Soot Evolution With Cyclic Crank-Angle-Resolved Two-Color Thermometry in an Optical Diesel Engine Fueled With Biodiesel Blend and ULSD

Abstract

Biodiesel is a desirable alternative fuel for the diesel engine due to its low engine-out soot emission tendency. When blended with petroleum-based diesel fuels, soot emissions generally decrease in proportion to the volume fraction of biodiesel in the mixture. While comparisons of engine-out soot measurements between biodiesel blends and petroleumbased diesel have been widely reported, in-cylinder soot evolution has not been experimentally explored to the same extent. To elucidate the soot emission reduction mechanism of biodiesel, a single-cylinder optically-accessible diesel engine was used to compare the in-cylinder soot evolution when fueled with ultra-low sulfur diesel (ULSD) to that using a B20 biodiesel blend (20% vol.lvol. biodiesel ASTM D6751-03A). Soot temperature and KL factors are simultaneously determined using a novel two-color optical thermometry technique implemented with a high-speed CMOS color camera having wide-band Bayer filters. The crank-angle resolved data allows quantitative comparison of the rate of in-cylinder soot formation. High-speed spray images show that B20 has more splashing during spray wall impingement than ULSD, distributing rebounding fuel droplets over a thicker annular ring interior to the piston bowl periphery. The subsequent soot luminescence is observed by high-speed combustion imaging and soot temperature and KL factor measurements. B20 forms soot both at low KL magnitudes over large areas between fuel jets, and at high values among remnants of the fuel spray, along its axis and away from the bowl edge. In contrast, ULSD soot luminescence is observed exclusively as pool burning on the piston bowl surfaces resulting from spray wall impingement. The soot KL factor evolution during B20 combustion indicates earlier and significantly greater soot formation than with ULSD. B20 combustion is also observed to have a greater soot oxidation rate, which results in lower late-cycle soot emissions. For both fuels, higher fuel injection pressure led to lower late-cycle soot KL levels. The apparent rate of heat release (ARHR) analysis under steady skip-fire conditions indicates that B20 combustion is less sensitive to wall temperature than that observed with ULSD due to a lesser degree of pool burning. B20 was found to have both a shorter ignition delay and shorter combustion duration than ULSD.

Characteristics of turbulent n-heptane jet flames in a hot and diluted coflow

“…scale=0.8 soot temperature and soot KL factor could therefore be potentially attributed to the occurrence of enhanced soot oxidation in the low soot temperature and KL zones, leaving the average temperature and soot KL factor to be dominated by the soot signal from the local high temperature and soot concentration regions [29]. Focusing on quasi-steady periods for the flames, prior to the end of injection, it can be seen that a decrease in the ambient O 2 condition did not appear to significantly impact on the average soot temperature and soot KL factor values of the flames, until it was reduced to 10 vol.% O 2 .…”

Spray and Combustion Investigation of Post Injections under Low-Temperature Combustion Conditions with Biodiesel

“…A novel color band approach, which was first introduced by Larsson 30 and further expanded upon by Svensson et al 31 was implemented to provide soot temperature and soot KL (a factor that is proportional to the soot volume fraction and gas layer thickness 31,32 ) information.…”

“…Following the approach of Zha et al, 32 to reduce the computational time during image processing, two universal surfaces ( Fig. 5) that map the domains of the red and green pixel intensities to soot temperature and KL surfaces, were generated.…”

Suppression of soot of a diesel engine fueled with biodiesel–diesel blends

“…Zha et al . performed in‐cylinder soot evolution studies in an optical diesel engine fueled with B20 biodiesel blend and ultra‐low sulfur diesel. It was observed that B20 had more splashing during spray wall impingement and shorter ignition delay and combustion duration than diesel.…”

“…It was reported that the presence of methyl or ethyl functional group resulted in reducing the sooting propensity compared to n-alkanes, caused by both thermal and kinetic mechanisms. Zha et al [17] performed in-cylinder soot evolution studies in an optical diesel engine fueled with B20 biodiesel blend and ultra-low sulfur diesel. It was observed that B20 had more splashing during spray wall impingement and shorter ignition delay and combustion duration than diesel.…”