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Roadmaps Explored: Thermal propulsion systems will still play a part in the automotive sector

This year the Advanced Propulsion Centre (APC) successfully launched the Automotive Council’s updated product and technology roadmaps at LCV2017. The Automotive Council’s consensus roadmaps have been charting globally significant technology trajectories since they were first produced in 2009 and have provided a solid foundation for engagement between government, academia and industry.

Over the coming weeks, the APC will explore what the technology roadmaps mean for the future of propulsion in the automotive industry. Using data collected from the roadmapping process and insights from the experts in the field, the APC intend to add colour and texture to the roadmaps through a series of online articles. In this first post, the APC explores the key messages of the thermal propulsion systems roadmap and gain insights from both of the APC spoke leads.

Rumours of my death have been greatly exaggerated…

In the corridors of most automotive conferences, the future of the internal combustion engine is a topic that always inspires intense debate. In the wake of numerous government announcements on petrol and diesel cars, the debate has shifted beyond automotive circles and has caught the attention of the mainstream media. However, if you scratch beneath the media headlines, you will find consensus that there’s still a role for internal combustion engines. Last month the UK’s Department for Transport’s clarified their recent 2040 ambition and revealed that PHEVs could be sold beyond 2040 as they offer consumers zero emission capability.

To some commentators this new information seemed like a relaxation of government policy, however, make no mistake: the clarification does not mean business as usual for engine manufacturers. Thermal propulsion systems (the Automotive Council’s term for engines) need to evolve with the changing landscape and deliver a step-change improvement in efficiency and emissions reduction. The phrase captures technologies that go beyond just the base engine and combustion cycles to include system level technologies such as control strategies, boosting and after-treatment systems.

The Automotive Council’s new Thermal Propulsion System Roadmap, updated by the Advanced Propulsion Centre, aims to chart the potential evolution of thermal propulsion systems in the context of deep change in the automotive industry. In this article we discuss the main changes from the 2013 roadmap and offer key insights from the APC Spoke leads.

Hybridisation is an opportunity, not a threat

In 2013 the Automotive Council launched the Internal Combustion Engine Roadmap at LCV2013. Its launch was effective in coalescing industry and academia around a common set of technologies that were crucial for the UK’s future research and development activities in advanced internal combustion engines. Given the positive reception of the previous roadmap, the 2017 Thermal Propulsion Systems Roadmap embraces the technological and social shifts facing the automotive industry.

Looking at how the passenger car market is developing, almost all of the major OEMs have acknowledged that their future vehicle platforms will have to be hybridised. However, in 2013, the development of hybrid vehicles was primarily driven by global fuel economy and CO₂ standards. But, in recent years, growing concerns around poor air quality are stimulating the release of more zero emission capable vehicles such as PHEVs. This includes volume manufacturers such as Toyota, through to high-performance manufacturers such as McLaren and Ferrari who are also embracing the performance enhancements hybridisation offers.

Yet the focus on air quality should not distract from improving CO₂ emissions. Across the automotive industry, manufacturers are increasingly feeling the dual pressure of reducing pollutant emissions and CO₂ emissions from thermal propulsion systems. James Gaade, Senior Manager of Powertrain Research at Jaguar Land Rover, shares his views on the development of hybrid powertrains:

“The co-development of electrified propulsion technologies alongside thermal propulsion systems is crucial in delivering the next generation of vehicles. From 2020, every new Jaguar Land Rover model line will be electrified – this includes vehicles that are fully electric, plug-in hybrid and mild hybrid. The various levels of electrification provide us the flexibility to meet the regulatory requirements as well as a wide range of customer requirements”

It’s this flexibility that illustrates electrification is not a threat to thermal propulsion systems but complimentary. The new Thermal Propulsion Systems roadmap recognises that well integrated hybrid systems can enable the engine to operate more efficiently as the hybrid system takes over at lower loads. Chris Brace, Professor of Automotive Propulsion at the University of Bath and the APC’s ICE System Efficiency Spoke lead, welcomes this acknowledgement in the new roadmap:

“A key strength of this new roadmap is that it incorporates both traditional engine system technologies, such as boosting and after treatment systems, as well as enabling systems such as transmissions and hybrid systems. This reflects a shift in the automotive industry that vehicle manufacturers must consider the impact of electrified technology on thermal propulsion systems” 

This isn’t to say that improvements in light duty thermal propulsion systems could not occur. Earlier this summer Mazda announced its new Spark Controlled Compression Ignition (SCCI) engine which uses a compression ignition combustion cycle to improve the efficiency of its gasoline engines. Mazda’s new combustion concept is reported to improve powertrain efficiency by approximately 20-30 per cent compared to its conventional gasoline engines and will replace the existing Skyactiv-G petrol engines in 2019.

The automaker also announced that its SCCI engine range will also be coupled to a plug-in hybrid system by 2021. This reinforces the roadmap message that future innovations in thermal propulsion systems for light duty applications will need to be optimised to operate in hybrid powertrain systems.

Heavy duty vehicles pose longer term questions

Another key change in this new roadmap is the recognition that there may be divergent technology strategies in vehicles experiencing light duty cycles and those with heavier duty cycles. As discussed above, manufacturers in the passenger car sector are responding to the challenges of air quality and decarbonisation by electrifying new products. But for heavy duty vehicles, such as long haul trucks and large off-highway machinery, full electrification proves challenging. Batteries do not deliver the required energy density compared to liquid fuels so using large, heavy batteries that occupy packing space isn’t commercially viable.

Electrification will play a role in heavy duty vehicles, but it’s likely to be limited to ancillaries where it makes commercial sense – at least in the short term. In certain applications, such as vehicles that experience inner city operation, hybrid and EV powertrains could gain traction. Nevertheless for long haul freight, fuel cost remains a significant commercial driver so improving base engine fuel efficiency still remains a high priority. The new roadmap recognises this challenge so in order to stimulate further innovations in heavy duty thermal propulsion systems, challenging peak brake thermal efficiency targets have been set. Figure 1 plots the roadmap targets against current best in class products (squares), publicly-funded projects (squares with commentary) and industry projections (circles).

There are two important points that emerge from this graph. Firstly the Thermal Propulsion Systems Roadmap targets extend to 2035, providing the UK research community a longer term vision that can spur on earlier stage research. Secondly the roadmap targets relate to the first mass market introduction of a technology. This is important because while some collaborative projects shown on the graph have achieved higher brake thermal efficiencies than the Automotive Council’s targets, the projects still require significant development to transition into mass market products. Therefore the roadmap’s focus on first mass market introduction ensures technology developers and universities keep their eye on vehicle manufacturer requirements.

The roadmap targets are broadly consistent with other research programmes, but how attainable are they? There is a general consensus that 55 per cent brake thermal efficiency can be achieved using existing architectures alongside waste heat recovery systems and advanced boosting systems.

But once you go beyond 55 per cent brake thermal efficiency, more radical concepts are required. Dr Rob Morgan, the APC’s TPS Thermal Efficiency Spoke lead, who is leading the University of Brighton’s research into next generation thermal propulsion systems, believes there’s scope for more radical improvements in combustion systems:

 “In order to achieve the long term efficiency and emission targets the new roadmap sets out for heavy duty, novel operating cycles are needed. These go beyond traditional petrol and diesel cycles we’re used to seeing and may include radical concepts such as split cycle and stirling cycles. Ideally if these new cycles could be co-optimised to use a near carbon neutral fuel, thermal propulsion systems become a long term sustainable solution”

While the Automotive Council’s Energy and Fuels roadmap provides details on the various energy carriers for the automotive sector, the Thermal Propulsion Systems Roadmap does note the importance of fuelling. More specifically, the roadmap recognises a short term focus on optimising thermal propulsion systems for available alternative fuels (such as compressed natural gas) with a transition to co-developing thermal propulsion systems with next generation sustainable liquid and gaseous fuels. This is crucial in sustaining the life of thermal propulsion systems as current diesel and gasoline blends are currently too carbon intensive to achieve longer term decarbonisation goals. Therefore if the carbon intensity of fuels is lowered then thermal propulsion systems could compete against batteries on a life cycle basis, noting the harmful environmental impact of battery manufacturing.

Thermal propulsion systems are still firing on all cylinders  

The new roadmap acknowledges that thermal propulsion systems will still be an integral part of our transport system for many years to come. For light duty vehicles thermal propulsion systems will form part of a co-developed hybrid system offering lower (and for PHEVs zero) emissions capability to consumers as well as lower CO₂. In the heavy duty sector, thermal propulsion systems will be electrified to varying degrees but remain the primary propulsion device for the foreseeable future. Technology developments in heavy duty cycles will focus on incremental efficiency improvements in the short term, to potentially more radical combustion cycles and next generation sustainable fuels in the longer term. To access the detailed commentary and additional information on the technology targets for the Thermal Propulsion System Roadmap, please click here.

The Advanced Propulsion Centre would like to thank all the participants who attended the Thermal Propulsion Systems roadmap workshop – your input was valuable in delivering the updated roadmap. Special thanks also go to members of the steering committee who gave their time to ensure the APC represented the challenges facing the community. 

A blog post by Jon Regnart.