Toluene planar LIF in an optically accessible engine
Citation for published version (APA):Bakel, van, B. J. C., Zegers, R. P. C., Luijten, C. C. M., Dam, N. J., & Goey, de, L. P. H. (2011). Toluene planar LIF in an optically accessible engine. In Proceedings of COMBURA'11 - Book of Abstracts, 10-11 october 2011, Ede, The Netherlands (pp. 49-50).
Document status and date: Published: 01/01/2011 Document Version:
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Toluene Planar LIF in an optically accessible engine
B.J.C. van Bakel*, R.P.C. Zegers, C.C.M. Luijten, N.J. Dam, L.P.H. de Goey
Department of Mechanical Engineering, Eindhoven University of Technology, The Netherlands www.combustion.tue.nl
Introduction
Engine manufacturers are searching for ways to make diesel engines cleaner to comply with envi-ronmental regulations. Premixed Charge Com-pression Ignition (PCCI) is a concept to achieve this.
PCCI uses an early injection to give more time for fuel mixing. Because the fuel is premixed with the air, start of combustion cannot be controlled with the injection timing. The start of combustion will take place when local equivalence ratio, tem-perature and pressure initiate it.
For better understanding of the conditions at start of combustion one would like to know the temperature distribution inside the cylinder before ignition. These data will be used to validate and optimize simulation models. To measure the tem-perature fields, Toluene Laser Induced Fluores-cence is used.
Toluene LIF
When toluene is excited with a 248 nm laser, the spectrum of its fluorescence is dependent on temperature. The fluorescence spectrum shifts to longer wavelengths (red shift) with increasing tem-perature, see Figure 1. This property is used in this investigation to find the temperature field in an engine before ignition. The fluorescence signal is captured with two cameras with different band pass filters. The ratio between the two intensities is a measure for the temperature. This way a 2-D temperature image can be obtained, which is inde-pendent of toluene concentration and laser fluctua-tions.
Fig. 1: Toluene spectra and camera detection bands
Experimental apparatus
For the experiments a single cylinder optically accessible engine is used, see Figure 2. The en-gine is driven by an electrical motor and kept at a constant speed with an eddy current brake. The optical accessibility is achieved with a sapphire window in the piston and a sapphire ring in the liner. The piston is elongated to house the 45 de-gree mirror which deflects the light from the com-bustion chamber towards the cameras.
The toluene is injected with a port fuel injection system and will be vaporized by the heated inlet air. Heptane is injected with the diesel injector, representing the diesel injection event.
The cameras are set up in front of the 45 de-gree mirror. One camera is pointed directly at the mirror and the second camera is looking via a 300 nm long pass mirror at the engine mirror. This set-up splits the signal into a long wavelength part (>300 nm) and a short wavelength band (<300 nm). The Cameras are equipped with band pass filters, 280±10 nm and 320±20 nm respectively.
Fig. 2: Optically accessible engine schematic
Calibration
To calibrate this method, toluene is injected in the inlet channel so it is sucked in during the intake stroke. Measurement images are taken at different crank angle degrees. At these different CAD the air in the cylinder is assumed to have a uniform tem-perature. The measured in-cylinder pressure curve is fitted with a simulation model to determine the temperature calibration graph, see Figure 3. The ratios belonging to these temperatures are found with the measurement images.
* Corresponding author: B.J.C.v.Bakel@student.tue.nl COMBURA 2011, the ReeHorst, Ede
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 300 400 500 600 700 800 R a ti o [-] Temperature [K]
Fig. 3: Calibration graph
Measurements
To visualize the temperature field inside the cyl-inder during and after injection, toluene is added to the fuel. The directly injected fuel consists of 90% heptane and 10% toluene. Measurement images are made during (Figure 4) and after injection (Fig-ure 5). In this way the development of the tempera-ture field after injection can be analyzed. These measurement series are done for different injection timings to investigate the influence of premixing of the fuel.
Fig. 4: Measurement images of both cameras and ratio image of a spray, during injection.
Fig. 5: Measurement images of both cameras and ratio image after the injection.
Results and discussion
The limited signal strength is a serious concern, which makes interpretation of the ratio data not straightforward. This is currently the subject of analysis. Also the use of the ICCD camera is very sensitive to small changes in measurement cir-cumstances. For different recording speeds, the background level is different. It is very important to subtract the right background because signal lev-els are low and the images are used for a ratio image. A second camera issue is that the chip temperature has to be kept at constant value. Changes in chip temperature cause different back-ground- and noise levels. We hope to present the results of this analysis on the Combura confer-ence.
Acknowledgements
This project is supported by the Dutch Technol-ogy Foundation STW, which is the technical sci-ences division of NWO, and the Technology Pro-gramme of the Ministry of Economic Affairs. Shell Global Solutions, DAF Trucks, Wärtsilä and TNO Automotive are also acknowledged for their contri-butions to the project. The authors kindly appreci-ate the support of the technicians of the Eindhoven Combustion Technology group: Bart van Pinxten, Hans van Griensven, Gerard van Hout and Theo de Groot.
