Freezer trucks and fresh-air powered engines: the coolest things from Croydon since Kate Moss?

Engineering start-up Dearman's innovative new engine is powered by liquid nitrogen: it keeps frozen food trucks cold and massively reduces diesel pollution at the same time.

by Andrew Saunders
Last Updated: 17 May 2017
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Never mind Silicon Valley, Silicon Roundabout, or even Silicon Fen – one of the most original of UK technology start-ups is to be found instead in a shed-like unit on a trading estate just off the Purely Way in Croydon.

This modest spot is home to Dearman, a high tech engineering business which makes an innovative kind of piston engine running not off petrol, diesel or even hydrogen, but fresh air (well, liquid nitrogen to be exact, which in its gaseous form makes up 78% of the atmosphere so is almost the same thing).

Invented by lifelong tinkerer Peter Dearman over 40 years ago, the Dearman engine was intended to power a new generation of zero-emission road vehicles (an early homemade prototype is shown below. A later more powerful demo specimen took to the streets of Bishops Stortford under the bonnet of a 20 yr old Vauxhall Nova back in the noughties).

But as Dearman co-founder and deputy CEO Michael Ayres (pictured with the latest engine at the top of this article) explains, the engine has ended up instead being developed for an entirely different application – powering the freezer units of refrigerated trucks.

That’s a pivot any tech entrepreneur would be proud of, but it was absolutely necessary if this clever piece of British garden shed technology was going to stand a chance of realising its business potential, he says. ‘I’ve been around clean tech for a bit, and the classic routine is for someone to say "Right, I’ve got a new energy storage technology, what’s the biggest market I could go for?" And the answer is always passenger cars.’

Just because you can do something, doesn’t mean you should – cars are a seriously tricky market to break into for newcomers. ‘The incubation period for getting any new technology onto a passenger vehicle is really long – maybe a decade. And how many of the OEMs [the big carmakers] haven’t already signed up a battery partner? Not many.’

Cooling down truckloads of frozen pizzas or chilled ready meals may not have quite the same glamour as making liquid nitrogen powered cars, but it’s a market that is ripe and ready for disruption, says Ayres. ‘Transport refrigeration was picked because the incumbent technology isn’t really compatible with anything that is going to happen environmentally over the next few years’.

It’s all down to emissions and the growing backlash against diesel pollution. The auxiliary diesel engines used to power conventional refrigeration units are almost unregulated and thus very dirty. Indeed they chuck out so much pollution that in a modern truck, the diesel powered TRU (transport refrigeration unit) can be responsible for 70% of the vehicle’s total NOx emissions and 90% of the particulates, despite being many time smaller than the main propulsion engine.

So replacing the TRU’s in Europe’s 1m strong refrigerated fleet with zero-emissions alternatives would be the equivalent, Dearman has calculated, of taking 50m diesel cars off the road.

A pretty arresting statistic for governments struggling to find a politically acceptable way to deal with plummeting air quality and diesel pollution. So tightening the rules on refrigerated trucks looks like an easy win, and when that happens Dearman’s nitrogen powered TRUs will be there to clean up.

‘Air quality is more of a near term problem for policymakers than climate change’ says Ayres. ‘People aren’t yet saying that there are thousands of people dying in the EU from climate change, but they are from poor air quality.’

Outside in the car park a test bed truck fitted with a Dearman TRU is being refuelled with liquid nitrogen (LiN), a process involving lots of hoses, frost-rimed valving and pools of cold vapour: all very Cape Canaveral.

The obvious drawback to the system – that it requires each truck to carry its own independent LiN supply rather than just using diesel from the main tank – is more than compensated, says Ayres, by the advantages.

Like a conventional internal combustion engine, the Dearman exploits a heat gradient to generate power, but instead of starting at ambient temperatures and getting hotter it starts at the temperature of liquid nitrogen, minus 196 degrees centigrade (the other key difference from a regular IC engine is that nothing is burned, the power comes from the rapid expansion of the gas).

‘The Dearman is like a steam engine except that it runs about 300 degrees cooler. So even a truckload of frozen chickens is like a boiler. It produces about twice as much cooling power as it does shaft power, that steered us to refrigeration.’

This means that it can use the heat extracted from the refrigerated compartments to cool them even further, making it much more efficient. The demo truck’s party trick is the ‘25 minute pull down’ cooling a full-sized reefer truck down to -21 degrees centigrade in almost half the time it takes a diesel-powered system.

How does it work? This where it gets a bit tricky: those who are interested in the thermodynamics, read on. Otherwise skip this bit. Liquid nitrogen from the tank passes through a heat exchanger in the refrigerated compartment, where it partially cools the contents, becoming a gas in the process but remaining at the same super-low temperature thanks to the latent heat of evaporation.

It then enters the engine where it mixes in the cylinder with a heat exchange fluid (mostly water) at ambient temperature. The fluid warms the cold gas which expands rapidly, pushing the piston down. The nitrogen is vented through the exhaust, but the heat exchange fluid is recycled.

He won’t be drawn on prices, but higher upfront costs are offset by cheap running and the futureproof appeal of zero-emissions. Long term trials are underway with Sainsbury’s and another un-named ‘branded food supplier’, leading, they all hope, to a slew of orders. ‘We pick these customers carefully –extended trials are hugely expensive for us so we want people who will place orders, with big enough fleets to really move the dial.

‘The story really starts with the UK and Europe as one, but in the medium term a lot of the business will be in India and China – the cold chain doesn’t really exist in those countries so there is a chance for a green field low-carbon approach.’

Other possible applications include stationary back up or peak-reducing electricity generation, and even bus aircon in hot countries. ‘In places like Singapore the air conditioning takes up to 40% of the total power required by a bus.’ A more powerful multicylinder prototype (under test, below) is being developed for these uses.

Back inside in the workshop, Dearman engines are currently hand assembled in very small numbers. The internal parts – pistons, cylinders, crankshaft, valvegear – would be pretty familiar to anyone who has seen a car or motorbike engine in bits on a bench. That’s another advantage, he says – no exotic or expensive bits or materials are required. ‘The engine is quite like an internal combustion engine, so many of the components we need already exist and there’s a great supply chain in the UK.’

The company was founded by Ayres and two others in his spare room back in 2011. The business is now funded through a mix of private equity (from biotech specialist Park Vale Capital) and public grant money (including from Innovate UK and £6m from the Advanced Propulsion Centre). It’s a combination which Ayres says has proved surprisingly synergistic – private investors like the validation of winning government grants, and the government in its turn is reassured by the involvement of private investors that that there is a market for the end product.

Some £40m in total has been raised so far – not bad for a hi-tech start up with not an app, smartphone or social media platform so much as mentioned in its business plan. The firm employs around 70 people, many of them engineers from an automotive or aerospace background.

‘I’ve always been fascinated by engineering despite the fact that I trained as an economist. Working in this business provides an endless stream of fascinating challenges and I’m never bored at work.’

Commercial partnerships with UK refrigerated transport outfit Hubbard, and industrial gas specialist Air Products are in place, and will eventually lead to the partners manufacturing and supplying TRU’s using Dearman technology.

Profitability is in sight, he says, perhaps a couple of years down the line, at the end of which the company will have changed a lot. ‘The tech development is coming to an end, it’s more about how we turn this into products now. You have to do things very differently if you want a repeatable process.’

And as for their home in the not so leafy sprawl a few miles south of Crystal Palace (conventionally London’s southernmost point, at which the capital ends and suburbia begins) Ayres thinks the place deserves more creds as a location for a fast-growing business.

‘Croydon is a good home for us given what we are doing. We have partners in the Midlands who have a lot of churn, but we can say to our 20-30 year olds "Yes you can live in London and have a great job where you will be doing world firsts on an almost weekly basis.

‘It’s also an advantage because it’s easy for policy makers and foreign visitors to come and see us when they are in London. If we were somewhere like Strathclyde that wouldn’t be the case.

‘That really makes a difference because we are doing something pretty left field – there is no trade association so we have to put a lot of effort in ourselves.’

And if that effort comes off, the coolest thing in Croydon since la Kate could soon be pretty hot.


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