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Dearman Engine signs MOU with Hubbard Products for integration of liquid air engine TRU; report details liquid air benefits

Dearman liquid air engine in a TRU system. Click to enlarge.

The Dearman Engine Company has signed a Memorandum of Understanding with Hubbard Products Ltd to manage the vehicle integration of the Dearman engine liquid air transport refrigeration system (TRU) (earlier post). Part of the worldwide Zanotti group, Hubbard Products is the UK’s principal designer, manufacturer and supplier of refrigeration systems and units and the leaders in refrigeration for commercial vehicles and refrigerated vans.

The objective of this collaboration is to advance the technical, commercial and industrial development of the Dearman engine transport refrigeration system to a stage where Hubbard can manufacture, integrate and market cooling systems incorporating the Dearman engine in commercial volumes. The announcement of the MOU was concurrent with a release of a report—Liquid Air on the Highway—detailing the environmental benefits of the liquid air engine.

The Dearman engine is a novel piston engine powered by the vaporization and expansion of liquid air or liquid nitrogen. Ambient or low grade waste heat is used as an energy source with the cryogen providing both the working fluid and heat sink. The Dearman Engine process involves the heat being introduced to the cryogenic fluid through direct contact heat exchange with a heat exchange fluid (HEF) inside the engine.

The specific first objective is for Dearman and Hubbard to collaborate to deliver approximately five field trial prototypes of the refrigerated vehicle system to an end user in the UK, early next year. Dearman is already engaged in discussions with two major supermarkets.

In terms of technical responsibility, Dearman would supply the engine systems and Hubbard the refrigeration equipment combined with off-vehicle systems integration elements. Hubbard would not manufacture the Dearman engine itself but will act as the system integrator contracted by the major multiples who buy it, such as supermarket chains.

Hubbard’s membership of the Zanotti Group, which has also approved this MoU, gives Dearman the potential for a global refrigeration system partner.

Liquid air. Air turns into a liquid when cooled to around -196 ˚C using standard industrial equipment. This process can be driven by renewable or off-peak energy. 710 literes of ambient air becomes about 1 liter of liquid air, which can be stored in an unpressurised, insulated vessel. When ambient or low grade waste heat is reintroduced to liquid air it boils and turns back into a gas, expanding 710 times in volume. This can be used to drive an engine. It also exhausts lots of cold, making it highly relevant for processes which require power and cooling.

The novelty of the Dearman Engine lies in its use of a heat exchange fluid (HEF – water or water and glycol mix) that promotes extremely rapid rates of heat transfer inside the engine, allowing a small, single-stage Dearman engine to achieve levels of thermal efficiency that would otherwise require more costly, multi-stage expansion with re-heating. In this way the Dearman engine also reduces the size of bulky and inefficient external heat exchanger that handicapped earlier cryogenic engine designs.

A Dearman Engine power cycle.

Liquid Air on the Highway. A new report published today by the Liquid Air Energy Network, the Centre for Low Carbon Futures, and the University of Birmingham, has found that replacing just 13,000 refrigerated transport units in the UK with a liquid air engine zero-emission solution could reduce reduce annual emissions of NOx by more than 1,800 tonnes—equivalent to taking almost 80,000 Euro 6 trucks or 1.2 million Euro 6 diesel cars off the road. Annual emissions of PM would fall by 180 tonnes, equal to removing more than three times the entire UK articulated truck fleet from the road, or 2.2 million Euro 6 diesel cars.

An analysis by the consultancy E4tech shows that a TRU emits six times as much NOx and 29 times as much PM as a Euro 6 truck engine. Compared with a Euro 6 diesel passenger car, the TRU emits almost 93 times as much NOx and 165 times as much PM.

The report—the result of a 9-month study—found that adoption of liquid air technologies in trucks and buses more broadly could save Britain 1.3 billion liters (343,000 gallons US) of diesel; more than one million tonnes of carbon; and £115 million (US$193 million) by 2025, net of all costs.

The report, part-funded by the UK’s Technology Strategy Board and launched at an event hosted by the Society of Motor Manufacturers and Traders (SMMT), explores the potential benefits and implications of introducing liquid air engines in commercial vehicles in Britain over the next decade. While a number of engine concepts are being developed, the report focuses on the two closest to commercial deployment:

  • A zero-emissions power-and-cooling engine for truck and trailer refrigeration. The refrigeration unit currently being developed by the Dearman Engine Company uses liquid air or nitrogen to produce both cooling and shaft power.

    First the cryogen is vaporized in a heat exchanger in the refrigeration compartment, so cooling it down; then 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. This would produce even greater well-to-wheels emissions savings than simple evaporation of liquid nitrogen compared to a diesel TRU.

  • A diesel-liquid air “heat hybrid” engine for buses, trucks and other commercial vehicles. A heat hybrid consists of a diesel engine and a liquid air engine integrated so that waste heat and cold are exchanged between the engines to increase the efficiency of both and reduce diesel consumption.

    A conventional internal combustion engine loses roughly two-thirds of the fuel energy as waste heat—about one third each through the radiator and exhaust. The heat lost through the radiator is low grade (~100°C) which conventional technologies find difficult to harvest. However, since the Dearman Engine bottom temperature is -196°C, even low grade waste heat can be converted into shaft power at practical conversion efficiencies of up to 50%.

    The cooling loop of a diesel engine contains a mixture of water and glycol—just like the heat exchange fluid in a Dearman engine. This means the ICE waste heat could be transferred either directly, combining radiator fluid and HEF in a single circuit, or indirectly, via two separate circuits connected by a heat exchanger.

    A heat hybrid would convert waste heat from the ICE into extra shaft power through the Dearman engine. An ICE-DE heat hybrid could consume up to 25% less diesel, and deliver progressively larger CO2 savings as the carbon intensity of grid electricity used for liquefaction falls.

The Dearman Engine Company is developing both applications, and its refrigeration engine begins on-vehicle testing this summer, with commercial production scheduled from 2016.

The report also demonstrates how viable liquid air is as a potential “fuel”. Liquid air is not yet produced in commercial quantities, but liquid nitrogen, which can be used in the same way, is widely available. The roll-out of liquid air vehicles could be fueled entirely from existing spare liquid nitrogen capacity until at least 2019.

All of Britain’s major cities are within commercial delivery distance of the existing liquid nitrogen distribution network, and refueling equipment for fleet vehicles could be easily installed at operators’ existing depots.




Sez the energy density of liquid air is equivalent to an EV battery, and liquid air is a great way to store surplus energy, particularly as cryogenics are sensitive to daytime power production costs. This should particularly benefit Scotland which is now aiming toward 40% reliance on wind power, and which has the land to avoid deepwater turbines of indeterminate expense.

This tech is ancillary to proposed tech to store air at high pressure underwater in balloons, for energy storage. The precompression only makes liquifaction and molecular diffusion easier. Michigan might be a goodplace to start.

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