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In this paper, four full-scale concrete columns with high-strength spiral stirrups (HSSS) are constructed and tested under low-cycle repeated loading. The specimens consisted of two castin- place columns and two precast concrete columns encased by a partly square steel pipe and bolt bars.The structural analysis of the HSSS columns of precast concrete conducted here is novel, and past experimental data for this are not available.To assess the seismic behavior and failure mechanisms of the new connections, quasi-static tests were carried out on columns prefabricated with them and cast-in-place specimens.The responses of all columns were compared, and the results showed that the failure modes of all columns are the large eccentric damage, and the destruction of all specimens occur at the column foot. The anti-seismic property of the precast HSSS concrete columns was comparable to that of the HSSS cast-in-place columns. A comparison of such performance parameters as energy dissipation and coefficient of ductility revealed that the precast HSSS concrete columns are suitable for use in earthquake zones.

Kerosene, an intermediate component of wide distillation fuel, has drawn increasing attention for low-temperature combustion mode due to its compromise of evaporation and ignition characteristics between diesel and gasoline. This study focuses on the comparison of spray and combustion characteristics between diesel and kerosene under low-temperature combustion mode conditions based on visualization tests in a constant volume chamber. Different injection pressures, ambient temperatures, and oxygen concentrations were tested at a constant ambient density of 16.67 kg/m3. The image processing results reveal that the liquid penetration distance of kerosene shows a maximum reduction of 33.5% compared to diesel with a smaller cone angle and spray area at 160 MPa and 800 K. At the same time, the ignition delay of kerosene is 0.9 ms longer than that of diesel, and the injection and combustion processes of kerosene are separated, making it much more similar to the premixed combustion. An increase in injection pressure improves the spray penetration distance but exerts little influence on the flame lift-off length and ignition delay for both fuels. Kerosene presents a lower spatially integrating natural luminosity, especially at low injection pressure. The liquid spray penetration distance and the ignition delay of kerosene are more sensitive to the increase in ambient temperature. However, the higher ambient temperature presents a greater effect on the SINL of diesel. With the decrease of ambient oxygen concentration, the ignition delay, flame lift-off length, spatially integrating natural luminosity, and soot oxidation rate of both fuels decrease obviously. Especially at 15 vol.% ambient oxygen, kerosene presents a much weaker luminosity. These results imply that kerosene exhibits a very similar trend to diesel in terms of spray and combustion characteristics. Moreover, kerosene has a stronger potential to reduce soot formation than diesel with a better fuel-air mixing process under low-temperature combustion mode conditions. [ABSTRACT FROM AUTHOR]

An energy management strategy (EMS) is important in marine hybrid propulsion systems while the global optimal solutions are more significant for the EMS to improve the fuel economy of system. Aiming at finding the more accurate global optimal solutions for EMS, an improved dynamic programing (DP) algorithm was proposed to overcome the basic DP algorithms' weaknesses and improve the fuel economy. Then the model of gas-electric hybrid propulsion system was also established to verify the strategies. What's more, the improved DP algorithm was applied to the minimum natural gas consumption and charge-sustaining strategy. And a bi-level optimization scheme that decoupled the interaction between the EMS and components matching was also studied. The results showed that the improved DP algorithm not only avoided the shortcomings in the basic DP algorithm such as the weak effect of penalty functions and curse of dimensionality but also gave more accurate solutions. Compared to the basic DP, the improved DP algorithm can reduce the gas fuel consumption by 3.67% and the computational complexity decreases 100 times. [ABSTRACT FROM AUTHOR]

The improvement of injector performance is important for the operation of common rail (CR) fuel systems. In this study, the optimization work has been carried out on a large-flow common rail injector. First, to simulate the injection process, a one-dimensional (1-D) model was developed and validated against the experimental data. The mathematical approximation model was also established to correlate the injection performance with the factors. Then, a multi-objective model by taking three design objectives into account was established and solved. Finally, Pareto front was obtained and the final optimization solution was determined. Furthermore, an extensive validation and analysis for the optimized results under various operating conditions was also carried out. Results shows that the three objectives, total response time, injection pressure fluctuation and injection pressure drop respectively, are improved by 11.75%, 39.12%, and 10.03% under the typical condition. And the proposed multi-objective optimization program based on design of experiment (DOE) technique, response surface methodology (RSM) and Elitist Non-dominated sorting genetic algorithm (NSGA-II) in present work can exhibit a good capability to optimize the problem of the injection performance in a CR fuel system. [ABSTRACT FROM AUTHOR]

In order to reduce efficiency losses and improve the aerodynamic efficiency of axial turbines used in industry, the flow fields of the turbine stage were investigated numerically and experimentally under different axial gaps in this work. The influence of the axial gaps on the flow unsteadiness and the flow field distribution is discussed. The results show that the aerodynamic efficiency of the turbine stage increases when the axial distance is reduced. The difference in entropy increases under different axial distances are mainly found in the section from the stator inlet to the rotor inlet: the turbine not only has a better time-average aerodynamic performance, but also has a better transient aerodynamic performance under working conditions with a small axial distance. Additionally, the maximum disturbance amplitudes of the stator and rotor are located near the trailing edge of the stator and the leading edge of the rotor, respectively. Compared with the wake disturbance of the upstream stator to the downstream adjacent rotor, the reverse disturbance of the downstream stator to the adjacent upstream rotor is more sensitive to the change in the blade spacing. [ABSTRACT FROM AUTHOR]

Uniaxial compression tests were carried out based on acoustic emission technology to study the rule and process of the damage evolution of marble powder concrete (MPC) under compression. The fracture characteristics of MPC are examined by analyzing the variation characteristics of acoustic emission signal parameters. The damage evolution model of MPC is established based on the characteristic parameters. The results showed that the strength loss rate of MPC decreased with the curing time, and the maximum strength loss rate of 28 d was 6.2% when the substitution percentage was 15%. According to the analysis of acoustic emission parameters, the compression failure process of MPC can be divided into three stages, the acoustic emission activity is higher in the early stage of loading, the relative stress during critical instability failure is reduced, and the substitution percentage is reduced by 4.2% at 15%. MPC is mainly fractured by tensile failure. With the increase in marble powder substitution percentage, the proportion of tensile mode cracks in stages I and II decreased. The proportion in stage III showed an increasing trend, and the failure characteristics gradually changed from brittleness to ductility. The fluctuation amplitude of the b-value increased with the substitution percentage, and the highest volatility was 18.5% when the substitution percentage was 15%. The crack propagation behavior gradually changed from stable growth to unstable growth. When the substitution percentage is lower than 15%, the damage development of MPC in the middle of stress (relative stress 20~70%) is relatively slow, and the damage development is accelerated in the late stress stage. [ABSTRACT FROM AUTHOR]

In order to demonstrate the relationship between the fuel injection quantity and the structural parameters of the fuel system for large marine diesel engines, an AMESim model of a double-valve controlled fuel system is proposed. The accuracy of the model is validated in view of fuel injection quantity and system pressures. The correlation analysis is performed to illustrate the effects of single parameters and the interactions between different parameters on the fuel injection quantity. Considering the high calculation cost of the simulation model, the prediction model between the fuel injection quantity and the structural parameters for each working condition is obtained based on D-optimal design of experiments and the response surface methodology in this article. For the maximum deviation between the calculated and predicted fuel injection quantity is only 4.27%, the prediction models could be used for further analysis. And the results show that the diameters of high-pressure fuel tube (HPFT), small and big ends of pressure amplification piston (PAP) are the key single parameters. The absolute values of their correlation coefficients are between 0.77 and 0.87, between 0.22 and 0.43 and between 0.14 and 0.26 respectively. The correlation coefficients for the other parameters are all relatively small. For interactive parameters, the absolute values for all the correlation coefficients are less than 0.1. And the interactions between the diameters of big and small diameters of PAP, between the diameter of small end of PAP and the diameter of HPFT, between the diameter of HPFT and the pre-tightening force of needle spring influence the fuel injection quantity relatively obviously. [ABSTRACT FROM AUTHOR]

Common rail (CR) fuel pumps are characterized by pulsating supply, and instantaneous flow ripple is the main reason for the variation in supply consistency. To analyze the transient supply consistency of CR pump, a test bench for transient supply performance was originally designed and established. The potential effects exerted by pump speed and operating pressure on the pressure ripple were obtained under different fuel metering valve (FMV) openings. On this basis, an approach for the calculation of instantaneous flow ripple was proposed by combining impedance theory and hydraulic transmission line method (TLM). Furthermore, the coefficient of variation (CoV) of flow ripple amplitude was applied to evaluate the cycle-to-cycle consistency in fuel supply process. The results show that the rotational speed together with the plunger number determines the frequency of flow ripple. The pump presents a greater flow ripple amplitude under high speed and low pressure conditions, which further leads to an intense pressure ripple. Besides, in most operating points, the CoV is around 0.15, indicating a good transient supply consistency. When the FMV is partially open, under the coupled effect of FMV operating frequency and plunger movements, the value of CoV shows an oscillating trend as a function of speed. • A transient supply performance test bench for common rail fuel pumps was developed. • The transient pressure ripple characteristics were analyzed. • The instantaneous flow ripple in a pump was obtained. • An evaluation index for fuel supply consistency of a common rail pump was proposed. • The cycle-to-cycle fuel supply consistency performance was investigated. [ABSTRACT FROM AUTHOR]

The coherence of the fuel injection quantity determines the working stability of the common rail system. The variations in the parameters of the common rail injector have significant influence on coherence of the fuel injection quantity of the system. The bond graphs for the main components of the common rail injector were proposed, respectively, based on the bond graph methodology in this article. The fuel injection quantities of the system at different rail pressures and injection pulse widths had been obtained by numerically solving and programming the obtained state equations in MATLAB. The predicted results of the fuel injection quantity by the model are in excellent agreement with the experimental measurements which were obtained from a test bench. Through the correlation analysis of the influential factors on the fuel injection quantity, the correlation coefficients between the fuel injection quantity and the single influential factor and quadratic influential factor at different rail pressures and injection pulse widths were obtained, respectively. Moreover, the variation characteristics of correlation between the fuel injection quantity and its influential factors had been analyzed in detail. The results show that the nozzle hole diameter and the inlet orifice diameter are the main influential factors on the fuel injection quantity among the selected parameters. The quadratic factors under the action of the parameter itself and the quadratic factors under the interaction between the delivery chamber diameter and nozzle hole diameter, needle seat semi-angle and needle cone semi-angle, nozzle hole diameter and inlet orifice diameter and inlet orifice diameter and outlet orifice diameter have significant effect on the fuel injection quantity, and they are the main influential factors on the fuel injection quantity among the quadratic factors. [ABSTRACT FROM AUTHOR]