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Aerosol characterization in rocket plumes
J. AeroJol Sci. Vol. 30, Suppl. 1, pp. $215-$216, 1999 O 1999 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0021-8502/99/$ - see front matter
Pergamon
A E R O S O L C H A R A C T E R I Z A T I O N IN R O C K E T P L U M E S P. Whitefield~, M. Ross2, D. Hagen I and A. Hopkins ~ ~Cloud and Aerosol Sciences Laboratory, University of Missouri-Rolla, Rolla MO 65409-0430 2Environmental Systems Directoratel The Aerospace Corporation, PO Box 92957 Los Angeles CA 90009
KEYWORDS particulate size distributions, alumina, solid rocket motors, global ozone depletion
METHOD The measurements were made with an aerosol sampling instnunent consisting of two subsystems: (1) a real time particulate counter (RPM) providing concentration and size distribution in a window covering 0.34 to 4 ~un at 1 Hz sampling rate and (2) a grab-tank sampling system (GTS) providing particulate size distribution in a window covering 0.01 to 0.4 ~tm. The two instruments were carded in the WB-57F main payload bay. Independent, unheated, sampling inlets (6.35 mm and 9.53 mm diameter for the RPM and GTS, respectively) extended into, and were parallel to, the airflow outside the aircraft boundary layer. The RPM is based on a commercial laser particle counter, adapted for the stratospheric plume measurements. The GTS was chosen as the primary method for measuring the aerosol size distribution for sizes from 0.01 to 0.4 ~tm because of the relatively brief duration of the rocket plume wake encounters. Submicron aerosols are typically characterized using condensation nuclei (CN) counting techniques and differential mobility analysis (DMA), which can require a stable sample source for up to 120 seconds [Hagen et al., 1993]. Typical plume encounters are only tens of seconds in duration, however, precluding the possibility of a real time DMA characterization. GTS samples were acquired during plume encounters by serially filling nine evacuated pressure vessels on command from the WB-57F aircrew based on a cockpit display of RPM data to indicate plume ingress and egress. A few seconds following sample acquisition, each tank was pressurized to one atmosphere with particle-free dry air to minimize modification of the sample by diffusion and agglomeration losses, then sealed. For particulate in the size range and concentrations of interest (< 103 cm"3) the GTS sample modification can be estimated using the MAEROS model [Gelbard, 1983] that describes the time-dependent evolution of an aerosol size spectrum, accounting for coagulation, turbulence, and particle deposition due to gravitational settling, diffusion, thermophoresis, and diffusiophoresis.
$215
$216
Abstractsof the 1999EuropeanAerosolConference
RESULTS The concentration and size distribution of aerosol in the stratospheric exhaust plumes of two Space Shuttle rockets and one Titan IV rocket were measured using a two component aerosol sampling system carried aboard a WB-57F aircraft. Aerosol size distribution in the 0.01 to 0.4 micron diameter size range was measured using plume samples acquired during plume encounters and returned to the ground for post-flight analysis. Size distribution and total aerosol concentration in the 0.34 micron to 4 micron diameter range was measured at 1 Hz sample rate during plume encounters using a laser aerosol counter. The complete 0.01 to 4.0 micron aerosol size distributious in the Space Shuttle and Titan IV exhaust plumes are discovered to be very similar and can be taken as representative of the size distribution of the alumina particulate in the exhaust from large solid rocket motors (SRMs). Broadly consistent with previous estimates of the alumina size distribution, the measured distributions display a trimodal form with modes near 0.005 microns, 0.09 microns, and 2.03 microns. Our measurement of the relative mass fractionation among the three modes contradicts pervious estimates, however. While the smallest mode has been estimated to contain as much as 10\% of the total mass of SRM exhaust alumina, our measurements show that the smallest mode contains less than 0.05\% of the total alumina mass emitted by large SRMs. This fraction is so small so as to significantly reduce the likelihood that heterogeneous reactions on the alumina surface from SRM emissions could produce a significant global impact on stratospheric chemistry. REFERENCES Hagen, D. E., P. D. Whitefield, M. B. Trueblood, and H. V. Lilenfeld, particulates and aerosols characterized in real time from harsh environments using the UMR MASS, AIAA 29th Joint Propulsion Conference, Paper 93-2344, 1993. Gelbard, F., MAEROS User Manual, NTIS NRC Fin No. A1198, NUREG/CR-1391, SAND800822, 1983.
Pergamon
A E R O S O L C H A R A C T E R I Z A T I O N IN R O C K E T P L U M E S P. Whitefield~, M. Ross2, D. Hagen I and A. Hopkins ~ ~Cloud and Aerosol Sciences Laboratory, University of Missouri-Rolla, Rolla MO 65409-0430 2Environmental Systems Directoratel The Aerospace Corporation, PO Box 92957 Los Angeles CA 90009
KEYWORDS particulate size distributions, alumina, solid rocket motors, global ozone depletion
METHOD The measurements were made with an aerosol sampling instnunent consisting of two subsystems: (1) a real time particulate counter (RPM) providing concentration and size distribution in a window covering 0.34 to 4 ~un at 1 Hz sampling rate and (2) a grab-tank sampling system (GTS) providing particulate size distribution in a window covering 0.01 to 0.4 ~tm. The two instruments were carded in the WB-57F main payload bay. Independent, unheated, sampling inlets (6.35 mm and 9.53 mm diameter for the RPM and GTS, respectively) extended into, and were parallel to, the airflow outside the aircraft boundary layer. The RPM is based on a commercial laser particle counter, adapted for the stratospheric plume measurements. The GTS was chosen as the primary method for measuring the aerosol size distribution for sizes from 0.01 to 0.4 ~tm because of the relatively brief duration of the rocket plume wake encounters. Submicron aerosols are typically characterized using condensation nuclei (CN) counting techniques and differential mobility analysis (DMA), which can require a stable sample source for up to 120 seconds [Hagen et al., 1993]. Typical plume encounters are only tens of seconds in duration, however, precluding the possibility of a real time DMA characterization. GTS samples were acquired during plume encounters by serially filling nine evacuated pressure vessels on command from the WB-57F aircrew based on a cockpit display of RPM data to indicate plume ingress and egress. A few seconds following sample acquisition, each tank was pressurized to one atmosphere with particle-free dry air to minimize modification of the sample by diffusion and agglomeration losses, then sealed. For particulate in the size range and concentrations of interest (< 103 cm"3) the GTS sample modification can be estimated using the MAEROS model [Gelbard, 1983] that describes the time-dependent evolution of an aerosol size spectrum, accounting for coagulation, turbulence, and particle deposition due to gravitational settling, diffusion, thermophoresis, and diffusiophoresis.
$215
$216
Abstractsof the 1999EuropeanAerosolConference
RESULTS The concentration and size distribution of aerosol in the stratospheric exhaust plumes of two Space Shuttle rockets and one Titan IV rocket were measured using a two component aerosol sampling system carried aboard a WB-57F aircraft. Aerosol size distribution in the 0.01 to 0.4 micron diameter size range was measured using plume samples acquired during plume encounters and returned to the ground for post-flight analysis. Size distribution and total aerosol concentration in the 0.34 micron to 4 micron diameter range was measured at 1 Hz sample rate during plume encounters using a laser aerosol counter. The complete 0.01 to 4.0 micron aerosol size distributious in the Space Shuttle and Titan IV exhaust plumes are discovered to be very similar and can be taken as representative of the size distribution of the alumina particulate in the exhaust from large solid rocket motors (SRMs). Broadly consistent with previous estimates of the alumina size distribution, the measured distributions display a trimodal form with modes near 0.005 microns, 0.09 microns, and 2.03 microns. Our measurement of the relative mass fractionation among the three modes contradicts pervious estimates, however. While the smallest mode has been estimated to contain as much as 10\% of the total mass of SRM exhaust alumina, our measurements show that the smallest mode contains less than 0.05\% of the total alumina mass emitted by large SRMs. This fraction is so small so as to significantly reduce the likelihood that heterogeneous reactions on the alumina surface from SRM emissions could produce a significant global impact on stratospheric chemistry. REFERENCES Hagen, D. E., P. D. Whitefield, M. B. Trueblood, and H. V. Lilenfeld, particulates and aerosols characterized in real time from harsh environments using the UMR MASS, AIAA 29th Joint Propulsion Conference, Paper 93-2344, 1993. Gelbard, F., MAEROS User Manual, NTIS NRC Fin No. A1198, NUREG/CR-1391, SAND800822, 1983.