A Study of the Homogeneous Charge Compression Ignition Combustion Process by Chemiluminescence Imaging
1999 (English)Conference paper (Refereed)
An experimental study of the Homogeneous Charge Compression Ignition (HCCI) combustion process has been conducted by using chemiluminescence imaging. The major intent was to characterize the flame structure and its transient behavior. To achieve this, time resolved images of the naturally emitted light were taken. Emitted light was studied by recording its spectral content and applying different filters to isolate species like OH and CH.
Imaging was enabled by a truck-sized engine modified for optical access. An intensified digital camera was used for the imaging. Some imaging was done using a streak-camera, capable of taking eight arbitrarily spaced pictures during a single cycle, thus visualizing the progress of the combustion process. All imaging was done with similar operating conditions and a mixture of n-heptane and iso-octane was used as fuel.
Some 20 crank angles before Top Dead Center (TDC), cool flames were found to exist. They appear with a faint structure, evenly distributed throughout the combustion chamber. There was no luminosity recorded between the end of cool flames and the start of the main heat release. Around TDC the main heat release starts. Looking at a macro scale, we find that the charge starts to burn simultaneously at arbitrary points throughout the charge. Since the thermal boundary layer is colder than the bulk of the charge, the local heat release is delayed close to the walls. As a result, the total heat release is slowed down. Ensemble averaged 1 images show this wall boundary effect clearly when plotted against CAD. The peak intensity at the main combustion event is one order of magnitude greater than that of the cool flame and the structure is a lot more protruding.
Since spontaneous emission imaging is a line-of-sight integration, the flame structure appears a bit smeared. The micro scale structure is very similar from one cycle to another, but there are large variations between cycles on the macro scale.
Place, publisher, year, edition, pages
, SAE, 1999-01- 3680
Arbitrary points, Boundary effects, Chemiluminescence imaging, Combustion pro-cess, Cool flame, Crank angle, Emitted light, Ensemble-averaged, Experimental studies, Flame structure, Heat release, Homogeneous charge compression ignition combustions, iso-Octane, Line-of-sight, Local heat, Macro scale, Micro-scale structures, n-Heptanes, Operating condition, Optical access, Peak intensity, Single cycle, Spectral content, Thermal boundary layer, Time-resolved image, Top dead center, Total heat release, Transient behavior
IdentifiersURN: urn:nbn:se:kth:diva-177505DOI: 10.4271/1999-01-3680ScopusID: 2-s2.0-84859364963OAI: oai:DiVA.org:kth-177505DiVA: diva2:873101
SAE International Fall Fuels & Lubricants Conference, Toronto, Canada.
QC 201511232015-11-232015-11-232015-11-23Bibliographically approved