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For passenger vehicles that means a huge investment in electrification and pushing the combustion engine out. In the UK it even means not selling hybrid powertrains any more and heading straight to battery-electric vehicles, or, perhaps, a push for hydrogen technology.
The latter would be a great help for commercial vehicles too, especially larger heavy goods vehicles that cover higher mileages and couldn’t run on only a battery. But, as good an alternative as hydrogen may become, it’s nowhere near being adopted yet, which means one thing – combustion engines need to become more efficient, pumping out fewer emissions, whether that’s CO2, NOx or particulate matter.
Dynamic skip fire
There are many technologies being looked at, but one that hasn’t been developed to any sort of maturity in commercial vehicles and diesel engines is cylinder deactivation. Volkswagen Group has used it with some success in its passenger vehicles, particularly in four-cylinder petrol units.
Tula Technology developed a dynamic skip fire system – an advanced, software-based, cylinder deactivation technology – which has the ability to selectively deactivate cylinders on an event-by-event basis to match the torque demand at optimum fuel efficiency while maintaining acceptable levels of noise, vibration and harshness. The technology was researched on relatively small two-litre, four-cylinder units, but now it’s being looked at in larger applications.
Cummins is working with Tula Technology to improve efficiency and reduce emissions in commercial vehicles. The technology is being developed using a Cummins X15 Efficiency Series six-cylinder diesel. The 15-litre combustion engine can produce between 298kW and 373kW of power and 1,966-2,508Nm of torque.
Researchers modified the engine and controller to integrate Tula’s dynamic skip fire control algorithms so cylinders could be fired or deactivated depending on need. Test data has been collected on a wide range of steady-state conditions and has been used to evaluate transient operation in simulation. Tests have been conducted to evaluate CO2 and NOx emissions on both a heavy-duty FTP test cycle and the Low-Load Cycle (LLC #7) proposed by California Air Resources Board.
Although the programme still has time to run, results look promising. On the FTP cycle, modelling predicted reductions of NOx emissions by 45% while simultaneously reducing CO2 by 1.5%. On the proposed LLC #7, predicted reductions of tailpipe NOx emissions were 66% while reducing CO2 by 4%.
Trade-off opportunities
Engineers suggest that further reductions in NOx emissions could be achievable with the addition of increased conventional thermal management, but that could reduce the CO2 benefit. Reductions in tailpipe NOx are achieved primarily through optimised exhaust temperature control, and improved conversion efficiency of the selective catalytic reduction aftertreatment system. The CO2 reductions are achieved primarily through reductions in pumping losses. The integration of dynamic skip fire cylinder deactivation allows for additional trade-off opportunities for reductions of CO2 and NOx emissions.
The challenge, other than mirroring the benefits in real life rather than in simulation, which is no small matter, is making sure that it can cope with the durability requirements of commercial vehicle applications. Heavy goods vehicles live on the road, clocking up hundreds of thousands of miles, so it needs to last, and, if anything does go wrong, it also needs to be easy to fix, as vehicle downtime can be disastrous for fleet owners.
But, as commercial vehicles are unlikely to adopt fully electric powertrains, whether battery or hydrogen, for some time because of the duty cycles they work to, eking out the maximum amount of efficiency and reducing emissions to the absolute minimum will be incredibly important.
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.