In-cylinder temperature measurements via fiber-based toluene lif and time-correlated single-photon counting

Abstract

Consulta en la Biblioteca ETSI Industriales (9147)

[EN] Since Nikolaus Otto developed the four-stroke internal combustion engine between 1862 and 1866 [21], a large number of improvements have been introduced on it. Innovative concepts for internal combustion engines (like homogenous charge compression ignition (HCCI) and direct-injected spark-ignition engines (DISI)), that promise high efficiency and low emissions, require a detailed knowledge about the ignition. Exact control of in cylinder conditions is crucial for the reliable operation of those engines and also the properties of the mixture determine the combustion process and thus effect pollutant formation and the emission of unburned hydrocarbons. It is therefore important to obtain quantitative information about the mixture conditions prior to ignition, i.e. of fuel/air ratio, oxygen concentration, fuel concentration and temperature distribution, in order to make a diagnostic of the behavior of the engine. Several laser-based diagnostic techniques for minimal-invasive measurements of species concentrations and temperatures have been developed during recent years and have become valuable tools to study technical combustion processes due to they do not influence the system under study by inserting probes and surfaces. Many techniques have been extended to two-dimensional imaging giving information about temperature and concentration distributions in different combustion systems. Data gained from such experiments are the basis for a comparison with and development of detailed mathematical modeling of chemical processes in laminar and turbulent flames including heat and species transport. Commercially available fuels contain numerous compounds that strongly fluoresce upon illumination with UV light. These compounds can be used as fluorescence tracers since their fluorescence signal depends not only on the concentration of the fluorescing species but also on environment temperature, total pressure and local gas composition. The most popular fluorescence tracer for gasoline engine application is toluene. This use of fluorescent tracers for fuel visualization based on laser-induced fluorescence (LIF) has grown to an important engineering tool in modern engine research. However, the constant improvements of quantitative interpretation of fluorescence signals requires fundamental knowledge of the compound¿s photo physical behavior, e.g. the dependence of the LIF-signal on temperature, fuel/air ratio, oxygen concentration, etc. Therefore, detailed measurements of LIF-signal intensities under well controlled experimental conditions are necessary for validating model descriptions of LIF-signal behavior. Then, optical diagnostics is a valuable tool for internal combustion (IC) engine research. Of particular value are micro optical systems such as fiber-optic spark-plug sensors for performing optical measurements without large modifications of engine combustion chamber design. The motivation for this work is to provide temperature measurement via laser-induced fluorescence using effective fluorescence lifetime of toluene determined by time-correlated single photon counting (TCSPC) and combined with a minimal-invasive fiber-optic spark plug sensor. This occurs in two steps. In the beginning measurements in a heated gas flow nozzle under defined conditions will provide a database of temperature dependant fluorescence lifetimes of toluene from 300 K until 600 K. Later these data (completed with fluorescence lifetimes of toluene from Stephan Faust experiments at higher temperature [25]), will be used as calibration data for obtaining a semi-empirical model in order to be able to predict fluorescence lifetimes as a function of gas temperature of toluene. In the second step, fluorescence lifetime of toluene will be measured in a single cylinder optical engine by means of the same fiber-optic spark plug sensor. This engine will work with iso-octane (90%) and toluene (10%) as a fuel, mixed with pressurized nitrogen after being injected in a suction tube and before going inside the cylinder. The results in these experiments will provide a curve of fluorescence lifetimes of toluene as a function of crank angle degrees (CAD). These fluorescence lifetimes with the semi-empirical model will provide in cylinder temperatures as a function of CAD, which is the goal of this work.