Academic literature on the topic 'Post quench delay'

This article describes the effects of intake-port throttling on diesel low-temperature combustion at a low and medium load condition. These conditions were known for their characteristically high hydrocarbon emissions predominantly from over-mixed and under-mixed mixture zones, respectively. The investigation was carried out to supplement current findings in the literature with valuable information on the formation of high hydrocarbon emissions with increasing swirl levels generated by intake-port throttling. This was achieved through the use of cycle-resolved high hydrocarbon measurements in addition to cycle averaged emissions and in-cylinder pressure-derived metrics. While there was negligible overall effect at the moderately dilute low-load conditions, increasing swirl has been shown to be beneficial to premixing efficacy under highly dilute conditions with extended ignition delay. This potential advantage was found to be nullified by the swirl-induced confinement of fuel and combustion products to the central region of the cylinder leading to poor late cycle burn rates and increased smoke emissions. High hydrocarbon emissions from the squish and head quench regions were reduced by an increase in swirl ratio.

ABSTRACT Galaxy mergers are a major evolutionary transformation whose effects are borne out by a plethora of observations and numerical simulations. However, most previous simulations have used idealized, isolated, binary mergers and there has not been significant progress on studying statistical samples of galaxy mergers in large cosmological simulations. We present a sample of 27 691 post-merger (PM) galaxies (0c ≤ z ≤ 1) identified from IllustrisTNG: a cosmological, large box, magnetohydrodynamical simulation suite. The PM sample spans a wide range of merger and galaxy properties (M⋆, μ, fgas). We demonstrate that star-forming (SF) PMs exhibit enhanced star formation rates (SFRs) on average by a factor of ∼2, while the passive PMs show no statistical enhancement. We find that the SFR enhancements: (1) show no dependence on redshift, (2) anticorrelate with the PM’s stellar mass, and (3) correlate with the gas fraction of the PM’s progenitors. However, SF PMs show stronger enhancements which may indicate other processes being at play (e.g. gas phase, feedback efficiency). Although the SFR enhancement correlates mildly with the merger mass ratio, the more abundant minor mergers (0.1 ≤ μ < 0.3) still contribute ${\sim}50{{\ \rm per\ cent}}$ of the total SFR enhancement. By tracing the PM sample forward in time, we find that galaxy mergers can drive significant SFR enhancements which decay over ∼0.5 Gyr independent of the merger mass ratio, although the decay time-scale is dependent on the simulation resolution. The strongest merger-driven starburst galaxies evolve to be passive/quenched on faster time-scales than their controls.

The fully frustrated ladder – a quasi-1D geometrically frustrated spin one half Heisenberg model – is non-integrable with local conserved quantities on rungs of the ladder, inducing the local fragmentation of the Hilbert space into sectors composed of singlets and triplets on rungs. We explore the far-from-equilibrium dynamics of this model through the entanglement entropy and out-of-time-ordered correlators (OTOC). The post-quench dynamics of the entanglement entropy is highly anomalous as it shows clear non-damped revivals that emerge from short connected chunks of triplets. We find that the maximum value of the entropy follows from a picture where coherences between different fragments co-exist with perfect thermalization within each fragment. This means that the eigenstate thermalization hypothesis holds within all sufficiently large Hilbert space fragments. The OTOC shows short distance oscillations arising from short coupled fragments, which become decoherent at longer distances, and a sub-ballistic spreading and long distance exponential decay stemming from an emergent length scale tied to fragmentation.

Abstract We measure the rate of environmentally-driven star formation quenching in galaxies at z ∼ 1, using eleven massive (M ≈ 2 × 1014 M⊙) galaxy clusters spanning a redshift range 1.0 < z < 1.4 from the GOGREEN sample. We identify three different types of transition galaxies: ‘green valley’ (GV) galaxies identified from their rest-frame (NUV − V) and (V − J) colours; ‘blue quiescent’ (BQ) galaxies, found at the blue end of the quiescent sequence in (U − V) and (V − J) colour; and spectroscopic post-starburst (PSB) galaxies. We measure the abundance of these galaxies as a function of stellar mass and environment. For high stellar mass galaxies (log M/M⊙ > 10.5) we do not find any significant excess of transition galaxies in clusters, relative to a comparison field sample at the same redshift. It is likely that such galaxies were quenched prior to their accretion in the cluster, in group, filament or protocluster environments. For lower stellar mass galaxies (9.5 < log M/M⊙ < 10.5) there is a small but significant excess of transition galaxies in clusters, accounting for an additional ∼5 − 10 per cent of the population compared with the field. We show that our data are consistent with a scenario in which 20–30 per cent of low-mass, star-forming galaxies in clusters are environmentally quenched every Gyr, and that this rate slowly declines from z = 1 to z = 0. While environmental quenching of these galaxies may include a long delay time during which star formation declines slowly, in most cases this must end with a rapid (τ < 1 Gyr) decline in star formation rate.

The QUENCH-14 experiment investigated the effect of M5® cladding material on bundle oxidation and core reflood, in comparison with tests QUENCH-06 (ISP-45) that used standard Zircaloy-4 and QUENCH-12 that used VVER E110-claddings. The PWR bundle configuration of QUENCH-14 with a single unheated rod, 20 heated rods, and four corner rods was otherwise identical to QUENCH-06. The test was conducted in principle with the same protocol as QUENCH-06, so that the effects of the change of cladding material could be observed more easily. Pre-test calculations were performed by the Paul Scherrer Institute (Switzerland) using SCDAPSIM, SCDAP/RELAP5 and MELCOR codes. The experiment started with a pre-oxidation phase in steam, lasting 3100 s at 1500 K peak bundle temperature. After a further temperature increase to maximal bundle temperature of 2050 K the bundle was flooded with 41 g/s water from the bottom. The peak temperature of ∼2300 K was measured on the bundle shroud, shortly after quench initiation. The electrical power was reduced to 3.9 kW during the reflood phase to simulate effective decay heat levels. The complete bundle cooling was reached in 300 s after reflood initiation. The development of the oxide layer growth during the test was rather defined by measurements performed on the three Zircaloy-4 corner rods withdrawn successively from the bundle. The withdrawal of Zircaloy-4 and E110 corner rods after the test allowed a comparison of the different alloys in one test. One heated rod with M5 cladding was withdrawn after the test for a detailed analysis of oxidation degree and measurement of absorbed hydrogen. Post-test examinations showed neither breakaway cladding oxidation nor noticeable melt relocation between rods. Different from the QUENCH-14 (M5) findings, the QUENCH-12 test with the E110 claddings performed under similar conditions had resulted in intensive breakaway effect at cladding and shroud surfaces during the pre-oxidation phase and local melt relocation on reflood initiation. The hydrogen production in QUENCH-14 up to reflood was similar to QUENCH-06 and QUENCH-12 bundle tests. During reflood 5 g hydrogen were released which is similar to QUENCH-06 (4 g) but much less than during quench phase of QUENCH-12 (24 g). The reason for the different behaviour of the Zr1%Nb cladding alloys is the different oxide scale properties of both materials.

Abstract When a pipeline requires a repair, a pressure-containing steel sleeve or an emergency repair fitting is often fillet welded to the in-service pipe to return the pipeline to normal service conditions. During welding, the flowing product rapidly quenches the fillet weld, promoting the formation of high hardness and low ductility microstructures in the heat-affected zone. The rapid cooling rates also limit the mobility of diffusible hydrogen introduced from the welding electrodes. The hydrogen can be trapped in the weld metal and heat-affected zone and concentrated in specific locations throughout the weld based on the welding deposition sequence. Fillet welds also contain inherent locations of geometric stress concentration at the weld toes and root locations. The elevated hydrogen concentration in the in-service weld, combined with the geometrical stress concentrations at the location of crack-susceptible microstructures, can increase the likelihood of forming a hydrogen-induced crack. Delayed non-destructive examination (NDE) is often employed to wait a sufficient time for any cracks to form so they can be detected. To reduce hydrogen concentration at the locations of stress concentration and NDE delay times, post-heating can be applied to the in-service weld. Elevating the temperature within the weld can enable hydrogen diffusion and reducing the cracking propensity. The rapid heat removal due to flowing product requires post-heating techniques with high energy outputs that will not overheat the steel surfaces. Electromagnetic induced current (induction heating) methods can produce sufficient thermal energy in the electrically conductive steel pipe and sleeve. Coupled numerical finite element analysis (FEA) models were utilized to simulate various induction cable arrangements and thermal convection coefficients, representative of various pipeline products. The analysis of the induction heating arrangements for the studied thermal convection coefficient was conducted to achieve a minimum temperature of 120 °C in the fillet weld root and toes to enable sufficient thermal driving force for hydrogen diffusion while ensuring the pipe and sleeve surface temperature does not exceed 200 °C. An optimal induction heating procedure was found to which could achieve the target temperatures within a reasonable heating time such that NDE delay times of in-service welds can be reduced by 5–6 times.