Ethanol partially premixed compression ignition was computationally investigated to understand the effect of the injection strategy on efficiency, emissions, and noise for a heavy-duty engine having displacement of 2123 cm3 and a compression ratio of 17.3 at medium load. Computational fluid dynamics (CFD) modeling with detailed chemistry was performed using the CONVERGE CFD package for a single sector from the intake valve closure to the exhaust valve opening. A double-injection strategy was used, and the start of first injection (SOFI), start of second injection (SOSI) and percentage of mass injected in the first injection (MIFI) were varied while keeping all other parameters constant. Results show that the variation in SOFI has a non-monotonic effect on the combustion phasing and the peak pressure rise rate (PPRR), whereas SOSI can be used to control the combustion phasing. In addition, variation in MIFI is an effective way to control combustion phasing and the peak rate of pressure rise. By an optimum choice of SOFI, SOSI, and MIFI, it is possible to attain high efficiency and low PPRR and emissions. The role of the delayed combustion in the cooler squish zone in moderating the heat release rate is also highlighted.
Erosion of gas turbine grade ceramic matrix composites (CMC) has recently attracted attention because it limits performance and component life in hot engines. This study developed physics of erosion failure evolution including delamination, cavity formation, and fiber loss using an integrated computational material engineering (ICME) approach. The erosion behavior of two CMC systems at two elevated temperatures (ET) under two high velocities is tested utilizing a high velocity oxygen fuel (HVOF). Two CMC erodent systems were selected, and experiments showed that erodent type and size affect erosion degradation which shows sensitivity to retained strength test after erosion. A computational Multi-Scale Progressive Failure Analysis (MS-PFA) predicted the erosion and post-erosion behavior of CMC’s. Prediction of material degradation, micro-crack formation, interfacial degradation, and retained strength closely matched test observations. Method: A Multiphysics-based ICME methodology, and virtual design of experiment (DOE) software method includes: 1) Thermo-physics modeling of galvanic ash particles of layered ceramics predicting the mass transfer, 2) Micro-Mechanical Material model including layered CMC interphase and microcrack density, predicting progressive erosion evaluation and delamination, fracture toughness and hardness, and 3) Finite element explicit software predicting: a) Erosion rate as a function of impact angle under ambient temperature conditions; b) Effect of erodent concentration on erosion rate; c) Erosion rate as a function of velocity at 815°C and 1200°C under normal impact conditions; d) Variation of erosion rate with impingement angle and particle size, and velocity range; and e) Erosion rate as a function of erodent concentration, particle size, temperature and velocity under normal impact conditions.
Electrical resistance has become a technique of interest for monitoring SiC-based ceramic composites. The typical constituents of SiC fiber-reinforced SiC matrix composites, SiC, Si and/or C, are semi-conducive to some degree resulting in the fact that when damage occurs in the form of matrix cracking or fiber breakage, the resistance increases. For aero engine applications, SiC fiber reinforced SiC, sometimes Si-containing, matrix with a BN interphase are often the main constituents. The resistivity of Si and SiC is highly temperature dependent. For high temperature tests, electrical lead attachment must be in a cold region which results in strong temperature effects on baseline measurements of resistance. This can be instructive as to test conditions; however, there is interest in focusing the resistance measurement in the hot section where damage monitoring is desired. The resistivity of C has a milder temperature dependence than that of Si or SiC. In addition, if the C is penetrated by damage, it would result in rapid oxidation of the C, presumably resulting in a change in resistance. One approach considered here is to insert carbon “rods” in the form of CVD SiC monofilaments with a C core to try and better sense change in resistance as it pertains to matrix crack growth in an elevated temperature test condition. The monofilaments were strategically placed in two non-oxide composite systems to understand the sensitivity of ER in damage detection at room temperature as well as elevated temperatures. Two material systems were considered for this study. The first composite system consisted of a Hi-Nicalon woven fibers, a BN interphase and a matrix processed via polymer infiltration and pyrolysis (PIP) which had SCS-6 monofilaments providing the C core. The second composite system was a melt-infiltrated (MI) pre-preg laminate which contained Hi-Nicalon Type S fibers with BN interphases with SCS-Ultra monofilaments providing the C core. The two composite matrix systems represent two extremes in resistance, the PIP matrix being orders of magnitude higher in resistance than the Si-containing pre-preg MI matrix. Single notch tension-tension fatigue tests were performed at 815°C to stimulate crack growth. Acoustic emission (AE) was used along with electrical resistance (ER) to monitor the damage initiation and progression during the test. Post-test microscopy was performed on the fracture specimen to understand the oxidation kinetics and carbon recession length in the monofilaments.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.