Fabrication and test of a MEMS combustor and reciprocating device

We propose the concept of a microelectromechanical system (MEMS) scale reciprocating device powered by burnt gas and we have fabricated its prototype to investigate the applicability of the concept in a microscale power generator. In this investigation, combustion in a microscale chamber was studied using thermodynamic principles to estimate theoretical power output. We have carried out an evaluation of relevant subsystems and fabrication processes to realize the heat engine in such a small scale for further development of similar devices. A variable depth microcombustion chamber was built in-house to test the combustion characteristics in a small volume. Measurements include pressure transition after ignition and high-speed flame visualization. Test conditions include combustion chamber depth around the flame quenching distance, below which combustion theory predicts no burning. By analyzing the measured data, the combustion efficiency and available work were obtained and used for the design of a reciprocating MEMS device. The results of the combustion measurements required that the chamber height be I mm or more for stable ignition and flame propagation. Based on these findings of the microcombustion experiment, we formulated a MEMS fabrication process and made a reciprocating device. The device has a combustion chamber with a volume of 1 mm(3), and the cross section of the cylinder has a rectangular shape with a height of 1 mm and a width of 2 mm. Photosensitive glass was chosen as a structural material. A thick photoresist mold and electroplating were used for constructing the overall structure. A single stroke experiment with hydrogen as a fuel was recorded by a high-speed digital video camera showing piston displacement at reasonable speeds. (Some figures in this article are in colour only in the electronic version).