Bakker, P.C.

Dam, N.J.

Willems, R.C.

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Fate of Forgotten Fuel High-Speed Laser-Induced Incandescence GRC Laser Diagnostics in Combustion [1] L.A. Melton. Soot diagnostics based on laser heating. Applied Optics, Vol. 23, No. 13, 1984.   / Combustion Technology Photo-acoustic soot measurements o Photo-acoustic measurements to determine soot volume fraction. o The LII signal deviates from a proportionality with the soot volume fraction 𝑁𝑝𝑑𝑝3 [1]. The PA signal has no deviation. o Comparing the LII and PA signal potentially yields information about the local soot particle size (Figure 4) . Figure 3: First 25 shots normalized to the last laser pulse as a function of  three fluences. At low fluence the effect of local gas heating is evident, as the signal increases in intensity. For the high fluence case, sublimation is the dominant effect and the signal decreases in a step-wise fashion.  Experiment setup                    Figure 1: Experiment setup used for both feasibility measurements (candle flame) and photo-acoustic measurement (co-flow burner). HS-LII feasibility o High-speed (5kHz) measurements to study the behavior of the LII signal during the first 25 laser pulses (Figure 3). o Two dominant effects: local gas heating and sublimation. o Technique is feasible for fluences < 0.1 J/cm2. Figure 2: Incandescence of the flame over time. The laser has been shut down at t = 0.0 ms. The natural convection in the flame transports fresh soot particles upwards. Figure 4: LII as a function of PA signal, both normalized to their value at 45 mm HAB. The deviation from the line LII = PA indicates that particles grow with HAB. Background The aim of this project is to first test the feasibility of the HS-LII technique and  explore some of its possibilities. The final goal is to perform HS-LII measurements on an optical Diesel engines to study the late phase of the combustion process. This information can be used to further improve the efficiency of a Diesel engine. Convection speed o Soot is destroyed using a focussed laser beam, after which the laser is shut down and the incandescence is recorded (Figure 2). o Estimated convection speed of 65 cm/s, which corresponds to 25 laser pulses heating the same soot particles. Robbert Willems     (r.c.willems@student.tue.nl) Peter-Christian Bakker    (p.c.bakker@tue.nl) Nico Dam      (n.j.dam@tue.nl) 

Fate of forgotten fuel - high-speed laser-induced incandescence

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