Turbine technology | Rethinking the combustor
because gas that is no longer consumed as turbine fuel can instead be transported, liquefied or sold.
Fast deflagration not detonation Pressure gain combustion is frequently associated with detonation-based concepts, including pulse detonation engines and rotating detonation combustors. These technologies offer theoretical thermodynamic benefits, but also create demanding integration, durability and control challenges.
Finno Exergy has taken a different approach. Its system is based on controlled, pulsating fast deflagration rather than detonation. Deflagration is the combustion mode already used in conventional gas turbine combustors and internal combustion engines, although the Finno process is considerably faster and operates cyclically. At the centre of the system is a proprietary combustion chamber incorporating controlled air and fuel delivery, ignition and valve systems. Air and fuel are introduced into the chamber, rapidly combusted and discharged towards the turbine in a repeating sequence. The pressure generated during each combustion event is higher than the pressure of the compressed air entering the chamber. When the full cycle is considered, the system can therefore produce a net pressure gain across the combustor.
The combustor outlet remains open towards the turbine during operation. The turbine is consequently exposed to pulsating flow rather than the relatively steady flow produced by a conventional combustor.
This interaction is a critical aspect of the concept. The combustor cannot be considered in isolation: its interaction with the turbine, compressor, shaft system and engine controls must be understood as part of an integrated transient system. Finno Exergy combines its combustion hardware with a dedicated control system co-ordinating valve timing, fuel injection, ignition and the combustion cycle. The objective is to produce rapid and repeatable combustion while maintaining stable operation across the required operating range. The use of fast deflagration is expected to provide a controllable route towards industrial implementation while retaining the thermodynamic advantage of pressure gain.
Building on recip and gas turbine technology combined
The origins of Finno Exergy’s technology are closely linked to large reciprocating engine combustion systems. The company’s development team combines experience from piston engines, gas turbines, combustion research and energy technology commercialisation.
The Finno concept incorporates characteristics from both reciprocating engines and gas turbines. As in a piston engine cylinder, the Finno PGC combustor operates cyclically and generates a pressure rise through rapid combustion. Unlike a piston engine, however, it has no piston and delivers its high-energy exhaust directly to a turbine. The system can therefore be viewed as a bridge between two established technology families: the pressure-rise combustion of an internal combustion engine; and the high power
density and continuous shaft output of a gas turbine. For industrial users, the objective is not to replace the complete gas turbine architecture. Finno Exergy is developing the technology so that the conventional gas turbine combustion system can be replaced while retaining the principal compressor and turbine components. The retrofit would ideally be implemented during a planned major overhaul or life-extension programme. The asset owner could inspect, repair or replace life-limited components while installing the new combustion technology within the same project. The result would not simply be an old machine with a new combustor, but a comprehensively refurbished asset combining renewed mechanical life, upgraded controls and improved thermodynamic performance.
Development with Shell A major milestone for Finno Exergy came in 2020, when the company won the New Energy Challenge, an innovation competition organised by Shell and its partners. Finno Exergy subsequently entered the Shell GameChanger programme. Between 2021 and 2024, the company worked with Shell to develop and test a small-scale prototype of its pulsating combustion system.
The programme demonstrated the fundamental operating principle and generated experimental data for further development. It also supported improvements to the combustion system, control strategy and simulation tools required for scale-up. In parallel, Finno Exergy and Shell assessed potential applications and routes to market. Industrial gas turbines were identified as the most suitable initial opportunity because they typically operate for high annual hours, consume large quantities of fuel and remain in service for several decades. Even a moderate efficiency improvement can therefore create considerable lifetime value. The assessment also highlighted the importance of selecting the right gas turbine architecture. Modern aeroderivative and highly integrated annular-combustor machines can be difficult retrofit targets because of their compact layouts and close interaction between the combustor and turbine design. Older heavy-duty machines with can-type combustion systems offer a more practical starting point.
In these machines, individual combustion cans are arranged around the engine, providing more physical space and a clearer interface between the combustion system and the existing turbomachinery.
Frame 3 and Frame 5 gas turbines were therefore identified as priority platforms for piloting and early market deployment.
Why Frame 3 and Frame 5? Frame 3 and Frame 5 gas turbines have been used extensively in power generation, oil and gas facilities, pipeline compressor stations and industrial mechanical-drive applications. Many have been operating for decades but remain valuable because of their robust construction, maintainability and established service infrastructure. Their efficiency, however, is generally lower than that of newer gas turbines, creating a potentially strong business case for an efficiency
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retrofit. The Frame 3 offers a suitable platform for an initial demonstration because of its smaller size and accessible combustion architecture. The Frame 5 represents a larger commercial opportunity because of its installed base and higher fuel consumption.
A pressure gain retrofit could be combined with a major overhaul or life-extension programme covering, as required, the rotor, compressor, turbine, bearings, casings, auxiliaries and controls. This combined approach would extend the operating life of the asset, reduce fuel consumption and avoid or defer the cost and delivery time associated with a new turbine.
It could also limit the risks of replacing an existing mechanical-drive machine. In pipeline compressor stations and LNG facilities, the gas turbine is often closely matched to its driven compressor and integrated into a larger process system. Replacement can affect package layout, controls, process interfaces, foundations and operating permits. Retaining the existing core architecture therefore has value beyond the purchase price of the gas turbine itself. Current supply constraints strengthen this business case. With new turbine manufacturing slots committed years in advance, maintaining and upgrading the installed fleet is becoming a strategic capacity option rather than simply a maintenance decision. For operators that need additional years of reliable service but cannot justify or wait for complete replacement, a life-extended and efficiency-upgraded machine could offer an attractive solution.
Assessing a 10 MW retrofit In 2025, Finno Exergy completed a simulation- based feasibility study in co-operation with a gas turbine original equipment manufacturer. The study examined the potential replacement
of the conventional combustion system of an existing 10 MW industrial gas turbine with Finno Exergy’s pulsating pressure gain system. The work considered not only the theoretical
cycle benefit, but also how the compressor and turbine would respond to the unsteady flow produced by the combustor. Conventional gas turbine performance tools
are generally based on steady-state or quasi- steady assumptions. A pressure gain combustor requires a transient approach because pressure, temperature and mass flow vary during each combustion cycle. The simulations assessed whether the turbine could convert the pulsating flow into useful shaft power and whether the compressor could remain within an acceptable operating range. The results indicated that a reduction in fuel
consumption exceeding 10% could be achievable at the assessed operating point while retaining the existing principal turbomachinery. A reduction of this magnitude would also
result in an approximately corresponding decrease in direct carbon dioxide emissions when the same fuel is used and the same useful output is produced. For an industrial gas turbine operating for several thousand hours per year, the economic value could be considerable. The exact benefit would depend on operating hours,
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