1 Heat transfer to a single plastic resin particle – Experimental investigations by flames and laser pulses

Heat transfer is of crucial importance to understand the conversion kinetics and the behavior during combustion of fuels such as plastics particles. In this work, the heat transfer onto single plastic resin particles (5x7 mm) by flames and a pulsed laser was studied by recording time resolved series of images with a high speed CCD (charge coupled device) camera. Images in the visible spectrum were recorded with a time resolution between 1 ms and 25 ms for a total duration of up to 60 s. A pulsed Nd:YAG laser was used in this study. For comparison, also a McKenna flat flame burner and a Bunsen burner operating on fuel-rich to fuel-lean CH4/air mixtures were used. The plastic resin particles were drilled and mounted horizontally on a thin wire. In the middle of the particle under investigation, a thermocouple was placed. For the experiments with the laser, the particle was suspended in room air (illuminated area 2 mm2, pulse duration 10 ms, pulse energy 5-30 J, laser wavelength 1064 nm). For the experiments in the flames, the particle was placed in different areas of the flame in a temperature range between 670 and 1470 K. A laser pulse energy of 5 J was found necessary to ignite the particles. At pulse energies of 30 J strong ablation was noticed. The mass loss was 0.6 mg (at 5 J) to 3.1 mg (at 30 J). The ablated material did not burn completely, but left a cloud of soot behind. In the laser experiments, only a small temperature rise of approx. 10 K was measured inside the particle. The laser-induced flame could not be sustained, it extinguished again after 5-20 s. The mass loss was determined after 10 consecutive laser shots. The plastic particles suspended in the flames took considerably longer to react. Only after approx. 10 s of heat transfer, a flame could be seen. The full process was studied. The effects of particle swelling, volatilization and char combustion were studied in the flames. (Fast) combustion of gaseous material, stemming from ablation and volatilization, could be discerned from (slow) combustion of the solid particle. The composition of the plastic resin particles was found to have a strong influence on the heat transfer. ∗ Corresponding author: [email protected] Proceedings of the European Combustion Meeting 2007