Abstract
In the past few decades, energy conservation and carbon reduction have become a very important issue around the world. In order to replace conventional internal combustion (IC) engines with green energy engines, several kinds of green energy sources have been studied for their feasibilities to power motor vehicles. High pressure compressed air is considered as one of the green energy sources for its advantage of low carbon emission. This study focuses on the investigation of piston-type air-powered engines with experiments and theoretical calculation. The results have been used for the analysis of fluid characteristics and power performance of the engines, and evaluation of practical applications. After analysis, this study proposes two methods to improve efficiency and performance of piston-type air-powered engines At first, thermodynamic model of single cylinder piston-type air-powered engine has been built with MATLAB to study the power performance and fluid characteristics. Assumptions like compressible flow and ideal gas law were also applied. Next, a commercially available small air engine was examined with a test stand to understand its performance. Later, a modified 100 c.c. one-cylinder piston-type air-powered engine was tested with detailed fluid characteristics such as air flow rate, cylinder pressure, inlet and outlet pressure, inlet and outlet temperature, while measuring its power output at the supplied pressure ranging between 4 to 8 bar and different flow rates. The modified air engine was adapted from an internal combustion engine acquired from KYMCO motorcycle manufacturer. The acquired information has been further examined and compared with the theoretical calculation with MATLAB. After the investigation, this study proposes two methods to improve the power output and overall efficiency of the piston-type air-powered engine: First, a dual-cycle or known as split-cycle air engine is proposed for re-cycling the exhaust compressed air by adding another cylinder into the system. While another cylinder of split-cycle engine is added and it is larger than the original one, the compressed air energy using rate can be improved about 20% with the same power output. Second, increasing the intake temperature of the engine and expand/compress the air with isothermal process instate of isentropic process. It can improve the power output of piston-type air-powered engine around 8%. However, the improvement between isothermal process and isentropic process is not as much as the required work for the engine modification.