Z. Wu, W. Jing, W. Zhang, W. L. Roberts, T. Fang
Fuel
185, pp. 829-846, (2016)
In this paper, spray combustion of diesel (No. 2) and diesel-gasoline
blend (dieseline: 80% diesel and 20% gasoline by volume) were
investigated in an optically accessible constant volume combustion
chamber. Effects of ambient conditions on flame emissions were studied.
Ambient oxygen concentration was varied from 12% to 21% and three
ambient temperatures were selected: 800 K, 1000 K and 1200 K. An
intensified CCD camera coupled with bandpass filters was employed to
capture the quasi-steady state flame emissions at 430 nm and 470 nm
bands. Under non-sooting conditions, the narrow-band flame emissions at
430 nm and 470 nm can be used as indicators of CH∗ (methylidyne) and HCHO∗ (formaldehyde), respectively. The lift-off length was measured by imaging the OH∗
chemiluminescence at 310 nm. Flame emission structure and intensity
distribution were compared between dieseline and diesel at wavelength
bands. Flame emission images show that both narrow band emissions become
shorter, thinner and stronger with higher oxygen concentration and
higher ambient temperature for both fuels. Areas of weak intensity are
observed at the flame periphery and the upstream for both fuels under
all ambient conditions. Average flame emission intensity and area were
calculated for 430 nm and 470 nm narrow-band emissions. At a lower
ambient temperature the average intensity increases with increasing
ambient oxygen concentration. However, at the 1200 K ambient temperature
condition, the average intensity is not increasing monotonically for
both fuels. For most of the conditions, diesel has a stronger average
flame emission intensity than dieseline for the 430 nm band, and similar
phenomena can be observed for the 470 nm band with 800 K and 1200 K
ambient temperatures. However, for the 1000 K ambient temperature cases,
dieseline has stronger average flame emission intensities than diesel
for all oxygen concentrations at 470 nm band. Flame emissions for the
two bands have a smaller average emission area under higher ambient
oxygen concentration and temperature for both fuels, while dieseline has
a slightly larger average flame emission area than diesel for most
cases. The experimental findings were further analyzed and discussed
based on an empirical model of the distributions of air and fuel. Both
experiment results and theoretical model show that dieseline has wider
430 nm and 470 nm band emissions than diesel under all conditions.