Experimental verification of principal losses in a regulatory particulate matter emissions sampling system for aircraft turbine engines.

A sampling system for measuring emissions of nonvolatile particulate matter (nvPM) from aircraft gas turbine engines has been developed to replace the use of smoke number and is used for international regulatory purposes. This sampling system can be up to 35 m in length. The sampling system length in addition to the volatile particle remover (VPR) and other sampling system components lead to substantial particle losses, which are a function of the particle size distribution, ranging from 50 to 90% for particle number concentrations and 10-50% for particle mass concentrations. The particle size distribution is dependent on engine technology, operating point, and fuel composition. Any nvPM emissions measurement bias caused by the sampling system will lead to unrepresentative emissions measurements which limit the method as a universal metric. Hence, a method to estimate size dependent sampling system losses using the system parameters and the measured mass and number concentrations was also developed (SAE 2017; SAE 2019). An assessment of the particle losses in two principal components used in ARP6481 (SAE 2019) was conducted during the VAriable Response In Aircraft nvPM Testing (VARIAnT) 2 campaign. Measurements were made on the 25-meter sample line portion of the system using multiple, well characterized particle sizing instruments to obtain the penetration efficiencies. An agreement of ± 15% was obtained between the measured and the ARP6481 method penetrations for the 25-meter sample line portion of the system. Measurements of VPR penetration efficiency were also made to verify its performance for aviation nvPM number. The research also demonstrated the difficulty of making system loss measurements and substantiates the E-31 decision to predict rather than measure system losses.

Phase-doppler interferometry with probe-to-droplet size ratios less than unity. I. Trajectory errors.

Phase-Doppler interferometry in which a probe volume that is much smaller than the droplets being measured has been shown to work well when coupled with a phase-ratio and intensity-validation scheme that is capable of eliminating trajectory-dependent scattering errors. With ray-tracing and geometric-optics models, the type and magnitude of trajectory errors were demonstrated quantitatively through stochastic trajectory calculations. Measurements with monodispersed water droplet streams and glass beads were performed to validate the model calculations and to characterize the probe volume. Scattered-light intensity has also been shown to provide a robust means of determining the probe cross-sectional area, which is critical for making accurate mass flux measurements.

Phase-Doppler interferometry with probe-to-droplet size ratios less than unity. II. Application of the technique.

Practical limitations associated with the use of small probe volumes with respect to the droplet size that is being measured by the phase-Doppler interferometry technique are discussed. An intensity-validation scheme and corresponding probe volume correction factor have been developed that reject trajectory errors and account for the rejections in calculation of the probe cross-sectional area. The intensity-validation scheme also provides a tractable method of setting the photomultiplier tube gain and laser power. Volume flux measurements in dilute sprays have shown a significant improvement over those made by standard phase-Doppler interferometry techniques at small beam waist/droplet size ratios.

Response characteristics of the phase Doppler particle analyzer for sizing spherical particles larger than the light wavelength.

A theoretical model, based on the geometrical optics approach, has been developed to simulate various aspects of the phase Doppler particle analyzer (PDPA). The model has taken into consideration the nonuniform (Gaussian) illumination of the particles as they pass through the measurement probe volume. Instrument response curves have been generated for various scattering angles by performing spatial and temporal integration of the scattered intensity distribution over the receiver surface. Experimental and theoretical investigations have established the applicability of this instrument to both forward scattered and backscattered angles.

Sizing fine particles with the phase Doppler interferometric technique.

A theoretical model based on the Lorenz-Mie theory was used to study the response characteristics of the Aerometrics phase Doppler particle analyzer (PDPA). The validity of the model was verified experimentally, and its suitability for calculating measurement uncertainties was established. The theoretical and experimental results suggest that size resolutions of the order of +/-0.3 microm are possible when the PDPA is used to measure small spherical particles (< 10 microm). We show that the optical configuration of the PDPA plays an important role in establishing the sizing uncertainty of the instrument.

Method for measuring the size and velocity of spheres by dual-beam light-scatter interferometry.

A method is described for obtaining real-time in situ size and velocity measurements of spherical particles or droplets using crossed-beam interferometry. The optical arrangement, which is similar to a dual-scatter laser Doppler velocimeter (LDV), consists of two laser beams focused to a crossover region. Droplets passing through the focal volume scatter light to the collecting lens situated at some off-axis angle. The dual-beam light scatter is analyzed by the geometric optics theory to relate the scattered fringe pattern to the droplet diameter. Because the droplet size measurement is based on the relative phase shift between the two light waves passing through it, the method is independent of the incident intensity, droplet absorption, or absolute scattering intensity. Experimental measurements of monodisperse droplet streams show good agreement with the theory. The technique can be applied to spray-droplet measurements over the size range of 3 microm to 5 mm. By using large off-axis scatter detection angles, the measurement of the droplet size and velocity distributions in relatively dense spray environments is made possible.