• Kupper, Martin
• Bergmann, Alexander
• Kraft, Martin
• Pulko, Jožef

Abstract

Summary: With regard to a realization of an in-situ Laser-Induced Incandescence (LII) system for measurements in an exhaust pipe of an automobile, components suitable for such an application were chosen and tested. Key components for the proposed LII system are a super-compact high-power DPSS laser (CTR HiPoLas®), fast KETEK silicon photomultipliers (SiPM) as detectors and a dedicated optical measurement setup. A measurement cell was specially designed for optimized collection of the incandescent radiation and high flexibility, to allow testing the components under controlled conditions and verify that the detected signal is LII.Therefor with a defined aerosol from a soot generator (Jing 5201 miniCAST – Combustion Aerosol STandard) signals were collected at different laser energies and soot concentrations. By comparison of the recorded behavior with the literature incandescence could be identified as the only source of the signal. Further long-term tests at an AVL engine testbed were performed.<br/><br/>Motivation and results: Laser-Induced Incandescence (LII) is a promising and widely konwn technology in science for studying soot in flames and aerosols. Its capability of measuring different parameters of the aerosol at once [1] with high accuracies meeting legally mandated limits is makes it of high interest also for measuring soot concentrations in automotive exhausts. Due to the fast nature of the LII process very fast measurements of transient events, like fast changes in engine load and the thereby occurring short and high soot emissions, are possible. The limits in this regard are set by the repetition frequency of the laser and the capability of the detectors and electronics used. This work presents the first attempt to realize a highly compact in-situ LII system applicable directly at an automotive exhaust pipe.<br/>Measurements using aerosol from the CAST proved the incandescence signals to be clearly distinguishable from scattered laser light and yielded corresponding LII signals. So, a setup could be realized with the capability to stimulate and detect pure LII. Further the setup was transferred to an engine testbed for a long-term measurement on exhaust gas. The fundamental feasibility of the components in an in-situ LII probe is thereby proved. It thus appears very likely that previously used extractive cells and large-scale laser sources can be replaced by this approach, providing a true in-situ particle sensor. Further testing is ongoing, as are the tests with real automotive exhausts. Due to the challenging analysis of LII Signals the effort for now is confined on the hardware realization, what is on its own also challenging if pure signals are wanted. A processing unit, capable for real-time analysis, is currently used just for data collection. Currently we not aim towards analysis and calibration of the system, instead a design of an in-situ probe was developed.<br/>

Topics

• impedance spectroscopy
• combustion
• Silicon