Thermocouple temperature measurements in diesel spray flame for validation of in-flame soot formation dynamics

Abstract

It is well known that the soot formation is governed by equivalence ratio and temperature. However, there are only few examples of temperature measurements in the soot formation region of diesel spray flame, which has been impeding better understanding and model validation. In this study, the time histories of temperature at different axial locations in a single-shot diesel spray flame were measured in a constant volume vessel using a 50-mm-thin wire type R thermocouple and used to demonstrate their usefulness for the model validation of in-flame soot formation dynamics. The measured temperature was (1) compared and cross-checked with two-color temperatures of diesel flame periphery and core, (2) compared with predicted temperature from large eddy simulation of the diesel flame for validation and (3) contrasted with previous laser spectroscopic measurements of soot precursors (polycyclic aromatic hydrocarbons) in diesel spray flame and predicted soot processes from the large eddy simulation of diesel spray flame employing detailed chemical kinetics. The measured steady-state temperature increased from upstream to downstream in diesel spray flame corresponding to the progress of mixing and combustion. The measured temporal histories of temperature exhibited notable increase after the end of injection duration considered due to entrainment of ambient gases and resulting heat release in the wake of the injection pulse. The thermocouple-measured ''core'' temperatures and two-color ''peripheral'' temperatures of diesel flame were significantly different as up to 700 K in the upstream and gradually converged to around 2000 K in the downstream. The thermocouple-measured and large eddy simulation-predicted temperature histories showed similar general trends; however, 500 K as significant discrepancy was observed between the measured and predicted temperatures of the polycyclic aromatic hydrocarbon onset locations in diesel spray flame, suspected partially due to deficiency in the current polycyclic aromatic hydrocarbon formation model employed in the simulation.

Soot temperature characterization of spray a flames by combined extinction and radiation methodology

“…The temperature gradient is quite big at upstream locations, where the temperature increases from spray axis to the flame periphery, while the temperature distribution becomes more uniform when moving downstream. It is consistent with Aizawa et al's research [34], where they measured the in-flame temperature at different location by means of a thermocouple.…”

Experimental Investigation of Heat Transfer in a Flat-wall Impinging Diesel Spray Flame under Diesel-like Conditions

“…The high ambient temperature, on the other hand, greatly reduced the liquid phase concentration in the evaporating spray in Figure 3(b), which encouraged spray atomization and the combination of air and fuel. The author has already addressed the additional discussion on mixture formation under non-evaporation and evaporation in a previous paper [27]. The amount of liquid spray is represented by the white color's intensity.…”

Infrared high-speed thermography of combustion chamber wall impinged by diesel spray flame

“…A comparison of the flame luminosity images among different injection pressures in Figure 4 shows shorter existence and higher brightness of the flame luminosity at higher injection pressures, indicating shorter flame-to-wall contact duration and higher flame temperature. The temperature of the combusting diesel spray is considered not to exceed 1500 K at the stagnation point on the wall during the flame impingement except at the first contact between the flame tip and the wall, referring to the thermocouple temperature measurements of diesel spray flame core at a similar experimental condition by Aizawa et al 47 It should also be noted that 2-D temperature measurements of wall-impinging flame within the ϕ35 mm front view images for example via 2-color method would be useful for better understanding of the wall heat transfer. However, suppressed luminosity signal from the cooled flame contacting the wall biased by strong luminosity signal from the hot flame behind is suspected to complicate the interpretation of the signal intensity and degrade the measurement accuracy.…”