A ReaxFF molecular dynamics study of pyrolysis and coking inhibition by low/zero-carbon fuel additives in aviation fuels

Historically, the commercial aviation industry has relied on a very limited number of well-proven, conventional fuels for certification and operation of aircraft and engines. The vast majority of today’s engines and aircraft were designed and certified to operate on one of two basic fuels; kerosene-based fuel for turbine powered aircraft and leaded AVGAS for spark ignition reciprocating engine powered aircraft. These fuels are produced and handled as bulk commodities with multiple producers sending fuel through the distribution system to airports and aircraft. They are defined and controlled by industry consensus-based fuel specifications that, along with the oversight of the ASTM International aviation fuel industry committee, accommodate the need to move the fuel as a commodity. It was therefore expedient to build upon this framework when introducing drop-in jet fuel produced from non-petroleum feed stocks into the supply chain. The process developed by the aviation fuel community utilizes the ASTM International Aviation Fuel Subcommittee (Subcommittee J) to coordinate the evaluation of data and the establishment of specification criteria for new non-petroleum (alternative) drop-in jet fuels. Subcommittee J has issued two standards to facilitate this process; ASTM D4054—“Standard Practice for Qualification and Approval of New Aviation Turbine Fuels and Fuel Additives”, and ASTM D7566—“Standard Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons”. This paper will describe how the aviation fuel community utilizes the ASTM International consensus-based process to evaluate new candidate non-petroleum jet fuels to determine if these new fuels are essentially identical to petroleum derived jet fuel, and, if they are, to issue specifications to control the quality and performance of these fuels.

Aviation turbine engine fuel specifications are governed by ASTM International, formerly known as the American Society for Testing and Materials (ASTM) International, and the British Ministry of Defence (MOD). ASTM D1655 Standard Specification for Aviation Turbine Fuels and MOD Defence Standard 91-91 are the guiding specifications for this fuel throughout most of the world. Both of these documents rely heavily on the vast amount of experience in production and use of turbine engine fuels from conventional sources, such as crude oil, natural gas condensates, heavy oil, shale oil, and oil sands. Turbine engine fuel derived from these resources and meeting the above specifications has properties that are generally considered acceptable for fuels to be used in turbine engines. Alternative and synthetic fuel components are approved for use to blend with conventional turbine engine fuels after considerable testing. ASTM has established a specification for fuels containing synthesized hydrocarbons under D7566, and the MOD has included additional requirements for fuels containing synthetic components under Annex D of DS91-91. New turbine engine fuel additives and blend components need to be evaluated using ASTM D4054, Standard Practice for Qualification and Approval of New Aviation Turbine Fuels and Fuel Additives. This paper discusses these specifications and testing requirements in light of recent literature claiming that some biomass-derived blend components, which have been used to blend in conventional aviation fuel, meet the requirements for aviation turbine fuels as specified by ASTM and the MOD. The "Table 1" requirements listed in both D1655 and DS91-91 are predicated on the assumption that the feedstocks used to make fuels meeting these requirements are from approved sources. Recent papers have implied that commercial jet fuel can be blended with renewable components that are not hydrocarbons (such as fatty acid methyl esters). These are not allowed blend components for turbine engine fuels as discussed in this paper.

An overview is presented of the three primary ASTM International standards regarding aviation turbine fuels: D1655 Standard Specification for Aviation Turbine Fuels, D4054 Standard Practice for Qualification and Approval of New Aviation Turbine Fuels and Fuel Additives, and D7566 Standard Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons. Emphasis is on how the three standards relate to and interact with each other. The discussion draws out some less obvious implications of these documents and addresses the question whether the focus on source and manufacturing process rather than composition is still appropriate.

In an attempt to bring in sustainable energy resources into the current combustibles mix, recent European legislations make obligatory the addition of biogenic fuels into traditional fossil gasoline. The preferred biogenic fuel, for economic reasons, is predominantly ethanol. Even though likened to fossil gasoline constituents, ethanol has a dissimilar chemical formulation that may lead to a potentially hazardous physicochemical phenomenon, particularly in the presence of water. Owing to increased financially driven propensity to utilize motor vehicle gasoline as aviation gasoline fuel, this may result in potentially hazardous situations, specifically in running smaller or compact General Aviation aircraft. The potential risks posed by ethanol admixtures in aircraft are phase separation and carburettor icing. Gasoline mixed with ethanol is also prone to an increased vulnerability to vapor lock that happens when fuel turns into vapor in the fuel pumps due to high temperatures and lessened ambient pressure at high altitudes. This article provides a literature review on phase separation issues in aviation gasoline fuel and motor gasoline fuels in aviation.

Pyrolysis study of conventional and alternative fuels behind reflected shock waves

: The investigation was concerned with the contribution of selected components and additives of high-temperature aircraft fuels to thermally induced deposits before and after 52 weeks storage at 130F. Of particular concern is the influence of these fuel constituents on thermal stability quality of these jet fuels during storage. The study utilizes a microfuel coker test apparatus to measure the thermal stability of test fuels and blends. The contribution of selected fuel components, labeled with carbon-14, to deposit-forming mechanisms is determined by radioactive counting techniques. Twenty-eight blends of the five test fuels with carbon-14-labeled fuel additives or components reached the final stage of storage at 130F and received final analyses for deposit forming tendency. These additives included an amine-type antioxidant, a metal deactivator, and a corrosion inhibitor. Also included in this study group were oleic acid and 1,5-hexadiene. All three additives showed a great tendency to degrade and react during storage and thermal stress. It was found that oleic acid interacts with cadmium present in aircraft fuel systems to produce deleterious effects upon the thermal stability quality of the fuel. Results showed changes in thermal stability quality of many of these blends containing sulfur compounds. Four additional special studies were conducted as preliminary investigations to continued research of jet fuel stability characteristics.

The virial stress is the most commonly used definition of stress in discrete particle systems. This quantity includes two parts. The first part depends on the mass and velocity (or, in some versions, the fluctuation part of the velocity) of atomic particles, reflecting an assertion that mass transfer causes mechanical stress to be applied on stationary spatial surfaces external to an atomic‐particle system. The second part depends on interatomic forces and atomic positions, providing a continuum measure for the internal mechanical interactions between particles. Historic derivations of the virial stress include generalization from the virial theorem of Clausius (1870) for gas pressure and solution of the spatial equation of balance of momentum. The virial stress is stress‐like a measure for momentum change in space. This paper shows that, contrary to the generally accepted view, the virial stress is not a measure for mechanical force between material points and cannot be regarded as a measure for mechanical stress in any sense. The lack of physical significance is both at the individual atom level in a time‐resolved sense and at the system level in a statistical sense. It is demonstrated that the interatomic force term alone is a valid stress measure and can be identified with the Cauchy stress. The proof in this paper consists of two parts. First, for the simple conditions of rigid translation, uniform tension and tension with thermal oscillations, the virial stress yields clearly erroneous interpretations of stress. Second, the conceptual flaw in the generalization from the virial theorem for gas pressure to stress and the confusion over spatial and material equations of balance of momentum in theoretical derivations of the virial stress that led to its erroneous acceptance as the Cauchy stress are pointed out. Interpretation of the virial stress as a measure for mechanical force violates balance of momentum and is inconsistent with the basic definition of stress. The versions of the virial‐stress formula that involve total particle velocity and the thermal fluctuation part of the velocity are demonstrated to be measures of spatial momentum flow relative to, respectively, a fixed reference frame and a moving frame with a velocity equal to the part of particle velocity not included in the virial formula. To further illustrate the irrelevance of mass transfer to the evaluation of stress, an equivalent continuum (EC) for dynamically deforming atomistic particle systems is defined. The equivalence of the continuum to discrete atomic systems includes (i) preservation of linear and angular momenta, (ii) conservation of internal, external and inertial work rates, and (iii) conservation of mass. This equivalence allows fields of work‐ and momentum‐preserving Cauchy stress, surface traction, body force and deformation to be determined. The resulting stress field depends only on interatomic forces, providing an independent proof that as a measure for internal material interaction stress is independent of kinetic energy or mass transfer.

The biocidal and biostatic activities of seven glycol monoalkyl ether compounds were evaluated as part of an effort to find an improved anti-icing additive for jet aircraft fuel. Typical fuel contaminants, Cladosporium resinae, Gliomastix sp., Candida sp., Pseudomonas aeruginosa, and a mixed culture containing sulfate-reducing bacteria were used as assay organisms. Studies were carried out over 3 to 4 months in two-phase systems containing jet fuel and aqueous media. Diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, and 2-methoxyethanol were generally biocidal in aqueous concentrations of 10 to 17% for all organisms except Gliomastix, which required 25% or more. 2-Ethoxyethanol, 2-propoxyethanol, and 2-butoxyethanol were biocidal at progressively lower concentrations down to 1 to 2% for 2-butoxyethanol. The enhanced antimicrobial activity of these three compounds was attributed to cytoplasmic membrane damage because of the correlation between surface tension measurements and lytic activity with P. aeruginosa cells. The mechanism of action of the less active compounds appeared to be due to osmotic (dehydrating) effects. When all requirements are taken into account, diethylene glycol monomethyl ether appears to be the most promising replacement for the currently used additive, 2-methoxyethanol.

Molecular dynamics study on viscosity coefficient of working fluid in supercritical CO2 Brayton cycle: Effect of trace gas

When a functional or structural impairment of cardiac output has occurred, the cardiovascular system will attempt to compensate for the reduced blood flow. Unfortunately, many of the resulting processes, such as the renin angiotensin aldosterone system, will progressively weaken the heart, resulting in the condition called heart failure. The renin angiotensin aldosterone regulatory system is currently targeted with medicine for heart failure. Many successes for the prolongation of patient age have been achieved by inhibition of angiotensin II synthesis and action. It has become apparent that this approach is suboptimal. Antagonists of aldosterone have provided better treatment options, however, side-effects are still observed. In the search for an alternative therapeutic application, we have studied a novel treatment involving the selective inhibition of aldosterone biosynthesis. The scope of this study has involved the in silico design and prediction of novel inhibitors, the synthesis of these inhibitors and analogues, and finally the in vitro measurement of their potency. The biosynthesis of aldosterone is performed by two cytochrome p450 enzymes, 11B1 and 11B2, denoted as CYP11B1 and CYP11B2, respectively. From these two family members, only CYP11B2 can perform the final synthesis step that converts 18-hydroxycorticosterone into aldosterone. CYP11B1 performs the synthesis of glucocorticoids that are responsible for metabolic, immunologic and homeostatic functions. Because these glucocorticoid actions should not be inhibited, the newly designed medicine must be CYP11B2 selective. Since CYP11B1 is highly homologous to CYP11B2, we have performed an in silico study that allows us to model the interactions of substrates and inhibitors in both the active sites of CYP11B1 and CYP11B2. Using comparative modelling, we have constructed models for the three dimensional architecture of both proteins. These models have been validated by investigating the torsional properties of the protein backbone and residue side chains, the overall protein packing and the dynamic behaviour of the protein models. Subsequently, the models have been used to evaluate the binding mechanisms and conversion mechanisms for the natural steroidal ligands of CYP11B1 and CYP11B2. A hypothetical binding mode has been proposed for 18-hydroxycorticosterone in CYP11B2, featuring the presence of stabilising hydrogen bonding interactions required for its conversion. Quantum mechanical analyses on the conversion of the steroids involved have shown a favourable conversion for this conformation, thereby supporting our hypothesis. In addition, the quantum mechanical analyses have provided insights on steroid conformations in the active sites during conversion. The suitability of the protein models for inhibitor design has been tested by subjecting the models to a case study with four known inhibitors of CYP11B1 and CYP11B2. Using molecular dynamics and molecular docking, the inhibitor potencies for CYP11B1 and CYP11B2 have been predicted, and their interactions with the proteins have been evaluated. The trends in inhibitor potency found by these computational methods have been confirmed by in vitro inhibition measurements. As a next step, the molecular docking study has been expanded to improve the confidence in the predictive power of the models. Using the protein states evaluated by the molecular dynamics study, the molecular docking results of inhibitor analogues have been investigated and the predictive power of the models has been qualitatively improved. In a final approach, we have performed a ligand-based investigation of the inhibitor analogues to determine which ligand characteristics are important for the potency for CYP11B1 and CYP11B2. To this end, we have conducted decision tree analyses on the physico-chemical properties of inhibitor substituents, resulting in a collection of descriptors that can be used for the prediction and design of novel inhibitors. We have shown that a combination of synthesis, molecular modelling and experimental measurements form a promising approach towards the design of potentially new inhibitors.

Eleven derivatives of chalcones ( PZ1–PZ11 ) were synthesized by incorporating N‐methyl piperazine on the para position of the aromatic B ring of chalcones. The A ring is substituted with different electron‐donating and withdrawing groups. All the final derivatives were evaluated for their monoamine oxidase A and B inhibition studies. From the series of compounds PZ‐7 was found to possess good MAO‐B inhibitory activity with an IC 50 value of 2.60±0.22 μM, followed by PZ‐9 with an IC 50 value of 3.44±0.20 μM, when compared with reference compound pargyline 2.69±0.48 μM. PZ‐7 also considerably reduced the cell mortality triggered by rotenone in SH‐SY5Y neuroblastoma cells. The docking study found that PZ‐7 showed a docking score of −10.809 kCal/mol, with a polar interaction with Gln206, and π‐π stacking interaction between the B ring of chalcone. A molecular dynamics simulation study showed higher stability of the protein–ligand complex. Overall, compound PZ‐7 could serve as a promising MAO‐B inhibitor with neuroprotective action.

COVID-19 is caused by the SARS-CoV-2 virus. In this study, around 300 herbal compounds were screened virtually to find the best anti-COVID-19 structures. An extensive search in electronic databases was done. Around 300 herbal compounds, which were previously proven to be antiviral structures, were extracted from articles and considered our primary database. Then, molecular docking studies were performed to find the best inhibitors of the main SARS-COV-2 proteins, including spike protein (PDB 7BWJ), RNA-dependent RNA polymerase (PDB 6M71) and main protease (PDB 5R7Z). The molecular docking and dynamics studies revealed that fangchinoline as an alkaloid could bind to the main protease of the virus more potent than lopinavir (-42.26 vs. -30.9 kJ/mol). Fangchinoline can be orally active based on drug-like properties. According to the molecular dynamic study, the complex between the fangchinoline and SARS-CoV-2 main protease is stable. chebulagic acid is a benzopyrene tannin that could inhibit RNA-dependent RNA polymerase (RdRp) better than remdesivir (-43.9 vs. -28.8 kJ/mol). The molecular dynamic study showed that chebulagic acid-RdRp interaction is stable and strong. Furthermore, suramin could neutralize different variants of COVID-19 spike proteins (wild type, and alpha and beta variants). However, suramin is not orally active but it is a potential inhibitor for different coronavirus spike proteins. According to the promising in silico results of this study, fangchinoline, chebulagic acid and suramin could be introduced as potential lead compounds for COVID-19 treatment. We are hopeful to find a reliable remedy shortly through natural compounds.

A ReaxFF and DFT study of effect and mechanism of an electric field on JP-10 fuel pyrolysis

Novel 10,11-dihydro-5H-dibenzo[b,f]azepine triazoles hybrids: Synthesis, in vitro antioxidant activity and xanthine oxidase inhibition and computational study

BackgroundActivation of WNT signalling pathway was involved in a neuroprotective mechanism against amyloid beta toxicity (1). Inhibition of this pathway is associated with GSK‐3 beta activation, tau hyperphosphorylation, neuronal apoptosis (1), (2) and is implicated in Alzheimer’s disease (1). DKK‐1 competes with Wnt for the binding to LRP5/6 receptor (3) and disrupts the Wnt‐induced Fzd‐Wnt‐LRP6 complex (4) and thus antagonizes the neuro‐protective effect of WNT. In this study, we have targeted the DKK‐LRP interaction through virtual screening the first time to develop novel anti‐Alzheimer’s agent.MethodBased upon crystal structure information and protein validation using Ramachandran Plots, a crystal structure (PDB: 3S8V) was selected for further works. In this study, we have targeted the surface of LRP 5/6, which is interacting with DKK and grid was generated on LRP. The virtual screening of Asinex database library (N=19642) was done against this grid. Molecules were selected on the basis of good dock score and binding free energy calculation using MMGBSA in Schrodinger GLIDE (5)(6). The protein ligand complex structure stability were also evaluated by molecular dynamic simulation study (7). ADMET profile of the screened ligands were evaluated using Quick prop module of Schrodinger.ResultAfter running the virtual screening protocol (HTVS: SP: XP), 14 compounds were screened out, which showed significant binding top the DKK1 binding interface of LRP. These compounds were further evaluated on basis of docking score and MMGBSA. On the basis of After then on the basis of ADME profile selected 2 compound id ZINC000100138828 and ZINC000247940500 for further molecular dynamic simulation study which were shown the compound ZINC000100138828 had an avg. RMSD of ∼4.0Å, also the RMSF is 2.4 Å for overall protein side chain residue was reduced with reference to the apo form. It is displays rich interaction profile and strength with core binding residues (A: Pro833, B: Tyr706, B: Glu708, B: Arg751 and B: Ile681).ConclusionZINC000100138828 is a potent binder to the DKK1 binding surface on LRP5/6. It needs further in‐vitro and preclinical validation as a potential anti‐Alzheimer’s agent.