POWERTRAIN
the breadth of understanding needed to work in teams developing complex, highly integrated designs. We are just beginning to see the potential of electrified powertrains designed as one system, yet the skill sets needed to develop them are in short supply. These are the challenges that we
are addressing with IAAPS, a new powertrain research and innovation centre that will focus on collaboration between our academics and companies of all sizes, and on educating engineers to have ‘T-Shaped’ skills: that is a depth of expertise in their field, augmented by broad expertise in complementary fields and also collaboration and team leadership skills.
Q
WHAT ALTERNATIVE FUELS ARE THERE? The University of Bath has more than 40 academics working on powertrain innovation and leads the development of the UK government’s Thermal Propulsion Systems automotive technology roadmap. Our view is that there are two possible pathways: ideally, engines will be optimised for the best possible fuels, but realistically, at least into the medium term due to variability in world markets, they will have to remain flexible and able to work efficiently with a wide range of fuels. Fuels are so key to reducing emissions that we feel more profile should be given to this area of research, especially with regulators and governments as consistency of supply is a key limiting factor. In the short term, reducing the carbon intensity of conventional fuels would deliver a substantial reduction in CO2
,
straight into the existing vehicle fleet, a fact recognised by fuel suppliers who are now making welcome investments in this area. In the five to seven year timeframe,
there are already dual- and bi-fuel systems that show great promise, such as lean burn direct injection CNG/LNG with gasoline. In the medium term (seven-15 years) we may see higher bio content made not from virgin agricultural crops, but from waste products. I can see great potential for hydrotreated vegetable oil (HVO) and biomass to liquid (BTL) low carbon fuels, which may be mixed with conventional fuels to
reduce their carbon content. In the longer term, there is great potential for alternative thermodynamic cycles such as fuel cells and combustion engines co-developed with ‘sun-to-liquid’ fuels for near zero emissions. The commercial availability of these fuels revolves around a number of complex decisions, so the continuing development of global energy systems analysis tools are vital to inform the fuel pathway choices and therefore also engine development priorities. Research must be focused on an objective with commercial viability, which means taking the time to understand the global picture right from the beginning.
Q
HOW MUCH MORE EFFICIENT CAN PISTON ENGINES BECOME? Taking a mid-point between diesel and gasoline, a typical new engine would have a peak engine system brake thermal efficiency of around 42%. We expect that to increase to around 48% by 2025 and 53% by 2035, with Heavy Duty vehicles then up to 60%. Initially this will be highly efficient, very dilute, low-temperature combustion and heat recovery, then potentially through new combustion cycles. NOx and PM will be essentially solved by 2025, regardless of fuel: with appropriate combustion management and aftertreatment, exhaust levels can be below the ambient levels found in most zero emissions zones. The term ‘piston engine’ includes
a lot of novel architectures, but they are all a decade or more from volume production. While researching the UK Government’s automotive technology roadmap, we were given compelling cases for many approaches, including split cycle concepts and linear piston generators. When ICE evolves to a point where it is the junior partner in an electrified powertrain system, it could be any of these or it could be rotary, or even something that has not yet been proposed. There are great synergies between electrification and ICE in
Professor Sam Akehurst
hybrid vehicles. When the level of hybridisation is high enough, then the engine can be much more effectively optimised around a more constrained operating envelope.
Q
HOW ARE ADVANCES IN MODELLING AIDING ENGINE DESIGN? This is a great question as new modelling and simulation tools are crucial to unlocking new powertrain designs and their development will be a key focus of IAAPS. Virtual prototyping and testing will enable more efficient, lighter vehicles to be developed more quickly, but only if we can ensure our models accurately reflect the real world and our test protocols are representative of how vehicles are used. One of our objectives is to focus not just on more sophisticated models that provide more detailed insights, but also on closing the gap between the simulation and the real world. There are, for example, still significant challenges around the fundamental science of combustion and battery degradation modelling. Even when the system can be modelled, the resource and time requirements for complex multiphysics
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