LII Measurement Comparison on Standard Flame(s)
For the preparation of the workshop on LII to be held in Duisburg, Germany, Sept. 25-28, 2005 the organizers proposed target flames and sample data. The aim was to have as many groups as possible use their experimental approach to measure LII (and potentially additional quantities) in a pre-defined identical environment. Three target flames were chosen that seem widespread in combustion labs: the Gulder burner, Santoro burner and McKenna burner. Specifications for each burner are included below.
Since the time of the first workshop, there have been advances to the measurement and data interpretation methodologies and so we are asking participants to provide new measurements from a standard source. Measurements for any of the three standard burners/conditions are requested. Measurements could include LII based soot volume fraction and particle size as well as any other relevant measurements such as local gas temperature, physical sampling based soot morphology measurements, elastic light scatter, etc. In order to improve the utility of this comparison it is asked that you set your burner up as close to the specified conditions as possible. If you have any questions about the standard conditions please do not hesitate to ask.
Selection of a Single (Preferred) Standard Flame
The advisory committee for the LII workshop has discussed trying to select one of the three burners as a preferred measurement burner (in the hopes of getting more labs to provide results for one flame); however, there remains advantages/disadvantages and outstanding concerns for each of the burners. With the time remaining before the workshop, it is not possible to resolve the concerns, select one burner, and get measurements from all participating labs. Furthermore there remains value in applying LII in different flames as each has different characteristics and measurement challenges. For this reason, the call for measurements still includes all three burners.
Nonetheless, there is still a standing interest in resolving the uncertainties in each of standard flames and selecting one as a preferred standard flame.
In addition to an inventory of burners, there is a need to answer some questions about the stability and repeatability of the different burners. To this end, we invite anyone interested to provide information on the following:
- stability of measurements for a given burner over time, e.g.:
- fluctuations in instantaneous measurements
- variation 1 minute after start up to 3 hours
- repeatability of measurements for a given burner for repeated ignition or day to day (e.g. repeated measurements 15 minutes after ignition)
- repeatability amongst multiple copies of the same burner
- influence of different shroud gas/flames on the McKenna burner performance (e.g. nitrogen, air, fuel lean flame)
- influence of chimneys or screens on flame and/or measurements (i.e. how does optical access holes influence the measurements (magnitude, stability, etc.)
- flame symmetry
- differences in the soot production for the stainless steel or bronze McKenna burner
Measurements of the above should be submitted to Kevin Thomson. During the session on standard burner measurements, time will be allocated for the people who have made measurements related to the stability and repeatability of the burners to present their findings.
Nomination of Other Standard Burners
The three standard burners are all steady laminar burners. It would be good to designate a standard unsteady flame burner. If you would like to nominate a burner as a possible standard unsteady flame burner, please contact Kevin Thomson. Once again, time will be allocated during the discussion of standard burner measurements to present information on candidate burners.
Specifications for Standard Burners
The standard flow conditions for the burner are: 194 standard mL/min of ethylene (20oC, 1 atm) and 284 standard L/min of air. The flame is intended to be unconfined and so mesh screens only (nothing solid) is recommended to improve flame stability. The standard measurement height is on burner centerline, 42 mm above the tip of the fuel nozzle.
The standard flow conditions for the burner are: 231 standard mL/min of ethylene (20oC, 1 atm) and 43 standard L/min air. The flame is confined by a solid wall cylinder (diameter 101.6 mm diameter, 195 mm high) with optical access provided as needed for the particular measurement. The standard measurement location is on burner centerline, 50 mm above the tip of the fuel nozzle.
This is a commercially available burner (http://flatflame.com/ ). The McKenna burner is offered with either a stainless steel or bronze plug. At previous workshops, the stainless steel burner was selected as the standard; however, there have been some problems with flame symmetry reported. Therefore the standard will likely be changed to the bronze plug version. A final decision will be based on feedback from the LII community so if you have a preference for one burner over the other, please indicate it.
The standard flow conditions are:
- Ethylene/air flame
- Equivalence ratio: 2.1
- Total gas flow: 10 slm
- Co-annular (i.e. shroud) flow condition: not specified
- Stabilization plate at 21 mm height above burner.
- diameter of the plate: 60 mm/ thickness of the plate: 20 mm
- Measurement position: centerline location at 12 mm height above burner
- Measurement approximately 15 mins after ignition to provide more or less defined thermal conditions