Decline in global resources of petroleum based fuels such as diesel and gasoline have attracted attention of researchers towards alternative fuels which are capable of providing both, energy security and protection against environmental degradation due to emission of hazardous pollutants. As an oxygenated fuel, biodiesel has emerged as a potential alternative fuel, which can be used in diesel engines on large-scale to reduce CO, HC and PM emissions. In this experimental study, Jatropha curcas derived biodiesel (18100) and its 20% (v/v) blend with mineral diesel (1820) was tested in a production-grade single cylinder diesel engine for evaluating its combustion characteristics. Since soot and NOx emissions are major concerns in CI engine combustion, it is very important to investigate their in-situ spatial distribution, so that effective control measures can be devised. For this, endoscopic visualization technique was implemented on a modified prototype engine to evaluate the effect of biodiesel blending percentage and engine load on in-situ spatial distribution of in-cylinder soot and flame temperature distributions. Inherent oxygen content of biodiesel helped in achieving superior combustion; as a result, in-cylinder soot formation was lower than baseline mineral diesel. Spatial flame temperature distribution was also relatively lower in biodiesel. Endoscopic visualization technique was found to be effective in evaluating different combustion characteristics in a modified prototype engine. (C) 2016 Elsevier Ltd. All rights reserved.