Cummins testing cylinder skipping to reduce NOx emissions

Reducing NOx emissions is a focus of both the U.S. Environmental Protection Agency (EPA) and the California Air Resources Board (CARB), which has proposed strict curbs on NOx for 2027. In January the EPA published an advanced notice of proposed rulemaking that could lead to the first federal revision in NOx emissions since 2001.

NOx emissions in the United States dropped by more than 40% between 2007 and 2017, but more than 100 million people live in areas where ozone and particulate matter (PM) pollution exceed federal standards. The EPA estimates heavy-duty vehicles will be a large contributor to NOx emissions within the transportation sector in 2025.

Cummins, the American Trucking Associations (ATA), the Engine Manufacturers Association (EMA) and the Owner-Operator Independent Drivers Association (OOIDA) are among manufacturers and independent organizations supporting a 50-state standard. 

A national standard would eliminate a potential hodge-podge of state rules that could increase the cost of truck manufacturing and create logistics problems in where certain trucks could travel.

Skipping around

Diesel Dynamic Skip Fire is a cylinder deactivation technology that, like its name suggests, skips certain cylinders from firing in a diesel engine depending on the driver’s need. 

Dynamic Skip Fire was first used in General Motors’ (NYSE: GM) gasoline-fueled vehicles early in the last decade, Tula CEO Scott Bailey told FreightWaves. Today more than 500,000 GM vehicles on the road have the technology, which has shown to improve fuel efficiency by up to 15%, as well as reducing carbon dioxide (CO₂) emissions.

“There are many similarities,” Bailey said. “Whether it’s a gasoline, spark-ignited engine or compression-ignited engine, you have to modify the valvetrain. So we need the capability to deactivate cylinders on an individual basis.

“When you get into specific controls, [a] diesel engine has a little bit more complexity. So there are a few more knobs to turn with EGR [exhaust gas recirculation] and air path and so on,” he said. “But much of that difference really shows up more on the Cummins’ side of the equation than on the Tula side.”

Delayed testing

Cummins installed dDSF technology in a Freightliner Cascadia with an X15 Efficiency Series 6-cylinder engine. But testing so far is limited to dynamometer and the laboratory. Even that is suspended by coronavirus-prompted shelter-in-place orders keeping most Cummins’ engineers homebound.

“We expect significant reductions in NOx emissions by utilizing [dDSF] in combination with current after-treatment systems,” Farrell said. “We certainly wouldn’t want to say this is something that in and of itself could get us to those levels.”

Cummins started working with Tula a year ago. It probably won’t decide on whether to use dDSF in production until later this year. Six-cylinder engines make up most of Cummins’ on-road portfolio used by all major truck manufacturers.

“It’s complicated with COVID-19 right now because I don’t when we’re going to actually test, but we’re still on plan… this year so that we could at least be clearer about what we project the benefits to be in numbers’ terms,” Farrell said. “Commercialization is just another layer.”