Optical analysis of internal mixture formation and combustion processes
Research into the processes of engine combustion, both with compression ignition and with spark ignition, focuses on their efficiency in terms of fuel consumption and the formation of emissions. The fuel properties in particular, but also the design of the injection process or the engine geometry with regard to mixture formation, have a significant influence on the efficiency and stability of the combustion process. This applies to both liquid as well as gaseous fuels such as hydrogen. In order to develop an understanding of the limits of operating parameters, it is essential to analyze the course of cyclic variability in individual combustion cycles. To this end, it must be possible to record these effects in detail beyond the capabilities of conventional engine measurement technology. Optical and laser supported measurement technology can be used to record the processes of mixture formation, ignition, combustion and emission formation in two or three dimensions.
Due to the rapid processes involved in turbulent flame propagation, appropriate measurement technology with sampling rates ≥ 10 kHz is absolutely essential, as otherwise stochastically occurring events will not be recorded. In the field of mixture formation and oil detection, measurement techniques such as tracer LIF or Mie scattered light measurement technology are used. Chemiluminescence measurements are used to assess ignition and combustion. The simultaneous application of several measurement techniques increases the gain in knowledge.
As part of a DFG-funded large-scale equipment application, modern measurement technology in the form of a high-speed camera, an image intensifier, a high-speed laser and a UV endoscope was recently procured for the TME, which can be used in particular for the analysis of internal engine mixture formation and combustion processes.
Future developments of internal combustion engines demand the strict adherence of emission laws with simultaneous reduction of the fuel consumption. To avoid the occurrence of emissions and for the optimal use of the fuel, the layout of the injector and the optimized charge flow is crucial. For the assessment and the analogy of the developed canal and combustion chamber geometry as well as the interaction with the jet spray and also for the analogy between different fuels, there are two transparent engines available at the TME.
The gasoline transparent engine distinguishes itself by a modular design. Therefore the test bench can be customized towards customer requirements regarding hub and drill hole. The test stand can be equipped with a flow model or a cylinder head and is essential for flow and carburetion analysis.
The transparent diesel engine that is available next to the gasoline transparent engine is primarily used for fuel analysis and the analysis of the characteristic ignition behavior.
For the application of the optical measuring technique there is a High-Speed Nd : YLF Laser, a Nd : YAG Laser, High-Speed Cameras as well as image amplifiers available.The use of measuring techniques is:
- Particle Image Velocimetry: Analysis of the Charge Flow and Flow Phenomena
- Mie Stray Light: Analysis of Carburetion of the liquid Stream
Tracer Laser Induced Fluorescence: Carburetion Analysis in the Gas Phase
- Soot Lights: Visualization of hot Soot during the Combustion
- OH* Chemiluminescence: Visualization of Areas with Combustion Reactions
- Laser Induced Incandescence: Visualization of the Soot (including cold Soot)