SOOT FORMATION IN LAMINAR DIFFUSION FLAMES SOOT FORMATION IN LAMINAR DIFFUSION FLAMES

Abstract Laminar, sooting, coflow diffusion flames at atmospheric pressure have been studied experimentally and theoretically as a function of fuel dilution by inert nitrogen. The flames have been investigated with laser diagnostics. Laser extinction has been used to calibrate the experimental soot volume fractions and an improved gating method has been implemented in the laser-induced incandescence (LII) measurements resulting in differences to the soot distributions reported previously. Numerical simulations have been based on a fully-coupled solution of the flow conservation equations, gas-phase species conservation equations with complex chemistry, and the dynamical equations for soot spheroid growth. The model also includes the effects of radiation reabsorption through an iterative procedure. An investigation of the computed rates of particle inception, surface growth and oxidation, along with a residence time analysis, helps explain the shift in the peak soot volume fraction from the centerline to the wings of the flame as the fuel fraction increases. The shift arises from changes in the relative importance of inception and surface growth combined with a significant increase in the residence time within the annular soot formation field leading to higher soot volume fractions, as the fuel fraction increases

Fuel additive effects on soot across a suite of laboratory devices, part 2: Nitroalkanes

This is the second in a series of papers to summarize results of the impact of nonmetallic fuel additives on soot. The research was conducted by a university, industry, and government team with the primary objective of obtaining fundamental understanding of the mechanisms through which additive compounds blended into a fuel affect soot emissions. The work involved coordinated testing across a suite of laboratory devices: a shock tube, a well-stirred reactor, a premixed flat flame, an opposed-jet diffusion flame, and a high-pressure turbulent reactor. This article summarizes results on the addition of nitroalkanes to a base fuel consisting of n-heptane and toluene as a simple surrogate for jet fuels. In these experiments, the nitroalkanes serve as chemical probes of key reactions leading to soot. The effects of nitroalkane addition on soot were found to be device and condition dependent with no simple trends across the suite of devices. Copyright © Taylor & Francis Group, LLC

Assessment of a new self-rating scale for post-traumatic stress disorder

Background. In post-traumatic stress disorder (PTSD) there is a need for self-rating scales that are sensitive to treatment effects and have been tested in a broad range of trauma survivors. Separate measures of frequency and severity may also provide an advantage. Methods. Three hundred and fifty-three men and women completed the Davidson Trauma Scale (DTS), a 17-item scale measuring each DSM-IV symptom of PTSD on 5-point frequency and severity scales. These subjects comprised war veterans, survivors of rape or hurricane and a mixed trauma group participating in a clinical trial. Other scales were included as validity checks as follows: Global ratings, SCL-90-R, Eysenck Scale, Impact of Event Scale and Structured Clinical Interview for DSM-III-R. Results. The scale demonstrated good test–retest reliability (r = 0·86), internal consistency (r = 0·99). One main factor emerged for severity and a smaller one for intrusion. In PTSD diagnosed subjects, and the factor structure more closely resembled the traditional grouping of symptoms. Concurrent validity was obtained against the SCID, with a diagnostic accuracy of 83% at a DTS score of 40. Good convergent and divergent validity was obtained. The DTS showed predictive validity against response to treatment, as well as being sensitive to treatment effects. Conclusions. The DTS showed good reliability and validity, and offers promised as a scale which is particularly suited to assessing symptom severity, treatment outcome and in screening for the likely diagnosis of PTSD