Visualization of soot formation from evaporating fuel films by laser-induced fluorescence and incandescence

Abstract

Late-evaporating liquid fuel wall films are considered a major source of soot in gasoline directinjection engines. In this study, a direct-injection model experiment was developed to visualize soot formation in the vicinity of evaporating fuel films. Isooctane is injected by a multi-hole injector into a wind tunnel with an optically accessible test section. Air flows continuously at low speed and ambient pressure through the test section. Some of the liquid fuel impinges on the quartz-glass windows and forms fuel films. After spark ignition, a turbulent flame front propagates through the chamber and ignites pool fires near the fuel films, leading to locally sooting combustion. A laser light sheet with a wavelength 532 nm excites laser-induced fluorescence (LIF) of large polycyclic aromatic hydrocarbons (PAH) with five or more aromatic rings, considered as soot precursors, near the evaporating fuel films. Additionally, a light sheet at 1064 nm excites laser-induced incandescence (LII) of soot particles. Two intensified CCD cameras simultaneously detect the LII and LIF signals, and thus visualize PAH and soot. In complementary line-of-sight imaging, the fuel spray, chemiluminescence of the flame, and soot incandescence are captured with a high-speed color camera. In addition to this fuel-injection experiment, a sooting laminar coflow flame burning ethylene in air (Santoro burner) is used for preliminary in-situ measurements. In the latter, PAH LIF is detected in a hollow cone region, indicating the transition from fuel to small PAH in the dark region and the growth of the latter into large PAH in the cone region. The edges of the PAH LIF cone are covered by regions of high soot LII signal, indicating the nucleation region where soot forms from PAH. In the wind tunnel, layers of PAH are found in the close vicinity of the evaporating fuel films. Soot forms mostly spatially separated from the PAH and with high spatial intermittency. The chemiluminescence in the bottom of the images indicates the oxidation of soot and PAH, being transported downstream.

Experimental study of the effect of CO2 on temperature and soot volume fraction in C2H4/air co-flow laminar diffusion flame

“…The accurate measurements on soot volume fraction and ame temperature play a remarkable role in depth revealing the impact of CO 2 on soot formation. The laser spectrum detection has been employed in the combustion diagnosis, the high precision measurements of soot volume fraction can be achieved via the light extinction (LE) technology, [23][24][25] and laserinduced uorescence (LIF) technology. [23][24][25] The soot volume fraction in the C 2 H 4 counterow diffusion ame was calculated by Wang et al 26 employing the LE technology.…”

“…The laser spectrum detection has been employed in the combustion diagnosis, the high precision measurements of soot volume fraction can be achieved via the light extinction (LE) technology, [23][24][25] and laserinduced uorescence (LIF) technology. [23][24][25] The soot volume fraction in the C 2 H 4 counterow diffusion ame was calculated by Wang et al 26 employing the LE technology. The experimental studies proved that the decrease of soot volume fraction was 25.2% with 20% CO 2 -F. M. Sirignano et al 27 revealed that the decrease in soot volume fraction was 65% with the CO 2 -O using the LIF technology.…”

Evaporation of Fuel Film formed by an Impinging GDI Spray on a Hot Wall with High Surface Roughness

“…Kollpe, et al [6] had measured piston surface temperature in a GDI engine using a thinfilm thermocouple embedded piston. Furthermore, they investigated the influence of various parameters such as injection pressure and injection timing on detail temperature history of piston top.…”