Measurement and analysis of the dimensionless extinction constant for diesel and biodiesel soot: Influence of pressure, wavelength and fuel-type.

摘要

The dimensionless extinction constant of soot is an important parameter that is used for the measurement of soot concentration, soot temperature and radiative properties of soot-containing environments. In this dissertation, the dimensionless extinction constants, Ke of soot produced from a small laminar flame burning ultra low sulfur diesel (ULSD) and soy methyl ester (B100) biodiesel fuel were measured under a variety of operating conditions in which the pressure was varied from 1 atm to 5 atm. Experiments were also performed using visible light source (He-Ne laser) at 632.8 nm and in the infrared spectrum using a solid-state diode laser at 1064 nm. Experiments were performed using a Transmission Cell Reciprocal Nephelometer (TCRN) in which simultaneous gravimetric sampling and light extinction techniques (GSLE) were employed.;The GSLE technique and apparatus were significantly improved for this investigation to provide accurate values of Ke for both diesel and biodiesel soot. The improvements included the design of a high pressure combustion chamber and a diffusion flame burner for high soot yield, analysis and experimental modifications to reduce the influence of soot deposition, detailed calibration of the mass, soot sampling, and light extinction measurements to reduce uncertainties in the measurement of Ke.;The measurements of the Ke values for diesel and biodiesel soot ranged from 9.4 to 12.8.;These values are significantly higher than the traditional value of Ke equal to 4.9 (used in many previous light extinction soot experiments) that is calculated using refractive index and the Rayleigh limit solution. The use of the traditional value can introduce significant errors (over-predicting soot volume fraction by a factor of two or more) in the soot concentration measurements. The Ke values measured in this dissertation can be used for accurate analysis of experimental measurements of light extinction for soot volume fraction, temperature and soot volume fraction measurements using two-wavelength pyrometry and soot concentration and distribution using laser-induced incandescence methods.;The variation in the measured Ke values was influenced by fuel-type, wavelength and operating pressure. Additional analysis of the physical and fractal properties of the soot, which can influence the scattering component and beam shielding effects on the dimensionless extinction constant, was performed. These measurements included the primary particle size, radius of gyration of the agglomerate, and fractal dimensions employing non-subjective image processing of electron micrographs. The nanostructure of the particles (including fringe length and tortuosity of the carbon lamella), which can influence the absorption component of the dimensionless extinction constant, was analyzed using high resolution transmission electron microscopy.