This paper presents a H-2-diesel fuel co-combustion study undertaken on a supercharged, direct injection, diesel engine investigating the combustion characteristics and emissions production at a range of engine loads (IMEP), EGR levels and intake air boosting conditions. The utilisation of EGR and intake air boost with H-2-diesel fuel co-combustion allows simultaneous NOx and particulate emissions reduction at conditions closer to on-road driving conditions. The results showed that while H-2 can be favourable in reducing CO2 and particulate emissions, it causes an increase in NOx emissions when the intake energy contribution from H-2 is increased. A reduction in the number of fine and ultrafine particles (diameter 0.05-0.2 mu m) was observed when H-2 was added to the engine, especially at the low and intermediate intake air boost levels. At high EGR levels (equivalent to 2% intake O-2 concentration reduction) significant reductions in exhaust particulate mass of up to 75% were observed at 15% energy from H-2. An attempt was made to identify the optimum H-2 operating window at the different engine loads, intake air boost and EGR levels. (C) 2016 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.