Abstract
•Spray combustion of diesel-gasoline blend was tested in constant volume combustion chamber.•Multiband flame emission was measured for different ambient conditions.•Flames of the two fuels become shorter, thinner and stronger with increased ambient oxygen concentration and temperature.•Experimental observations were analyzed by an empirical model.
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: 800K, 1000K and 1200K. An intensified CCD camera coupled with bandpass filters was employed to capture the quasi-steady state flame emissions at 430nm and 470nm bands. Under non-sooting conditions, the narrow-band flame emissions at 430nm and 470nm can be used as indicators of CH∗ (methylidyne) and HCHO∗ (formaldehyde), respectively. The lift-off length was measured by imaging the OH∗ chemiluminescence at 310nm. 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 430nm and 470nm narrow-band emissions. At a lower ambient temperature the average intensity increases with increasing ambient oxygen concentration. However, at the 1200K 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 430nm band, and similar phenomena can be observed for the 470nm band with 800K and 1200K ambient temperatures. However, for the 1000K ambient temperature cases, dieseline has stronger average flame emission intensities than diesel for all oxygen concentrations at 470nm 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.