Engines that run on diesel fuel are very important to the functioning of contemporary society. At the same time, they are a significant contributor to the pollution of the atmosphere. Because both the comfort of the atmosphere and the inter-related, we are unable to cut down on the usage of diesel at this time. This is a very precarious scenario. The number of vehicles that run on diesel continues to grow on a daily basis. We have no choice but to switch to alternate fuels such as biodiesel if we want to prevent this problem. In the current experiment, orange peel oil was combined with diesel in two distinct proportions: 20% orange oil and 80% diesel, and 40% orange oil and 60% diesel. The purpose of this was to compare the two different combinations. According to the findings, the mixture consisting of 40% orange oil and 60% diesel is the most effective one. Then, Calophyllum inophyllum oil was further added using a transesterification process mixed with potassium hydroxide, isopropyl alcohol, pH indicator, and methanol. Then, different cases were tested: (40% orange oil + 20% Calophyllum inophyllum + 60% diesel), (40% orange oil + 40% Calophyllum inophyllum + 20% diesel) and (100% diesel). The tests show that the break thermal efficiency of O40+C20+D40 and O40+C40+D20 is 4.36 % and 4.76 % which is almost similar. O40+C40+D20 increase the NOx emissions slightly, but it decreases the emissions of HC, CO, CO2, and smoke compared to O40+C20+D40. So, O40+C40+D20 is the best alternative fuel for diesel engines.