Time-resolved spray, flame, soot quantitative measurement fueling n-butanol and soybean biodiesel in a constant volume chamber under various ambient temperatures

The spray, flame natural luminosity and soot quantitative measurement by fueling n-butanol and soybean biodiesel were investigated on a constant volume chamber using multi laser diagnostics with high temporal resolution of 15,037 frames per second. The ambient temperature ranged from 700 K to 1000 K was applied to mimic the diesel in-cylinder environment covering both conventional and low temperature combustion conditions. Results demonstrate that the transient liquid penetration lengths gradually decrease with the development of injection in a burning spray. The transient liquid penetration length of n-butanol is less affected by the downstream flame and is shorter than that of biodiesel under similar conditions. The two fuels also present drastically different flame dynamics and emission characteristics during the combustion process. n-Butanol displays higher normalized combustion pressure indicating higher potential thermal efficiency. The flame can be observed at reacting spray jet and near wall region for biodiesel, while the main n-butanol flame is concentrated on reacting spray jet. Compared to biodiesel, the flame luminosity of n-butanol is lower and its propagation and distribution is less sensitive to ambient temperatures. Ambient temperature is confirmed as the dominant impact on the soot emissions as the net soot increases for both tested fuels with elevated ambient temperature. No soot emission is detected for either n-butanol or biodiesel at low ambient temperature of 700 K. The soot starts to appear at both downstream of the jet and near wall regions from 800 K for biodiesel whereas the soot do not emerge until 900 K for n-butanol. The soot concentration of n-butanol is also much lower and restricted within the downstream of the spray jet even at high ambient temperatures. A particular interesting observation is that the normalized time integrated soot mass for B50D50 (50% n-butanol and 50% low-sulfur diesel fuel in volume) is 20-30% lower than that of neat biodiesel fuel at different ambient temperatures even though the oxygen content in both fuels is nearly the same. The higher soot formation for biodiesel is explained by the fact that fuel-bound oxygen is less effective in reducing soot production and that higher viscosity and boiling point results in more local high equivalence-ratio region in mixing process. In this regard, n-butanol is more effective in suppressing the soot formation and shows stronger soot reduction capability than that of biodiesel.