If I told you that a “cryogenic engine” could revolutionize refrigerated trucking, you might ask, one, what the hell a cryogenic engine is, and two, why you should care about refrigerated trucking.
Let’s take the last bit first. Refrigerated trucks use up a lot of energy and emit tons of pollution as they move perishables around the U.S. and the rest of the world. Cold-chain trucks are some of the biggest on the road. They consume fuel both in their engines and in their cooling systems, which are diesel-powered and tend not to be government-regulated. It’s estimated that cold trucks use 25% more fuel than normal trucks, and normal trucks have a high emissions profile to start with.
The cryogenic–or liquid air–engine was invented by Peter Dearman, a British engineer. It uses a tank of liquid air, which is normal air that’s been cooled to minus 196 degrees Celsius. The engine passes small amounts of the liquid into a piston, where it comes into contact with another liquid at ambient temperature and expands. The reaction causes the liquid to turn to gas, releasing the energy stored from the cooling process. The gas then pumps the piston, and provides power.
What’s interesting is that as well as producing energy, the engine also provides cold that can be used in refrigeration. The result is a zero-emission refrigeration unit that uses no diesel. “Because we deliver power and cold, we can very simply replace that diesel engine with a liquid air engine, saving 20% of diesel consumption and the associated emissions impact,” explains Toby Peters, CEO of the Dearman Engine Company.
Liquid air is an alternative to hydrogen or batteries, which also store energy. Ideally, the electricity required to liquify the air in the first place would be off-peak renewable power that otherwise might be wasted. That could improve the economic case for solar and wind, and raise the engine’s overall environmental performance.
As well as refrigeration, the Dearman engine can also be used in combination with an existing diesel or natural gas vehicle. The “heat hybrid” system recovers low-grade heat from the radiator or the cabin, which it uses to increase the temperature of the contact liquid inside the piston. That in turn increases the efficiency of the process, and reduces fuel consumption.
“We’re not saying it’s a silver bullet,” says Peters. “What we’re saying is that it has interesting attributes and could have relevant applications. We can use it to reduce refrigerated transport emissions, particularly in the developing world, where there is massive demand. If we follow the business-as-usual model, it’s going to lead to a lot of problems with pollution.”
The advantage of liquid air is that it’s a known technology: the first car engine appeared in the late-1800s. It’s also relatively cheap to manufacture, according to Peters. Plus, a fueling infrastructure already exists, as liquid nitrogen has several industrial uses. And, the liquid itself is non-flammable and safe, provided it is stored correctly.
The Dearman company is currently trialling the refrigeration unit with a U.K. grocery chain. It hopes to go into production in about 20 months, Peters says.