Analysis of mixture structure and of its influence on combustion in a CAI engine

Vincent Knop (1, 2)

1 IFPEN - IFP Energies nouvelles
2 Cosworth Ltd

Homogeneous Charge Compression Ignition (HCCI) combustion mode theoretically relies on a perfectly homogeneous air/fuel mixture simultaneously releasing heat across the whole combustion chamber. However, practical implementation always leads to a staged combustion process that is still significantly quicker than conventional spark-ignition or compression-ignition combustion modes. The degree of combustion staging is central to the limitation of combustion-induced noise, to cycle efficiency, as well as to combustion stability and completion. The present study numerically explored on the whole operating map the mixture structure at ignition for a specific type of HCCI combustion, namely the Controlled Auto-Ignition (CAI) combustion mode attained through burnt gas trapping with negative valve overlap. The analysis of the complete CAI operating map outlined the similarity of mixture structure for any operating condition and the mixture/chemistry interactions depending on the end-of-compression temperature domain. Temperature stratification appeared as the key input defining combustion-induced noise and combustion stability but mean in-cylinder temperature and dilution combine with temperature stratification to define operating map limitations.

Mots clés: Homogeneous Compression Charge Ignition; Mixture stratification; Fuel kinetics; 3D CFD; Controlled Auto-Ignition

Domaines: Mécanique [physics.med-ph]

Vincent Knop. Analysis of mixture structure and of its influence on combustion in a CAI engine. International Journal of Engine Research, 2018, 19 (4), pp.393-410. ⟨10.1177/1468087417712160⟩. ⟨hal-01978548⟩