Liquid-Fueled Microcombustor for Portable Power Generation – A CFD Sensitivity Analysis

Thermal partial oxidation, or fuel-rich combustion, has received considerable attention in the past decades as a potential approach for power generation from hydrocarbon fuels with high energy densities. Hydrocarbons have a specific energy of approximately 40 MJ/kg, whereas the best lithium ion batteries have about 0.5 MJ/kg. As a result, a hydrocarbon-based device with a chemical-to-electric efficiency of only a few percent could have benefits over batteries.  Thus, there has been interest in utilizing the high energy density of hydrocarbon fuels harnessed by fuel cells in portable power generation. In particular, Solid Oxide Fuel Cells (SOFCs), operating at high temperatures (400-1000 °C), have shown significant promise in directly converting hydrogen and other hydrocarbons to electricity. While dual chamber and single chamber SOFC configurations have been explored for many years, the Flame-assisted Fuel Cell (FFC) can generate electricity by direct coupling of the SOFC with combustion exhaust. To date, little attention has been paid to utilizing liquid fuels in microscale combustors that could potentially augment hydrogen production, and thus power generation in FFCs. In an effort to develop a micro-scale portable power source, this research project focuses on the analytical assessment and experimental set-up and characterization of a liquid-fueled micro-combustor that is tested using both ethanol and methanol to be­­ oxidized by air. In the experimental setup, a syringe pump is used to regulate the fuel flow rate, where the oxidizer’s flow rate is set using a flow meter, which is then controlled through a data acquisition device. Fuel-rich combustion is performed with equivalence ratios ranging from 1 to 5. The exhaust is then passed to the GC (Gas Chromatography) station to analyze its gas composition and quantify how much hydrogen is produced, and thus how efficiently the power is generated. At equivalence ratios ranging from 1 to 5, flame characteristics are analyzed through visual inspection to determine flame instability and thus combustion efficiency. To obtain more insight into the operation conditions’ impacts and the optimized setup, we conduct computational fluid dynamics (CFD) analysis. CFD modeling is a powerful and convenient tool for simulating the atomization and the spray process. This will give us more insights on the impacts of atomizing fuels and the effect of the droplet size and its distribution on the spray and atomization process. This enables us to properly regulate fuel flow rate and evaluate the effects of it on the temperature flow field before oxidation occurs.