Investigations of the Influence of Mixture Preparation on Cyclic Variations in a SI-Engine, Using Laser Induced Fluorescence 950108
To study the effect of different injection timings on the charge inhomogeneity, planar laser-induced fluorescence (PLIF) was applied to an operating engine. Quantitative images of the fuel distribution within the engine were obtained. Since the fuel used, iso-octane, does not fluoresce, a dopant was required. Three-pentanone was found to have vapour pressure characteristics similar to those of iso-octane as well as low absorption and suitable spectral properties.
A worst case estimation of the total accuracy from the PLIF images gives a maximum error of 0.03 in equivalence ratio. The results show that an early injection timing gives a higher degree of charge inhomogeneity close to the spark plug. It is also shown that charge inhomogeneity gives a more unstable engine operation. A correlation was noted between the combustion on a cycle to cycle basis and the average fuel concentration within a circular area close to the spark plug center. The correlation coefficient when a second order polynomial was fitted reached a value of -0.8 when the engine operated with a high degree of inhomogeneity. The highest correlation coefficient between the duration of 0-0.5% heat released and the average fuel concentration was obtained within a radius of approximately 5-10 mm from the spark plug. When the standard disc-shaped combustion chamber was replaced with a turbulence generating geometry, the inhomogeneity of the charge became very low, independent of injection timing. No cycle to cycle correlations between fuel/air equivalence ratio and combustion were then noted.
Citation: Johansson, B., Neij, H., Aid‚n, M., and Juhlin, G., "Investigations of the Influence of Mixture Preparation on Cyclic Variations in a SI-Engine, Using Laser Induced Fluorescence," SAE Technical Paper 950108, 1995, https://doi.org/10.4271/950108. Download Citation
Bengt Johansson, Hans Neij, Marcus Aid‚n, Greger Juhlin
Lund Institute of Technology
International Congress & Exposition
Engine Combustion and Flow Diagnostics-SP-1090