Friction and Wear Reduction on Lightweight Engine Valves and Cylinder Bores in Internal Combustion Engines

The objective of this study is to develop new tribological methods for reducing friction and wear of critical internal combustion (IC) engine components, namely engine valves and cylinder bores, either using lightweight materials or advanced coatings. Increasing the components’ durability by improving their wear resistance and optimizing vehicles’ fuel economy by controlling the friction are among this study’s principal goals. Most lightweight materials used in IC engines, Al and Ti alloys, suffer from higher wear rates than conventional cast irons (CI) and steels. Ti alloy valves are proposed to replace steel valves, but their high temperature wear resistance needs to be enhanced. Thus the oxide formation on Ti alloys and its behaviour during high temperature sliding were studied for the development of robust valve contact surfaces. Similarly, Al engine blocks are used to supersede CI blocks, but the wear resistance of cylinder bores needs to be improved. Accordingly, the oxidational wear on thermal spray (TS) coated Al bores and its effect on roughness and lubricated friction were studied. Diamond-like carbon (DLC) coatings as adhesion mitigating counterfaces for Al and Ti alloys exhibit low friction properties, thus emerge as promising coatings for both valve seat inserts and piston rings. Thermal oxidation (TO) treatment performed on Ti alloys generated a TiO2 layer with an oxygen diffusion zone underneath. Compared to untreated alloys, lower sliding wear losses were achieved on TO-Ti alloys at 350 °C (intake valve working temperature) and 550 °C (exhaust valve working temperature). The propensity of crack growth in oxide layers was also reduced as determined by high temperature impact tests conducted using a self-built wear and impact tribometer. The high temperature friction and wear behaviour of W-DLC coating deposited by physical vapour deposition were studied. Low coefficient of friction (COF) values and wear rates were maintained up to 500 °C. The transfer layers consisting of amorphous carbon and monoclinic γ-WO3, as determined by transmission electron microscopy, were responsible for the low friction and wear. Requirements of cylinder bores differ from those of engine valves, as they operate under transitions of lubrication regimes. Thus Stribeck curves were constructed to screen suitable piston ring coatings and bore coatings with proper surface honing to reduce COF. TS coatings, deposited by a plasma transferred wire arc method, could improve the durability of Al bores, but their friction properties remain to be studied especially when oxidational wear occurs. Reciprocating tests were performed with in-situ Raman spectroscopy using base oil with and without zinc dialkyldithiophosphate (ZDDP). The ZDDP containing oil refrained oxidational wear and delayed the transition from the boundary to the mixed lubrication regime. This observation emphasized the importance of using smooth bore surfaces to reduce COF. The friction behaviour of smooth TS coatings were studied with reference to smooth and rough CI liners. TS coatings reduced COF mainly in the mixed lubrication regime due to the improved oil retention capability. DLC coated rings further reduced the boundary lubricated COF, as the formation of carbon transfer layers was favored when interfacial contact was more prominent. From an engineering point of view, this study showed the importance of understanding the microstructural aspects of sliding damage process in designing new surface engineering methods. These methods include generating preferential oxides to reduce high temperature friction and wear for lightweight engine valves; and developing durable and energy-efficient surfaces using the synergy of TS coatings, surface honing, lubricant additives and piston ring coatings for lightweight cylinder bores

Experimental study on nanoparticle deposition in straight pipe flow

Loss of the number of nanoparticles within pipe may lead to significant change of particle number distribution, total mass concentration and particles mean size. The experiments of multiple dispersion aerosol particles ranging from 5.6 nm to 560 nm in straight pipe are carried out using a fast mobility particle sizer. The particle size number distribution, total number concentrations, geometric mean size and volume are acquired under different pipe lengths and Reynolds numbers. The results show lengthening the pipe and strengthening the turbulence can promote the particle deposition process. The penetration efficiency of smaller particle is lower than the larger one, so the particle mean size increases in the process of deposition

Fraud Risk Factor Of The Fraud Triangle Assessing The Likelihood Of Fraudulent Financial Reporting

This research examines risk factors of the fraud triangle, core of all fraud auditing standards, for assessing likelihood of fraudulent financial reporting. Significant variables, including analyst’s forecast error, debt ratio, directors’ and supervisors’ stock pledged ratio, percentage of sales related party transaction, number of historical restatements, and number of auditor switch, belong to pressure/incentive, opportunity and attitude/rationalization. Results indicate fraudulent reporting positively correlated to one of the following conditions: more financial pressure of a firm or supervisor of a firm, higher percentage of complex transactions of a firm, more questionable integrity of a firm’s managers, or more deterioration in relation between a firm and its auditor. A simple logistic model based on examples of fraud risk factors of ISA 240 and SAS 99 gauges the likelihood of fraudulent financial reporting and can benefit practitioners

Fraudulent Statements Disclosure And Financial Distress: A Discrete-Time Survival Analysis

This study uses discrete-time survival analysis (DTSA) to examine the influence of fraudulent statements disclosure on the probability of financial distress not only in the initial period subsequent to disclosure, but future periods as well. Evidence indicates DTSA is superior to logistic regression and extends a richer depiction of the probability after a first-time fraudulent statement disclosure. After fraudulent statements disclosure, 24% of the reporting firms experienced financial distress in Year 1, with the hazard function declines progressively in subsequent years. We find total liability to total assets, directors and supervisors’ stock pledged ratio, and CPA (Certified Public Accountant) change are definitely linked to financial distress probability (p-value <0.05). A DTSA model not only includes financial ratios, but also considers corporate governance variables to produce more accurate classification than those of alternative models

On the α\alpha-index of minimally kk-(edge-)connected graphs for small kk

Let $G$ be a graph with adjacency matrix $A(G)$ and let $D(G)$ be the diagonal matrix of vertex degrees of $G$. For any real $\alpha \in [0,1]$, Nikiforov defined the $A_\alpha$-matrix of a graph $G$ as $A_\alpha(G)=\alpha D(G)+(1-\alpha)A(G)$. The largest eigenvalue of $A_\alpha(G)$ is called the $\alpha$-index or the $A_\alpha$-spectral radius of $G$. A graph is minimally $k$-(edge)-connected if it is $k$-(edge)-connected and deleting any arbitrary chosen edge always leaves a graph which is not $k$-(edge)-connected. In this paper, we characterize the minimally 2-edge-connected graphs and minimally 3-connected graph with given order having the maximum $\alpha$-index for $\alpha \in [\frac{1}{2},1)$, respectively.Comment: arXiv admin note: text overlap with arXiv:2301.0338

Hypoxic Conditioned Medium from Rat Cerebral Cortical Cells Enhances the Proliferation and Differentiation of Neural Stem Cells Mainly through PI3-K/Akt Pathways

Purpose To investigate the effects of hypoxic conditioned media from rat cerebral cortical cells on the proliferation and differentiation of neural stem cells (NSCs) in vitro, and to study the roles of PI3-K/Akt and JNK signal transduction pathways in these processes. Methods Cerebral cortical cells from neonatal Sprague–Dawley rat were cultured under hypoxic and normoxic conditions; the supernatant was collected and named ‘hypoxic conditioned medium’ (HCM) and ‘normoxic conditioned medium’ (NCM), respectively. We detected the protein levels (by ELISA) of VEGF and BDNF in the conditioned media and mRNA levels (by RT-PCR) in cerebral cortical cells. The proliferation (number and size of neurospheres) and differentiation (proportion of neurons and astrocytes over total cells) of NSCs was assessed. LY294002 and SP600125, inhibitors of PI3-K/Akt and JNK, respectively, were applied, and the phosphorylation levels of PI3-K, Akt and JNK were measured by western blot. Results The protein levels and mRNA expressions of VEGF and BDNF in 4% HCM and 1% HCM were both higher than that of those in NCM. The efficiency and speed of NSCs proliferation was enhanced in 4% HCM compared with 1% HCM. The highest percentage of neurons and lowest percentage of astrocytes was found in 4% HCM. However, the enhancement of NSCs proliferation and differentiation into neurons accelerated by 4% HCM was inhibited by LY294002 and SP600125, with LY294002 having a stronger inhibitory effect. The increased phosphorylation levels of PI3-K, Akt and JNK in 4% HCM were blocked by LY294002 and SP600125. Conclusions 4%HCM could promote NSCs proliferation and differentiation into high percentage of neurons, these processes may be mainly through PI3-K/Akt pathways

6-Fluoro-1H-indole-3-carb­oxy­lic acid

In the title compound, C9H6FNO2, all the non-H atoms are approximately coplanar, the carb­oxy O atoms deviating by 0.0809 and −0.1279 Å from the indole plane. In the crystal, O—H⋯O hydrogen bonds link the mol­ecules into dimers which are linked via N—H⋯O hydrogen bonds and π–π inter­actions [centroid–centroid distance = 3.680 (2) Å