Diesel fuel isn’t going anywhere.

I know I spend a great deal of time on my Truck Tech blog talking about new low- and even zero-emission drivetrain technologies. And rest assured, those systems are coming into trucking, sooner rather than later.

However, for the next two decades or so – quite possibly longer – the vast majority of North American fleets will rely on diesel fuel to move freight, particularly in long-haul applications.

The conventional wisdom is that new powertrain technologies will take root on the coasts, and then slowly work their way in toward the middle of the continent. There are a lot of reasons for this, including regulations, cost increases, availability of incentives, and, significantly, infrastructure.

So, for much of the interior of the continent, diesel will remain the only viable fuel option for most fleets for some time to come.

But that doesn’t mean we can’t use some of this amazing new technology to improve upon the performance of the diesel engine.

At the end of the day, emissions regulations and the push toward a net zero trucking industry by 2050 essentially boils down to one thing: Burn less diesel fuel until a time comes when the industry doesn’t need to burn any diesel fuel at all. And so, if the industry could come up with a cost- and weight-effective system that would give trucks a 30% boost in fuel economy for city driving, and a 15% boost on the highway, fleets would be interested, right?

Diesel-Electric Hybrid Powertrains

A new generation of “smart” diesel-electric hybrid powertrains can do just that. Which is why they may very well be an essential component in the next generation of Class 8 diesel powertrains currently under development.

A hybrid drivetrain is simply an electric motor added to the transmission of an otherwise conventional diesel (or gas) powertrain. The system stores kinetic energy captured when the trucks’ batteries are applied in a relatively small battery pack. When needed, the electric motor can help the transmission turn the drive wheels on the truck, to assist the diesel engine and keep it from burning extra fuel.

Diesel trucks are at their least efficient and pollute the most in the low end of the torque curve, when they’re working overtime to get a big truck up and rolling at cruise speeds. But, the electric motor in a hybrid drivetrain can provide instantaneous torque to the truck’s driveshaft. In many instances, the electric motor alone is powerful enough to get a truck up to around 30-25 mph while the diesel engine simply idles, until beginning to consistently contribute more and more horsepower to the torque curve once the truck has good forward momentum established. Once the diesel hits its fuel economy sweet spot in at highway speeds, the electric motor ceases contributing power to the drivetrain and until needed again.

The trucking industry first dabbled with hybrid diesel-electric drivetrains back in the early 2000s. While the systems worked well, they were heavy, hard to work on and eventually undercut by cheap fuel prices.

Today’s newer hybrid drivetrains are much lighter and use new electronic engine control technologies to react in a “smart” way to assist the diesel engine hammering away up front under the hood. These new electric motors can “talk” electronically with the truck’s automated transmission and pitch in to help not just when the truck is getting underway, but on steep grades or even when it’s faced with strong headwinds on a long westward cruise across the Great Plains. And, depending on the type of hybrid system, they can take over completely for the diesel engine and provide appreciable dedicated all-electric operation for the truck, which eliminates local emissions in urban or industrial areas.

They’re not just for diesel trucks, says Thomas Healy, founder and CEO of Hyliion.

“Hybrid powertrains are a great way for fleets to help address the needs of shippers and regulators today, without waiting for the infrastructure of tomorrow,” he said. “When paired with internal combustion engines (ICEs), particularly those running renewable fuels like renewable natural gas (RNG), these systems can deliver very similar (or greater, in some instances) emission reductions without radically changing the operational model of the fleet or imposing significant fleet or society-level infrastructure investments that total in the hundreds of billions of dollars.”

The hybrid drivetrain could be the perfect stop-gap technology that helps trucking transition away from diesel fuels with a minimum of disruption. Time will tell. But the technology is certainly promising and may well get the chance to prove its mettle in fleet operations soon.