Procedure for the Calculation of non-volatile Particulate Matter Sampling and Measurement System Penetration Functions and System Loss Correction Factors
This SAE Aerospace Information Report (AIR) provides a method for assessing particle losses that occur in a sampling system of specified geometry based on the nvPM mass and number measured at the end of the sampling system. Both size dependent diffusion loss and size independent thermophoretic loss mechanisms are included in the method. The penetration function of that system must be determined by measurement and/or by computation using an analytical method as described within this report. The outcome of this line loss assessment provides estimated correction factors for nvPM mass and number concentration with associated uncertainties based upon nvPM measurement uncertainties and method assumptions. These correction factors give an estimation of nvPM mass and number values at the inlet to the sampling system.
Rationale: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.