Cylinder skipping cuts NOx pollution 74% in Cummins-Tula testing

A two-year collaboration on cylinder deactivation between engine maker Cummins Inc. and engine controls technology startup Tula Technology cut nitrogen-oxide (NOx) emissions by a whopping 74% while reducing carbon dioxide (CO2) by 5%.

Cummins (NYSE: CMI) and Tula released a technical paper Tuesday at the Society of Automotive Engineers World Congress in Detroit. It details the breakthrough results from using Tula’s diesel Dynamic Skip Fire (dDSF) on a six-cylinder Cummins’ X15 HD Efficiency Series engine tested in a Class 8 truck. So far, DSF is used only on light vehicles.

“The path we were on seems to have been a very, very good path,” Scott Bailey, Tula Technology president and CEO, told FreightWaves. 

Dynamic Skip Fire cylinder deactivation debuted a decade ago on gasoline-powered General Motors (NYSE: GM) vehicles. More than 1 million GM vehicles use the system today.  

“Shutting down cylinders and allowing the ones that are still running to run at as close to their optimal thermal efficiency as possible [is] the control philosophy that supports DSF,” Bailey said.

The double benefit of lower NOx and CO2 emissions is unusual.

“We think anything that’s going to be a diesel powertrain for on-highway in the future could utilize [dDSF] to help meet the emission regulation and also get a CO2 improvement,” Lisa Farrell, Cummins’ Accelerated Technology Center director, told FreightWaves. “When you look at the technologies that are out there today, there aren’t a lot that give you both.”

Stricter emission rules loom

For trucking, which faces increasingly stringent emissions rules beginning in 2024 in California, dDSF could play a big role in meeting the new standards.

“We see the technology as being part of a group of technologies to meet future low NOx regulations,” Farrell said. “It would definitely get closer. But the technology by itself will not meet the standards.”

Tula, whose two-year exclusive development agreement with Cummins has ended, is discussing deals for dDSF with more than 20 manufacturers globally.

“Frankly, we’re overwhelmed,” said John Fuerst, Tula’s head of engineering.

Cummins is a possible customer for the technology. But Farrell said no launch dates are set. Tula has signed intellectual-property agreements and advanced-development agreements with several manufacturers. Non-disclosure agreements prevented Fuerst from identifying them.

“We look at what’s happening around the world with diesel-emission regulations. No matter where you are, there’s just extraordinarily challenging new emissions regulations on the books,” Bailey said.

Practically all major truck manufacturers make some of their own engines while relying on Cummins for others. That has become especially noticeable in medium-duty engines where Cummins will build all of Daimler Trucks’ medium-duty powertrains. It has similar agreements with Japanese manufacturers Isuzu and Hino Trucks.

Dual focus on electric motors

As the automotive and commercial-vehicle industries embrace zero-emission battery-electric powertrains, Tula is going along. About half of its 60 employees are working on engine controls to make electric motors more efficient.

“The control philosophies that underpin DSF also underpin our dynamic motor drive,” Bailey said. “What it really boils down to, whether it’s an electric motor or an internal combustion engine, every machine has some area of operation where efficiency is at its peak.”

Instead of deactivating cylinders — electric motors don’t have them — Tula pulses the motor to keep it operating at peak efficiency.

“This translates into less power from the grid, fewer batteries, more range, lower costs,” Bailey said. “You can spend that improved efficiency in a lot of different ways.”

Cummins testing cylinder skipping to reduce NOx emissions

Cummins will build medium-duty engines for Daimler Trucks

B6.7 engine from Cummins to power Isuzu Class 6, 7 trucks

Click for more FreightWaves articles by Alan Adler.