Abstract
This paper presents a measurement technique for visualizing the distribution of the in-cylinder mixture temperature and an experimental approach for analyzing the effect of the temperature distribution prior to ignition on homogeneous charge compression ignition (HCCI) combustion. First, a technique for visualizing the mixture temperature distribution based on the temperature dependence of laser-induced fluorescence (LIF) is described. Two different dopants, tri-ethyl-amine (TEA) and 3-pentanone, were chosen for use as fluorescent tracers because of their different temperature dependencies and fluorescent wavelength ranges. Fluorescence from TEA increases as the mixture temperature increases, while fluorescence from 3-pentanone decreases, making it possible to calculate the temperature based on the ratio between the two fluorescent intensity signals. Fluorescent intensity signals from these two tracers were spectrally separated by a dichroic mirror and captured separately by two optically filtered ICCD cameras. The effect of oxygen quenching on fluorescence was also taken into account in quantifying the mixture temperature distribution. As the next step, this method of measuring the temperature distribution was applied to an analysis of HCCI combustion. It is well known that the mixture temperature plays an important role in HCCI combustion. Non-uniform mixture temperature distributions were intentionally generated prior to ignition by a special intake system with a completely divided intake port fitted with separate electrical heaters. The air passing through each intake port was independently heated to produce several different in-cylinder mixture temperature distributions. The correlation between the temperature distribution prior to ignition and the ignition timing of HCCI combustion was shown experimentally by quantitatively comparing the LIF-measured temperature distribution in the combustion chamber and combustion flame images.
Keywords:Gasoline engine, temperature, measurement, LIF, HCCI