SAE AIR6504A

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 Particulate Matter (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 and ARP6320B, 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 cutoff of 10 nm, and no coagulation. This SAE Aerospace Information Report (AIR) revision provides updates to the system loss correction method with options for calculating the corrections using measured size distributions. Sampling system section 2 particle loss is also updated. Minor clarifications or editorial changes throughout the document are also included. The current calculation method uses an inferred size distribution from the ratio of mass to number and an assumed lognormal nvPM number size distribution. The update in this document describes three additional options for calculating nvPM loss correction factors using measured nvPM size distributions. The definition of the T1 location from the Diluter1 inlet to Splitter1 metal is updated. This is to clarify the sampling system section 1 thermophoretic loss calculation. An updated estimate of Diluter1 losses and any sampling system section 2 thermophoretic losses using a “thermophoretic loss” from Splitter1 to the Diluter1 outlet is prescribed using the new definition of T1 and the temperature at the exit of the Diluter1 T2 (assumed to be 333.15 K). This estimate is expected to be an interim revision while further work is performed to verify sampling system section 2 particle loss and improve uncertainty. To help this work, optional sampling system section 2 measured sampling system temperatures near the Diluter1 inlet, which are measured in some specific system designs, are reported as per ARP6320B. Minor wording changes were made to clarify some areas of the document.