Autoignition of n-butanol at elevated pressure and low-to-intermediate temperature

Autoignition experiments for n-butanol have been performed using a heated rapid compression machine at compressed pressures of 15 and 30 bar, in the compressed temperature range of 675–925 K, and for equivalence ratios of 0.5, 1.0, and 2.0. Over the conditions studied, the ignition delay decreases monotonically as temperature increases, and the autoignition response exhibits single-stage characteristics. A non-linear fit to the experimental data is performed and the reactivity, in terms of the inverse of ignition delay, shows nearly second order dependence on the initial oxygen mole fraction and slightly greater than first order dependence on initial fuel mole fraction and compressed pressure. Experimentally measured ignition delays are also compared to simulations using several reaction mechanisms available in the literature. Agreement between simulated and experimental ignition delay is found to be unsatisfactory. Sensitivity analysis is performed on one recent mechanism and indicates that uncertainties in the rate coefficients of parent fuel decomposition reactions play a major role in causing the poor agreement. Path analysis of the fuel decomposition reactions supports this conclusion and also highlights the particular importance of certain pathways. Further experimental investigations of the fuel decomposition, including speciation measurements, are required.     

An Improved Non‐CSD 2‐Bit Recursive Common Subexpression Elimination Method to Implement FIR Filter

The number of adders and critical paths in a multiplier block of a multiple constant multiplication based implementation of a finite impulse response (FIR) filter can be minimized through common subexpression elimination (CSE) techniques. A two‐bit common subexpression (CS) can be located recursively in a non‐canonic sign digit (CSD) representation of the filter coefficients. An efficient algorithm is presented in this paper to improve the elimination of a CS from the multiplier block of an FIR filter so that it can be realized with fewer adders and low logical depth as compared to the existing CSE methods in the literature. Vinod and others claimed the highest reduction in the number of logical operators (LOs) without increasing the logic depth (LD) requirement. Using the design examples given by Vinod and others, we compare the average reduction in LOs and LDs achieved by our algorithm. Our algorithm shows average LO improvements of 30.8%, 5.5%, and 22.5% with a comparative LD requirement over that of Vinod and others for three design examples. Improvement increases as the filter order increases, and for the highest filter order and lowest coefficient width, the LO improvements are 70.3%, 75.3%, and 72.2% for the three design examples.     

Performance of five equations of state for the prediction of vle and densities of natural gas mixtures in the dense phase region

This paper examines the degree of uncertainty of five Equations of State (EOS) for the prediction of densities in the dense phase region which is beyond the ranges of pressure and temperature originally specified for these equations. Predicted densities were compared with measured values for different hydrocarbon mixtures including a rich mixture. The results show that the GERG equation of state, originally specified for the range of P -8 C, outperforms all other equations in the region up to P=30 MPa and T > -8 C. In this range, its mean deviation from measured values of densities was found to be less than -0.015% and standard deviation ( ) also less than 0.015%. The AGA-8 equation, which identified several regions of pressures and temperatures with different uncertainties, also performed quite well with a mean deviation of -0.2% and less than 0.4% in the region up to P=30 MPa. The other equations showed relatively high deviation: ～2.7% for BWRS,-5.1% for PR and 2.5% for RKS. Unlike GERG and AGA-8, however, these three equations can also be used to predict the vapour-liquid-equilibrium (VLE). VLE predictions were compared with measured values for eight binary mixtures of methane (C1) and ethane (C2). It is recommended to use PR for VLE prediction, as quite good agreement between measured data and prediction by PR was demonstrated.     

Internal curing of engineered cementitious composites for prevention of early age autogenous shrinkage cracking

This investigation was carried out to study the effects of using a replacement percentage of saturated lightweight fine aggregate (LWA) as an internal curing agent on the shrinkage and mechanical behavior of Engineered Cementitious Composites (ECC). ECC is a micromechanically-based, designed high-performance, fiber-reinforced cementitious composite with high ductility and improved durability due to tight crack width. Standard ECC mixtures are typically produced with micro-silica sand (200 µm maximum aggregate size). Two replacement levels of silica sand with saturated LWA (fraction 0.59–4.76 mm) were adopted: the investigation used 10 and 20% by weight of total silica sand content, respectively. For each LWA replacement level, two different ECC mixtures with a fly ash-to-Portland cement ratio (FA/PC) of 1.2 and 2.2 were cast. In a control test series, two types of standard ECC mixtures with only silica sand were also studied. To investigate the effect of replacing a portion of the silica sand with saturated LWA on the mechanical properties of ECC, the study compared the results of uniaxial tensile, flexure and compressive strength tests, crack development, autogenous shrinkage and drying shrinkage. The test results showed that the autogenous shrinkage strains of the control ECCs with a low water-to-cementitious material ratio (W/CM) (0.27) and high volume FA developed rapidly, even at early ages. The results also showed that up to a 20% replacement of normal-weight silica sand with saturated LWA was very effective in reducing the autogenous shrinkage and drying shrinkage of ECC. On the other hand, the partial replacement of silica sand with saturated LWA with a nominal maximum aggregate size of 4.76 mm is shown to have a negative effect, especially on the ductility and strength properties of ECC. The test results also confirm that the autogenous shrinkage and drying shrinkage of ECC significantly decreases with increasing FA content. Moreover, increasing FA content is shown to have a positive effect on the ductility of ECC.     

The effect of reprocessing on the mechanical properties of the waste fabric reinforced composites

In this study, waste cotton fabric reinforced polymer matrix composite plate has been processed by a-custom-made recycling extruder. Two different (12.5% and 25% fibers by weight) waste fabric reinforced composite plates were produced and reprocessed six times to assess repetition effect of processing on the mechanical and rheological properties on plates. Effects of reprocessing were evaluated by the tensile testing and impact testing besides SEM, DSC, XRD and MFI rheological and characterization analysis. Test results of composite plates were compared with the pure low density polyethylene (LDPE) plate. Test results show that the tensile strength was increased till the 4th reprocessing step while reducing impact properties. In further reprocessing, tensile properties have been decreased as a consequence of the fabric/fiber damage. Thermal effect of reprocessing was limited according to the comprehensive characterization and rheological analysis.     

Electrochemical and optical properties of biphenyl bridged-dicarbazole oligomer films: Electropolymerization and electrochromism

4,4′-Di(N-carbazoyl)biphenyl monomer (CBP) was synthesized and coated onto ITO–glass surface by electrochemical oxidative polymerization. Its CV shows two distinct one-electron and stepwise oxidation processes occurred at 1.29 and 1.61 V. By using this property, the monomer was electrochemically polymerized separately at these oxidation states and thus, two different oligomer films were obtained afterwards. Their spectro-electrochemical and electrochromic properties were also investigated. Switching ability of the oligomers was evaluated by kinetic studies upon measuring the percent transmittance (%T) at their maximum contrast point, indicating that these oligomers were found to be suitable material for electrochromic devices.     

Identifying cylinder liner wear using precise coordinate measurements

This paper aims at exploiting the accurate precise measurements of CMM machine in exploring and investigating the wear happening between contacting solid surfaces. For instance, excessive wear, if detected by the CMM measurements, in a cylinder bore of an internal combustion engine can dramatically affect its performance quality, sealing function, scheme of lubrication, and eventually its service life span. In such case, the finger print would be the original design GD&T tolerances. Widely spread availability of CMM machines at a reasonable cost may make the applicability of this novel technique of wear detection feasible. In this work, precise and accurate measurements of deviations in roundness, straightness, and concentricity in a cylinder bore of an air cooled Automotive Diesel Engine dismantled for an overhaul using a CMM machine have been executed and analyzed to validate this technique. Thus, the results have been presented, discussed, analyzed and interpreted in order to evaluate the status of the engine during operation. Locations of remarkable deviations representing aggressive wear happenings in the cylinder bore are detected and investigated. The measurements, within the limits of uncertainty attributes, could reflect the performance quality of the engine, the suitability of the applied scheduled maintenance plan, and may also point at possible adverse operating conditions contributed to this wear. In the light of the findings, recommendations may thus be drawn and offered to the engine designer to improve his design. For instance, surface treatments and coatings could be preferably changed, or an innovative constructional modification may be suggested to homogenize the wear occurrence in the cylinder bore during operation. This may extend the operating life span of the cylinder and in turn reduces the maintenance expenses. This novel technique for the wear development recalling proved to be successful and reliable tool to diagnose the root causes of the wear aggression occurrence.     

Fast Keypoint Recognition Using Random Ferns

While feature point recognition is a key component of modern approaches to object detection, existing approaches require computationally expensive patch preprocessing to handle perspective distortion. In this paper, we show that formulating the problem in a naive Bayesian classification framework makes such preprocessing unnecessary and produces an algorithm that is simple, efficient, and robust. Furthermore, it scales well as the number of classes grows. To recognize the patches surrounding keypoints, our classifier uses hundreds of simple binary features and models class posterior probabilities. We make the problem computationally tractable by assuming independence between arbitrary sets of features. Even though this is not strictly true, we demonstrate that our classifier nevertheless performs remarkably well on image data sets containing very significant perspective changes.     

MC‐MIPOG: A Parallel t‐Way Test Generation Strategy for Multicore Systems

Combinatorial testing has been an active research area in recent years. One challenge in this area is dealing with the combinatorial explosion problem, which typically requires a very expensive computational process to find a good test set that covers all the combinations for a given interaction strength (t). Parallelization can be an effective approach to manage this computational cost, that is, by taking advantage of the recent advancement of multicore architectures. In line with such alluring prospects, this paper presents a new deterministic strategy, called multicore modified input parameter order (MC‐MIPOG) based on an earlier strategy, input parameter order generalized (IPOG). Unlike its predecessor strategy, MC‐MIPOG adopts a novel approach by removing control and data dependency to permit the harnessing of multicore systems. Experiments are undertaken to demonstrate speedup gain and to compare the proposed strategy with other strategies, including IPOG. The overall results demonstrate that MC‐MIPOG outperforms most existing strategies (IPOG, IPOF, IPOF2, IPOG‐D, ITCH, TConfig, Jenny, and TVG) in terms of test size within acceptable execution time. Unlike most strategies, MC‐MIPOG is also capable of supporting high interaction strengths of t > 6.