Pressure gain combustion (PGC) is widely considered to improve gas turbine thermal efficiency substantially. However, there is no consensus on the modelling in gas turbine performance simulation. Even though it remains the main tool for design studies, the steady-state 0D representation has difficulties in modelling the inherently intermittent behaviour of pressure gain combustion. Selecting the optimal gas turbine design is therefore difficult as common PGC models tend to under-or overestimate performance. In this paper, an algebraic combustor model is inferred from published CFD data and varied to have an optimistic and pessimistic representation. These models among others will be used in an optimisation to identify the best gas turbine design with respect to thermal efficiency. The consideration of the secondary air system and blade metal temperatures ensure a realistic case study. At the end of this paper, sensitivity studies shed light on cycle design at uncertain combustor performance. The selected PGC models achieve an improvement in thermal efficiency between 3.8-6.6 percentage points compared to conventional isobaric combustion. However, this is less than half the 13.3 percentage points gain promised by ideal isochoric combustion.

Pressure gain combustion evokes great interest as it promises to increase significantly gas turbine efficiency and reduce emissions. This also applies to advanced thermodynamic cycles with heat exchangers for intercooling and recuperation. These cycles are superior to the classic Brayton cycle and deliver higher specific work and/or thermal efficiency. The combination of this revolutionary type of combustion in an intercooled or recuperated gas turbine cycle can, however, lead to even higher efficiency or specific work. The research of these potentials is the topic of the presented paper. For that purpose, different gas turbine setups for intercooling, recuperation, and combined intercooling and recuperation are modeled in a gas turbine performance code. A secondary air system for turbine cooling is incorporated, as well as a blade temperature evaluation. The pressure gain combustion is represented by analytical-algebraic and empirical models from the literature. Key gas turbine specifications are then subject to a comprehensive optimization study, in order to identify the design with the highest thermal efficiency. The results indicate that the combination of intercooling and pressure gain combustion creates synergies. The thermal efficiency is increased by 10 percentage points compared to a conventional gas turbine with isobaric combustion.

No abstract

A large number of engineering systems include non-linear or even non-smooth behaviour. During development and optimisation of mechanical systems, a comprehensive dynamical analysis may be essential. Set-oriented Numerical Methods offer a new and efficient approach to global dynamical analysis without the requirement for a detailed a priori knowledge of the system dynamics. This paper shows the basic concepts behind this method and presents its application to a simple model of a vibro-impact device for ultrasonic/sonic drilling. In this drilling device an impacting mass transmits vibrational energy from a piezoelectric actuator as shock waves into a drill stem. Relative global attractors will be derived which show statistical distributions for the occurrence of all possible states. Periodic solutions can be identified parallel to the evaluation of chaotic behaviour. Thus a global understanding of the system performance can be obtained, offering new ways for model verification and system design.

No abstract