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Cummins & Tula demonstrate Diesel Dynamic Skip Fire (dDSF) cylinder deactivation; up to 66% reduction in NOx on CARB LLC #7

Cummins Inc. and Tula Technology, Inc., developer of Dynamic Skip Fire cylinder deactivation technology (earlier post), collaborated on a significant technical demonstration of diesel Dynamic Skip Fire (dDSF) cylinder deactivation. By using dDSF software to control cylinder deactivation in a diesel engine, Cummins and Tula demonstrated significant reductions in emissions and fuel consumption.

Like DSF for gasoline engines, dDSF uses individual cylinder deactivation control strategies to meet torque demand at optimal fuel and aftertreatment efficiency. dDSF improves fuel efficiency by firing all events at the most efficient ratio of air to fuel, allowing optimal combustion at all engine output levels.


Cummins’ X15 Efficiency Series 6-cylinder diesel engine enhanced with Tula’s diesel Dynamic Skip Fire (dDSF)

The project started in early 2019 with the goal of optimizing cylinder deactivation strategies for diesel engines, which could result in emission reduction benefits. Advancements through the project are expected to help address future, more stringent NOx regulations.

The collaboration work was carried out on a Cummins X15 Efficiency Series 6-cylinder diesel engine, which already offers class-leading fuel economy. The joint development team modified the engine system to integrate and leverage Tula’s Dynamic Skip Fire (DSF) control algorithms to command combustion or deactivation on a cylinder-event basis.

The partners prepared a paper “Diesel Dynamic Skip Fire (dDSF): Simultaneous CO2 and NOx Reduction” for the Vienna Motor Symposium (running this week online as a “Virtual Congress”), which presents and quantifies the success of dDSF in increasing efficiency and reducing CO2 and NOx.

The Cummins-Tula team collected test data on a wide range of steady-state conditions which was used to evaluate transient operation in simulation. The engineers evaluated CO2 and NOx tailpipe emissions benefits on both a Heavy-Duty FTP test cycle and the Low-Load Cycle (LLC #7) proposed by California Air Resources Board (CARB) for its upcoming rulemaking.

  • On the HD FTP cycle, dDSF technology modeling predicted reductions of NOx emissions by 45% while simultaneously reducing CO2 by 1.5%.

  • On the proposed LLC #7, dDSF technology modeling predicted reductions of tailpipe NOx emissions by 66% while simultaneously reducing by CO2 by 4%.

Further reductions in NOx emissions should be achievable with the addition of increased conventional thermal management over the cycles with a reduction in the cO2 benefit. The reduction of tailpipe NOx is achieved primarily by optimized exhaust temperature control, resulting in improved conversion efficiency of the Selective Catalytic Reduction after-treatment system. The CO2 reductions are achieved primarily through reductions in pumping losses. Cylinder deactivation thus allows for additional trade-off opportunities for reductions of CO2 and NOx emissions.

The reduction of tailpipe NOx is achieved primarily by optimized exhaust temperature control, resulting in significantly improved conversion efficiency of the aftertreatment system. The technology achieves CO2 reductions through improvements in combustion and reductions in pumping work. Further, dDSF delivers improved tailpipe emissions while simultaneously reducing fuel consumption, allowing for further optimization of these critical parameters.

Our partnership with Cummins has given us the opportunity to expand our DSF technology beyond its success in gasoline engines. Demonstrating the capability to improve fuel efficiency while also achieving very effective emissions control is extremely important for all diesel engine applications in the future.

—R. Scott Bailey, president and CEO of Tula Technology

dDSF is under development for possible future product application. Further work is required to determine whether the technology can meet durability, reliability and cost targets for future products. The collaboration will continue with exploring future system optimization and viability to control noise, vibration and harshness in commercial vehicle applications.

We will continue to innovate the diesel engine system to make it lighter, more reliable, powerful and fuel-efficient, and we are encouraged by the progress demonstrated in this collaboration and what it could mean for future diesel technology.

—Lisa Farrell, Director, Advanced System Integration, Cummins Inc.

Tula Technology is a privately held company backed by Sequoia Capital, Sigma Partners, Khosla Ventures, GM Ventures, Delphi Technologies, and Franklin Templeton.



Are they controlling the valves or just the fuel injection? With a spark ignition engine, you need to control the valves but maybe with a diesel, you can just control the fuel injection which is much easier.


I am almost 100% sure that they must control the valves. Otherwise, a significant increase in exhaust temperature (and FC reduction) would not be possible. Perhaps someone who has looked at the paper could comment. If it would have been so easy as just to modulate injection, we would have seen this long ago.

This technology should have a bigger potential on LD engines.


I found this quote after a quick search:

"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."


All right, here we have better info:


You open the valves to eliminate needless compression.

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