Knock Control in Shockless Explosion Combustion by Extension of Excitation Time

Abstract

Shockless Explosion Combustion is a novel constant volume combustion concept with an expected efficiency increase compared to conventional gas turbines. However, Shockless Explosion Combustion is prone to knocking because it is based on autoignition. This study investigates the potential of prolonging the excitation time of the combustible mixture by dilution with exhaust gas and steam to suppress detonation formation and mitigate knocking. Analyses of the characteristic chemical time scales by zero-dimensional reactor simulations show that the excitation time can be prolonged by dilution such that it exceeds the ignition delay time perturbation caused by a difference in initial temperature. This may suppress the formation of a detonation because less energy is fed into the pressure wave running ahead of the reaction front. One-dimensional simulations are performed to investigate reaction front propagation from a hot spot with various amounts of dilution. They demonstrate that dilution with exhaust gas or steam suppresses the formation of a detonation compared to the undiluted case, where a detonation ensues from the hot spot.

Shock Tube and Kinetic Study on the Effects of CO2 on Dimethyl Ether Autoignition at High Pressures

“…Mixtures M3 and M4 enabled a comparison of the effect of N 2 and CO 2 dilution up to 40% vol on ignition delay time for stoichiometric DME/air mixtures. This is done since diluted air/fuel mixtures have been proposed to tailor the characteristic excitation times and, thus, avoid the detonation development in the presence of hot spots in autoignition-based combustion concepts. , In addition, the influence of pressure on ignition delay times for a CO 2 -diluted stoichiometric mixture was investigated for pressures of 15, 35, and 50 bar. Finally, the influence of equivalence ratio, φ, on ignition delay times of CO 2 -diluted DME/air mixtures was studied at a pressure of 35 bar for lean (φ = 0.5), stoichiometric (φ = 1.0), and rich (φ = 2.0) mixtures, see mixtures M4, M5, and M6 in Table .…”

“…While experimentally determined laminar burning velocities and ignition delay times are commonly used for developing and validating chemical-kinetic models of fuel oxidation, such data are scarce for mixtures with significant amounts of CO 2 . Experimental data on laminar burning velocities of CO 2 -diluted mixtures are available for several fuels, such as methane, − methane/hydrogen (or natural gas/hydrogen) blends, − hydrogen, syngas, − iso-octane, , and DME. , The studies suggest that CO 2 has both physical and chemical influences on laminar burning velocity. The chemical effects identified for CO 2 are due to its direct participation in some important elementary reactions and as a third-body collider thanks to its high collision efficiency .…”

“…None of these reaction wave propagation modes are desirable for SEC, which aims for homogeneous autoignition throughout the volume of combustion mixture. Based on a numerical study, Zander et al 7 proposed the use of a dilution of combustion mixture to extend its excitation time, i.e., a characteristic time scale for the heat release, and in this way prevent the formation of detonation from a hotspot in SEC. Similarly, Dai et al 8 showed in a direct numerical simulation that CO 2 dilution extends the excitation time of a combustion mixture and thus offers a possibility for controlling the mode of reaction wave propagation issuing from a hotspot.…”

Comprehensive Thermodynamic Analysis of the Humphrey Cycle for Gas Turbines with Pressure Gain Combustion

“…In a pulsed resonant combustor, the partial confinement of the combustible mixture is the main source of discrepancies. Finally, perturbations cause small but important departures from the ideally defined shockless explosion combustion process [24].…”

A 1D Multi-Tube Code for the Shockless Explosion Combustion

“…It solves the reactive Euler equations by a finite volume method and models the SEC tubes as long-stretched cylinders with axially varying cross-section and a one-dimensional distribution of the state variables along their axis. The software has been employed to study SEC in single-tube operation, e.g., to develop an efficient reduced chemical model designed to probe particular gasdynamic effects of the SEC process [3], or to investigate the sensitivity of the process with respect to various chemical parameters [7].…”