Tula Developing Dynamic Skip Fire Technology For All Energy Sources

Tula Developing Dynamic Skip Fire Technology For All Energy Sources

Technology June 2020 Tula Dynamic Skip Fire All Energy Sources

Ever since its introduction to the market in 2019, Silicon Valley-based Tula Technology’s innovative cylinder deactivation technology, Dynamic Skip Fire, has found increasing acceptance in the North American market, with General Motors selling over half a million units featuring this proprietary technology

In its effort to further improve vehicle fuel efficiency and emissions, the company has now collaborated with global power leader Cummins on a significant technical demonstration of diesel Dynamic Skip Fire (dDSF). DSF as a technology, nonetheless, is not limited to petrol and diesel alone.

Cleaner mobility, aided by electrified powertrain, has been the subject of intense discussion and debate world over. Most developed and many developing countries have committed to completely do away with fossil fuel-based, internal combustion engine (ICE) vehicles over the next couple of decades. Of course, this has led many companies to completely overhaul their business strategies. It is interesting that, in such times, there are companies that wholeheartedly believe in the sizeable opportunity in improving vehicle efficiency and reducing emissions.

One such company is the Silicon Valley-based, 12-year-old, Tula Technology, which specialises in controls technology to optimise propulsion efficiency across vehicle segments and energy domains – petrol, diesel, hybrids, electrics and other alternative fuels.

Tula’s genesis is in itself a fascinating story. Adya Tripathi, the company’s founder and Chairman, had a background in digital audio amplification technologies. Tripathi did not really know much about internal combustion engines, but the fundamentals and was just convinced that the control algorithms from the consumer electronics space could apply very well in the automotive engine domain. The result: a combined team of digital consumer electronics engineers and automotive powertrain controls engineers, who have made Tula’s proprietary diesel skip fire (DSF) technology a potential winner world over.

All of Tula’s early work was focussed on ICEs, particularly on spark-ignited petrol engines with an objective to derive improved fuel efficiency and CO2 reduction. The company broadened its focus in the last few years to include diesel engines, with the primary aim to reduce emissions. The diesel dynamic skip fire (dDSF) is a result of all that effort.

In April this year, Tula along with Cummins announced a collaboration, whereby using dDSF software to control cylinder deactivation, both companies demonstrated significant reductions in emissions and fuel consumption. The base platform used for the collaboration work was a Cummins X15 Efficiency Series 6-cylinder diesel engine that claimed to deliver class-leading fuel economy. This engine system was modified to integrate and leverage Tula’s DSF control algorithms to command combustion or deactivation on a cylinder event basis.

R Scott Bailey, President and CEO, Tula Technology (L) expects the advancements through the project to help address future, more stringent NOx regulations. In an exclusive chat with Auto Tech Review, Bailey and John Fuerst, Senior Vice President – Engineering, Tula Technology (R) offered detailed perspectives on the technology, its various future possibilities as well as the direction Tula wishes to take in times to come.

Tula is aiming at not just making diesel engines a practical, pragmatic, and cost-effective choice, but a clean choice as well


The fundamental control concept of dynamic skip fire, whether it is supplied to diesel or petrol engines, the controls themselves don’t change radically. The technology helps best match the torque required by the system by selectively firing cylinders, and doing it in a way that the operator, driver, or passengers really have no idea that anything is different. Essentially, the solution constantly downsizes the engine to the right, effective displacement through cylinder firing. That philosophy and control approach doesn’t change, whether it’s a spark-ignited gasoline engine or a compression-ignited diesel engine. The control philosophies and algorithms are very similar.

However, in a diesel engine, the engine control system and the air path control is much more complex than on petrol engine. The interplay of turbochargers and exhaust gas recirculation is much more complex, and that has to be comprehended, explained Fuerst. Compared to petrol engines, the other significant changes in the diesel engines are with respect to size, displacement, reliability and kilometres driven within the normal life. This complexity meant Tula had to work with outside partners such as Jacobs Vehicle Systems on new valvetrain technology, specifically for diesel.

In the gasoline side, Tula has worked with Eaton, Schaeffler, Delphi and others getting the valvetrain to support individual cylinder deactivation, as well as to get the controls fast and reliable enough. While that wasn’t too much of an issue with petrol engines, with diesels, there was a need to adapt the specific controls because of the air path complexity, as well as the valvetrain. Tula’s specific algorithms, however, didn’t change dramatically.


In addition to the DSF and dDSF control technologies, Tula has been making significant efforts on a dynamic motor drive (DMD), which is based on essentially the same control philosophies, but focussed on pure electric propulsion. In fact, Tula’s goal is to be a propulsion system efficiency company, regardless of the nature of the propulsion system, whether it be IC spark-ignited, IC compression-ignition, some combination of hybrids in-between or pure electric.

Despite the global move towards pure electrification, it is estimated that between now and the 2040 or 2050 timeline, some two billion more ICEs will be produced. That is largely the opportunity Tula is eyeing to address, with Bailey saying it is even their responsibility to make those engines – or for that matter, every propulsion opportunity – as efficient and as clean as they can possibly be.

The focus around diesel is particularly intriguing, considering the disrepute diesel has earned in the last few years. Among the many applications for diesels – short haulage transport and last mile delivery are considered viable for electrification, but for any long haul or heavy transport, and even off-road applications, electrification isn’t seen as a viable opportunity anytime soon. So, from a pure, practical, pragmatic, and cost-effectiveness standpoint, diesels would continue to be the only viable solution. That is what Tula is aiming for – to not just make diesel engines a practical, pragmatic, and cost-effective choice, but a very clean choice as well.

Tula’s emphasis on the dDSF technology is really attacking, if you will, the Achilles heel of the diesel engine, which is primarily NOx emissions, said Bailey. The use of dDSF results in a dramatic reduction of NOx emissions, while at the same time, also provide significant CO2 advantage to the owner, which could be to the tune of 3-5 %. Although modest considering the CO2 advantage of 15 % in spark-ignited engines, Bailey considers this a real breakthrough.

Diesel engines have certain basic advantages against petrol engines, and Fuerst believes there is a tremendous opportunity, particularly in the NOx control area. Although there are many ways to go after NOx, one of the keys to NOx conversion is having enough temperature in the selective catalytic reduction (SCR) system. Diesels have cool exhaust, and that’s one of the biggest challenges. To convert or eliminate NOx, exhaust aftertreatment systems need to operate at a minimum temperature of 200 °C, explained Fuerst.

Add to that the fact that there is a trade-off between CO2 advantage or fuel consumption advantage in diesel engines versus NOx reduction. The only technology, claimed Fuerst, that can simultaneously reduce CO2 and NOx is cylinder deactivation. The way cylinder deactivation does that in a diesel engine is by running fewer cylinders to deliver the same power output, and also significantly reducing the excess air that diesel engines have in their combustion cycle.

The world needs a range of options and the value of those options may vary a bit by market, region, or energy availability


Bailey said the talk around electrification has absorbed too much of the world’s attention. The world needs a range of options and the value of those options may vary a bit by market, region, or energy availability. On its part, as mentioned earlier, Tula has been making significant efforts on a dynamic motor drive (DMD), which is based on essentially the same control philosophies of the DSF, but focused on pure electric propulsion.

Tula is working on electric machines, electric motor and electric generator controls using some of its technologies, insights and intellectual property that have been patented. The company has been working on electric machine control for the last 18 to 24 months, and believes that technically the concepts can be relatively common across those three.

Then, there are possibilities around biofuels and natural gas-based propulsion as well. From a technology perspective, Fuerst confirmed that the DSF technology works 100 % effectively on biofuels, methane, natural gas, propane or ethane mixtures, whether on the spark-ignited side or on the compression-ignition side. Currently, the company is collaborating on a methane project with German Tier I supplier FEV. Likewise, with the considerable amount of gas available in world markets, CNG is a great opportunity and Tula has CNG projects underway. CNG for the commercial arena falls very nicely into the sweet spot of what Dynamic Skip Fire and dynamic cylinder deactivation can handle, Bailey said.

“We’re going to have to pick selectively the technologies that fit certain applications. I think we’re going to find different combinations, which will end up being particularly appropriate for specific use cases. Longer into the future, we’ll have hydrogen fuel cells as a more viable option for long haul transport. But I think the next several decades are going to be really dominated by the growth of variations on the conventional powertrain industry. We were quite happy with spark-ignited gasoline and diesel for quite some time, and then the world has gotten a lot more complex,” said Bailey.

One of the greatest things about ICE cylinder deactivation is that it can be fairly agnostic to the fuel source. Tula surely hasn’t lost sight of the fact that it has to have the same capability in pure electric propulsion, hence it continues to work on the three main areas of petrol diesel and EVs, and then some of the spaces in between, including hybrids.


To convert a gasoline engine into DSF capability, deactivation devices and hardware needs to be put on every cylinder, and they need to be independently controlled, typically with a hydraulic valve per cylinder. That adds to the cost. Adding a DSF on a petrol light duty engine could cost around $50 per cylinder, while that can be anywhere between $50 and $250 in a diesel engine, depending on how big the engine is. In the electrical space, Tula sees an opportunity to improve efficiency without really materially increasing the cost of the underlying e-machine. Fuerst explained, “the opportunity in terms of value and cost looks very promising even though the opportunity is a few percent of efficiency, whereas we talk about 5 to 15 % in petrol and diesel, and two-thirds reduction in NOx.”

While the DSF technology has been proven in larger six- and eight-cylinder engines, we wanted to know of its potential in smaller two-, three- or four-cylinder engines. Two cylinders are too few to make any sense, said Fuerst, but confirmed Tula is working with several customers already on three-cylinder engines. The opportunity on cycle-based improvement in three-cylinder engines is close to 5 %, that is 5 % fuel consumption reduction on real-world driving emission cycles. “Even looking at a potential of, let’s say, a $50 per cylinder cost, a 3-5 % fuel consumption will still get a you very nice payback,” said Fuerst.

Overall, DSF can deliver about 8 % improvement in four-cylinder engines, while hybrid integration could potentially deliver 1-3 % of additional benefit. In six-cylinder engines, the benefit could be in the 10 % range, and with the V8 range of engines for General Motors, Tula is claiming a 15 % better performance.

“Across the range, we really strive to offer one of the highest values in the industry. We focus a great deal on the realities of, where is a good value proposition for the customer. Below three-cylinder, there’s just not enough savings and gain to justify the added cost to the engine and the work and the complexity and the controls,” Bailey justified.


Tula is currently working on projects with multiple OEMs in all the major automotive markets around the globe, except India. The company hasn’t focused on India yet primarily because the country’s preference for small engines isn’t particularly well suited for DSF. With the dDSF now, which aligns with India, Bailey is hoping to engage in some discussions with some major manufacturers in this market. However, it was clear he wants to tread with caution. There’s probably one engine cycle worth of development work that needs to be done in India to implement the DSF technology, he said.

Bailey reiterated Tula’s interest in the Indian market, but ruled out any current thinking on using it for offshore engineering work. He was, however, quick to retort that he would never say never! The company, in fact, has remained small overall with just about 65 to 70 employees, mostly concentrated in California, but with a few people on the ground in Europe, China and a small office in Michigan. He is mindful of the fact that over time he would need to evolve the company’s footprint, particularly in markets with active OEM engagements. And when that becomes necessary, Tula will invest in the right size and resources to meet the requirements, he said.

The use of dDSF results in a dramatic reduction of NOx emissions, while at the same time, also provide significant CO2 advantage to the owner, which could be to the tune of 3-5 %.


If there’s one thing that is certain from Tula’s perspective, it is that internal combustion engines would continue to remain relevant for a long time to come. It is also certain that a large part of those ICEs would be increasingly electrified. Tula is preparing itself for that phase of the industry transformation by developing an electric DSF (eDSF), along with a variant of that, which is for Miller combustion engines, called mDSF; m standing for Miller.

With spark-ignited engines, there are two paths being worked upon; one is focused on advanced combustion, while the other is primarily focussed on electrification. There is a third leg around very lean combustion concept. Although very expensive, Bailey said there is a lean combustion DSF product as well. The diesel path is going to be a function of initial focus around commercial vehicles, evolving to medium-duty and light-duty passenger cars, and CVs with smaller displacement engines. In terms of implementation, this technology is a little behind the petrol side in the market. The third major area of our focus is our dynamic motor drive (DMD) technology, which as of now is quite far in the horizon, but all of these have to be part of our portfolio.

Further down, Tula is looking at a variant particularly aimed at autonomous and connected vehicles. “One of the things that the xDSF will do, independent of whether it’s ‘e’, ‘m’, or ‘d’, is to respond to demands for torque and adjust the effective displacement of the engine accordingly. And it does that in real time cycle-by-cycle basis. So it is very fast,” Bailey said.

Consider a situation, where you have the ability to not just react but proactively adjust the displacement of the engine. Tula has done some work on that as part of a grant from the US Department of Energy, together with the Ohio State University and Delphi Technologies. The proactive nature of the technology allows for quite a bit more in terms of additional fuel efficiency and CO2 reductions, Bailey said.

All put together, Tula Technology has developed a portfolio of products that addresses the full propulsion system efficiency play, which will be rolled out at different timeframes. Bailey believes the products that it currently has under development are well-suited for the next few engine generations and propulsion system generations. At some point, Tula would also work on self-calibration and adaptive calibration, concepts that would bring into play a lot of machine learning capabilities.

“As the vehicle ages and as the system continues to evolve, it just recalibrates itself and becomes as efficient over time or more efficient over time, simply because the machine learning has enabled that,” said Bailey with an eye on the future.

Adding a perspective on autonomous riving, Fuerst said in that scenario, it is the computer in the vehicle that would drive the vehicle, not the person. In that situation, the benefits of DSF, dDSF, DMD (dynamic motor drive) or eDSF, could potentially double. All of those benefits that the company is engineering and creating today are significantly enhanced in the context of autonomous and computer controlled vehicles.

TEXT: Deepangshu Dev Sarmah

PHOTO: Tula Technology