Doctor of Philosophy (PhD)
Department of Mechanical & Industrial Engineering
Conventional fuel testing device-CFR engine requires large quantities of fuels, which makes it unsuitable for research of small samples of fuels. This current study seeks to address this limitation by using an externally heated microcombustor as an alternative fuel testing device. Mainly three combustion behaviors have been observed inside a microcombustor: strong flames at higher flow rates, Flames with Repetitive Extinction and Ignition (FREI) at intermediate flow rates, and weak flames at marginal flow rates. In previous studies, weak combustion behavior has been proven suitable to study fuel properties from small samples of fuels. Microcombustor experiments typically rely on flame images. Imaging of weak flame needs long camera exposures due to reduced CH* emissions, hence weak flame experiments are not suitable for high throughput testing. FREI and strong flames give stronger CH* emission signals and can provide high throughput testing ability. The objective of this work is to investigate the potential of FREI and strong flames for fuel research and screening purposes. A major novelty of this work is to evaluate FREI behavior through lowspeed imaging and a microphone. FREI ignition and extinction temperatures of methane, ethane, propane, dimethyl ether and ethylene are shown to be fuel specific. The strong flame behavior is used to obtain insights into laminar flame speed of fuels. The respective impacts of microcombustor diameter, external heating, and unburned mixture equivalence ratio have been studied well. The open-source CFD package OpenFOAM with the detailed chemistry solver LaminarSMOKE is used to study FREI behavior of stoichiometric propane-air mixtures at engine relevant pressures. In simulations, critical fuel properties - i.e., FREI ignition and extinction temperatures, quenching diameter, and flame thickness, are found to decrease with increasing pressure similar to conventional IC engine behavior. Overall, fuel specific behavior of microcombustion and elevated pressure simulation results have shown microcombustion potential for fuel characterization for IC engines.
Sharma, Pawan, "Ignition and Extinction Behavior of Fuels in a Microcombustor" (2019). LSU Doctoral Dissertations. 4800.