Propulsion and Power Research最新文献

This paper presents the Nusselt number and friction factor model for hydrocarbon fuel under supercritical pressure in horizontal circular tubes using an artificial neural network (ANN) analysis on the basis of the back propagation algorithm. The derivation of the proposed model relies on a large number of experimental data obtained from the tests performed with the platform of supercritical flow and heat transfer. Different topology structures, training algorithms and transfer functions are employed in model optimization. The performance of the optimal ANN model is evaluated with the mean relative error, the determination coefficient, the number of iterations and the convergence time. It is demonstrated that the model has high prediction accuracy when the tansig transfer function, the Levenberg-Marquardt training algorithm and the three-layer topology of 4-9-1 are selected. In addition, the accuracy of the ANN model is observed to be the highest compared with other classic empirical correlations. Mean relative error values of 4.4% and 3.4% have been achieved for modeling of the Nusselt number and friction factor respectively over the whole experimental data set. The ANN model established in this paper is shown to have an excellent performance in learning ability and generalization for characterizing the flow and heat transfer law of hydrocarbon fuel, which can provide an alternative approach for the future study of supercritical fluid characteristics and the associated engineering applications.

In this paper, transient phenomenon during start up process of a pump fed liquid rocket engine is investigated through numerical simulation. The engine studied in this work is designed such that engine systems are not wetted with propellant until the engine is commanded to start. This is achieved by positioning the valves for propellant admission at the interface of test stand/flight stage and the engine. To evaluate engine performance during start transient for such systems, unsteady flow simulation was conducted using Method of Characteristics and equations for priming. The same has been reported in this work. The results indicated a brief period of abrupt pressure rise at pump upstream after opening of the propellant admission valves, during the process of priming of engine systems at valve downstream. The peak pressure obtained was significantly higher than the propellant tank pressure as well as the steady state pump suction pressure. The transitory pressure rise was found to occur due to flow resistance at impeller inlet caused by formation of a forced vortex for orienting the flow through impeller blades during off design transient regime. The maximum pressure at pump upstream, as computed from start transient simulation, was used as a design input for pump inlet feed lines. The engine was realized and subsequently qualified in a ground test facility. Hot test data obtained for pressure and flow rate during transient regime were found to be in good agreement with the simulation results.

This study discusses the development of a mathematical model that is capable of predicting the drop size mean diameter of the spray generated by a pressure swirl atomizer, considering the effects of the liquid's viscosity and the geometrical parameters of this type of injector, as well as the angle of incidence of the inlet channels (ψ and β) and atomization parameters (k, ϰ), obtained from hyperbolic relations. Additionally, this model investigates the phenomena of rupture and stability that are observed in the conical liquid film, in which the importance of a new geometrical parameter of atomization, “ϰ”, which immediately influences the drop size diameter of the spray, should be highlighted. The results that are obtained using this model are compared with analytical results of Couto, Wang and Lefebvre, Jasuja, Radcliffe and Lefebvre, experimental results and numerics (Hollow cone atomization model), using the Ansys Fluent software for the validation and consistency of the model proposed in Rivas (2015). This model yields good approximations as compared to that yielded using other alternative mathematical models, demonstrating that the new atomization geometric parameter “ϰ” is an “adjustment” factor that exhibits considerable significance while designing pressure swirl atomizers according to the required SMD. Furthermore, this model is easy to use, with reliable results, and has the advantage of saving computational time.

A concept for plasma detachment in a magnetic nozzle is developed based on the detachment region which is found to decrease with the taper angle of the coils employed in the proposed flexible three coil setup. On tapering the coils while resulting in the same cross-sectional area, the plasma plume outside the throat grows radially that leads to an enhancement in the thrust from 2.67 mN to 5 mN at the final detachment plane for a rise in the taper angle from $0$ to 13°. The maximum thrust can reach about 9 mN when the middle coil is shifted closer to the right coil along with increasing middle-to-outer-coil diameter (inner) ratio from 1 to 3. Proposed three-tapered-coils arrangement for a magnetic nozzle turns out to be a robust candidate for space propulsion offering the ability to control plasma detachment and tune thrust in-flight simply via mechanical movements without changing the current.

Providing stable combustion of lean-burn natural gas engines was always a big challenge, particularly during a low load operation. In transient sea conditions, there is an additional concern due to irregular time-varying loads. Therefore, this study aimed at investigating the part-load operation of a marine spark-ignition lean-burn natural gas engine by simulating the entire engine. The engine's essential components are modeled, including air manifold, intake valves, fuel system, controllers, combustion chamber, exhaust valves, exhaust manifold and turbocharger.

In steady-state, the results of emission compounds from modeling have been compared to measured data from 25% to 100% loads. For transient conditions, for the sample time of about 50 min, the fuel flow and turbocharger output are selected from the vessel logged data and compared with the simulation results. The model has shown the great potential of predicting the engine response throughout the steady-state and transient conditions. Simulating the engine at part-load transient condition showed that the unburned hydrocarbon formation, known as methane slip in lean-burn gas engines, is more than the part-load steady-state. This increase of methane slip is due to the combustion instability in lower loads and flame extinguishing in such transient conditions. The engine measured data shows a double amount of methane slip in a 25% load than the 100% load in steady-state. However, the simulation output in the transient conditions confirms an increase in methane slip over four times than equivalent steady-state load. Moreover, the lean-burn gas engine releases less NO_X in part-load operation in a steady-state due to lower in-cylinder temperature. In transient conditions, there is remarkable instability in excess air ratio. Due to this instability, there is a rich mixture in instantaneous time steps during loads up. Therefore, it will result in an unusually high amount of NO_X, and more than two times in comparison with the equivalent steady-state output.

Recently, reactivity controlled compression ignition (RCCI) has been proposed in order to achieve a higher thermal efficiency with lower emissions than conventional combustion. In RCCI mode, as the fuel types and their combinations affects the reactivity stratification inside cylinder, thus combustion control, in present study, iso-propanol was evaluated as low-reactivity fuel (LRF) when petroleum diesel, commercial biodiesel and their blends were high-reactivity fuels. It is of great importance that iso-propanol and biodiesel be used together in RCCI mode, as they significantly affect the in-cylinder stratification due to their high octane/cetane number. Therefore, the reactivity controlled compression ignition (RCCI) combustion characteristics was investigated in a diesel research engine using iso-propanol, petroleum diesel, biodiesel and their blends as fuels. Tests were conducted on varying loadings (from 20% to 60% of max torque) and premixed ratios of LRF (Rp = 0, 0.15, 0.30, 0.45, and 0.60) at a constant engine speed of 2400 rpm. Results, which were compared with conventional diesel combustion (CDC), showed that, as the premixed ratio (Rp) of low-reactivity fuel (iso-propanol) increased, ignition delay (ID) period prolonged while combustion duration (CD) and rate of pressure rise (RoPR) reduced assisted to reduce NO emissions and smoke opacity in the exhaust. NO and smoke opacity reduced simultaneously for biodiesel-propanol combinations up to 40% under 20% load and 0.60 premixed ratio of LRF compared to CDC. Propanol premixed ratio of 0.30 at 60% load was found to be optimum concerning lowest emissions. In conventional mode, HC emissions reduced by up to 52% when biodiesel and its blends with diesel fuel are used, whereas they increased significantly in RCCI mode. According to overall results, it is concluded that RCCI performed better than CDC at entire load.

Biodiesel is derived from waste cooking oil (WCO) by transesterification. Methyl ester was prepared by mixing diesel and biodiesel oils as 20% by volume. Nano particles as TiO₂, Al₂O₃ and CNTs were blended with biodiesel blend at different concentrations of 25, 50, and 100 mg/l to enhance the physicochemical fuel characteristics to obtain clean and efficient combustion performance. An experimental setup was incorporated into a diesel engine to investigate the influence of these nano-materials on engine performance, exergy analysis, combustion characteristics and emissions using WCO biodiesel-diesel mixture. Enriching methyl ester mixture with 100 ppm titanium, alumina and CNTs (B20T100, B20A100 and B20C100) increased the thermal efficiency by 4%, 6% and 11.5%, respectively compared to B20. Biodiesel blending with nano additives B20T100, B20A100 and B20C100 decreased the emissions of CO (11%, 24% and 30%, respectively), HC (8%, 17% and 25%, respectively) and smoke (10%, 13% and 19%, respectively) compared to B20. However, the noticeable increase of NO_x was estimated by 5%, 12% and 27% for B20T100, B20A100 and B20C100, respectively. Finally, the results showed the rise in peak cylinder pressure by 5%, 9% and 11% and increase in heat release rate by 4%, 8% and 13% for B20T100, B20A100 and B20C100, respectively. The fuel exergy of B20T100, B20A100 and B20C100 are lower than biodiesel blend B20 by 6.5%, 16% and 23% but the exergetic efficiency are increased by 7%, 19% and 30% at full load about B20.

This model is dedicated to visualizing the nature of magnetite-water nanoliquid induced by a permeable plate having variable magnetic effect, non-linear radiation, heterogeneous and homogeneous chemically reactive species. The system of momentum, thermal and concentration expressions is formulated and transformed from the partial to ordinary differential systems by using the adequate transforms. This highly non-linear system is solved through RKF (Runge-Kutta-Fehlberg) numerical method. Important parameters such as suction/injection, magnetic, and radiation effects as well as other relevant parameters are investigated. The graphs show that the rise in radiation parameter numerically improves the thermal distribution, implying a faster heat transfer rate. Non-linear radiation has greater effect on temperature than the linear radiation. While the volume concentration effect reveals that the friction factor increase with the enhancement of nanoparticle concentration. It is also observed that, plate velocity decreases the skin-friction but increases the wall heat transfer for both suction and blowing cases. The results indicate that the current research has a strong agreement with the relevant data in a limiting approach.

The crystal orientation significantly affects the low-cycle fatigue (LCF) properties of single crystal (SC) superalloys. However, the orientation-dependent LCF life model with precise mechanisms and strong applicability is still lacking. This investigation aims at establishing an energy-based LCF life evaluation method that could consider the orientation effect. First, the influencing factors of anisotropy were identified through the literature review. Secondly, the multiaxial formula of the Ramberg-Osgood (R–O) equation was established to describe the anisotropic cyclic deformation characteristics. Furthermore, the strain energy density of SC superalloys was determined based on this equation, and the effective strain energy density was introduced to account for the effect of orientation. Finally, the energy-based method was validated by its application to several SC superalloys. Results showed that the crystallographic orientation with a lower Young's modulus usually exhibits better LCF resistance. This phenomenon could be attributed to the different values of strain energy density dissipated in one cycle. The multiaxial R–O relationship could capture the anisotropic cyclic deformation response of DD6. Compared with the classical methods, the energy-based model is favored by its precise mechanism and strong applicability. And it also exhibited better prediction accuracy. Most data points of different crystallographic orientations lay within the ±3 error band.