In this paper, effect of varying fuel injection pressures and injection timings on particulate size number distribution and spray characteristics was investigated in a single cylinder, common rail direct injection (CRDI) compression ignition (Cl) engine fueled with Karanja biodiesel blends vis-a-vis baseline mineral diesel. The investigation results of spray tip penetration and spray area of biodiesel blends and diesel showed that higher fuel injection pressure result in a longer spray tip penetration and larger spray area than that at lower injection pressures at same elapsed time after the start of injection (SOI). In order to compare the effect of fuel injection parameters, 10, 20 and 50% Karanja biodiesel blends at 1500 rpm engine speed were compared with baseline data from mineral diesel. It was observed that average particulate size increased with retarding the SOI timings. Particulate number concentration was lowest for 10% biodiesel blend, which increased with further increase in biodiesel content in the blended test fuel. Addition of even very small quantity of biodiesel in the test fuel helped in reducing particulate emissions. (C) 2014 Elsevier Ltd. All rights reserved.