Testing of a sophisticated cylinder deactivation technology on a Cummins engine showed a 74% reduction in nitrogen oxides (NOx) emissions.

Cylinder deactivation is viewed as one of the main strategies to get NOx down (and fuel economy up) to meet future emissions standards, and companies such as Eaton and Jacobs Vehicle Systems have been developing these systems for several years. Sophisticated software can optimize those cylinder deactivation strategies, and Cummins has been working with Silicon-valley-based tech company Tula to evaluate that technology.

Tula’s Dynamic Skip Fire is an advanced cylinder deactivation control strategy that makes decisions for an engine’s cylinders on an individual basis to best meet torque demands while saving fuel and maintaining performance. The company’s original Dynamic Skip Fire (DSF) software has been shown to significantly reduce CO2 emissions in gasoline engines and has been in production since 2018 with more than one million vehicles on the road. Diesel Dynamic Skip Fire, or dDSF, is a version designed for diesel engines.

Cummins and Tula tested the effectiveness of dDSF in reducing NOx and carbon dioxide  emissions on a Cummins X15 HD Efficiency Series diesel engine in a Class 8 truck.

Low-load cycle performance was estimated with a well-calibrated powertrain simulation tool. This system showed a 74% reduction in NOx and a 5% reduction in CO2 compared with today’s clean diesel technologies. In comparison with current engine technologies and modifications to the thermal management techniques, dDSF saved 20% in fuel, validating dDSF as a more fuel-efficient means of reducing NOx, according to a news release.

“Tula’s dDSF technology provides significant benefits to reducing NOx and CO2 emissions under low-load vehicle operation, which will aid our efforts to produce more reliable, more powerful engines while meeting our environmental goals,” said Lisa Farrell, director of Cummins’ Accelerated Technology Center, in a statement.

We asked Tula Senior VP of Engineering John Fuerst for some more details about how this technology works.

HDT: As I understand it, Jacobs already has a cylinder deactivation strategy in place with Cummins. Does Tula operate on top of Jacobs? 

Fuerst: “Jacobs, and Eaton, Schaeffler, Fulin, and others, supply valve train components including deactivation devices. A simple two-mode deactivation strategy can be implemented without Tula IP [intellectual property. Jacobs Vehicle Systems did provide the deactivation hardware to our dDSF development project with Cummins. Yes, it makes sense to say ‘Tula operates on top of (controls) the Jacobs (or other providers’) deactivation devices. Tula’s IP doesn’t replace anyone; it brings the patented DSF functionality to the engine.”

HDT: It sounds to me like Tula is a software company providing an injection timing algorithm that work in conjunction with the CDA infrastructure already in place in the engine? 

Fuerst: “Yes, close. We license IP that enables the licensee to deploy Tula’s dDSF strategies (algorithms), which require individual cylinder deactivation capability and event-based fuel scheduling. Typical ‘already in place’ CDA is for two-mode deactivation, meaning half the engine is deactivated, or none of it is. Tula’s strategies require all cylinders to be independently deactivatable so that such an ultimate deactivation flexibility can enable the DSF strategies.”

HDT: The name “skip-fire” implies that one or more injection/combustion event would be prevented from occurring occasionally. Is the ratio of combustion events to skipped events mapped by Tula's software, or does the software shut down one or more cylinders for “prolonged periods” to increase the load on the still-functioning cylinders?

Fuerst: Yes, there is mapping involved relative to “firing fractions,” which mean the ratio of firing events to total events. Sometimes a particular cylinder can be deactivated for many cycles, but only as a result of the total strategy responding to torque demand and other constraints. ‘Prolonged periods’ are undesirable for many reasons. Therefore a DSF strategy will ensure regular changes in which cylinders are deactivated.”

HDT: Since the aim of any CDA [cylinder deactivation] strategy is to raise exhaust temperature in low-load situations and thus increase the conversion efficiency of the selective catalytic reduction, how does Tula accomplish this more efficiently than traditional CDA strategies? 

Fuerst: Traditional two-mode CDA is inflexible – only a single deactivation mode is possible. Transitions between full fire and deactivation are constraining and costly. DSF enables infinite flexibility, from zero firing fraction through full fire, with smooth, low-cost transitions. This significantly improves the deactivation benefits while avoiding important downsides of fixed or two-mode CDA.”