Investigation of Mixture Quality Effect on CAI Combustion

Latest Developments in Gasoline Auto-Ignition Modelling Applied to an Optical CAI (Tm) Engine

“…But, to stay as close as possible to an industrial application, the PRF has to be carefully chosen to represent the behaviour of the commercial 95-octane unleaded gasoline. The experimental work realised at IFP showed that, for the present operating point, the PRF that best fits the results with commercial gasoline is the PRF 65 (35% n-heptane and 65% iso-octane) [7]. Consequently, the present calculation results are realised with a PRF 65 and compared with experimental measurements for this Primary Reference Fuel.…”

“…The simulation of the gas exchange process aims to better understand the influence of the adapted valve lift strategies on the in-cylinder mixing process and the resulting mixture homogeneity for species and/or local temperature. This type of 3D CFD calculation is not more difficult with CAI™ than with conventional SI or CI combustion and has already been reported at IFP and elsewhere [5,7,11].…”

“…Two types of valve lift strategies are recognised as efficient to promote CAI™ combustion in a four-stroke engine [7]: the negative valve overlap strategy and the burnt gas re-breathing strategy. The Negative Valve Overlap (NVO) strategy is design to only evacuate during the exhaust process the amount of burnt gases that would not be useful for heating up fresh mixture during the following cycle [10].…”

“…It consists of an adiabatic compression machine (compression ratio is 9.6:1) following a specific piston motion law. The consequent volume evolution is the following: (7) In the above expression, the volume is expressed in cm 3 and time in s. Dimensions of the chamber were calculated knowing the compression ratio and that the squish height and bore of this Rapid Compression Machine (RCM) are identical. One may deduce: (8) Thanks to this RCM [33], the auto-ignition delay is observed for different PRF (90 and 100) and several initial pressures as a function of the temperature at the end of compression and the Fuel/Air equivalence ratio.…”

“…Controlled Auto-Ignition (CAI™) uses burnt gases not only as diluent but also as an in-cylinder heat source [5][6][7][8][9][10]. This requires a precise control of the amount of burnt gases and of the mixture formation to control auto-ignition occurrence and timing.…”