Experimental Investigations for Turbulent Premixed Flame Analysis

Increasingly stringent pollutant emission regulations have constrained car manufacturers to reduce the fuel consumption and pollutant emissions of internal combustion engines. Downsized engines appear to be the most promising way to achieve this in terms of emission reduction as well as investment minimization. The design of downsized internal combustion engines requires the understanding and quantification of thermo-fluid-dynamic processes at high pressure, high temperature and with high dilution rate. This study aims to carry out preparatory work in a fan-stirred spherical combustion vessel at conditions representative of those occurring in downsized engines. First, experimental correlations giving the laminar burning velocity from the initial pressure, the initial temperature, the dilution rate and the equivalence ratio are proposed. Then the turbulent flow inside the vessel is characterized in terms of turbulent rms velocities and integral length scales, without combustion, using Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV) measurements. The integral length scale remains constant at all fan speeds and all investigated pressures and temperatures. It appears to be an inherent parameter of the experimental setup. The intensity level increases linearly up to 2.8 m/s with the fan speed. Close approximations of homogeneous and isotropic turbulence (HIT) are achieved using this setup. The flame progress is then tracked using high speed tomography. Results of the characterization of the turbulent flow are shown to be still relevant during the turbulent flame propagation. This validation stage is essential for the characterization of turbulent flames as a function of the turbulent flow characteristics. Lastly, using the turbulent combustion diagram, a comparison with turbulent flame propagation in a research engine is carried out and the relevance of the present experimental setup is highlighted.