Developments in transport refrigeration systems using liquid nitrogen expansion and mechanical vapour compression.

A cost effective, zero-emission alternative for Transport Refrigeration Units (TRU) is provided by the Dearman Engine, a highly efficient Rankine-cycle piston engine powered by the phase-change expansion of liquid air or liquid nitrogen. When used in refrigeration applications, the system uses both the latent heat of vapourisation of the liquid nitrogen, and a secondary vapour cycle driven by the Dearman engine to provide cooling, whilst a secondary fluid circuit is used to both cool the vapour cycle condenser and improve the efficiency of the expander. This paper summarises recent improvements in Dearman Engine refrigeration systems, with development of a second generation engine, analysis of the relationship between vapour cycle and Dearman engine performance, and test results for alternative refrigerants and compressors presented. These developments demonstrate improved performance when compared to conventional diesel-powered refrigeration systems, together with zero operational emissions of carbon dioxide, NOx and particulate matter.