Research database

Among the most pressing issues affecting the energy sector, the dependency of the aviation and power generation sectors on the combustion of fossil fuels is of paramount importance. The demands on the energy and transportation sectors – representing more than 80% of the global energy demand – is expected to increase by a further 25% by 2040 , and the de-carbonization of these sectors is necessary to achieve climate change mitigation objectives. During this transition, gas turbines (GT) will play a pivotal role in achieving a sustainable energy portfolio thanks to their complementarities with existing and proposed systems and through the efficient utilization of hydrogen as fuel. Within the aviation sector, a lack of electrification options due to limited range and insufficient power for medium and long-haul flights means that aero-engines will maintain their primary role for the foreseeable future. Meanwhile, a greater proportion of energy generation from wind, solar, and other renewable energy sources for electricity generation requires a responsive and flexible means of load balancing which is a role well suited to GTs. The net effect of these forces is the need for next generation GT engines that can achieve several simultaneous objectives: (1) the ready adoption of hydrogen while (2) increasing efficiency, (3) decreasing specific fuel consumption, and (4) developing the next generation of GT technologies. Unfortunately, direct adoption of hydrogen into existing gas turbines is not a simple process due to differing combustion properties compared with traditional hydrocarbons. Lean, premixed flames such as in modern combustion devices are susceptible to instabilities , flashback , and auto-ignition while the low gas density of hydrogen typically requires a rescaling of the burner flow paths to reach appropriate velocities. Added to these considerations is the constant need to increase the efficiency of the system. Current combustors utilize essentially the same process as a hundred years ago, namely the constant pressure combustion cycle where the efficiency is essentially already maximized. This means that nearly all efficiency gains in the past decades have been achieved at ever greater cost, particularly in the areas of materials and cooling strategies to increase the turbine inlet temperature. Therefore, to realize future efficiency gains, it is necessary to consider alternative hydrogen combustion processes that do not rely on constant pressure. In this H2POWRD project, we intend to harness hydrogen’s potential with rotating detonation gas turbines (RDGT). Rotating detonation combustion (RDC) is an innovative combustion technology that utilizes a detonation wave propagating at supersonic speeds around the perimeter of an annular combustion chamber. This results in a combustion process with increasing total pressure, also referred to as pressure gain combustion (PGC). The key concept is illustrated in Fig. 1a-c. In the time between successive laps of the detonation wave in the RDC, fresh reactants are injected and rapidly mixed before the next detonation wave arrives and the products expand toward the turbine. What makes this technology attractive is that the combustion occurring under the aerodynamic confinement of the detonation wave is significantly more thermodynamically efficient than constant pressure combustion and is easier to integrate than other PGC technologies such as pulsed detonation combustion (PDC) or constant volume combustion (CVC). Due to the low TRL of the technology and the fact that the efficiency is affected by the coupling of the RDC with the turbine, it is difficult to provide exact efficiency improvement values, however expected values have ranged from several percentage points up to 15% . These efficiency increases are expected to be more significant in medium-to-low pressure ratios . An easier calculation is that for the same initial conditions, the enthalpy of the detonation products is approximately 35% higher than for traditional constant pressure combustion, which is attributable to the reduction in flow work on the expanding gas. Even though not all of this increase will be practically realizable, the realistic potential is for a several point increase in thermodynamic efficiency and at least 10% reduction in specific fuel consumption. International interest in rotating detonation has been growing rapidly, with an approximately 30% year-over-year compounding increase in the number of publications (averaged since 2010) , however most of these advancements are being made outside of Europe with the US (41%), China (38%), and Japan (6%) far outpacing Europe. While most of these international efforts mainly concentrate on rocket applications, European Figure 1: Representation of RDC concept (a) and 2D flow fields (b-c), with the unsteady outlet fluctuations (d-g) institutions have a strategic opening to seize leadership in the civilian use of RDGTs. This program builds on the results of a previous H2020 MSCA ITN INSpiring Pressure gain combustion Integration, Research, and Education (INSPIRE). The INSPIRE programme focused on preliminary investigations of the feasibility of PGC technologies (namely RDC and CVC) and the surrounding systems. INSPIRE highlights the potential of the RDC to achieve the objectives emphasized above and asserts the imperative focus of research efforts on RDC technologies. Therefore, the INSPIRE consortium expanded to include additional competencies and further develop a work programme focused around enhancing a deeper understanding RDGTs within the new framework of H2POWRD. The core scientific programme is composed of three work packages and a training and dissemination programme designed to maximize the impact for the DCs as well as the scientific and public communities. Integrating RDCs into a GT does present several technological challenges and opportunities that need to be explored and overcome. The root cause of many of these challenges stems from the unsteadiness of the flow field as shown in Fig. 1d-g for a small set of geometries. Due to the periodic nature of the detonation wave passage, the flow at the outlet is characterized by large fluctuations in pressure (magnitudes of several bars), Mach number (ranging between 0.7 and 1.5), velocity (from 200 to 1000 m/s), and flow angle (+/- 30°) occurring in the kilohertz frequency range. Strongly unsteady flow is not suited for the efficient performance of the turbine and must therefore be conditioned before entering the turbine inlet. Three objectives must be reached: (1) achieve a target subsonic or supersonic inlet condition, (2) reduce the amplitude of the fluctuations and (3) reduce the overall gas temperature. Furthermore, the aerodynamics of the vanes will need to be investigated to understand and optimize their performance in the unsteady flow in the first stage, beyond which the fluctuations are rapidly attenuated. Another source of technological challenges associated to RDCs is related to the detonation rotating inside the combustion chamber, which imposes strong constraints on the design of the injector. The latter must satisfy a delicate compromise between the need for: (1) a rapid injection and mixing of reactants (occurring in the hundreds of microseconds) before the return of the detonation, (2) minimized pressure losses, and (3) a maximized resistance to disturbance from the detonation wave. Throughout this system, attention also needs to be given to the required cooling of the combustor liner and the reduction of the gas temperature through additional mass injection to stay within maximum turbine inlet temperatures and to the possible usage of flow control techniques to govern secondary flow development. The frequencies and amplitudes of the processes in RDCs push the limits of modern experimental and numerical techniques. Cnsequently, the work plan in H2POWRD incorporates a combined effort of state-of-the-art experimental analysis and techniques with cutting-edge numerical tools and computational resources.