Multidimensional analysis of the impact of motion variation on exergetic performance in a free piston linear hydrogen engine

Abstract

Linear engine is a promising new energy conversion device which supports variable stroke (or compression ratio) operation for thermal optimization. Previous studies have shown that hydrogen fuel is well adapted to the new engine due to fast combustion. In order to further explore the energy efficiency optimization path of linear hydrogen engine (LHE), this study proposes a multidimensional simulation to investigate the effect of motion stroke variation on exergetic performance of a two-stroke LHE. Meanwhile, a comparative evaluation of exergy between the LHE and a crankshaft hydrogen engine (CHE) is also presented. The results demonstrate that, the irreversible exergy of LHE is slightly higher, but the peak thermomechanical exergy, final chemical exergy, heat transfer exergy and work transfer exergy are lower than CHE, which is attributed to its more homogeneous gas mixture, lower pressure and temperature. The 68 mm stroke achieves more complete combustion and higher temperature for LHE, which promotes the reduction of the final chemical exergy, but inevitably leads to more heat transfer exergy. Shortening the stroke keeps the heat transfer loss of LHE within an acceptable range and effectively reduce the irreversible exergy loss, thereby maximizing the work transfer exergy and increasing the engine efficiency.