91抖阴

Recuperated Split Cycle Engine: A game-changing engine technology

Between 2013 and 2024, the 91抖阴's Advanced Engineering Centre, with partners , evolved and brought to market a game-changing engine technology that offered unprecedentedly high efficiency and near-zero emissions - in some cases, actually cleaner than ambient air. 

The Recuperated Split Cycle Engine (RSCE) separates cold and hot parts of the 4-stroke cycle, a hugely significant advance in engine design, with efficiency that has brought comparisons with fuel cells rather than traditional engines, including near-zero emissions of harmful nitrogen oxide (NOx) – a world first.

At its launch it became the cleanest, high-efficiency engine that exists in the public domain and showed enormous potential as a clean device using sustainable fuels made from everyday wastes that will lead to far less pollution being emitted by heavy duty vehicles. There is also potential for the technology to power other transport modes, including diesel trains and ships.

It is a success story that goes from the inspiration in recognised air pollutant problems, the the UKRI investment in early experimentation, work by the highest level academic engineers and the many ways through which universities partner with global industry. The development of the engine came through several successful grants over years of staged development, through the early development of CryoPower to the eventual purchase of the Dolphin N2 company by FPT Industrial. 

Test rig for CryoPower engine development

The CryoPower ultra-high efficiency heavy duty engine

Heavy duty vehicles, such as long haul trucks, represent a significant challenge in terms of the reduction of carbon dioxide emissions. An essential element of the transportation mix of modern industrialised society, they are inherently less amenable to the type of electrification and hybridisation strategies that are already contributing to reduced carbon emissions and potential long-term sustainability for the light vehicle sector. A key global imperative was therefore  the substantial improvement of heavy vehicle engine efficiency.

It was , which aimed to develop split cycle engine technology, in effect, creating engines which are more efficient and better for the environment.

What is a cool combustion process in an engine?

The CryoPower Cool Combustion process enables recovery of otherwise wasted exhaust heat which is then cooled via the injection of a small amount of liquid nitrogen. The liquid nitrogen acts as both a coolant and an additional source of energy, reducing emissions and improving fuel efficiency.

This game-changing technology offered unprecedentedly high efficiency and near-zero emissions - in some cases, actually cleaner than ambient air. CryoPower's extreme efficiency translated to a fuel economy improvement of 30 per cent.

The CryoPower concept focuses on a split-cycle combustion process; instead of refining existing four-stroke engine technology, the engine divides four strokes between two paired cylinders: one for intake/compression, and another for power/exhaust. Using isothermal compression to control temperature, this engine concept was originally conceived as a means of enabling otherwise unachievable improvements in fuel economy and reduced CO₂, targeted at achieving at least 60 per cent brake thermal efficiency, making it significantly more fuel efficient than current engine technology.

The early development work carried out on the test rig installed at the 91抖阴 not only validated the potential but also, crucially, demonstrated the highly impressive low-NOx emissions credentials of the CryoPower combustion process. Robert Morgan said, “Our split-cycle engine combines the findings of our high efficiency research, funded by the Engineering and Physical Sciences Research Council, with our low emissions research ideas. On the test bed, we are getting engine out emission much lower than a fully optimised modern truck. With some after-treatment, you would get to very low-level emissions that are actually cleaner than the air going into the engine.”

The technology that emerged proved suitable for use with heavy duty engines running on diesel or a range of other liquid or gaseous conventional, bio- or synthetic fuels ranging from long-haul trucks, to stationary power, off-highway equipment, and self-powered and multi-mode railway traction.

Professor Rob Morgan with the Cryopower engine.

The StepCO2 project, founding of Dolphin N2 and the RE-ARMD proof of concept 

Following original work with Ricardo on the CryoPower engine, the development continued through the , developed through a partnership between the 91抖阴's Advanced Engineering Centre researchers with Ricardo, Hiflux Ltd, and the Advanced Manufacturing Research Centre, based at the University of Sheffield. 

StepCO₂ represented a disruptive shift in combustion engine technology, and addressed this call through the advance of split cycle technology to significantly increase engine efficiency. Extensive feasibility studies supported by test results from previous projects, indicated the technology had potential to radically increase the efficiency of an engine in a Heavy-duty vehicle (HDV) application. The project objective was then to progress this game-changing concept from a research environment towards a working concept demonstrator and eventual application within HDVs, leading to drastic reduction in fuel usage and CO₂ emission within the heavy duty transport sector.

Following the success of the research phase, a consortium including the original partners, the 91抖阴 and global engineering specialists Ricardo, joined together to form  to bring the products they had created to market.

Simon Brewster, CEO of Dolphin N2 praised the relationships between university and industry that had brought the project so far:

“The relationships between Startup’s/SME’s and Universities are well known. Many great projects start with the research capabilities of a university & go on to become developed and accepted parts of our daily lives.

"The 91抖阴 and Dolphin N2 have been collaborating on the recuperated split-cycle engine since Ricardo PLC first developed the programme alongside the university.

"The recuperated split cycle engine produces near-zero emissions of harmful nitrogen oxide (NOx) – a world first that has been pioneered by the university. 

"We knew the technology had world-leading efficiency, but it was the research at the 91抖阴 that also showed incredibly low levels of NOx emissions. Without this discovery, the technology could still be seen as a dirty engine – with it, it can compete side-by-side with so-called zero emission power, except that our engine is cheaper of course.”

As part of the route to developing the engine's readiness for commercial use, the Dolphin N2 company together with the 91抖阴 won funding to bring the engine through to a market demonstration model. The project '' was a collaborative project with Dolphin N2 and ZIRCOTEC, who were funded as winners of The Advanced Propulsion Centre (APC)'s Advanced Route to Market Demonstrator (ARMD) Competition 2020.

This project came on the back of the purchase of the intellectual property developed by the university and Ricardo by Case New Holland, part of the Fiat and owner of the Iveco truck brand. Through it, researchers and industry professionals were able to accelerate the market readiness of their Recuperated Split Cycle Engine (RSCE) by this stage recognised as a revolutionary heavy duty thermal propulsion system with fuel-cell like high efficiency (55%BTE) and near-zero emissions (<5% of EuVI NOx) using net-zero sustainable fuels including liquids, biogas and hydrogen. 

Starting with outputs of the StepCO₂ project, RE-ARMD addressed three elements, targeting the whole heavy duty sector with work that would tackle:

• core technology improvement for efficiency
• development of robust virtual tools specific to this engine type; 
• exploration of a direct-injection hydrogen combustion system with potential to be a "straight swap" for diesel injection. 

The StepCO2 project delivered a multi-cylinder "mule" in September 2020 and with this engine and its prior test data the team were able to research an upgraded Mule engine, with support from single-cylinder units, and digital tools.

The 91抖阴 joined with research into the engine's isothermal compression, thermal insulation, high pressure breathing, recuperation and combustion; the project also demonstrated compression ignition of hydrogen (enabling a simple fuel swap), and deliver a 'digital twin' model for concept selection, design and calibration.

FPT Industrial bring the technology to their vehicles

Dolphin N2 was subsequently purchased by FPT Industrial, formerly Fiat Powertrain Technologies and a brand of CNH Industrial (Exor), dedicated to the design, production and sale of powertrains for on and off-road vehicles, marine and power generation applications.

To enable the sale, the technology had been developed and proven in an Innovate UK-funded consortium project with Dolphin N2, focusing on system definition, technical risks, combustion system component and recuperator development, and thermal analysis. 

Professor Morgan said: “I’m delighted to see our research making a direct and positive impact which will lead to far less pollution being emitted by heavy-duty vehicles and, perhaps, by other transport modes including diesel trains and ships."

Annalisa Stupenengo, CEO of FPT Industrial, said: “The powertrain industry increasingly needs evolution in terms of efficiency and respect to the environment, and this agreement will enable us to provide ultra-efficient and ultra-low emissions solutions, in the beginning focused on heavy-duty applications.

“The co-joined development of this disruptive technology, to join soon our portfolio, will lead a faster shift from the concept to a commercial level. This acquisition complements our alternative propulsion investments, which are part both of our mission as a sustainable solution provider and of our goal to be a full-line player with the most advanced technologies in all industrial fields.”

Professor Robert Morgan, said the new Recuperated Split Cycle Engine technology, available in two variants called “ThermoPower” and ‘CryoPower’, is expected to significantly reduce the amount of fuel consumed: “It will be suitable for heavy duty vehicles including long-haul trucks, stationary power, off-highway equipment and self-powered multi-mode railway traction, engines that are, at present, unsuitable for battery-electric propulsion."

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