News: Cummins and Tula Work Together To Advance Diesel Tech

Sophisticated Cylinder Deactivation Tech To Reduce NOx & CO2

Diesel engines are a critical part of our everyday life, powering trucks that deliver goods to stores, buses and trains, construction equipment, generators and ships. They’re incredibly efficient engines, but in spite of impressive emissions improvements over the past two decades, remain big contributors to air quality problems.

While moves are underway to replace diesel engines with fuel cells or battery electric power, in the interim the federal Environmental Protection Agency and California’s Air Resource Board are in the process of laying out regulations that will call for future new diesel engines to produce less NOx, a key precursor to smog. Other regulations from both agencies require future engines to also be more efficient, producing less CO₂, the greenhouse gas (GHG) contributing to global warming. At the level of emissions current engines function, engineers have said there is often a tradeoff between technology that will reduce NOx and that which will reduce CO₂. The pressure from companies and drivers out on the road is to always increase fuel economy without taking a performance hit.

Cummins, one of the world’s leading diesel engine maker, has joined forces with Tula Technology, which characterizes itself as a Silicon Valley automotive company, to explore a sophisticated cylinder deactivation system that could solve the conundrum. If it’s proven, the result would be a diesel engine that could reach a near-zero emissions level.

The Tula technology, in this application dubbed Diesel Dynamic Skip Fire (dDSF), is already in use in some of General Motors’ gasoline engines. I was able to test an early prototype version of the gas version, which was impressive in its ability to transparently raise the efficiency of the engine. Tula president and CEO Scott Bailey said his company has been engaged “deeply” with Cummins for about a year and is also working with other diesel engine manufacturers. He added: “Diesel Dynamic Skip Fire could be applied to any engine.”

Starting with an Efficient Engine

The Cummins project takes the company’s most efficient heavy-duty engine, the X15 Efficiency Series, a 15-liter six-cylinder engine typically found in Class 8 big rigs. The engine is the most fuel-efficient one in Cummins’ lineup and claims to have the best fuel economy of any big-bore engine in the industry. Those numbers are always relative to the load being hauled and the route a truck is on, but gains of a fraction of a percent count a lot when you’re driving 100,000 miles a year. The best drivers with previous generation Cummins engines reported full-load cross country fuel economy in the nine mpg range.

The X15 Efficiency is offered in different configurations of 400-500 horsepower and up to 1,850 pound-feet of torque. Cummins noted that it already meets the 2021 GHG and fuel economy standards. It would appear that with the Tula the goal is to hit proposed 2024 NOx standards without paying a penalty in fuel economy.

Bailey added that while working with an engine that was class-leading in efficiency did present some challenges and compression ignition engines present more complex air path controls, this engine also provides a great platform on which to test the technology and show its potential. The Tula software uses algorithms to fire or deactivate a given cylinder on a cylinder-event basis, resulting in the ability to control exhaust temperatures that are critical to optimizing emissions control equipment.

Modeling work showed that with the Tula technology integrated into the Cummins engine, low-load NOx emissions were reduced while fuel consumption also dropped. The two companies documented their work in a paper released for the Vienna Motor Symposium entitled “Diesel Dynamic Skip Fire (dDSF): Simultaneous CO2 and NOx Reduction.”

No production commitments have been made as the collaboration continues to explore the full potential of the Tula system.