Effects of Flame Temperature on PAHs and Soot Evolution in Partially Premixed and Diffusion Flames of a Diesel Surrogate

Abstract

In this paper, polycyclic aromatic hydrocarbons (PAHs) and soot formation in rich partially premixed flames and nonpremixed flames were studied using a blend of n-heptane and toluene. The flames were diluted with Ar, N 2 , and CO 2 to control the flame temperature. Laser-induced fluorescence, laser-induced incandescence, and two-color pyrometry were used to study the effects of flame temperature on the PAHs and soot evolution. Results show that temperature distributions are similar for different gas dilutions at low flow rates. However, the high-temperature area increases dramatically in size at high flow rates and it depends on diluents in the order Ar > N 2 > CO 2 with regard to flame temperature. With an increase in the flow rate of Ar, the higher growth rate of flame temperature and bigger region of high-temperature region can lead to a higher growth rate from small to large PAHs and higher soot volume fraction. However, for CO 2 dilution, the increased flow rate results in the increase of formation of large PAHs, but soot formation is reduced due to the fact that lower flame temperature suppresses the soot formation. Therefore, it can be concluded that the evolution of PAHs and soot strongly depends on flame temperature.

Macrostructure and NOx emission evolution characteristics of lean‐premixed flames under combustion instability

“…The emissions of soot were very tiny under lean‐premixed combustion. But it should be noted that tiny soot will deposit on the thermocouple, increase its emissivity, and therefore increase the radiation correction 45 . The flame has inverted V shape temperature distribution in the combustion chamber along radial direction; the temperature drops from the 30‐mm level to the 90‐mm level.…”

“…43,44 The flame temperature is one of the main factors affecting soot formation. For better understanding the soot evolution with fuel under different flame temperatures, Liu et al 45,46 studied the surrogate of diesel fuel consisting of the blends of n-heptane and toluene. To get the different flame temperatures, different heat-capacity dilution gases of Ar (low heat capacity), N 2 , and CO 2 (high heat capacity) were added into the premixed fuel−air system and formed fuel-rich partially premixed flames and diffusion flames.…”

Production of Carbon Black in Turbulent Spray Flames of Coal Tar Distillates

“…Temperature readings are recorded at 100 Hz to capture the flame temperature before the measurement is disrupted by soot deposits on the thermocouple bead. The current conditions are chosen to minimize temperature measurement challenges, previously reported in heavier sooting flames [22,23].…”

Mitigating combustion instability and NOx emissions with annular oxyfuel jets into the flame shear layer region

“…Last but not least, the flame temperature is one of the main factors affecting flame soot formation, 50 which will be changed under gas dilution 51 . For better understanding the soot evolution with fuel under different flame temperatures, Liu et al 52–54 studied the surrogate of diesel fuel consisting of the blends of n ‐heptane and toluene. To get the different flame temperatures, different heat‐capacity dilution gases of Ar (low heat capacity), N 2 and CO 2 (high heat capacity) were added into the premixed fuel–air system and formed fuel‐rich partially premixed flames and diffusion flames.…”