This article presents the bench testing results of a four stroke, four cylinder, direct injection, unmodified, diesel engine operating on pure rapeseed oil (RO) and its 2.5 vol%, 5 vol%, 7.5 vol% and 10 vol% blends with ethanol (ERO), petrol (PRO) and both improving agents applied in equal proportions as 50:50 vol% (EPRO). The purpose of the research is to examine the effect of ethanol and petrol addition into RO on diesel engine emission characteristics and smoke opacity of the exhausts. The biggest NOx emissions, 1954 and 2078 ppm, at 2000 min(-1) speed generate blends PRO10 (9.72%) and EPRO5 (11.13%) against, 1731 and 1411 ppm, produced from ERO5 (12%) and ERO10 (13.2% oxygen) blends. The carbon monoxide, CO, emissions emitted from a fully loaded engine fuelled with three agent blends EPRO5-7.5 at maximum torque and rated speed are higher by 39.5-18.8% and 27.5-16.1% and smoke opacity lower by 3.3-9.0% and 24.1-17.6% comparing with RO case. When operating at rated 2200 min(-1) mode, the carbon dioxide, CO2, emissions are lower, 6.9-6.3 vol%, from blends EPRO5-7.5 relative to that from RO, 7.8 vol%, accompanied by a slightly higher emission of unburned hydrocarbons HC, 16 ppm, and residual oxygen contents O-2, 10.4-12.0 vol%, in the exhausts. (C) 2008 Elsevier Ltd. All rights reserved.