AbstractThe research was motivated to experimentally study the effect of alcohol addition on the performance, combustion characteristics, particle size distribution (PSD) and exhaust emissions of a common rail direct injection (CRDI) diesel engine fueled with diesel‐castor oil blended fuels. The main properties of the blended fuels were measured by the standard test procedures. The results revealed that, compared with diesel fuel, the brake specific fuel consumption (BSFC) was increased by an average of 7.7%, 8.5% and 16.5% for DA80B10E10, DC80B20, and DC60B20E20 fuels respectively. The brake thermal efficiency (BTE) kept almost identical for the blended fuels. The peak in‐cylinder pressure was about 0.4 MPa higher and the heat release rate (HRR) was evidently higher than that of diesel fuel, and the combustion duration was 5–12 crank angles shorter. The blended fuels exhibited bi‐modal PSD, and diesel fuel showed uni‐modal behavior under all operating conditions. The total number concentration (TNC) of particles was larger, but the geometric mean diameter (GMD) was lower than that of diesel fuel. Nitrogen oxide (NOx) emissions were increased by about 30% and hydrocarbon (HC) was evidently higher for the blended fuels under almost all operating conditions, but carbon monoxide (CO) emissions were about 22% lower than that of diesel fuel.