The influence of a ferrous picrate based homogeneous combustion catalyst on the combustion characteristics and fuel efficiency was studied using a fully instrumented diesel engine. A naturally aspirated four stroke, single cylinder, air cooled, direct injection diesel engine was tested at engine speeds of 2800 rpm, 3200 rpm and 3600 rpm under variable load conditions, with different dosing ratio of the catalyst in a commercial diesel fuel. The results indicated that the brake specific fuel consumption decreased and the brake thermal efficiency increased with the addition of the catalyst. At the catalyst dosing ratio of 1:10,000, the brake specific fuel consumption was reduced by 3.3-4.2% at light engine load of 0.12 MPa and 2.0-2.4% at heavy engine load of 0.4 MPa due to the application of the catalyst. From the in-cylinder pressure and heat release rate analysis, it was found that the catalyst reduced ignition delay and combustion duration of fuel in the engine, resulting in slightly higher peak cylinder pressure and faster heat release rate. (C) 2011 Elsevier Ltd. All rights reserved.