 8.8% for spirulina but carbon dioxides was found to be higher by 0.38% for rapeseed, 0.61% for fish oil. The blend of B20 shows a decrease in emissions at 1500 rpm with 100% engine load. The numerical results are verified against experimental results conducted under the same operating conditions.