ERC Researchers Create World’s Smallest Internal Combustion Engine Air Compressor

Achievement date: 

Researchers affiliated with the Center for Compact and Efficient Fluid Power (CCEFP), an NSF-funded Engineering Research Center (ERC) headquartered at the University of Minnesota, have created the world’s smallest internal-combustion-engine air compressor that directly converts hydrocarbon fuel to compressed air.


This creation satisfies the need for untethered and tiny power supplies, which can power new portable tools and technologies that use pneumatic actuators. Power supplies of this type can replace battery-powered electric air compressors, which are inefficient and bulky. The project supports CCEFP’s goal of developing new fluid-power supplies that are much smaller than anything currently available; it also supports revolutionary portable and wearable applications, including human-assist devices. Additionally, this work generates new knowledge about the science and engineering of homogeneous charge compression ignition (HCCI) free-piston engine compressors.  


CCEFP researchers have taken a different approach from battery-powered devices by developing an engine compressor that uses HCCI and a free-piston configuration to maximize efficiency and minimize space. A prototype engine is about 12 cm long (see schematic and prototype in accompanying figure). The prototype pressurized a 530 mL air tank to 6.7 bar (97 psi) in 38 seconds.

The overall approach for developing the tiny engine was based on an integrated program of modeling and testing. Comprehensive mathematical models of the ignition, fluid flow, and mechanical motion of the parts were required, supported by testing of components from very small conventional engines and testing of prototypes. Performance measurements on the tiny engine-compressor prototypes can be used to improve and calibrate the mathematical models. Extensive work is also aimed at accurate models of the combustion and scavenging processes, which are keys to high operating efficiency.