Ricardo Developing Liquid Nitrogen-Diesel Engine for Trucks

February 22, 2018 by John O'Dell

Ricardo, a British engineering company that has produced engines for World War I tanks and modern McLaren supercars, is developing a liquid-nitrogen enhanced engine that’s seen as a potential game-changer for long-haul trucking.

The new engine promises to reduce truckers’ fuel costs and extend the future of the diesel engine by slashing toxic and smog-causing emissions. But it’s far from a sure thing. Ricardo has bench tested its individual components but has yet to assemble a working power plant.

The company estimates that it will take at least five years to assemble the engine, to bolt everything together, certify it for commercial use and bring the first of the CryoPower motors to market.

But Ricardo believes the CryoPower clean-diesel engine will offer a 20 percent reduction in fuel costs and reductions of up to 30 percent in toxic and greenhouse gas emissions.

The fuel savings would represent about $12,500 per year per truck for long-distance freight movers, Ricardo said.

Another firm claiming the same scale of fuel efficiency and emissions reduction, at a lower cost, already is testing one version of its engine. San Diego-based Achates Power has developed an opposed piston engine that it says will cost about 10 percent less than a conventional diesel. The company says its engine can be scaled for use in cars and trucks and should be ready for the road by 2020.

Ricardo’s timetable is dictated by developmental complexity.

“The principle is relatively straightforward; the challenge is turning theory into practice,” Simon Brewster, the former Ricardo executive now heading its CryoPower spinoff, Dolphin N2, told Trucks.com.

CryoPower, a clean diesel engine that can slash emissions and cut fuel costs, was developed by British engineering firm Ricardo and University of Brighton

CryoPower, a clean diesel engine that can slash emissions and cut fuel costs, was developed by British engineering firm Ricardo and University of Brighton. (Photo: Ricardo/University of Brighton)

The cost of bringing the technology to the trucking world could leave some uneasy.

“On-road applications would likely require increased capital expenditures by fleet owners for the additional components required, such as nitrogen tanks” and the incremental cost of the engine itself, said Shreyas Sirsi, a senior vice president of AlixPartners’ automotive and industrial practice.

“The promise is even greater diesel engine efficiency while reducing one of diesel’s biggest challenges— nitrogen oxide emissions and soot. A conventional diesel cannot generally do both,” said Bill Van Amburg, senior vice president and head of trucking programs for Calstart, the Pasadena-based coalition for advanced transportation technologies.

But even if the CryoPower engine works well, “the big issues of nitrogen production and distribution remain,” Van Amburg said.

Answering such questions is what the next step is all about, said Brewster. The engine will be cost competitive with any standard diesel that can meet stringent U.S. and European emissions regulations, he said.

The engine has been under development for the past decade by Ricardo’s engineers, working with engineers and researchers from the University of Brighton, located near Ricardo headquarters and technical center in Shoreham-by-Sea on England’s southern coast.

The engine’s name refers to the cryogenic, or super-cold, state of liquid nitrogen. It is injected into the engine’s intake cylinders to boost the efficiency of the fuel combustion process, resulting in reduced fuel consumption and emissions

“There’s a level of complexity in implementing the hardware and making it all work together,” Brewster said.

Building a completed engine is the next step and Dolphin’s first task — along with attracting investment for the project.  “We will have a demonstrator in 18 months, and we could have a production-ready engine for trucks in five to six years,” he said.

The CryoPower engine design retains about 80 percent of the bits and pieces of a standard heavy-duty diesel engine, but adds a heat exchange chamber, which Ricardo calls a “recuperator.” Special nitrogen injectors also are needed, along with a variety of pumps and lines to move air and fuel.

Another key difference: A standard internal combustion engine completes the full compression, ignition and exhaust cycle in each cylinder, while Ricardo’s engine separates the functions. It isolates some cylinders for the air intake and compression cycle and uses others for the ignition-exhaust cycle.

In a six-cylinder version of the CryoPower engine, liquid nitrogen — at a temperature of minus 320 degrees Fahrenheit — is injected into a pair of intake-compression cylinders, where it works to chill the air. That increases the efficiency of the compression process because cold air is dense and requires less work from the engine to compress.

The Crypower system adds several components to a conventional diesel engine, alters the air intake, fuel combustion cycles.

The Cryopower system adds several components to a conventional diesel engine, alters the air intake, fuel combustion cycles. (Photo: Ricardo/University of Brighton)

The nitrogen-enriched compressed air is then pumped into the recuperating chamber, where heat from the engine’s exhaust is used to warm it again. At the same time, the exhaust gas cools down as its heat is transferred into the compressed air. Cooler exhaust reduces NOx emissions.

In the final phase, the reheated, nitrogen-enriched compressed air is fed into the engine’s four combustion-exhaust cylinders and the diesel fuel is injected. The increased nitrogen content of the compressed air makes it burn hotter, consuming more of the diesel fuel in the combustion process.

About twice as much liquid nitrogen as diesel fuel is used by the engine. A long-haul truck using 80 gallons of diesel for a 1,000-mile trip today would use 56 gallons of diesel and the equivalent of about 100 gallons of liquid nitrogen for the same trip with Ricardo’s engine.

The cost of liquid nitrogen at today’s prices, as low as 50 cents per gallon in some markets, would reduce overall fuel cost savings by 20 percent.

The trucking industry is under pressure around the globe to reduce emissions. Companies are experimenting with a variety of alternative fuels and power plants to find a replacement for the conventional diesel engine.

Electric motors provide the needed torque to get heavy loads moving, but they have range issues because of limits imposed by battery capacity, weight and bulk.

Many liquid fuels developed to replace diesel in internal combustion engines lack diesel’s energy density, require costly engine and fuel system modifications or are constrained by lack of fueling infrastructure.

Liquefied and compressed natural gas have become popular alternatives, though. Ricardo settled on liquid nitrogen as a fuel enhancement in part because “the necessary cryogenic storage and fuel tanks and fuel-handling systems are already in place” for liquefied natural gas trucks, Brewster said.

The liquid nitrogen for a long road trip could be carried in on-board tanks filled at the trucking company’s home terminal, Brewster said. That would eliminate the need, and expense, of locating nitrogen fueling facilities at truck stops.

But insulated tanks that would keep the nitrogen cold enough to remain liquid are much bulkier than standard fuel tanks, so the nitrogen and its related storage system likely would reduce a truck’s valuable cargo capacity by about 1,000 pounds.

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