In this study, performance of a diesel engine operated with Jatropha and Palm biodiesel blends at high idling conditions has been evaluated. The result obtained from experiment elucidate that, at all idling modes HC and CO emissions of both blends decreases, however, NOx emissions increases compared to pure diesel fuel. Jatropha biodiesel has higher viscosity compared to Palm biodiesel, which might have degraded the spray characteristics and caused slightly improper mixing which might have led to slightly incomplete combustion, thus at both idling conditions, Jatropha blends emitted higher CO and HC compared to Palm biodiesels. Compared to diesel fuel, CO emissions were 5.9–9.7%, 17.6–22.6%, 23.5–29%, 2.9–6.4%, 5.9–14.5% and 11.8–17.74% less, HC emissions were 10.3–11.5%, 24.13–30.76%, 34.5–39%, 6.9–7.7%, 26–27% and 31–35% less and NOx emissions were 8.3–9.5%, 14–15%, 22–25%, 5–7.14%, 10–11.3% and 17–18% more respectively for 5, 10 and 20% blends of Palm and Jatropha biodiesel. Compared to diesel fuel, at high idling conditions brake specific fuel consumption all Palm and Jatropha biodiesel–diesel blends increased. Compared to diesel fuel, BSFC were 1.14–1.35%, 2.28–2.96%, 7.1–8.35%, 2.28–2.69%, 3.98–5.39% and 8.83–9.29% more respectively for 5, 10 and 20% blends of Palm and Jatropha biodiesel.
