The ‘long and forced’ march toward lower truck emissions continues
Posted: March 18, 2019 by John G. Smith
ATLANTA, Ga. – The push to reduce vehicle emissions has been relentless. Eaton’s Mihai Dorobantu, director – technology planning and government affairs, refers to it as nothing less than a “long and forced march”. And it’s not done yet.
While 2021 emissions limits can be met with incremental equipment changes, those established for 2024-27 will require levels of smog-producing NOx and carbon dioxide to be cut “pretty significantly”, he said during a media briefing at the annual meeting of the Technology and Maintenance Council (TMC).
“How do we reduce emissions, keep increasing performance, and do that in a cost-effective manner?” he asked. After all, each new layer of emissions-reducing technology is making designs evermore “fragile”, with costs, weights, and complexity on the rise.
Eaton hopes to address this with a focus on integrated systems, which will require components to be modular and smarter.
“We believe the future will be a mix of diesel engines and electrification in some applications,” he added, noting how the company projects 11% of trucks to be electrified by 2030.
Each engineering path will require different advancements, too.
Combustion engine updates
The Twin Vortices Series (TVS) EGR pump is one piece of Eaton’s emissions-reducing strategy.
Updating combustion-related systems is no small task, in part because of opposing forces at play.
Consider aftertreatment systems as an example. While they are effective at high loads, they can struggle under low loads or when engines are at idle. Simply adding higher levels of catalysts would do the job, but that would be an expensive and heavy proposition, he said. Instead, Eaton is looking to better manage engine exhaust to create the temperatures that aftertreatment systems need.
In the engine itself, emissions can be reduced through approaches such as modular variable valve actuation, closing intake valves, opening exhaust valves, and internal exhaust gas recirculation. There are also options including cylinder deactivation, Twin Vortices Series (TVS) EGR pumps, and hydraulic lash adjusters.
“We can command different valve behavior,” he explained, referring to the way modular variable valve actuation could alter the motion of a rocker arm or valve – essentially modifying cam profiles on the fly. Eaton’s Late Intake Valve Closing Capsule will keep an intake valve open beyond the timing driven by the cam, leading to the benefits that come with a Miller cycle. And opening an exhaust valve at the top of a compression stroke while coasting could increase aftertreatment temperatures by 20-30 C.
There are also new approaches to addressing valve lash. Today, manufacturers require the lash to be readjusted when an engine breaks in, as well as other times during the truck’s life. “It keeps them away from the optimal, the absolute optimal, combustion strategy,” he said. But the automatic hydraulic lash adjusters that were first developed for passenger cars are now being rolled out for diesels, delivering on a promise of uniform combustion and reducing noise in the process.
Gasoline engines already deactivate cylinders to save fuel under low loads, but that approach could also be used to increase the load on two or three cylinders in a diesel engine, he said. And the benefits are not limited to boosting fuel economy by 5-25% at low loads and idle.
Follow the path to the aftertreatment system. If exhaust is pumped through a cold catalyst, a lot of the NOx continues to be released into the air, he said. A catalyst needs to be somewhere around 250 C to be 98-99% efficient, but temperatures can run closer to 150 C when a truck is idling or at a low load. “Neutral coasting has a limitation today because it cools down the aftertreatment system,” he added, referring to one approach that’s being used to improve fuel economy.
Running two or three cylinders would generate the required temperatures.
Deactivating valves also makes it possible to trigger engine decompression events during every other stroke – in other words, doubling the engine braking capabilities. “The need for [engine] brakes goes up the same time you’re downspeeding the engine,” he said, referring to another strategy that has been used to enhance fuel economy.
Other emission-eliminating options will involve electric power. A lot of it.
“We’re on the cusp of going to 48 volts,” he said, referring to vehicle systems. “For long-haul we believe 48 volt is happening.”
One way Eaton hopes to control costs is through a high-voltage power distribution unit, with modules that are sized for various currents. “We allow OEMs to mix and match, and only have to pay for the power distribution they need,” he said.
As an alternative to the high-torque and heavy electrical motors used in buses, Eaton has also unveiled a two-speed transmission that makes it possible to reduce motor sizes and also deliver the torques needed when the wheels first begin to roll and for high-speed driving.
The costs of an electric motor are often driven by the available torque, he explained. This approach can reduce the size of a motor by a factor of four.
Of course, electric vehicles will also require charging infrastructure, and 4 megawatt charging does not yet exist.
“For longhaul trucking electrification in the span of the next 10-20 years, probably the technology is hydrogen,” he said, referring to the way the energy will need to be stored and carried.
Utility companies have an obvious interest in addressing the need. Dorobantu referred to the transportation sector as a “juicy target” because there are limits to how many homes require electricity. But there is a challenge of delivering the energy at the right time. Solar and wind power, for example, tend to be intermittent, and trucks will need to be recharged at random times.
“Hydrogen then becomes a buffer. It really becomes an energy storage device,” he said. “You can deliver hydrogen like you deliver diesel today.”
Just don’t expect that to happen overnight.
“We’re very far away,” Dorobantu said, referring to the need for the solar and wind power network to grow; a hydrogen generation and distribution network to be established. “There’s a lot of ifs here.”