Hyliion Holdings Corp., a developer of modular power plant technology, has announced the successful demonstration of an uninterrupted multi-fuel transition in its next-generation KARNO reactor design, capable of handling liquid and gaseous fuels seamlessly. Operating without any hardware changes, the system transitioned through natural gas, hydrogen, diesel, and back to natural gas in a continuous sequence.

The demonstration validates Hyliion’s integrated reactor architecture, in which gaseous and liquid fuel pathways are unified within one system rather than across specialized hardware configurations. Earlier KARNO milestones validated each fuel category on reactor designs optimized for that fuel type. This unified design, which adds to Hyliion’s extensive intellectual property portfolio, is the platform through which the Company is realizing its long-standing vision of true fuel-agnostic capability.

The demonstration, performed in Hyliion’s lab using an optical reactor configuration, enables direct visual observation of fuel behavior and provides engineering teams with real-time insight into reaction characteristics across fuel types. This capability supports continued refinement of the controls software that automatically detects fuel composition and adjusts operating parameters during transitions.

“True fuel agnostic capability is not a feature added to a Power Module. It has to be designed into the product architecture from the foundation,” said Thomas Healy, Founder and CEO of Hyliion. “When we acquired the KARNO technology, the long-term plan has always been to achieve a single architecture capable of operating across the full fuel spectrum. This demonstration confirms we are on the right path.”

The transition sequence executed during the demonstration covered fundamentally different oxidation regimes within a single reactor:

• Natural gas: the most widely available pipeline fuel and the baseline for distributed power applications
• Hydrogen: operated as a discrete fuel rather than as a blend
• Diesel: a liquid hydrocarbon, validating the integrated reactor’s ability to operate across phase boundaries.

Return to natural gas: confirming the architecture supports bidirectional transitions without recalibration

Stable operation during fuel transition across this sequence on the same hardware demonstrates that the controls system, internal architecture, and thermal management approach work consistently across fuel categories that conventional generators handle through separate product lines or hardware variants.

The implications across Hyliion’s priority markets are substantial. For data centers, a single KARNO Power Module can operate on pipeline natural gas under normal conditions and transition to alternative fuels during gas curtailments or supply disruptions, eliminating the need for separate backup generator systems.

In the case of defense applications, fuel flexibility translates directly to mission resilience. A fuel-agnostic generator reduces the need for fuel-specific variants in forward-deployed environments and can operate on whatever fuel the supply chain delivers.

“Unifying liquid and gaseous fuel pathways in a single reactor is an engineering problem we have been working on to truly unlock Stirling engine benefits,” said Josh Mook, Chief Technology Officer of Hyliion. “This demonstration confirms the architecture is sound, and that the KARNO technology can deliver flexible, onsite, on-demand power using various fuels the customer may choose.”