Numerous investigations have been conducted to determine the effect of fuel composition and molecular structure on particulate emissions using exhaust gas analysis, but relatively few measurements have been obtained in-cylinder or under conditions where fuel effects can be isolated from other variables. In this work, dimethoxymethane was used as the base fuel to produce a non-sooting flame in a constant volume combustion vessel at 1000 K, and a density of 16.6 kg/m3. A second fuel was then added incrementally to determine an incipient soot limit. Line-of-sight extinction measurements were used as the primary diagnostic tool to determine if a correlation exists between soot and fuel properties. These data indicate that fuels with carbon double bonds are more prone to soot than the single bonded fuels. Each of the four pure additives tested began to soot at a structure-weighted available oxygen-to-carbon ratio near one. The commonly used two-color method for measuring temperature and soot concentration (KL) was used as a secondary method. A method for calibrating and analyzing the uncertainty of the temperature and KL measurements with a single color RGB digital camera was demonstrated. Images of reacting jets of different soot concentrations are shown along with an uncertainty analysis. The resulting temperature and KL maps show uneven distributions for flames of various fuels. Analysis shows that the temperature and KL values of heavily sooting fuels are primarily a result of conditions (temperature and soot concentration) within a 1—2 mm region on the surface of the jet, where a turbulent diffusion flame is present. As soot concentration decreases, the region of influence affecting the result thickens, allowing more influence from within the jet, lowering the measured temperature. Therefore, a low-sooting jet appears to have a lower temperature than a high-sooting jet. Extinction and two-color soot measurement results were compared. The two-color KL values were seen to level off at around 0.5, but continue to increase monotonically as soot increased. The broad band method is therefore not good for absolute soot measurements. Natural luminosity measurements were sensitive to the first appearance of soot, but were non-linear.
College and Department
Ira A. Fulton College of Engineering and Technology; Mechanical Engineering
BYU ScholarsArchive Citation
Svensson, Kenth Ingemar, "Effects of Fuel Molecular Structure and Composition on Soot Formation in Direct-Injection Spray Flames" (2005). All Theses and Dissertations. 319.
combustion, soot, diesel, fuel structure, fuel composition