43rd AIAA Aerospace Sciences Meeting and Exhibit, Jan 10–13, Reno, Nevada Effect of Chamber Width on Flame Characteristics in Small Combustion Chambers Yoshifumi Tsuji * University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo, 113-8656 ,Japan Bennett Sprague, † David C. Walther, ‡ Albert P. Pisano § and Carlos Fernandez-Pello § Mechanical Engineering, University of California, Berkeley, Berkeley, CA 94720 USA The objective of this study is to understand the combustion process in confined chamber when the size is small and the ignition energy is limited. As a first step, the geometry of a1.0kW Wankel engine, which has a displacement of 5.0 cm 3 , has been chosen and a static combustion chamber with volume 141- 282 mm 3 has been built. Three parameters: pressure, temperature, and chamber size are being investigated. Visualization of flame front via the schlieren technique was used to measure the prop- agation speed of the flame. These images are taken with a high-speed camera at a frame speed of 2000 fps with 486 μsec exposure time. Flame instability was observed inside the smallest chamber of 4mm. Front shape changed from a smooth and round one to a wrinkled surface. Chamber length is much shorter than length obtained analytically based on adiabatic Darrieus-Landau instability. The mechanism for the onset of the instability triggered by the increase of the heat loss is analytically derived and compared with experimental results. Nomenclature γ Adiabatic exponent ρ in Initial density inside the chamber, kg/m 3 ε The scaled activation energy ε c Critical scaled activation energy A Cross-sectional area, m 2 c p Specific heat capacity, J/kg · K E Activation energy, K Fo Fourier number n Order of reaction Q Specific heat release, J/kg q Scaled heat release S b Flame speed, m/s S b0 Normal flame propagation speed, m/s T in Initial temperature Subscripts in Initial state I. Introduction In order to better understand the combustion process that occurs in engines of small scale, the ignition and subsequent combustion event has been independently examined to mitigate the effects of engine processes (such as sealing, compression ratio, spark timing, oil contamination, etc.) on the ignition and combustion event. As a first step, the geometry of a 1.0kW Wankel engine, which has a displacement of 5.0 cm 3 , has been chosen and a static closed combustion chamber which mimics the combustion process at the top dead center (TDC) position has been built. The chamber is quasi-sealed; the inlet and outlet orifices have been * Graduate Student, Department of Aeronautics and Astronautics † Graduate student, Mechanical Engineering, Berkeley CA ‡ Research Engineer, Mechanical Engineering, Berkeley, CA § Professor, Mechanical Engineering, Berkeley, CA Copyright c  2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. 1 of 9 American Institute of Aeronautics and Astronautics Paper 2005-0943