Articles
In the early 1980s, I left academia to develop a new internal combustion engine. The core idea was an interacting pair of rotors, aimed at supporting agricultural mechanisation in developing countries.
The idea eventually crystallised as the rotary power couple engine, which was supported to proof of concept in the late 1990s by two entrepreneurs from the Low Countries. By 2007, this work had led to successful spin-outs of miniature fuel atomisation technology and a rotary supercharger for diesel engines.
However, a report in 2013 on the potential of liquid air for green energy storage made me see the ideal application of the rotary engine: to deliver shaft power from pressure released by atmospherically warming liquid air.
Our EpiQair concept depends on change of state. The rotary system liquefies air by cooling it to -200°C. When power regeneration is required, atmospheric heat warms it to ambient temperature in a confined volume, resulting in a large pressure rise, which powers our engine. It is like an air battery; you can put energy in, store it and take it out when required.
Clearly, EpiQair could offer the engine industry not only a zero-carbon solution but also one to set new standards of power density and attractively low production cost compared with current engines – as well as with battery and fuel-cell alternatives.
Liquid-to-gas state change has previously been used for water-powered steam engines, and in the 19th century liquid-air-powered piston engines were used in early cars. However, mechanical friction absorbed 80% of the available energy, so internal combustion engines rose to prominence and liquid-air engines were forgotten.
Crucially, the EpiQair engine provides the two missing elements: a virtual absence of mechanical friction and the ability to provide high-speed operation with high working cycle frequency. The paired rotor interaction provides an expansion cycle completed in a quarter-turn, with expansion ratio of 400:1, at speeds of up to 20,000rpm with nine expansion cycles per revolution. This interaction can deliver 1.5MW, or 2,000hp, from working chambers totalling 1,200cm3 in a highly compact four-rotor engine configuration.
Super-critical air as working fluid is injected at near-ambient temperature and density, similar to that of the liquid air from which it is derived. Heat stored during liquefaction is used to inject super-heated water to maintain constant temperature during expansion.
EpiQair is the first example of a heat engine with no thermal gradients in the engine structure and therefore no thermal stresses, yet it is capable of achieving power density 20 times greater than that of modern internal combustion engines.
We anticipate that air battery costs will be substantially lower – around 50% – than with chemical battery technologies.
We plan to build and test prototype engine and generator systems and develop a prototype liquefaction plant with the Birmingham University Centre for Cryogenic Energy Storage.
We expect EpiQair to enter the energy storage market to supply smooth power to the grid, thereby eliminating the inherent interruptions of renewable source power.
Although funding is the main barrier to entry, we see the biggest market potential for energy storage in China. We have had talks with Goldwind, a Chinese wind-turbine manufacturer, which has said the country will need 20GW of energy storage by 2020. Our scaleable displacement technology is ideally suited to meeting China’s micro-grid structure requirements.
Funding: Epicam makes it to low-carbon finals
Epicam recently made it into the final stages of the national Shell Springboard competition, created to help businesses scale up their low-carbon technologies. The six finalists each received £40,000 in funding to further develop and grow their business. Epicam was pipped to the post for the ultimate £110,000 prize by an industrial carbon-scrubbing technology from University of Leeds’ spin-out company C-Capture. Epicam will use the additional funding to build and test a commercial-scale prototype of the EpiQair engine.