Adrien Brassat

Controlling GCAI (Gasoline Controlled Auto Ignition) in an Extended Operating Map

Abstract The gasoline controlled autoignition (GCAI) is a modern combustion method with which the fuel consumption and the pollutant emissions can be reduced. The major drawback of the combustion method is the limited operating map. In this contribution it is shown how the operating map can be extended towards lower loads by the use of a spark plug for a spark-assisted GCAI combustion. Compared to the GCAI combustion, the spark plug is used additionally and the controller has to be adapted, such that the spark-assisted GCAI combustion is also considered. As controller a model-based predictive controller (MPC) is developed. In this contribution a special focus is set on the investigation of the underlying model for the MPC.

Detailed Simulation of Cycle-To-Cycle Fluctuations at Gasoline Auto Ignition Engines and Derivation of a Synchronous Simulation and Control Approach

Abstract For gasoline engines the controlled auto ignition (GCAI) operating mode provides the potential to enable the fuel consumption benefit of stratified lean combustion systems without the drawback of additional NOx aftertreatment. The auto-ignition process depends strongly on stratification of air, residual gas and fuel. Furthermore, the thermodynamic state of the charge is of major importance to control combustion. Due to the high amount of residual gas in the combustion chamber, the preceding cycle and its combustion has a high effect on the next cycle by directly affecting the thermodynamic state of the in-cylinder charge. In addition to RANS calculations with k-e turbulence modeling this paper investigates the effects leading to cycle-to-cycle combustion fluctuations in a GCAI engine by using LES with Smagorinsky turbulence modeling. The auto-ignition process is simulated with 3D CFD calculation of flow, injection and mixture formation, which is bi-directionally coupled to a multi-zone reaction kinetics solver. This 3D approach enables to analyze the thermodynamic conditions in the combustion chamber that lead to auto-ignition. Thus, the temporal and spatial occurrence of exothermic reactions and their influence on the engine process are specified in detail. To reduce the computational effort of multi-cycle calculations which take cycle-to-cycle fluctuations into account, a reduced simulation approach is derived from the 3D CFD. This approach uses 1D gas exchange calculation with GT-Power coupled with online reaction kinetics simulation. Due to the small computational effort, this approach offers the possibility of a coupling to a controller design environment for synchronous simulation and control. Both simulation approaches are validated against test bench measured data. The 3D CFD approach shows a nearly exact agreement to the measured mean pressure curve. Also the cycle-to-cycle fluctuations are resolved. They can be described by flucutations in fuel mixture, residual gas and temperature stratification. The reduced simulation approach calculates the released heat for all cases with a maximum error of 5 %. This is sufficient to determine the control variable indicated mean effective pressure very well.

Extended Charge Motion Design: CAE Based Prediction of Gasoline Engine Pre-ignition Risk

A simulation model to predict pre-ignition phenomena in spark ignition engines is presented. The model uses a semi-detailed reaction scheme to calculate auto-ignition reactions of the in-cylinder charge at the end of and after the compression stroke. In order to reduce simulation time for the calculation of auto-ignition chemistry, a zonal chemistry approach is employed, which simplifies the description of the thermodynamic engine cylinder state. Auto-ignition of gasoline is modeled by a chemical reaction scheme of a primary reference fuel (PRF). Boundary conditions for the pre-ignition analysis are obtained from flow simulations of the in-cylinder charge motion and mixture formation as well as FE heat load analysis for accurate wall temperature determination. By means of this approach, physical mechanisms due to the influence of hot surfaces are studied. In order to investigate whether lubrication oil from the piston head has the potential to promote auto-ignition events, initial two-phase flow simulation studies are presented. Results of the chemistry predictions are compared to experimental measurements from the single cylinder engine test bench.