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Small-scale Combustion Betty Bui ME 258 Fall 2012 Introduction • Lithium versus Hydrocarbons Small-scale Combustions • Advantages • More efficient • Reduce waste and emissions (CO and NOx) • Disadvantages • Manufacturing • Properties not linear • Heat recirculation • Heat loss • Pollutant formation Categories Definition based on Physical length Flame quenching diameter Device scale Combustion regime Length scale Examples Applications Mesoscale 1 - 10 mm Rotary engine (UCB) MEMS power Microscale 1 - 1000 µm Micro-reactor (UIUC) Thruster Mesoscale ~Quenching diameter (equilibrium) Swiss-roll combustor (USC) Power generation Microscale Quenching diameter ~ Mean-free path (nonequilibrium) Fuel Cells Nano-particle reactors Microscale Smaller than conventional Micro-thrusters (PSU) engine size Micro-gas turbine (MIT) Energy conversion Micro-satellites Micro-air planes Timeline of Development • • • • • • • • • • 1998: Waitz – 1st micro-combustor of 0.13cm3 2002: Weinberg – Swiss Roll Combustor 2002: Sirignano – Liquid fuel flow directly on walls 2003: Liedtke and Schultz – Liquid film in annulus around tube 2004: Kaiser and Kyritsis – Meso-scale catalytic combustor via electrostatic spray 2004: Wang – Swirl-stabilization combustion 2005: Anh - Gas-phase and catalytic combustion in Swiss-Roll 2005: Spadaccinni – Hybrid micro-combustor 2005: Yuasa – Flat-flame micro-combustor 2006: Marbach and Agrawal –Porous inert material Approaches • Excess Enthalpy • Regenerative preheating • Redistribute thermal energy • Minimizing heat losses • Heat Exchanger • Counter-flow current • Heat Transfer • Convection • Radiation Swiss Roll Combustor (SRC) • Combustion Chamber • Pair of long channels Porous Inert Media (PIM) • Two concentric cylinders • Preheated reactants in annulus prior to PIM Conclusion • Swiss-roll combustor and Porous Inert Media • • • • • Excess Enthalpy Regenerative Reheating Heat transfer modes Leaner combustion Reduced emissions Questions?
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