Search Results

Large Eddy Simulation (LES) appears today as a prospective tool for engine study. Even if recent works have demonstrated the feasibility of multi-cycle LES, they have also pointed out a lack of detailed experimental data for validation as well as for boundary condition definition. The acquisition of such experimental data would require dedicated experimental set-ups. Nevertheless, in future industrial applications, unconditional dedicated experimental set-ups will not be the main stream. To overcome this difficulty, a methodology is proposed using system simulation to define fluid boundary conditions (crank-resolved intake/exhaust pressures and temperatures) and wall temperatures. The methodology combines system simulation for the whole experimental set-up and LES for the flow in the combustion chamber as well as a part of the intake and exhaust ducts. System simulation provides the crank-resolved temperature and pressure traces at the LES mesh inlet and outlet.

In spark-ignition engines, cyclic variability limits the optimisation of operating conditions (choice of spark advance and/or injection timing) since it induces load variations and the occurrence of misfire and/or knock. This, in turn, restricts the operation range of new concepts such as downsizing or stratified combustion. To understand the basic physical phenomena behind cyclic variations, careful experimental studies are necessary to simultaneously characterise the combustion and the unsteady flow in the complete engine set-up. With a well-characterised experimental engine set-up, Large Eddy Simulation (LES) modelling can be easily combined with experiment in order to tackle intricate physical phenomena couplings. This paper describes an experimental database acquired on an optical research engine. The single-cylinder spark-ignition engine is equipped with four valves, a pentroof combustion chamber and a flat piston. The database is dedicated to the validation of LES models.

In spark-ignition engines, Cycle-to-Cycle Variations (CCV) limit the optimization of engine operation since they induce torque variations and the occurrence of misfire and/or knock. A mean for limiting the related negative impact of CCV on fuel consumption and emissions would be control strategies able to address them. At present, engine simulation codes used for control purposes can only describe CCV linked to variations of gas exchanges in the air loop. CCV of the in-cylinder flow motion cannot be naturally captured by classical quasi-dimensional combustion chamber models. A convenient way to mimic CCV is to impose stochastic distributions of the combustion model parameters. Nevertheless, it is not always clear if these perturbations have physical bases as well as realistic ranges of variation.