Simultaneous high-speed visualization of soot luminosity and OH1 chemiluminescence of alternative-fuel combustion in a HSDI diesel engine under realistic operating conditions |
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Authors: | Markus Jakob Thomas Hülser Andreas Janssen Philipp Adomeit Stefan Pischinger Gerd Grünefeld |
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Affiliation: | 1. College of Electromechanical Engineering, Qingdao University of Science and Technology, Qingdao 266061, China;2. Department of Energy Engineering, Zhejiang University, Hangzhou 310027, China |
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Abstract: | Crude-oil independent liquid fuels are currently being developed for future HSDI diesel engines. Thus, it is the primary objective of the present study to characterize the combustion of selected reference fuels under realistic conditions, in particular with regard to flame lift-off and soot formation. The experiments are conducted in an optically-accessible and a comparable all-metal HSDI engine at part load, using n-decane, n-heptane, 1-decanol, and conventional diesel, respectively, as the fuel. Two image-intensified, high-speed CMOS cameras are employed simultaneously, in order to visualize the highly unsteady combustion process in terms of OH1 radicals and soot, respectively, with relatively high temporal resolution and data throughput.The results demonstrate the influence of the fuel properties, in particular cetane number and volatility, on mixture formation, ignition, combustion, soot formation, and emissions. Relatively high soot emissions for n-decane can basically be explained by its short ignition delay, small lift-off length, and lack of fuel-bound oxygen. The soot formation process seems to be more important for the relative engine-out emissions than soot oxidation under the investigated conditions. Furthermore, a very strong correlation between the ignition delay and the flame lift-off length (during injection) is found. This indicates that lift-off stabilization is essentially determined by autoignition. |
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