Int. J. Alternative Propulsion, Vol. 1, No. 2/3, 2007 275 Copyright © 2007 Inderscience Enterprises Ltd. Development and characterisation of small-scale rotary engines S. Bennett Sprague, Sang-Won Park, David C. Walther, Albert P. Pisano and A. Carlos Fernandez-Pello* Department of Mechanical Engineering, University of California at Berkeley, Berkeley, CA 94720-1740, USA Fax: +1-510-642-1850 E-mail: sprasb@me.berkeley.edu E-mail: intropia@me.berkeley.edu E-mail: walther@eecs.berkeley.edu E-mail: appisano@me.berkeley.edu E-mail: ferpello@me.berkeley.edu *Corresponding author Abstract: This paper describes the development and characterisation of small-scale rotary engines with displacements in the range of 78–1500 mm 3 for portable applications in the range of 10–200 W of power output. Small-scale combustion engines present a number of research challenges including manufacturing tolerances, sealing, thermal management, ignition, combustion efficiency and porting. Four engines have been characterised using a custom test bench and show an increase in performance due to design changes that mitigate the challenges associated with small-scale engines. The volumetric power density has been increased from 11 W/cm 3 in a 348 mm 3 engine operating with a supercharged hydrogen/air mixture to 22 W/cm 3 in a 1500 mm 3 engine operating with naturally aspirated liquid hydrocarbon fuel. The thermal efficiency has also been increased from 0.2 to 4%. Continued improvements in sealing, thermal management, combustion efficiency and friction reduction will allow further increases in engine performance. Keywords: rotary engine; meso-scale combustion; portable power. Reference to this paper should be made as follows: Sprague, S.B., Park, S-W., Walther, D.C., Pisano, A.P. and Fernandez-Pello A.C. (2007) ‘Development and characterisation of small-scale rotary engines’, Int. J. Alternative Propulsion, Vol. 1, No. 2/3, pp.275–293. Biographical notes: S. Bennett Sprague is currently a PhD candidate in the Combustion Processes Laboratory at the University of California, Berkeley. He received his Master’s degree in Mechanical Engineering from the University of California, Berkeley in 2004. His research interests include combustion at the microscale and small-scale combustion engines. Sang-Won Park is currently a PhD student in the Combustion Processes Laboratory at the University of California, Berkeley. He received his Master’s degree in Mechanical Engineering from the University of California, Berkeley in 2005. His research interests include fuel delivery systems for small-scale engines and microelectro mechanical systems. David C. Walther is a research specialist with the Berkeley Sensor and Actuator Center (BSAC) at the University of California, Berkeley. He received his PhD in Mechanical Engineering (Thermosciences) from the University of