It took Peter Dearman 30 years to develop his liquid air engine, tucked away in a tiny garage workshop in Hertfordshire, UK. But it only took Toby Peters, the Chief Executive of the Dearman Engine company, a tiny fraction of that time to decide that he wanted in. Not letting his initial excitement get the best of him, Peters took the technology to the University of Leeds to see if the science stacked up. Delighted with the positive results, he and Dearman teamed up and the Dearman Engine Company was born.
How does the Dearman liquid engine work?
The basic principle is if you take 710 litres of air and liquefy it, you get one litre of liquid air, which you store at atmospheric pressure. You just have to keep it cold, at -196 degrees Celsius, you don’t have to keep it under pressure. By introducing ambient heat, the liquid air boils and turns back into gaseous air: it expands 710 times and you can use that to drive an engine.
Historically, it was treated like a steam engine: you boiled a tank of liquid air and used the head of steam to drive the engine. But Peter came up with this very clever idea which was to keep it as a liquid and inject it into the piston. The void at the top of the cylinder just above the piston is filled with a heat exchanger – water and glycol mixed – into which a small droplet of liquid nitrogen is injected to get very rapid and instantaneous expansion inside the cylinder.
That then drives the piston down, which drives the engine. It exhausts the air to atmosphere and recycles the heat exchanging fluid. Peter’s invention was actually what Andy Atkins [Chief Engineer of technology at Ricardo] describes as an ‘internal steam engine’ by using this heat exchange fluid.
The clever bit is that by using heat exchange fluid we can integrate the engine with other engines. So although you can use this as a zero emission powertrain for zero emission vehicles, this is where it becomes really exciting. We can actually integrate it with a diesel engine and harness the waste heat of the coolant loop rather than the exhaust – the coolant loop is at 90-100 degrees Celsius and our tank is -196 degrees Celsius.
We can broadly put this alongside a diesel engine, harnessing the waste which could, on a bus, reduce fuel consumption by about 25-30%; 30% of every litre of diesel is lost out of the radiator, let alone what goes out the exhaust…
Rachael Hogg
This is an excerpt of an article first published in the Q4 issue of Megatrends magazine, to continue reading, simply download your free copy and turn to page 68.
