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Procedure for the Calculation of non-volatile Particulate Matter Sampling and Measurement System Penetration Functions and System Loss Correction Factors
- Aerospace Standard
Published October 10, 2017 by SAE International in United States
Downloadable datasets availableAnnotation ability available
This SAE Aerospace Information Report (AIR) describes a method for assessing size dependent particle losses in a sampling and measurement system of specified geometry utilizing the non-volatile PM (nvPM) mass and number concentrations measured at the end of the sampling system.1 The penetration functions of the sampling and measurement system may be determined either by measurement or by analytic computational methods.
Loss mechanisms including thermophoretic (which has a very weak size dependence) and size dependent losses are considered in this method2 along with the uncertainties due to both measurement error and the assumptions of the method. The results of this system loss assessment allow development of estimated correction factors for nvPM mass and number concentrations to account for the system losses facilitating estimation of the nvPM mass and number at the engine exhaust nozzle exit plane. As the particle losses are size dependent, the magnitude of correction factors can vary as a function of many factors including combustor technology and engine operating condition.
Implementation of the nvPM sampling and measurement system for aircraft engine testing, as per AIR6037, requires a sample line of up to 35 m and includes several sampling and measurement system components, which result in significant particle loss on the order of 50% for nvPM mass and 90% for nvPM number.
The system loss correction factors are estimated based on a model with the following inputs and assumptions: engine exhaust exit plane nvPM have a lognormal distribution, known size dependent values of nvPM effective density and geometric standard deviation, a minimum particle size cut-off of 10 nm, and no coagulation.
This SAE Aerospace Information Report (AIR) describes a method for calculating correction factors to account for system particle losses when performing non-volatile Particulate Matter (nvPM) measurement as specified in AIR6037. Such sampling and measurement systems have significant line length and several components that result in particle losses. The particle losses are size dependent and hence depend on many factors including combustor technology and engine operating condition resulting in a reduction in measurement of the order of 50% for nvPM mass concentration and 90% for nvPM number concentration. Estimation of engine exit plane nvPM mass and number concentrations are improved by developing a calculation method to account for these losses.
The approach used in this AIR will involve separate correction factors for measured nvPM mass and number concentrations, which will be calculated using measured or calculated line and component penetration efficiencies. These calculations will be based on assumptions of a lognormal particle size distribution at the engine exit with a known associated lognormal width, and an equivalent spherical particle shape with a corresponding known effective particle density. These resulting correction factors will then be used to estimate the total particle losses in the sampling and measurement system for nvPM mass and number, and will thus be used to infer the engine exit plane concentrations of nvPM mass and number.
Data Sets - Support Documents
|Table 1||Measured nvPM mass and number parameters necessary for system loss correction calculations|
|Table 2||Sampling and measurement system input parameters|
|Table 3||Carrier gas and particle properties used in the particle transport calculations|
|Table 4||nvPM Sampling and measurement system component and segment penetration fractions. In the loss calculation software tools, there are up to fifteen line penetration segments, η , available that can be used to construct continuous, individual mass and number segment line penetrations, η and η , from the probe inlet to the mass and number instruments. Each segment line penetration, η , will have a diameter, ID , wall temperature, T , sample gas temperature, T , and sample flow rate, Q , and will be used to compose the 5 sampling system sections. If fewer than fifteen segments are required to describe the sampling system, the lengths of the unused segments must be set to have zero length and identical wall and gas temperatures. The tools will then ignore the penetration contributions of these segments|
|Table 5||AIR6241 [Reference 220.127.116.11] minimum specifications for VPR penetration at four particle diameters|
|Table 6||Correction factors determined from test campaigns|
|Table 7||This example uses the loss tool and the standard input set listed in this table|
|Table C1||List of parameters and parameter variations used in the Monte Carlo error calculations. These consider variability over a single test point which represents random error in a single correction factor calculation.|
|Table C2||Parameterization of number correction factor relative errors|
|Table C3||Parameterization of mass correction factor relative errors|
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