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Reducing greenhouse gas emissions to limit global warming is becoming one of the key issues of the 21st century. Today, the transport sector is considered as one of the main contributor to this phenomenon and represented 24% of the world's CO 2 emissions in 2011. In the last decade the different transport sectors have thus decided to take measures and incentives to limit or reduce these emissions. For example, in the aeronautic field, the Advisory Council for Aeronautics Research (ACARE) wishes a reduction of about 50% for the CO 2 emissions of air transport before 2020 and about 65% in 2050 1 in Europe. These ambitious targets need to implement major improvements in existing propulsion system or to use ground-braking technologies. In this context, solutions based on Diesel Internal Combustion Engines (ICE) could be a relevant alternative way to succeed in drastic reduction of fuel consumption for low and medium power applications (<1000kW), including light-weight aircrafts, UAV, APU or medium to light-weight rotorcrafts. Indeed, in this range of applications, the specific fuel consumption of a Diesel ICE is, at least, 30 to 40% less than an equivalent turboshaft able to deliver the same power. Combined with complementary technological breakthroughs such as electrification 2,3 , potential benefits could then reach targets envisaged by ACARE. Nevertheless, the specific development of ICE's adapted to aeronautic purposes is a very complex process during which simulations tools have a key role to play for highlighting the most promising paths to explore. The objective of this paper is therefore to study the potential of high power density Diesel engines for the particular application of a rotorcraft. This simulation study takes into account realistic constraints (power, compactness, power to weight ratio, fuel economy...) and is notably focused on dedicated engine architectures, including two and four strokes configurations.. An evaluation of fuel consumption in realistic flight conditions is then performed coupling engine models with a helicopter simulator. The use of Diesel ICE leads to fuel consumption gains of the order of 40% but also increases the possible payload for long-range missions, compared to present turboshafts. The paper finally allows to draw perspectives of developments for future green rotorcrafts but also more generally for light and medium weight aeronautic applications. Nomenclature4T = Four-stroke engine 2T = Two stroke engine 2 CA50 = Crank Angle at which 50% of the fuel has burnt ICE = Internal Combustion Engine ISFC = Indicated Specific Fuel Consumption OGE = Out of ground effect SAR = Search and Rescue TM = Turbomachine (turboshaft) VBE = Best consumption operating speed VBR = Best range (autonomy) operating speed Vmax = Maximum speed