According to the World Health Organisation (WHO), air pollution is now the world’s largest single environmental health risk and reducing it could save millions of lives. The WHO estimates that in 2012, 3.7 million premature deaths worldwide were related to outdoor air quality.
The world is waking up to the impact of air pollution caused by the emissions from internal combustion engines (ICEs). In late July 2017, the UK government – having been ordered by the High Court to tackle air pollution, and in particular to reduce nitrogen dioxide levels – announced that sales of new petrol and diesel vehicles without an electric motor would be banned from 2040.
The news followed the announcement by the French government earlier in the month of its plans to ban the sale of petrol and diesel vehicles by the same date. Norway, which has Europe’s highest penetration of electric vehicles (EVs), has already set a target that all new cars sold by 2025 should have zero (electric or hydrogen) or low (plug-in hybrids) emissions.
The ICE has been the world’s favourite source of automotive power for more than a century. In the words of Ian Constance, CEO of the Advanced Propulsion Centre (APC), “It’s loved and loathed by many, but its flexibility and efficiency have enabled it to prosper.” These recent announcements don’t bode well for its future, however. Is it RIP, ICE?
The scale of the challenge
In November 2016, the APC and the Engineering & Physical Sciences Research Council (EPSRC) hosted a debate at the Royal Institution to address the question of whether a world driving towards electrification is also digging the grave for the ICE.
Underlining the scale of the challenge ahead was Dr Doug Parr, Greenpeace UK’s chief scientist. He noted that a recent study by the Royal Colleges of Physicians and of Paediatrics and Child Health linked outdoor air pollution to about 40,000 early deaths a year in the UK. Moreover, another study by the University of the West of England has concluded that UK air quality has improved little in the last 20 years.
Parr added that although the average CO2 emissions from new vehicles had fallen over the same period, steeper reductions in other sectors such as power generation and industry mean that transport is now the biggest contributor to the UK’s carbon emissions and therefore to climate change.
The figures revealed by these and other studies are causing a need for immediate action to clean up existing vehicles and are sparking a long-term shift away from ICEs to electrified powertrains. It’s no easy task to simply replace ICE power with battery-electric vehicles (BEVs), however.
As explained by another speaker at the debate, Adam Chase of E4tech, the ICE sets a very high benchmark for alternative powertrains to match. As a mature technology, the ICE can offer low cost, ease of manufacture and an established production infrastructure, good recyclability, extended range, low refuelling time, a highly developed maintenance, support infrastructure and exportability.
Nevertheless, a rapid change will come in the next 15 years or so, driven initially by ever-tougher CO2 emissions targets and air-quality legislation from inner cities. By this time sales of EVs and plug-in hybrids will begin to eclipse those of traditional ICE vehicles. As highlighted by Professor Neville Jackson, the chief technology and innovation officer of powertrain specialist, Ricardo, the rise of electrified vehicles has the potential to create its own problems.
Jackson noted that engine manufacturing is worth £7 billion to the UK economy, so there’s a considerable economic impact to consider. “If the internal combustion engine is going to disappear, we need to think about what we’re going to do next,” he said.
More than 2.5 million engines were made in the UK in 2016, according to figures from the Society of Motor Manufacturers and Traders (SMMT). Speaking after the UK government announced its 2040 phase-out target, SMMT chief executive Mike Hawes commented, “We could undermine the UK’s successful automotive sector if we don’t allow enough time for the industry to adjust.”
“As a mature technology, the ICE can offer low cost, ease of manufacture and an established production infrastructure, good recyclability, extended range, low refuelling time, a highly developed maintenance and support infrastructure and exportability.”
In addition, battery power in isolation does not yet offer a viable solution for heavy-duty vehicles, even if vehicle weight is reduced through new materials and more efficient structures. The comparatively low energy density of even the most efficient lithium-ion batteries of today, and the resulting weight penalty from large battery packs, has major consequences for the payload that can be carried, putting the viability of road freight at risk. All-electric HGVs will not be possible without major advances in battery technology and cost reductions. As another expert at the debate, Dr Robert Morgan from the University of Brighton noted, “For long-haul freight, fuel tanks of up to 1,000-litres are now seen. This would equate to a battery pack weighing 30 tonnes! Here, energy density is king, and a chemical fuel is the only practical solution.” However, the environmental challenges do not go away. “We still need a carbon-free, emissions-free propulsion system that can work with an energy dense supply.”
“For long-haul freight, fuel tanks of up to 1,000-litres are now seen. This would equate to a battery pack weighing 30 tonnes! Here, energy density is king, and a chemical fuel is the only practical solution.”
ICE: part of the solution
So where does this leave the ICE? First, it’s worth noting that recent announcements that put electrification centre-stage do not rule out a role for combustion engines in the future. For example, Volvo intends to electrify every new model from 2019 onwards, including introducing five BEV (battery electric vehicle) models by 2021, but that doesn’t mean that petrols and diesels won’t feature. Instead, the Swedish car maker will complement these with a range of petrol and diesel plug-in hybrid and 48V mild-hybrid options on all models.
Likewise, the UK’s 2040 legislation will mean that hybrid models remain on sale, acknowledging their utility in particular for longer journeys or in areas where the electric recharging infrastructure is less well developed. The door remains open for sustainable, low-carbon liquid fuels, too.
No surprise, then, that speakers at the RIP ICE debate highlighted the need for ICE development to continue.
To achieve future fuel-efficiency targets, we will need a range of solutions,” argued Jackson. “There is no simple solution to reducing carbon in all transport applications. The internal combustion engine will be the mainstay for road transport for the next 20-30 years, but will need significantly improved efficiency through advanced technologies and electrification. We will need to recover kinetic energy and also to use waste thermal energy to improve fuel efficiency.”
Such measures represent a step change in ICE utilisation, requiring a rethink in design and engineering for a technology that has undergone considerable evolution in its 150-year history, from turbocharging and direct fuel injection, to multi-valve heads, lightweight materials, exhaust after treatments and electric starter-generators. All of these and more have increased power while reducing fuel consumption, emissions and weight. Nevertheless, there is more work to be done to reduce the ICE’s thermal losses. The Mercedes-AMG Formula 1 engine, designed and built in Brixworth, UK, shows what’s possible. It is thought to be the world’s most efficient ICE, with around 50% thermal efficiency. That compares very favourably with about 29% for F1’s last normally aspirated, V8 engines, and around 40% for the Atkinson-Cycle motor in the current Toyota Prius, which is believed to be the current best-in-class among road-car petrol engines.
“The Mercedes-AMG Formula 1 engine, designed and built in Brixworth, UK, shows what’s possible. It is thought to be the world’s most efficient ICE, with around 50% thermal efficiency. That compares very favourably with about 29% for F1’s last normally aspirated, V8 engines, and around 40% for the Atkinson-Cycle motor in the current Toyota Prius…”
Jackson said that in the future, ICEs need to be thought of in the broader terms of ‘thermal propulsion systems’. The first contributing element is higher thermal efficiency, with gains to come from advanced waste-heat recovery systems (perhaps to include motorsport-style, exhaust-driven turbines), new and more efficient combustion cycles, “zero”-emissions combustion with high efficiency and even the use of cryogenics to capture and redeploy waste exhaust heat.
The second cluster of improvements relates to the overall system efficiency and encompasses everything from base engine design and new gas exchange technologies to the electrification of both ancillaries and the wider powertrain.
Both of these fields of development provide opportunities for UK powertrain specialists and the good news is that progress in many of these areas is already being made. For example, Dr Robert Morgan is leading a split-cycle engine project funded by the EPSRC and Innovate UK. At the APC debate, he presented details of how the project is developing a new thermodynamic cycle that could raise the best-in-class brake thermal efficiency (BTE) of heavy-duty diesel engines from 44% currently, to 60%, by deploying measures including isothermal compression, recuperation and fast-burning fuel.
“The emissions debate of the past couple of decades has been dominated by CO2 reduction, but while this trend will continue, recent government policy announcements have shown that the focus has now shifted to air quality concerns.”
“If we separate the compression and combustion processes into different chambers, we can independently optimise both the thermal and mechanical characteristics of the two processes – cooling during compression and holding the heat in during combustion/expansion,” Morgan explained.
“We can also recover waste heat before the combustion process, improving the fundamental efficacy of the overall cycle.”
The road ahead
Further into the future, the development of renewable liquid fuels and the hydrogen economy will hold the key to sustainable propulsion systems, according to the University of Bath’s Professor Chris Brace, Deputy Director of the Powertrain Vehicle Research Centre.
“We need high-energy-density fuel for both freight and aviation, if we want to maintain our way of life and meet the climate challenge,” he told the debate. “If we decarbonise liquid fuel for freight and aviation, we will surely take advantage of that in passenger cars.”
Brace noted that in 2016, scientists at Harvard University published a paper showing how an artificial Brace noted that in 2016, scientists at Harvard University published a paper showing how an artificial photosynthesis system could be used to make liquid fuels. In this system, which has achieved 10% efficiency at lab scale, solar energy is used to split water molecules and hydrogen-eating bacteria to produce the fuel. Identifying solid-oxide fuel cells as the ICE’s main competitor in the future, Brace argued that hybridisation will keep the ICE at the centre of propulsion systems for some time.
“In the extreme case we could operate it at a single speed/load. Our challenge is at the system level to make this possible and then to raise the efficiency of the combustion system using the freedom we have gained. In my opinion we will always be able to meet any practical air quality requirements with an ICE, although at a cost.”
The emissions debate of the past couple of decades has been dominated by CO2 reduction, but while this trend will continue, recent government policy announcements have shown that the focus has now shifted to air quality concerns. In the longer term, that will mean a migration to electric vehicles, perhaps with a hydrogen fuel cell at their heart, but there are important challenges to be met before that can become a reality, as Jackson notes:
“Whilst electrification will be a dominant future technology, this will require low-carbon electricity to be effective. And if we are to see significant production of fuel cell vehicles, we will need to see a route to green hydrogen in significant volumes.”
In the meantime, “reports of the ICE’s death have been greatly exaggerated,” as Jackson puts it, paraphrasing the famous quote from Mark Twain. The ICE will not be the main motive force for passenger cars beyond 2030, but ICE technologies will require continued development until pure-EVs are ready to take over. In HGVs, thermal propulsion systems could have a longer life still.
The APC believes that UK expertise will be key during this transition phase over the coming decades, through its ability to innovate and add value to the country’s existing engine manufacturing capability. In the longer term, this will help to protect jobs as the market moves from thermal to electrified propulsion systems.