How the Newest Cummins X15 Engine Meets EPA 2027 Emissions Regs

Cummins released details of its 2027 X15 diesel engine, which it says meets EPA 2027 emissions requirements while improving fuel economy — and without adding weight or using more diesel exhaust fluid.

The new engine features a vastly simplified exhaust aftertreatment system with an innovative electric heating system. This new heated aftertreatment design allows for optimal aftertreatment efficiency without compromising engine performance, according to Cummins.

The new engine builds upon the Cummins HELM engine platform, introduced earlier this year.

Cummins gave journalists a look at the 2027 X15 during a visit to the company’s corporate headquarters in Columbus, Indiana, in August.

The 2027 Cummins X15: A Billion-Dollar Engine

The X15 engine is an important technological enabler for Cummins, Jim Nebergall, executive director, market strategy, explained in his opening remarks to journalists.

“The 2017 X15 laid the foundation for a stable base to take Cummins into the 2027 emissions regulations,” he said. “We approached the design of this engine differently right from the start. For us, the X15 was all about reliability and uptime. We wanted this engine to be bulletproof. And it is. Now, it’s time to introduce the next generation of the X15 and maintain those attributes.”

In an age of confusing and often frustrating regulations, fleets consistently tell Cummins they simply want a reliable, low-cost, efficient engine that meets all regulatory requirements, Nebergall said.

“That’s why Cummins has invested over $1 billion in the 2027 X15,” he added. “That’s not just money spent on design and hardware. Cummins is also investing heavily in people, facilities and in strengthening our supply chain to make sure we have the components and products our customers will need in the future.”

Cummins' New X15 Optimized Aftertreatment

The X15 has been a hit for Cummins. But that doesn’t mean that the company's engineers couldn’t find ways to improve it.

The 2027 X15 will have new features such as a variable-geometry turbocharger, aggressive new engine brake, and a simplified exhaust aftertreatment system with the aforementioned electric heating system.

“Also new is a 48-volt, belt-driven alternator,” Nebergall added. “We went to a 48-volt system on the engine because we needed the extra electricity to power two electric heaters in the aftertreatment system.”

Selective catalytic reduction systems reduce emissions of nitrogen oxides (NOx) in diesel exhaust SCR using diesel exhaust fluid and a catalytic converter. However, during start-up, exhaust temperatures are too low for the reaction to work properly. That means that even diesel engines with modern SCR systems can emit emissions into the air when they’re cold.

And increasing the effectiveness of cold exhaust aftertreatment systems is a major new requirement in the 2027 Phase 3 Greenhouse Gas Emissions Regulations.

The new electric heaters get to optimal operating temperatures within seconds of starting the engine, Nebergall explained.

“Because the heaters create heat independent of that the engine is doing, we can now meet the EPA emissions regulations, no matter what the truck is doing. It doesn’t matter if the truck is being driven bobtail, for example.”

The new system doesn’t compromise fuel economy, Nebergall added. And it does not increase the rate of diesel exhaust fluid (DEF) consumption.

“Some of the competitive 2027 solutions we’ve looked at are consuming a lot more DEF."

What the Cummins X15 Exhaust Aftertreatment Heating System Does

Other advantages of the new X15 twin-module electric heating system Nebergall called out include:

• Enables on-demand thermal management
• Optimizes engine efficiency and performance without compromising thermal management
• Eliminates the need for additional catalyst volume to reach more stringent regulations
• Scalable to meet future regulations
• Maintenance free.

Taken as a whole, Nebergall said the 2027 X15 aftertreatment is really a balance of proven and new solutions developed by Cummins.

“We now have a modular design that will allow for greater flexibility when mounting on truck chassis,” he said. “And the new, parallel-flow design reduces back pressure and allows for an overall reduction in the length of the aftertreatment system.

"And, as noted, the design also eliminates the need for the engine to burn more fuel to generate heat necessary for optimized emissions reduction.”

Updated ECM for the ISX15 for 2027

An updated engine control module was needed to improve cybersecurity, explained Tom Marsh, Cummins project leader.

The 2027 emissions regulations also include a requirement for engine makers to document how they prevent hacking, Marsh said, "making sure that no one can take over the air through all the telematics systems we have and change anything about the way the engine operates.... So the new ECM has all of that cybersecurity technology built into it from the start."

The ECM also had to be able to control a more complex system, he said, for the current version and in the future.

"So if we add CDA [cylinder deactivation], variable valvetrain, and those kind of features in the future, the ECM is capable of driving all that new technology."

7% Better Fuel Economy

Overall, the 2027 X15 is weight-neutral compared to the current engine, Nebergall said. While the engine itself is significantly lighter than the current version, the aftertreatment system is heavier.

A new dual overhead cam design enables advanced valvetrain technology such as variable valve timing. This is combined with a new air management system boosted by the new variable-geometry turbocharger.

An all-new, 2,400 Bar fuel system uses a thermal recirculation valve. This valve primes the fuel pump for consistently efficient starts – including cold starts.

Cummins engineers also modified the piston bowl on the 2027 X15. Combined with a new cylinder design, this gives the X15 a higher compression ratio, which translates into higher overall efficiency.

According to Nebergall, the 2027 X15 will deliver up to 7% better fuel economy than the EPA24 version of the X15. This includes a 3% to 4% boost form the base engine design, combined with an additional 1% to 3% fuel economy boost from the powertrain.

This would include spec’ing components like the new Endurant automated manual transmission and the Cummins 14X HE SFR 2.05 axle, he added.

“That’s an important aspect going into 2027 that can’t be overlooked,” Nebergall said.

“Thanks to our partnership with Eaton, and our acquisition of Meritor, Cummins can now offer full powertrain solutions to our fleet customers. This includes engines, transmissions and axles that are fully integrated and designed to work together to provide maximum efficiency.”