Shockless Explosion Combustion: Experimental Investigation of a New Approximate Constant Volume Combustion Process

Abstract

Approximate constant volume combustion (aCVC) is a promising way to achieve a step change in the efficiency of gas turbines. This work investigates a recently proposed approach to implement aCVC in a gas turbine combustion system: shockless explosion combustion (SEC). The new concept overcomes several disadvantages such as sharp pressure transitions, entropy generation due to shock waves, and exergy losses due to kinetic energy which are associated with other aCVC approaches such as pulsed detonation combustion. The combustion is controlled via the fuel/air mixture distribution which is adjusted such that the entire fuel/air volume undergoes a spatially quasi-homogeneous auto-ignition. Accordingly, no shock waves occur and the losses associated with a detonation wave are not present in the proposed system. Instead, a smooth pressure rise is created due to the heat release of the homogeneous combustion. An atmospheric combustion test rig is designed to investigate the auto-ignition behavior of relevant fuels under intermittent operation, currently up to a frequency of 2 Hz. Application of OH*– and dynamic pressure sensors allows for a spatially and time-resolved detection of ignition delay times and locations. Dimethyl ether (DME) is used as fuel since it exhibits reliable auto-ignition already at 920 K mixture temperature and ambient pressure. First, a model-based control algorithm is used to demonstrate that the fuel valve can produce arbitrary fuel profiles in the combustion tube. Next, the control algorithm is used to achieve the desired fuel stratification, resulting in a significant reduction in spatial variance of the auto-ignition delay times. This proves that the control approach is a useful tool for increasing the homogeneity of the auto-ignition.

Part Load Control for a Shockless Explosion Combustion Cycle

“…To achieve homogeneous auto-ignition inside the combustion tube, it is necessary to adjust the ignition delay time as a function of the distance from the tube's inlet, i.e., as a function of the total residence time of a fuel particle before combustion. In experimental investigations, ignition is detected by several photomultipliers [4]. For the theoretical analysis considered here, the ignition time is calculated for simplicity in every grid cell of the numerical scheme.…”

“…ILC relies on a linear model that describes the impact of the control trajectory u k ∈ R n on the control variable y k ∈ R m , where u k and y k contain the sampled values of one cycle k. Due to real-time requirements and technical restrictions, the numbers n and m of input and output variables, respectively, had to be limited in the experimental investigation of SEC [4]. This makes sense in the simulation study as well, as tests have shown.…”

“…Recent investigations [4] have shown that resonant operation of SEC is not possible with affordable equipment under the ambient conditions that have been studied experimentally so far. Since the development of a part load control system requires a stable resonant operation, the approaches in this work are implemented within a numerical simulation of SEC with an elevated pressure.…”

Thermodynamic analysis of nutating disc engine topping cycles for aero-engine applications

“…Fig. 1 shows the thermodynamic benefit derived from an isochoric combustion process, when compared to an isobaric combustion process, in terms of the entropy generated for a fixed combustion temperature [11]. The benefit of an isochoric process stems from the 1 st law of thermodynamics, as the heat added to a fixed control volume increases the specific enthalpy of the system and raises its pressure with a small increase in entropy.…”

Aeroelastic assessment of a highly loaded high pressure compressor exposed to pressure gain combustion disturbances

“…This so-called pressure gain combustion (PGC) can be accomplished by different means. The leading paths are pulse detonation (Roy et al, 2004;Pandey and Debnath, 2016), rotating detonation (Zhou et al, 2016;Kailasanath, 2017;Paxson and Naples, 2017), wave rotors (Akbari and Nalim, 2009;McClearn et al, 2016) and shockless explosion (Bobusch et al, 2014;Reichel et al, 2016) combustion. Some other concepts are the piston topping (Kaiser et al, 2015) and the nutating disk (Meitner et al, 2006).…”