Heat exchanger (2) providing cooling to goods compartment from refrigeration unit

Heat exchanger (1) providing cooling to goods compartment from cryogen

Cryogenic storage vessel

Refrigeration unit and Dearman engine

Developing liquid air engines for transport and static applicationsTransport refrigeration (fleet)Process: The cryogen is vaporised in a heat exchanger in the refrigeration compartment, so cooling it. The high pressure gas is used to drive the Dearman engine, whose shaft power can be used to drive a conventional refrigeration compressor or for auxiliary power.

Need: Diesel-powered transport refrigeration units (TRUs) are inefficient and highly polluting. Refrigeration alone can consume as much as 20% of a truck’s diesel, and a TRU emits up to six times as much NOx (nitrogen oxides) and 29 times as much PM (particulate matter) as a modern Euro VI truck propulsion engine.

Advantage: The Dearman transport refrigeration unit is a significant advance on existing refrigeration systems that use liquid nitrogen because it produces both cooling and shaft power from a single unit of ‘fuel’. This means it is extremely efficient and cost effective.

Heat hybrid – buses and heavy duty urban vehiclesProcess: Heat from the internal combustion engine (ICE) cooling loop is used to ‘boil’ the liquid air or nitrogen and to warm the heat exchange fluid (HEF). The power produced by the Dearman engine is fed into the main gearbox, allowing the ICE to be downsized and operate more efficiently.

Need: An internal combustion engine loses roughly a third of the energy in its fuel through the radiator as low-grade waste heat, which conventional technologies find difficult

to harvest.

Advantage: A heat hybrid would be cheap to build and could reduce diesel

consumption by up to 25%. Modelling suggests heat hybrid delivery trucks would repay their investment in around four years, while heat hybrid buses would pay for themselves in under three.

ZEV (Zero-emission Vehicle)Process: As the transport refrigeration application. Power from the engine drives the vehicle’s propulsion system.

Need: Last-mile produce delivery in urban areas. Off-highway and underground mining vehicles (where cold operation is particularly valuable).

Advantage: ‘Free’ air conditioning or refrigeration from engine with no impact on range. Well-suited to shorter range low power vehicles such as auto-rickshaws (tuk-tuks), fork lifts, or mining fleets.

Auxiliary power and static cooling

Process: Large scale Dearman engines can be used to provide distributed cooling

and power on demand.

Need: Distributed cold stores are vital to the food security and the economic growth of developing countries. The system can be used for back-up power to replace diesel gensets.

Advantage: Very cold and fast cooling (pull down) can be achieved. Potential to integrate with renewable technologies.

BackgroundSince 2011, a team of engineers and energy pioneers has been developing a zero-emission engine fuelled by a cryogen – either liquid air and liquid nitrogen.

Using the idea of a cryogen as a working fluid in a piston engine, classic British ‘garden shed’ inventor Peter Dearman developed a novel way to increase incumbent cryogenic expansion technology.

This innovation led to the development of the Dearman engine, an innovative expansion engine that is zero-emission at the point of use. It delivers both cold and power from the same unit of cryogenic fuel.

Dearman is developing the engine into a modular family of technologies with relevance across on-/off-grid, static, and transport applications.

Process and designLiquid air or liquid nitrogen is pumped from an insulated storage tank through a heat exchanger.

Here it is exposed to heat – either ambient from freight or waste heat from the internal combustion engine (ICE). This heat causes the cryogen to re-gasify and rapidly expand.

In the engine the cyrogen is mixed with a heat exchange fluid (HEF) – this ensures near isothermal (constant rate) expansion, driving the engine’s piston.

The engine design is simple – made from aluminium and plastic parts that are easily sourced in existing supply chains. It will be relatively inexpensive to build.

The Dearman engine technology will be low maintenance and have low environmental impact.

Cryogens as a fuelUse: The Liquid Air on the Highway report demonstrated that the UK’s existing surplus liquid nitrogen production capacity can be used to roll out these technologies. It also cited that, in the future, liquid air might be a more economic fuel for applications in which separating air’s constituent parts is unnecessary.

Both cryogens can be used in Dearman’s technology, as their thermal properties are so similar.

Safety: Liquid nitrogen is already used in fleet refrigeration systems (natureFridge) and there are well-established safety protocols surrounding its use. There are already liquid air plants in use (Highview Power Storage) and Dearman looks forward to working with the industrial gas and cryogenic industries to further explore the safety of liquid air and its potential use a fuel in on-road fleets.

Results and developmentIf all applications grow as projected in the Liquid Air on the Highway report, the entire UK liquid air fleet would grow to 36,000 vehicles by 2025, and would saved→ more than 1 billion litres of diesel→ 1.4 million tonnes of CO2e (well-to-wheel)→ £113 million net of investment costs

Dearman liquid air technologies play to the UK’s strengths and expertise in cryogenics, manufacture and engineering. The technology has the potential to create 2,100 jobs in these areas.

dearmanengine.com

N2 tank

Fuel tank

HEF tank

Liquid air

Driveline

IC engine

Heat exchanger (2) providing cooling to goods compartment from refrigeration unit

Heat exchanger (1) providing cooling to goods compartment from cryogen

Cryogenic storage vessel

IC engine

Driveline

Liquid air

HEF tank

Fuel tank

Refrigeration unit and Dearman engine

N2 tank