ABSTRACT This paper reports the results of experimental tests performed at ENEA (Italian National Agency for New Technologies, Environment and Sustainable Development) in its “Casaccia” Energy Research Center to evaluate the energetic and environmental performances of a Heavy-Duty Compressed Natural Gas (HD CNG) engine fuelled with a hydrogen- methane blend of 15% in volume. A lean burn Mercedes 906 LAG engine has been optimized properly calibrating ECU engine maps regarding both ignition advance and air to fuel ratio (AFR). It was therefore possible to correct ignition advance to take into account the faster combustion speed given by the hydrogen content of the fuel mixture. Equivalence ratio (Lambda) has instead been modified in order to minimize the NO x emissions. All the tests were performed on a steady engine test-bed focusing the attention on the most important parts of the engine maps. The target of the activity was the reduction of energy consumption and CO 2 emissions, still catching targets on pollutant emissions to getting the homologation of the engine in the same environmental category of the original one. Experimental results showed a reduction of CO 2 variable with the ignition advance: decreasing the ignition advance timing the advantages are reduced. A reduction of CO 2 of about 9% can be observed, for the same overall levels of pollutant emissions. After the calibration procedure the engine has been object of formal EU homologation and is running on a city bus since the start of 2013. Results about the on-road experimental campaign (which will last 150.000 km) will be published in future. INTRODUCTION Among the strategies put in place to contain the environment impact of human society, the most interesting are those aimed at improving urban mobility : both acting on transportation aspects (traffic flows and transport modes), and on vehicle side (reduction of vehicles specific emissions). In Italy, in particular, the transport sector suffers from several criticalities. Among them, the high rate of motorization (the highest in Europe: 0.59 vehicles per capita) shows a clear polarization on the use of private vehicles (82% of terrestrial movements). Public transport certainly suffers the consequences of widespread car ownership offering a service which is normally not in line with users' demands, not promoting measures such as modal shift and others. This continuous effort to reduce emissions harmful to human health is combined with the need to reduce greenhouse gas emissions, to achieve the objectives of the Kyoto Protocol. Also at this regard, Italian situation appear disappointing, as stated by ISPRA [ 1] (Italian Institute for Environmental Protection and Research): “Total greenhouse gas emissions, in CO2 equivalent, excluding emissions and removals of CO2 from land use, land use change and forestry, decreased by Hydrogen-CNG Blends as Fuel in a Turbo- charged SI Ice: ECU Calibration and Emission Tests 2013-24-0109 Published 09/08/2013 Carlo Villante Università degli Studi del Sannio Giovanni Pede, Antonino Genovese, and Fernando Ortenzi ENEA Copyright © 2013 SAE International doi: 10.4271/2013-24-0109