Effects of intake high-pressure compressed air on thermal-work conversion in a stationary diesel engine

Compressed air energy storage is one of the green energy storage and conversion systems. In this work, the compressed air was directly supplied to a stationary diesel engine to investigate the effects of compressed air characteristics on the process of thermal-work conversation in diesel engines. Then, the thermal efficiency of supplying compressed air to a diesel engine is compared against a simple hybrid system that consists of a compressed air engine and a baseline diesel engine. The results indicate that the compressed air affects the thermal work conversion of diesel engine. The gross indicated mean effective pressure is being used to quantify the in-cylinder pressure work that transferred to the piston motion only for the combustion and expansion strokes, which increases as the pressure of compressed air increases and decreases as the temperature of the compressed air increases. The gross indicated thermal efficiency that represents the ability of thermal-work conversion is maximum at intake pressure of 300 kPa and intake temperature of 303 K with a value of 44.3%, which is 19.7% higher than that of the baseline diesel engine with 100 kPa intake pressure and 303 K intake temperature. The diesel engine using compressed air shows 6.64% higher overall efficiency than the simple hybrid system. The soot emissions increase with increasing intake pressure, and decrease with increasing intake temperature. As the intake temperature increases, NOx emissions increase. As the intake pressure increases, NOx emissions first decrease and then increase.