The effect of heat exchange fluid composition on the performance of a liquid nitrogen engine system

It has been proven that performance gains in liquid nitrogen (LN₂) engine systems, generating simultaneous cooling and auxiliary power, can be achieved through integration of a dedicated heat exchange fluid (HEF) circuit. The novel, HEF enhanced LN₂ engine system can be utilised as an optimised hybrid solution for commercial refrigeration trucks. Although the benefits arising from HEF addition have been researched, there are no articles investigating the effect of changing the HEF composition on engine performance. This article reports a detailed experimental investigation on the performance of a novel, HEF enhanced LN₂ engine system. The key contribution of the current study is the knowledge generated from investigating the impact of different HEF compositions on the engine performance under different HEF temperatures, N₂ inlet conditions and engine speeds. The HEF composition was varied through changing the water content in the mixture. A thermodynamic model based on an idealised cycle was used to assist interpretation of the experimental results and assess the potential of the proposed engine architecture. The experimental study demonstrated up to 42.5% brake thermal efficiency, up to 2.67 kW of brake power and up to 174 kJ/kg specific energy, which were higher than previously published figures for LN₂ engine systems. A reduction in the HEF water content was found to generally increase the engine power output at a HEF temperature of 30 °C. However, at a HEF temperature of 60 °C, the impact of HEF composition was found to be minor and nonmonotonic. The thermodynamic model predicted the upper and lower limits of the measured indicated power and indicated thermal efficiency with acceptable accuracy.