RUI: Indirect Measurement of Reaction Rates in Laminar Flames

California State L A University Auxiliary Services Inc., Los Angeles CA

Investigators

Abstract

Chemical reaction rates that are relevant to combustion chemistry are typically determined using theoretical computations or direct experiments. As with all experiments, these have limitations. In one commonly used setup (rapid compression machine), measurements are performed at conditions relevant to ignition in engines – intermediate temperatures and high pressures. In the other most commonly used device (shock tube), measurements can access a higher temperature, however they are typically limited to very low reactant concentrations. We will indirectly determine reaction rates at conditions that are inaccessible to these devices by using a flame. This measurement will occur at higher temperatures than the rapid compression machine and higher reactant concentration than the shock tube. Reaction rates that are relevant to combustion chemistry are typically determined using theoretical computations or direct experiments. As with all experiments, these experiments, such as shock tube (ST) and rapid compression machine (RCM) measurements, have limitations. RCM measurements are valuable at conditions relevant to ignition in engines – intermediate temperatures and high pressures. ST measurements can access a higher temperature, however they are typically limited to low reactant concentrations, and a radical pool that is not representative of flame chemistry. We propose a new experimental campaign to measure the laminar flame speed using a mesoscale diverging channel at mixture conditions where this quantity is sensitive to targeted elementary reaction rates. We will then use those flame speed measurements to improve characterization of the targeted reaction rates. This represents indirect experimental measurements of reaction rates using flame speed, an uncommon method to extract reaction rates that we have successfully demonstrated in previous work. Using an in-house, open-source software package, we have determined that the laminar flame speed for rich ethylene flames at atmospheric pressure is sensitive to three reactions. We are currently constructing an atmospheric pressure diverging meso-scale channel, and the proposed project would fund validation of laminar flame speed measurement in this channel at well-quantified conditions, as well as rich ethylene flames the mentioned reactions. We will then use the measurements as validation and optimization targets to improve characterization of these three reaction rates at temperatures where there are limited experimental measurements in the literature. If successful, this project will lead to future experimental campaigns targeting other reactions by measuring laminar flame speed. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.