The big breakthrough for diesel efficiency

Combustion redefined is perhaps the best description of a game-changing heavy duty engine concept developed by Ricardo. CryoPower promises a dramatic improvement of 30 percent in long-haul truck fuel efficiency and CO2 emissions, together with a substantial 20 percent reduction in fuel costs and potentially very low emissions. It also offers a cost effective route for use of renewable electricity in heavy duty transport. Anthony Smith talks to the team at Dolphin N2, the new Ricardo spin-out formed to pursue commercial development of the revolutionary CryoPower engine.

Heavy duty trucks and semitrailers transport the lifeblood of the modern industrial economy, be it on North American Interstates, German autobahns, Japanese expressways or the myriad highways crisscrossing
every continent. These ubiquitous vehicles ensure that the freight keeps
flowing: without them, trade in everything from raw materials, fuel and foodstuffs to finished products for our shops would simply stop.

It follows that heavy duty vehicles are a very significant consumer of fuel
and source of CO2 emissions. According to European Commission estimates, the heavy duty vehicle fleet represents approximately one quarter of all CO2 emissions due to road transport, as well as around 5 percent of the EU’s total greenhouse gas emissions – a greater share than international aviation or shipping. As a result, regulation of heavy duty vehicle CO2 emissions is now in the process of implementation by the EU,
echoing similar measures in Japan, the US, Canada and China.

But, as Ricardo chief technology and innovation officer Professor Neville Jackson explains, while technological solutions such as battery-electric and hybrid powertrains have helped decarbonize the passenger car and light duty commercial vehicle fleets, the reduction of CO2 from heavy freight applications is a far harder task: “The challenge with long-haul heavy
trucks is that the cost, mass and package envelope required for high-capacity battery systems limits the effectiveness of the type of powertrain electrification solutions that we can very successfully implement to reduce CO2 emissions in other segments of the market. In a transport industry already highly focused on operating margins as well as capital costs, any consequent restriction on available payload or range is extremely difficult to implement and is a very hard to sell to the operators.”

As a result, while battery-electric solutions can be very attractive for lighter duty distribution fleets and heavy duty short-haul drayage applications such as port complexes and distribution hubs, the conventional four-stroke diesel engine remains – almost universally – the power plant of choice for heavy duty, long-haul trucks. This makes it a prime candidate for a step-change boost in efficiency – something that CryoPower can now promise.

Ricardo redefines the combustion engine

By contrast, rather than incrementally improving upon existing technology, the Ricardo CryoPower split-cycle engine concept redefines the processes of reciprocating internal combustion to enable significantly improved internal thermal efficiency in comparison with today’s state-of-the-art engines. Instead of bolting on auxiliary exhaust heat recovery devices, the CryoPower concept aims to incorporate exhaust heat recovery into the engine’s actual operating cycle.

“With CryoPower we are to a large extent combining the best aspects of
a recuperated gas turbine – where the post-compressor gas receives heat energy from the exhaust prior to combustion – with the best attributes of a reciprocating combustion engine,” explains Jackson. “The technical approach is critical to the success of CryoPower technology, but cost is crucial too. Instead of the expensive materials and processes required to build a gas turbine, we are using essentially conventional reciprocating engine construction and materials.”

CryoPower breaks with the conventional four-stroke truck engine configuration and instead splits it into separate cylinders – one for induction and compression, the other for combustion and exhaust. This
enables the otherwise wasted exhaust heat to be recovered to the working gas after the end of compression. It also allows true Miller cycle operation as the intake and compression cylinder and combustion and exhaust cylinder can each be sized for maximum efficiency.

Read the full article in RQ 2018 Q1