When decarbonizing a diesel truck means removing the diesel fuel

When decarbonizing a diesel truck means removing the diesel fuel

The trucking industry is starting to come to terms with the idea that there’s no decarbonization magic bullet. Just as there’s no one-size-fits-all truck spec, there’s no all encompassing zero-emissions technology that’s going to meet all application and duty cycle demands. For fleets serious about decarbonization, it means finding the right mix of technologies they can put to work in the short term to reduce emissions as much as possible. We’re not waiting around for EV technology to catch up with work that internal combustion is already tackling. We’re talking about a one- to five-year time frame–the immediate future.

“There are sectors that are harder to electrify,” said BJ Johnson, co-founder and CEO of ClearFlame, a company that recently demonstrated that its proprietary technology could enable heavy-duty diesel trucks to operate on 100% renewable, plant-based fuels.

“What we’re doing is, it’s a little cheeky to say, but we’re taking the diesel fuel out of the diesel engine,” added Julie Blumreiter, ClearFlame’s co-founder and chief technology officer.

“We developed a way to get the diesel engine to run on ethanol fuel with the goal of complementing electrification by making it easier to decarbonize those hard to electrify applications by not requiring a change in user behavior,” Jonson said. “It allows fleets to keep refueling with liquids without requiring a change in the infrastructure that’s required with electrification. Everyone knows how to work on diesel engines and work with liquid fuels.”

But very few understand how a “diesel” operates when it’s a “diesel” engine in name only and it’s fueled with ethanol. So let’s start there.

ClearFlame demonstrated its ethanol-fueled engine technology by taking a Class 8 diesel truck running on a Cummins X15 500-HP, 15-liter heavy-duty engine, commonly used for long-haul truck and off-highway applications, and converting it to run on renewable E98 ethanol.

For these first test drives, the truck ran short routes–a few hours or so–without a load to get early experience with the vehicle.

“We have plans to put the truck under load on proving grounds and a chassis dyno soon,” Blumreiter said. “We have already shown on the engine dyno that we can hit the exact same torque curve and full power of the commercially available engine operating on diesel, so we are confident in being able to pull a load the exact same way on ethanol fuel. We’ll be checking those additional boxes of proof leading up to our first fleet handoffs in a few months.”

Initial testing was done on mostly flat terrain and in mild winter weather.

“We have also driven it up a ramp of about 4% grade; we have every expectation that the truck will be pulling 80,000 lb loads across the Midwest this summer, with altitude and extreme weather testing to follow,” Johnson said. According to the duo, the vehicles will be capable of hauling the same load in the same manner as the diesel vehicle prior to the ClearFlame modifications. But what can we expect in terms of fuel economy, or a related equivelent?

“Fuel economy will always vary based on load and conditions, but we know from all of the engine testing we’ve done that under the same conditions, the engine operates at equivalent thermal efficiency to diesel,” Blumreiter said.

“Stated another way, the ClearFlame truck has the same diesel gallon equivalent fuel efficiency as a traditional diesel engine,” Johnson said.

“We keep approximately 80% to 90% of the engine parts from the stock diesel,” Blumreiter explained. “We can do this in a similar manner to doing a diesel rebuild. You could convert that diesel engine to ethanol by choosing the ClearFlame components such as the piston, the injector, and other components that would make it ethanol compatible.”

Blumreiter also shared that the fuel system must have materials compatible with ethanol, as well as capacity to deliver fuel at the rate and timing ClearFlame requires for its calibrations.

“The other changes that we make are around the air and EGR systems,” she continued. “To get a fuel like ethanol to work in the diesel cycle, it requires a hotter environment – we do that by readjusting thermal management to take advantage of existing heat. We’ve removed the EGR cooler to recirculate hot exhaust gas, and reduce cooling on the air coming out of the compressor stage. Basically, we’re getting the fuel to act like diesel by having a hotter intake charge.”

Johnson noted that ClearFlame is in talks with OEMs to get this on the line as a new product. Rebuilds of existing trucks are one of ClearFlame’s business models, but he said that “it’s more of an invasive than a bolt-on retrofit because it requires a piston swap–and is more similar to a traditional reman/rebuild.

“We’re working on being able to introduce this technology on the assembly line as a product option the same way that some OEMs are offering a natural gas option. We envision OEMs saying, ‘You’re getting the 12-liter engine, and do you want the ethanol option or the diesel option?’”

As for why you’d choose that, Johnson stated that using standard corn ethanol will lower life cycle carbon emissions by 45% to 50% compared to diesel engine emissions, in contrast to only a 5-10% reduction using natural gas. There are also additional service benefits.

“You don’t need a DPF, and it’s a simplified version of SCR,” Johnson said. “We’re working on long-term projects with the Department of Energy to get beyond needing SCRs and moving toward a three-way catalysis. An exhaust system that doesn’t have soot in it and runs hotter will also keep your catalyst happier.”

In terms of operating costs, both Johnson and Blumreiter noted the ClearFlame engine’s high thermal efficiency and the low cost of ethanol, making for a net cost savings to fleets choosing to adopt this technology.

“You’re saving money as long as the fuel is priced competitively on a diesel gallon equivalent basis,” Johnson said.

“With previous alternative fuels and spark-ignited platforms, there was this trade off that you lost thermal efficiency in the engine. Since we get the fuel to behave as if it were diesel, that lets us keep the attributes of that engine that people have come to rely on.”

“Because of the equivalent thermal efficiency,” Johnson said, “​​we really only need to compare apples-to-apples on fuel, and we’ll win.”

The challenge, like all new decarbonization options, is adoption.

“The big challenge we have is that within the actual discourse, people still generally see more excitement around electrification,” Johnson said. “I think fleets right now are concerned, ‘If I decarbonize, but it’s not electric, will anyone care?’

“One of the big benefits of the ethanol sector compared to renewable natural gas and renewable diesel is that there is no fossil-intensive backbone to fall back on when the primary fuel falls short. The Renewable Fuels Association has a goal to get to net-zero carbon intensity ethanol by 2035, which could be the first overall fuel energy base to reach that point. There’s no reason ethanol can’t be competitive on both cost and carbon for the coming decades, and perhaps indefinitely.”

Regardless of technology, the one thing the fleet world cares about, as fleet managers well know, is results. The push to decarbonize fleet operations is real. It’s happening. How that happens is up to fleets to decide and the proof will be in the applications.

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