Rethinking Combustion Could Boost Gas Turbine Efficiency

Researchers at the U.S. Department of Energy’s (DOE) Advanced Turbine Program are eyeing advances in gas turbine efficiency through technologies based on different forms of combustion.

Currently, large gas turbine engines can achieve a combined cycle plant efficiency of just over 60%. This has been accomplished, in part, because of technology improvements that allow turbines to combust at higher temperatures. Still more efficiency increases are possible, and experts at the National Energy Technology Laboratory (NETL) are looking at the range of possibilities.

Gas turbine bladesOne option is pressure gain combustion (PGC). The process creates high temperatures and also increases pressure in a turbine by using a transient, rather than a steady, combustion process based on a controlled and continuous detonation.

The researchers plan to identify and address knowledge gaps, define a realistic pathway for implementing PGC in a gas turbine engine for land based power generation, and provide experimental data for model validation.

Increasing gas pressure during combustion can also increase thermal efficiency, impacting overall plant efficiency, and bringing the DOE turbine program goal of 65% efficiency within reach.

NETL says that gas turbine engines use what is known as a "constant pressure combustion process" that is based on a form of combustion known as deflagration. In practice, combustion through deflagration creates a pressure loss that results in decreased efficiency.

As an alternative, NETL researchers are looking at a combustion approach known as Rotating Detonation Combustion (RDC). This form of PGC creates a controlled, continuous detonation wave that rotates around the inside of a modified gas turbine combustion chamber. Because the detonation, which occurs in a small region at the front of the combustion chamber, is so rapid, the flow appears steady to the turbine.

Studies suggest this approach would result in a 2-4% improvement in combined cycle efficiency, which could translate to reduced carbon emissions.

NETL says that using a continuous detonation wave for pressure gain combustion to increase efficiency in gas turbine engines is not well understood and risky from a business perspective for industry to explore on its own.

DOE’s funding of research in PGC is intended to offset some of this risk and has facilitated ongoing collaborations on the technology.

NETL says that its PGC research has attracted the attention of academia and industry, and several NETL-funded projects have achieved success, including work with Aerojet Rocketdyne, Penn State University, the University of Michigan, Oregon University, and Purdue University.