Liquid logic: Peter Dearman, inventor of the liquid-air engine

Liquid logic: Peter Dearman, inventor of the liquid-air engine

Peter Dearman has spent almost his entire adult  life considering the possibilities of an engine that runs on liquid nitrogen.


Racing cars, self-driving vehicles and even military trucks are all relatively common sights at the Mira proving ground. But since the end of last year, the test facility in Warwickshire has seen a vehicle that’s far more ordinary and yet virtually unique: a refrigeration truck in which diesel fuel is replaced by liquid nitrogen. If road trials due to start in March are successful, the model could pave the way for a new form of zero-emission automotive propulsion.

The man behind the concept is Peter Dearman. A self-taught engineer in the grand British tradition of the garden-shed inventor, he is overseeing a new kind of engine that he has spent almost his entire adult life thinking about: one that runs on liquid nitrogen and, he thinks, could be an alternative to batteries and hydrogen fuel cells in low-emission vehicles.

‘Even with modern electric vehicles you can’t actually fast-charge them because it shortens your battery life and the realities of pumping that much power in is not really practical, but putting a liquid fuel in is a much better idea,’ he explained, when The Engineer met him last year at the Dearman Engine Company’s test lab in a rented facility at Imperial College London.

‘Then you’ve got hydrogen-handling problems that I don’t believe are solved… It’s always going to be expensive because transporting hydrogen is not an easy thing because of the very high pressures. Whereas this is a much more simple technology; it’s very easy to transport.’ On top of this, the large amount of available liquid nitrogen produced as a by-product of liquid oxygen means the fuel itself could be very cheap.

“Even with modern electric vehicles you can’t actually fast-charge them because it shortens your battery life”

However, a mass-market cryogenic car is still a long way off and may not be a viable product at all. Instead, Dearman is initially concentrating on how his technology could replace diesel engines in commercial vehicles, starting with the secondary motor that drives refrigeration in food-delivery trucks.

The idea behind a cryogenic engine is that allowing liquid nitrogen to boil produces compressed gas that can be used to generate mechanical and/or electrical power. Its only emission is a blast of harmless but potentially useful cold nitrogen gas. Dearman’s innovation is to circulate heat-exchange fluid inside the engine in a way that doesn’t flood it but keeps the gas relatively warm as it expands in order to maintain the engine’s efficiency.

Using this technology to replace the diesel generators on board refrigeration trucks has the potential to eliminate a significant but often-overlooked source of carbon and nitrogen oxides (NOx) emissions, at a time when governments are increasingly cracking down on vehicle pollution in cities. ‘It’s the easiest one to do because there’s a ready market for it,’ said Dearman. ‘If you try and develop something that’s not got a market it’s very much harder because you’ve got to create your own market. But [tighter] pollution laws are coming in just at the right time for us as we’re developing this.’


The trial engine will provide cooling and auxiliary power for a refrigeration truck.

Dearman’s original idea, however, stretches back several decades to a time when the world was first seriously considering how it might move away from fossil fuels. In fact, a liquid nitrogen engine was the first idea he had as an inventor. ‘Of course you get that moment when you decide to be an inventor and then you get a total blank and cannot think of anything,’ he said. ‘So what you have to do is look at things there’s a need for. There was quite a lot of talk about oil being a finite resource so that grabbed my attention.’

After leaving school at 15, Dearman worked on his family’s poultry farm. He shunned further education because, he said, he didn’t want to overshadow the memory of his clever older brother who had died in a car accident aged 16. Before long, however, his desire to become an inventor led him to take a job with a local metalworking company.

‘I wanted to get into engineering so I could make things,’ he said, adding that he realised being able to bring his ideas to life would be key to persuading people they would work. ‘I think if you just try to put ideas forward, nine out of 10 of them are going to be bad. It’s much better to make something that works and then people can make their own minds up. That’s a bit like what we’re doing now. We’ve gone into niche markets that don’t need a lot of persuading.’


Dearman and colleagues at work on his engine at their lab in Imperial College London.

But Dearman’s cryogenic engine idea remained parked for many years while he worked as what he describes as a freelance inventor for a variety of companies, at one point developing a more portable handheld microvent resuscitator that is widely used in ambulances. This experience also taught him a lesson about protecting intellectual property.

‘I end up in court quite often with these things,’ he said. ‘Big companies know they can take you to court. [One company] said I still worked for them and they owned all my ideas. The judge said: “How much do you pay him?” [The company said:] “Oh we don’t pay him.” It’s a ridiculous thing because it bankrupts you. But that’s the way it goes so you have to be a bit careful.’

When pressed for more details about this story, Dearman said he couldn’t remember them, not for the first time in our conversation. A difficult man to read, he would sometimes answer questions with one-word answers in a way that was impossible to tell whether he didn’t want to hide something away or just thought the topic unimportant. But he would also volunteer snippets of information with a knowing smile, leaving you equally confused as to his seriousness.

How did he finally build the first Dearman engine, for example? In the 1990s he saw a liquid-nitrogen-powered vehicle built by the University of Washington on an episode of technology television show Tomorrow’s World, he explained, prompting him to study the available research and build his own breakthrough engine. But how did he do it? Did he manufacture a prototype? ‘No I just put things together to show it could power a car.’

“There’s no strategic materials involved. Everything’s abundant and it’s all pretty cheap stuff.”

This reluctance to talk about his achievements was in line with his tendency for self-deprecation. ‘I’m what’s known as a broken-clock inventor: you have to think of hundreds of things and eventually one of them’s going to work,’ he said. ‘It’s best to get into niche areas because I’m not very clever. I just think about things all the time that other people don’t. I don’t think it takes anything special, it’s just a lot of people don’t want to think about things, or you get nutty ideas, which of course I get all the time.’

What he would talk about enthusiastically, however, was the potential he saw for his technology. It’s already found relative success in a grid-scale energy-storage system produced by sister company Highview, which has run a pilot plant since 2011. And, as well producing the refrigeration truck demonstrator, the Dearman Engine Company is working on a hybrid powertrain for large vehicles, which uses a cryogenic motor alongside a conventional internal combustion engine (ICE) to provide mechanical power to the wheels.

In this model, heat from the ICE will drive the boiling operation in the Dearman engine more efficiently, which in turn reduces the necessary size and fuel consumption of the main engine. The firm claims the technology could reduce diesel use by up to 25 per cent in commercial vehicles while costing significantly less than electric-hybrid systems.

Did he always have a particular vision that the engine would power passenger vehicles? ‘Not really,’ he said. ‘You just have to do it and hope that something happens. I always thought that fuel would become so expensive that people would want to look for alternatives… The thing about this system is there’s no strategic materials involved. Everything’s abundant and it’s all pretty cheap stuff. We’re using aluminium and plastic in the engine, nothing that’s horrendously expensive. There’s no limit to it.’

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