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We present a method based on Tikhonov regularization for solving one-dimensional inverse tomography problems that arise in combustion applications. In this technique, Tikhonov regularization transforms the ill-conditioned set of equations generated by onion-peeling deconvolution into a well-conditioned set that is less susceptible to measurement errors that arise in experimental settings. The performance of this method is compared to that of onion-peeling and Abel three-point deconvolution by solving for a known field variable distribution from projected data contaminated with an artificially generated error. The results show that Tikhonov deconvolution provides a more accurate field distribution than onion-peeling and Abel three-point deconvolution and is more stable than the other two methods as the distance between projected data points decreases. OCIS codes: 120.7000, 280.1740, 280.2470, 120.1740.

A new regulatory standard for non-volatile particulate matter (nvPM) mass concentration emissions from aircraft engines has been adopted by the International Civil Aviation Organisation. One of the instruments used for the regulatory nvPM mass emissions measurements in aircraft engine certification tests is the Artium Technologies LII 300, which is based on laser-induced incandescence. The LII 300 has been shown in some cases to demonstrate a variation in response to the type of black carbon particle measured. Hence it is important to identify a suitable black carbon emission source for instrument calibration. In this study, the relationship between the nvPM emissions produced by different engine sources and the response of the LII 300 instrument utilising auto-compensating laser-induced incandescence (AC-LII) method was investigated. Six different sources were used, including a turboshaft helicopter engine, a diesel generator, an intermediate pressure test rig of a single sector combustor, an auxiliary power unit gas turbine engine, a medium-sized diesel engine, and a downsized turbocharged direct injection gasoline engine. Optimum LII 300 laser fluence levels were determined for each source and operating condition evaluated. It was found that an optimised laser fluence can be valid for real-time measurements from a variety of sources, where the mass concentration was independent of laser fluence levels covering the typical operating ranges for the various sources. However, it is important to perform laser fluence sweeps to determine the optimum fluence range, as differences were observed in the laser fluence required, between sources and fuels. We discuss the measurement merits, variability, and best practices in the real-time quantification of nvPM mass concentration using the LII 300 instrument, and compare that with other diagnostic techniques, namely absorption-based methods such as photoacoustic spectroscopy using a photoacoustic extinctiometer (PAX) and a Micro Soot Sensor (MSS), and thermal-optical analysis (TOA). Particle size distributions were also measured using a scanning mobility particle sizer (SMPS). Overall, the LII 300 provides robust and consistent results when compared with the other diagnostic techniques across multiple engine sources and fuels. The results from this study will inform the development of updated calibration protocols to ensure repeatable and reproducible measurements of nvPM mass emissions from aircraft engines using the LII 300. [ABSTRACT FROM AUTHOR]

Comprehensive characterization of crumpled graphene materials is required to understand their morphologically dependent properties. This study connects the optical properties of crumpled few-layer graphene (FLG) aerosols and colloidal suspensions with particle morphology. The mass absorption cross-section (MAC) of crumpled FLG was measured in the aerosol phase and it is shown that such aerosols absorb visible light more efficiently than soot aerosols. The UV–Vis spectra of FLG suspensions in ethanol were correlated with the mean nanoparticle layer number and the lateral size. The measured optical properties were also simulated using discrete dipole approximation (DDA) applied to volume-reconstructed particles with refractive indices of graphene and graphite from literature. The measurements were more closely reproduced using the refractive index of graphite pellets rather than flat graphene on a substrate. Moreover, we show that a simpler Rayleigh–Debye–Gans (RDG) model can predict the wavelength dependence of the crumpled FLG absorption cross-section. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Laminar nonpremixed methane–air flames were studied over the pressure range of 0.5 to 4 MPa using a new high-pressure combustion chamber. Flame characterization showed very good flame stability over the range of pressures, with a flame tip rms flicker of less than 1% in flame height. At all pressures, soot was completely oxidized within the visible flame. Spectral soot emission (SSE) and line-of-sight attenuation (LOSA) measurements provided radially resolved measurements of soot volume fraction and soot temperature at pressures from 0.5 to 4.0 MPa. Such measurements provide an improved understanding of the influence of pressure on soot formation and have not been reported previously in laminar nonpremixed flames for pressures above 0.4 MPa. SSE and LOSA soot concentration values typically agree to within 30% and both methods exhibit similar trends in the spatial distribution of soot concentration. Maximum soot concentration depended on pressure according to a power law, where the exponent on pressure is about 2 for the range of pressures between 0.5 and 2.0 MPa, and about 1.2 for 2.0 to 4.0 MPa. Peak carbon conversion to soot also followed a power-law dependence on pressure, where the pressure exponent is unity for pressures between 0.5 and 2.0 MPa and 0.1 for 2.0 to 4.0 MPa. The pressure dependence of sooting propensity diminished at pressures above 2.0 MPa. Soot concentrations measured in this work, when transformed to line-integrated values, are consistent with the measurements of Flower and Bowman for pressures up to 1.0 MPa [Proc. Combust Inst. 21 (1986) 1115–1124] and Lee and Na for pressures up to 0.4 MPa [JSME Int. J. Ser. B 43 (2000) 550–555]. Soot temperature measurements indicate that the overall temperatures decrease with increasing pressure; however, the differences diminish with increasing height in the flame. Low down in the flame, temperatures are about 150 K lower at pressures of 4.0 MPa than those at 0.5 MPa. In the upper half of the flame the differences reduce to 50 K. [Copyright &y& Elsevier]