Phase-locked absorption tomography for retrieving 5 kHz time-resolved tracer profiles in solid fuel combustion

Turbulent mixing processes and species transport govern many important properties like stability and pollutant formation of reactive systems. We propose spectrally resolved absorption tomography as a viable tool to quantitatively assess species transport by imaging tracer pulses at high time resolution. Measurements on a gas-assisted solid-fuel combustor operating in air and oxy-fuel atmospheres are presented. The measurements are conducted using a scanning tomographic imaging system that has previously been validated for gas temperature measurements. As the scanning system itself is not able to achieve the necessary time resolution, a phase-locked tomographic scheme is applied, i.e. each measurement beam is acquired separately for several tracer pulses and phase-averaged. Hence, the full 5 kHz time resolution of the underlying tunable diode laser spectroscopy system can be utilized, granting insight into species transport in the recirculation zones as well as the flame brush. Despite a possible influence of the tracer injections on the inner recirculation zone, it is shown that qualitative differences between methane combustion and gas-assisted solid-fuel operating conditions can be detected, and influences of devolatilization as well as volatile combustion become visible