Ph.d.-forsvar Nasrin Arjomand Kermani

Design and prototyping of an ionic liquid piston compressor as a new generation of compressors for hydrogen refueling stations

The thesis presents the design, modeling, and fabrication of a new compressor technology that involves an ionic liquid piston as replacement for the solid piston in conventional reciprocating compressors to compress hydrogen in hydrogen refueling stations. The motivation comes from the need to achieve more flexible and efficient compressors with longer life spans in hydrogen stations. This can eventually lead to a cheaper hydrogen production and faster penetration of hydrogen fuel cell vehicles into the market.
A thermodynamic model simulating a single-compression stroke is developed to investigate the heat transfer phenomena inside the compression chamber; the system performance is evaluated, followed by the design processes.

Ionic liquids are molten salts which have negligible vapor pressure.  The ability to tune the physiochemical properties of ionic liquids by varying the cation anion combinations is the feature of these liquids that make them as promising candidates to replace the solid piston. However, due to a large number of available combinations for ionic liquids, it is essential to systematically investigate their performance for a particular application and narrow down the final choice. The ionic liquid:  1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide is recommended as the best candidate that can safely be used as a replacement for the solid piston. In addition, the corrosion behavior of various commercially available stainless steels and nickel-based alloys as possible construction materials for the components which are in direct contact with the selected ionic liquids is evaluated. Stainless steel alloy, AISI 316L, with high corrosion resistance and the lowest cost is selected as the material for all the components in direct contact with the ionic liquid, in the designed ionic liquid hydrogen compressor.

The new compressor consists of three main parts, namely pneumatic, hydraulic, and custom-designed hydraulic to pneumatic transformer, which work together to compress the hydrogen.  The proposed design addresses the limitations of the current technology and previously designed compressors using the liquid piston concept and ionic liquid, by introducing a custom-designed hydraulic to pneumatic transformer. As a proof of concept, a prototype for compression of hydrogen from 100 to 300 bar is built. The new compressor design has high potential to be used as an alternative to the conventional reciprocating compressors in hydrogen refueling stations, as it provides a simpler design with lower manufacturing costs, higher efficiency, much less sliding friction, possibility of internal cooling, higher functional reliability and less maintenance.


man 13 nov 17
10:00 - 13:00


DTU Mekanik


DTU Lyngby Campus, Bygning 101, Mødelokale 1