With pressure to reduceemissions and improve air quality, there is a drive towards electrification in the automotive industry. Does this mean the end is in sight for the internal combustion engine?
Professor Neville Jackson, chief technology officer at Ricardo, told a Royal Institution conference that he believes the industry needs advanced combustion engines. “The combustion engine is nowhere near the limit it can get to,” he said. “We need to recover energy as we slow down and reuse it as we speed up. For combustion engines we throw over half of the fuel energy away. We need to recover that, to produce more power or turn it into electricity.”
Jackson believes that electrification is almost certainly the right approach for city mobility. But for heavier vehicles, he said the industry needs to focus on improving engine efficiency and sustainable energy-dense, low-carbon liquid fuels.
Jackson thinks it is very likely that the electric vehicle’s decade will be 2030-40. So the industry needs to look carefully at the gap between where it is today and when the electric vehicle will really take off.
“The best engine on the market currently has 50% thermal efficiency,” he said. “There is some potential for split-cycle engines, recovering some exhaust energy to make it close to 60% thermal efficiency. You can also combine other cycles together: Stirling, combustion, Otto-type, and Ericsson cycles, and maybe we can get up to 70% thermal efficiency. It’s all about how we use more of that heat energy to be more efficient.”
Dr Rob Morgan, a reader in engineering at Brighton University, agrees that improving the engine’s use of heat energy is the way forward. He explained: “Some 22% of heat is lost through the cooling system. What is even worse is we have to spend energy to do that, applying fans, putting drag into the vehicle through the radiator. And 34% of energy is being lost through the tailpipe.
"We need to reduce and reuse. Can we take exhaust heat and put it through a generator and create some energy to be put back into the driveline? Can we reduce heat losses from the combustion chamber? We can put some insulation in there but it increases the temperature and that increases the amount of pumping work which makes it more difficult to get air in there and increases particulates.”
Morgan believes new thermodynamic techniques that change the way the engine cycles to improve efficiency, are the way forward. He also identifies the split-cycle engine, which splits the compression and combustion strokes into separate chambers, so one cylinder is hot and one is cold, as a promising example.
“We can independently optimise the cylinders so they are at the right temperature and the right compression hold or expansion ratio,” he said. “We can also actively cool during the compression stroke by spraying water during the compression cycle. By doing that we can reduce the compression workload to 20%. However, this reduces the exhaust heat, so we will generate less energy from combined heat recovery.”
Morgan said the challenges of this approach will be developing materials that are strong, lightweight and can withstand high temperatures. “We are adding complexity so we are going to need to move to intelligent and adaptive control systems,” he said.
One area where the future of the internal combustion engine seems assured is lorries. “There are trucks on the roads carrying 1,000 litres of diesel covering huge distances – that’s the equivalent of a 30-tonne battery,” said Morgan.
Truck manufacturers are continuing to invest in the diesel engine – that was the message coming from the IAA commercial vehicles show in Hanover, Germany.
Dr Johannes-Jörg Rüger, president of Bosch’s commercial vehicle division, said: “The diesel is definitely not dead. Electrification is not an option for long-distance transportation.
"We are still working on measures to make the diesel powertrain more efficient. We believe over time we can save up to 10% of fuel consumption, using technology such as waste heat recovery.”
Bosch and truck maker DAF are working on electrified auxiliary systems, such as water and hydraulic pumps to improve the engine’s overall efficiency. Hybridisation could also cut the fuel consumption of trucks by 6%, said Bosch.
Ron Borsboom, director of product development at DAF, said that the industry deserves more recognition: “There has been a lot of criticism about the lack of progress of trucks in terms of CO2 reduction. That is not true. Over the past 15 years we have managed to bring emissions down because we have invested heavily in ground-breaking technology.”
Turbocharger technology will also help improve efficiency. At the IAA show, Honeywell Transportation Systems demonstrated technology developed from the firm’s aerospace business, such as ball-bearing applications for faster transient response and lower fuel consumption. Typically, a Honeywell ball-bearing system features ceramic balls as part of a high-resistance steel cartridge design.
For cars, the amount of time-to-boost improvement attributable to ball-bearing technology can be between 20% and 70%. Secondly, the ball-bearing mechanism is shown to help deliver 2% fuel efficiency improvement compared to a conventional journal bearing. Lastly, ball-bearing turbos work well in cold start conditions because ball bearings are much less reliant on oil. So the high oil viscosity associated with cold start conditions is much less of an impediment to turbo responsiveness in ball-bearing turbos.
In addition, power management company Eaton showed off waste heat recovery system concepts that could help to improve fuel economy and reduce emissions under stricter government regulations. The concepts include indirect systems, which are based on the organic Rankine cycle, and its direct system, which uses an electrified approach. These systems use organic fluids from the aftertreatment system or engine, such as coolant/antifreeze or diesel exhaust fluid, to convert energy normally lost in the form of heat into useful power by boiling it and using the steam to run something like a turbine. Through simulations, the indirect systems have shown fuel economy improvements of 5%. Eaton is working with Shell, Paccar and Mississippi state on a US Department of Energy research programme.
The direct system uses Eaton’s electrically assisted variable-speed supercharger and electric waste heat recovery device to deliver precise air flow control to the engine, optimise exhaust gas recirculation flow, and control the breathing of the engine. This system has shown through simulation more than 20% improvement in fuel economy while also reducing emissions and NOx.
Gerard Devito, chief technology officer in Eaton’s vehicle group, explained: “With the demand increasing for innovations that deliver improved fuel economy while lowering emissions, we are looking at a variety of solutions including several waste heat recovery options that help meet these challenges.
“Based on preliminary modelling and simulation work on prototypes, we feel these solutions can be commercially viable in the near term.”