International audienceThis article presents a comparison between experiments and Large-Eddy Simulation (LES) of a spark ignition engine on two operating points: a stable one characterized by low cycle-to-cycle variations (CCV) and an unstable one with high CCV. In order to match the experimental cycle sample, 75 full cycles (with combustion) are computed by LES. LES results are compared with experiments by means of pressure signals in the intake and exhaust ducts, in-cylinder pressure, chemiluminescence and OH Planar Laser Induced Fluorescence (PLIF). Results show that LES is able to: (1) reproduce the flame behavior in both cases (low and high CCV) in terms of position, shape and timing; (2) distinguish a stable point from an unstable one; (3) predict quantitatively the CCV levels of the two fired operating points. For the unstable case, part of the observed CCV is due to incomplete combustion. The results are then used to analyze the incomplete combustion phenomenon which occurs for some cycles of the unstable point and propose modification of the spark location to control CCV

This paper describes a compressible Large Eddy Simulation (LES) used to investigate cyclic variations for nonreacting flow in an optical single cylinder engine setup. The simulated operating point is part of a large experimental database designed to validate LES for cycle-to-cycle prediction, and constitutes a first step towards the realization of fired operating points. The computational domain covers almost the whole experimental setup (intake and exhaust plenums, intake and exhaust ducts, cylinder) to account for acoustic phenomena. The assessment of the computation is performed in two regions of the domain: the intake and exhaust duct predictions are compared to the results of a Helmholtz solver and the experiment (pressure transducers and Particle Image Velocimetry (PIV)) while the in-cylinder dynamics are compared to PIV measurements. The ability of the B. Enaux · V. Granet (B) · O. Vermorel 154 Flow Turbulence Combust (2011) 86:153-177 developed methodology to capture the correct level of cycle-to-cycle variations is demonstrated considering in-cylinder pressure and velocity fields predictions. Cycleto-cycle variations in velocity are highlighted and localized using a proper orthogonal decomposition analysis.

No abstract

ElsevierBenajes Calvo, JV.; Novella Rosa, R.; De Lima Moradell, DA.; Tribotte, P.; Quechon, N.; Obernesser, P.; Dugue, V. (2013). Analysis of the combustion process, pollutant emissions and efficiency of an innovative 2-stroke HSDI engine designed for automotive applications. Applied Thermal Engineering. 58(1-2): 181-193. doi:10.1016/j.applthermaleng.2013 AbstractOn the last years engine researchers has been focused on improving engine efficiency in order to decrease CO 2 emissions and fuel consumption, while fulfilling the increasingly stringent pollutant emissions regulations. In this framework, engine downsizing arises as a promising solution, and 2-stroke cycle operation offers the possibility of reducing the number of cylinders without incurring in NVH penalties. An experimental investigation has been performed to evaluate the performance of a newly-designed poppet valves 2-stroke engine, in terms of finding the proper incylinder conditions to fulfill the emission limits in terms of NO X and soot, keeping competitive fuel consumption levels. Moreover, present research work aims to improve the existing knowledge about the gas exchange processes in a 2-stroke engine with poppet valves architecture, and its impact over the combustion conditions, final exhaust emissions levels and engine efficiency. The experimental results confirm how this engine architecture presents high flexibility in terms of air management control to substantially affect the in-cylinder conditions. The in-cylinder oxygen concentration and density, which are the product of a given trapping ratio and delivered mass flow, were linked to pollutant emissions and performance by their impact on instantaneous adiabatic flame temperature and spray mixing conditions. After the optimization process, it was possible to minimize simultaneously NO X , soot and indicated fuel consumption, without observing a critical trade-off between the pollutant emissions and the fuel consumption.

No abstract