%0 Journal Article %T Variable Valve Actuation Systems for Homogeneous Diesel Combustion: How Interesting are They? %+ IFP Energies nouvelles (IFPEN) %A Walter, B. %A Pacaud, P. %A Gatellier, B. %< avec comité de lecture %@ 1294-4475 %J Oil & Gas Science and Technology - Revue d'IFP Energies nouvelles %I Institut Français du Pétrole (IFP) %V 63 %N 4 %P 517-534 %8 2008-07 %D 2008 %R 10.2516/ogst:2008004 %Z Physics [physics]Journal articles %X With a high thermal efficiency and with low CO2 (carbon dioxide) emissions, Dieselengines would become leader of tomorrow's transport market. However, the evolution of the regulatoryconstraints leads to a drastic reduction of their NOx (nitrogen oxide) and particulate emissions. Anotherinteresting competitor to the NOx after-treatment systems is the use of new combustion concepts toreduce the raw emissions: homogeneous combustion (Homogeneous Charge Compression Ignition -HCCI- or Highly Premixed Combustion - HPC). Nonetheless, such concepts present non negligible drawbacks such as a limited zero NOx operatingrange, huge external gas recirculation (EGR) needs which forces a complete redesign of the air path circuitmaintaining a high level of full load performances, and above all excessive HC (unburned hydrocarbon)and CO (carbon monoxide) emissions at low load.The emerging Variable Valve Actuation technologies (VVA) could totally change the deal of the newcombustion processes especially through the internal EGR possibilities and the effective compressionratio reduction.Through the well known dual mode HCCI combustion concept NADI™ developed by IFP, this paperaims at evaluating the improvement potential of this kind of combustion concept with the use of severalintake and exhaust VVA configurations and makes a comparison between these approaches. The resultscome from a single cylinder engine equipped with a fully variable intake and exhaust VVA (camless).After a brief description of the VVA system and the possibilities offered, two aspects of the potential arestudied: – the different ways to obtain internal EGR and its main interests with the high potential to reduce HCand CO emissions at low load in homogeneous combustion (HCCI or HPC): 70% reduction on theHC emissions, 40% on CO emissions keeping same NOx emissions level; – the effective compression ratio reduction with a view to increase the maximum load with very lowNOx emissions. First, the ways to reduce the effective compression ratio are presented and then, thereduced possibilities given in this field due to decrease of air flow are analysed. %G English %2 https://ifp.hal.science/hal-02002027/document %2 https://ifp.hal.science/hal-02002027/file/ogst07086.pdf %L hal-02002027 %U https://ifp.hal.science/hal-02002027 %~ IFP %~ OGST