Air Engine

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Energies 2013, 6, 1731-1745; doi:10.3390/en6031731

ISSN 1996-1073 Article

Experimental Investigation on the Performance of a Compressed-Air Driven Piston Engine Chih-Yung Huang *, Cheng-Kang Hu, Chih-Jie Yu and Cheng-Kuo Sung Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan; E-Mails: (C.-K.H.); (C.-J.Y.); (C.-K.S.) * Author to whom correspondence should be addressed; E-Mail:; Tel.: +886-3-574-2916; Fax: +886-3-572-2840. Received: 3 December 2012; in revised form: 7 March 2013 / Accepted: 8 March 2013 / Published: 12 March 2013

Abstract: This study presents an experimental investigation of a piston engine driven by compressed air. The compressed air engine was a modified 100 cm3 internal combustion engine obtained from a motorcycle manufacturer. The experiments in this study used a test bench to examine the power performance and pressure/temperature variations of the compressed air engine at pressures ranging from 5 to 9 bar (absolute pressure). The engine was modified from a 4-stroke to a 2-stroke engine using a cam system driven by a crankshaft and the intake and exhaust valves have a small lift due to this modification. The highest power output of 0.95 kW was obtained at 9 bar and 1320 rpm. The highest torque of 9.99 N· occurred at the same pressure, but at 465 rpm. The pressure-volume (P-V) m diagram shows that cylinder pressure gradually increases after the intake valve opens because of the limited lift movement of the intake valve. Similar situations occurred during the exhaust process, restricting the power output of the compressed air engine. The pressure and temperature variation of the air at engine inlet and outlet were recorded during the experiment. The outlet pressure increased from 1.5 bar at 500 rpm to 2.25 bar at 2000 rpm, showing the potential of recycling the compressed air energy by attaching additional cylinders (split-cycle engine). A temperature decrease (from room temperature to 17 ° inside the cylinder was observed. It should be noted that pressures higher than C) that currently employed can result in lower temperatures and this can cause poor lubrication and sealing issues. The current design of a compressed air engine, which uses a conventional cam mechanism for intake and exhaust, has limited lift movement during operation, and has a restricted flow rate and power output. Fast valve actuation and a large

Energies 2013, 6 lift are essential for improving the performance of the current compressed air engine. This study presents a power output examination with the pressure and temperature measurements of a piston-type compressed air engine to be installed in compact vehicles as the main or auxiliary power system. Keywords: compressed air engine; experimental investigation; power performance; pressure; temperature


1. Introduction In the past few decades, energy conservation and carbon reduction have become very crucial issues worldwide. Scientists have been searching for solutions to reduce the extensive use of conventional internal combustion (IC) engines and/or reduce their carbon dioxide emissions. To find a replacement for conventional IC engines, researchers have studied several types of engines that use green energy to determine the feasibilities of installing these engines in motor vehicles. Examples include electric engines, natural gas engines, and hydrogen engines [1]. Electric vehicles are the most common green energy alternatives, and have been developed and commercialized for decades. However, slow battery recharging and a heavy battery weight are critical issues for electric vehicles. Hydrogen engines and natural gas engines can be used in the motor vehicles; however, the required tank size limits their applications. In recent years, high-pressure compressed air...
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