Larger engine displacements, renewable fuel, increase promise of natural gas trucks

Supporters of natural gas vehicles continue to point at their fuel of choice as a natural option in the drive to reduce unwanted emissions.

Electric grids still need to be updated to support battery-electric vehicles. But renewable natural gas (RNG) can be produced from waste — delivering a negative carbon intensity score that betters renewable diesel, biodiesel, and electric power alike, said Hexagon Agility senior commercial executive Eric Bippus, during a panel discussion at ACT Expo.

The fuel also offers an option for trucks that continue to rely on internal combustion engines, while compressed natural gas (CNG) prices have typically been more stable than those associated with a barrel of oil, he added.

“There’s a TCO [total cost of ownership] that’s very attractive, especially now,” Bippus said, referring to today’s diesel prices. And there’s no difference in operating ranges, eliminating a challenge with some alternative fuels that would require more trucks and drivers — resources that are also in short supply.

The Los Angeles County Sanitation District has found a solution by producing RNG from waste collected in the jurisdiction.

“We’re actually carbon-neutral,” said fleet manager Dave Bolderoff, who oversees 1,100 vehicles. “A big part of that is the production and use of that natural gas.” His fleet has 90 trucks running on RNG today, with plans to double that number in five to six years, supporting everything from heavy-duty tractors to vacuum equipment. Contracted haulers are obligated to run on renewable natural gas as well.

“I think it’s very close to that point that it is sustainable,” he said, when asked if incentives would be needed to support transitions to the fuel. Diesel is already triple the price of natural gas at the moment. “Some of that technology still needs to improve, but the TCO is on par with diesel today – even without grant funding. So [a grant is] not necessary, but it’s good to have.”

Based on today’s costs, natural gas is available at 7 US cents per kilowatt-hour, compared to the 28 cents paid for an equivalent amount of full electric power, and 83 cents for hydrogen fuel.

There were admittedly some growing pains when adopting the fuel. Staff using emergency response vehicles for overflowing sewers were reluctant to shift to an alternative fuel, wondering if it would be dependable. But the first of those trucks came in 2015, and the last one was online last September. When dealing with a major sewage overflow in Carson this Christmas, there were no issues with downtime at all.

Maintenance costs can be controlled by changing fuel filters and spark plugs at the right service intervals, he added.

The renewable natural gas also offers an option to divert organic waste from restaurants and grocery stores alike. The Los Angeles County Sanitation District uses a bio separator to create a pumpable slurry, which is shipped 25 miles away to a digester for waste water treatment plants. Anaerobic digestion creates the biogas.

It’s like a modern-day version of using a banana peel to power a flux capacitor in Back to the Future, he quipped.

Pollution becomes charging solution

It’s a better option than leaving facilities to burn off the gas, said Hyliion CEO Thomas Healy. “We can take pollution and use it to charge a battery pack as opposed to letting that pollution go off into the atmosphere … That’s what makes it a win-win solution for RNG.”

Hyliion, meanwhile, sees an option of using engines powered by natural gas to recharge batteries onboard hybrid-electric trucks. The benefit is that the range is not compromised. The fuel-powered generators can be turned off within city limits, and the hybrid system still offers batteries that deliver an operating range of 75 miles.

There are financial benefits as well. Healy refers to a fleet that was told it would need a $30-million upgrade to prepare a warehouse to support 50 battery-electric trucks.

There are also limits to using hydrogen, he said, referring to the grey hydrogen made from fossil fuels rather than renewable sources. “We need to start making green hydrogen.”

“There’s no one size fits all,” said Tom Swenson, Cummins manager – global regulatory affairs.

For its part, the engine maker is producing 6.7-, 9, and 12-liter engines that run on natural gas. A recently unveiled 15-liter design will deliver up to 500 hp and up to 1,850 lb-ft of torque. The target is to have that integrated in a truck by 2024.

Such an engine is particularly important because it supports the driver experience. “If the drivers hate it, they will figure out ways to make it not work,” he said. The 12-liter engine may be underpowered for many 80,000-lb. applications. But its 15-liter counterpart delivers a torque curve that essentially matches its counterpart.

One clear advantage over diesel is that natural gas engines can rely on a simple three-way catalyst that weighs just 100 lb. and is packaged like a muffler. It’s maintenance-free and has no filters to clean or replace. Unlike diesel there are no active regenerations, SCR fluid, or the related maintenance costs.

The X15N is also 200 lb. lighter than the existing ISC12N, and 500 lb. lighter than today’s 15-liter diesel, he said. Fuel economy is expected to be 10% better than with the 12-liter model, too.

But fleets adopting the engines will need to prepare for some changes. They require a different engine oil than diesel models, for example. But some oil formulas have been developed for platforms as diverse as diesel, natural gas, gasoline and propane.

Since the 15-liter engine is quieter than diesel designs, Cummins also received reports of a ticking sound. It turned out it was the sound of an air compressor that had traditionally been drowned out by the diesel power.

It is admittedly 15% less efficient than a diesel engine, but Cummins expects to close the gap to a range of 5-10% when the model is eventually released into the market.

“I don’t think there’s going to be a one-size-fits-all solution that’s going to be, you know, kind of what diesel is today,” said Hyliion’s Healy. “Electrification is happening. It is coming … The reality is it needs to be practical.”