MEMS liquid fuel delivery for small-scale combustion power systems

Commercial-Off-The-Shelf (COTS) and Microelectromechanical System (MEMS) based fuel delivery systems are investigated for improving the combustion efficiency of small-scale engines. Small engines, spanning the range from 10 Watts to 1,000 Watts, can provide compact and efficient power to extend the mobility and usage time for portable personal devices. For example, liquid fuel operated small-scale rotary internal combustion engines have been developed by researchers at University of California at Berkeley, and the fuel delivery system has been identified as key technology issue. Of particular interest is the concurrent optimization of both mass flow rate and droplet size on the fuel delivery system.;Initially, a COTS liquid dispenser is characterized and adapted to the Berkeley developed 1.5 cm3 (S1500) rotary engine. For the optimum combustion process, the S1500 rotary engine requires a methanol flow rate of 40 mg/sec with droplet size of 60 microm at rotational speed of 10,000 rpm. While the COTS dispenser does satisfy the flow rate requirement, the injector is not able to produce the required droplet size. The 2 unoptimized COTS fuel delivery system leads to low chemical energy conversion efficiency (4.7%) on the S1500 rotary engine. This low energy conversion efficiency corresponds to the S1500 rotary engine generating only 40.6 Watts at 9,600 rpm with methanol based glow fuel.;A novel MEMS based liquid fuel delivery system has been developed to overcome the shortcomings of available fuel delivery systems. The MEMS fuel delivery system has been designed, simulated, and optimized for a compact, high force, low power consumption device. Combining a hole-in-the-wall planar valve with a MEMS electromagnetic (EM) linear actuator provides efficient liquid fuel delivery system for the small-scale engines. Finite Element Method (FEM) analysis has been performed to estimate force fields acting on the MEMS EM actuator, and Genetic Algorithm (GA) has been implemented on the actuator design to maximize the actuation force with the minimum phase area. This optimized MEMS fuel delivery system has been fabricated by surface micromachining. In addition, a unique permalloy electrodeposition method has been developed for trench filling applications by implementing dry film photoresist. The method allows deposition of 100 mum thick permalloy without having undesirable side bump growth near the trench edges and successfully prevents the merger of the moving armature and stators.;Experimental measurements have been performed for the MEMS fuel delivery system. The MEMS EM linear actuator has generated the minimum actuation force of 1.34 mN with electromotive force of 30 AT. The fuel delivery system has delivered a 10 mg/sec flow rate at a driving pressure of 14 psi with insignificant leakage. The fuel delivery requirements for S1500 rotary engine with high rotational speed have been achieved by adaptation of multiple MEMS fuel delivery systems with reduced width of the microchannel. The maximum fluidic resistance and fluidic resistance ratio of the closed to the open position are determined as 1.83x1015 Ns/m5 and 1.82x102 respectively. These measurements are among the highest recorded metrics compared to the previously reported liquid micro valves. Because of these metrics, the MEMS fuel delivery system is well suited to fuel regulation applications for the engine where the typical fluidic resistance ratio is 100:1.