Project DIVAS aims to identify promising and innovative technological ways in order to cut off CO2 emissions (by 10%) on Diesel engines. Strong downspeeding approach is addressed, in order to overcome scientific and technological locks in air loop management (increasing air filling for low end torque). Considering results already obtained by simulation, two concepts with strong potential have been identified ; target of the project is to explore more deeply these concepts, by advanced dedicated research and experimental work on adapted engines : - compressor (mechanical clutching compressor or electric compressor) + turbocompressor : this new technological way allows high increase of air filling, with benefits in CO2 emission. We propose to study and adapt prototype engine (adaptation of air loop) with advanced control strategies in order to take maximum advantage of air path, to study current technological locks (drivability, compressor drive power...) and to confirm potential on experimental tool - variable valve actuation + turbocompressor : innovative concept of variable valve actuation is proposed in order to allow scavenging (enhancing turbocharging and air filling) without penalties well known in Diesel engines (deep valve pockets in piston). We propose to validate on experimental engine good results obtained in simulation, identifying transient behavior and explore more in details concept in par load operation : lowering fuel / air ratio, after treatment control. Coupling these two techniques will be performed at the end of the program, after identification of synergies. This project is complementary to Synergy project, that aims to perform downspeeding but with different technological ways (2-stage turbocharging, VVA for part load operation). Moreover, experimental tools share some features (combustion system, generic VVA definition on K9 multi cylinder engine), that helps to better identify benefits and drawbacks of each approach and dramatically reduces costs linked to conception and tests.