Investigations into a MEMS based free-piston microengine

The development of a MEMS based free-piston ″knock″ engine based on homogeneous charge compression ignition (HCCI) of hydrocarbon fuels was studied to develop a new portable power source with at least 10 times the energy density of batteries, and can generate around 10 w of electricity in a 1 cc package volume. The study involved experimental characterization of the fundamental of combustion; detailed chemical kinetic simulations into the auto ignition characteristics under high-compression; and the construction of a free-piston engine on a microscale. HCCI from isopropanol/air mixtures was demonstrated. Numerical simulations were used to assess necessary condition for complete combustion at scales needed for the engine to operate. The ignition delay times and the completeness of combustion were studied as a function of compression ratio, equivalence ratio, pre-heating, extent scavenging, wall quenching effects, and fuel mixtures using detailed chemical kinetic simulations for methane, ethane, butane, propane, nitromethane, and methanol under static and adiabatic compression. Due to the rapidity of the engine cycle and the high pressures involved, heat and radical loss had minimal effect even at these small dimensions. Despite operating at high compression ratios, monopropellents would not ignite in the required time, without substantial preheating of the fuel. Original is an abstract.