Ignition rate measurement of laser-ignited coals. Quarterly technical progress report, July 1, 1995--September 30, 1995

Over the last several decades many experiments have been conceived to study the ignition of pulverized coal and other solid fuels. We are constructing a laser-based apparatus which offers several advantages over those currently favor. Sieve-sized particles are dropped batch-wise into a laminar, upward-flow wind tunnel which is constructed with a quartz test section. The gas stream is not preheated. A single pulse from a Nd:YAG laser is focused through the tunnel and ignites several particles. The transparent test section and cool walls allow for application of two-color pyrometry to measure the particles` temperature history during ignition and combustion. Coals ranging in rank from lignites to low-volatile bituminous, and chars derived from these Coals, will be studied in this project. For each fuel type, measurements of the ignition temperature under various experimental conditions (particle size and free-stream oxygen concentration), combined with a detailed analysis of the ignition process, will permit the determination of kinetic rate constants of ignition. This technique offers many advantages over conventional drop-tube furnace experiments. One is the ability to directly measure ignition temperature rather than inferring it from measurements of the minimum gas temperature needed to induce ignition. Another advantage is the high heating rates achievable - on the order of 10{sub 6} K/s. This is a significant improvement over experiments which rely on convective heating from a hot gas, which typically achieves heating rates of 10{sup 4}K/s. The higher heating rate more closely simulates conditions in conventional coal combustors used for power generation