Thermodynamic acceleration of two-phase layered flows in channels with permeable walls of MGD-generators

When creating MHD (Magnetohydrodynamic) alternating current generators using liquid-metal working body, the latter is accelerated by piston method, in which the working body is a periodic structure of alternating zones of liquid metal (pistons) and zones of compressed gas, the latter is accelerated liquid-metal pistons. This raises the form stability problem for liquid metal pistons. Viscous frictional forces generated inside the pistons lead to the destruction of the pistons and significantly reduce the efficiency of the MHD unit. One solution is to use gas-permeable walls of the channels of MHD-generators, through the pores of which gas is injected. In this way, the piston flow is isolated from the side surface of the channel by the penetrating gas in the channel cavity. As a result, friction losses are drastically reduced. At the final values of the One solution is to use gas-permeable walls of the channels of MHD-generators, through the pores of which gas is injection coefficients, (? ≥ 0.03)the friction practically disappears. With the channel length determined by the coordinate of the maximum piston speed, 92% of the current marginal efficiency values can be achieved. The maximum efficiency of the runaway channel can be achieved by selecting the optimal value of the air injection coefficient. The operation of the devices commutating the injected gas must ensure that there is an injection in an area that is no more than twice the length of the piston.

Effects of stroke on spark-ignition combustion with gasoline and methanol

Besides electrification of the powertrain, new synthetic alternative fuels with the potential to be produced from renewable sources come into focus. Methanol is the most elementary liquid synthetic fuel and no novelty for use in internal combustion engines. This article presents pathways to achieve high efficiency spark-ignition methanol combustion on a direct injection spark-ignition single-cylinder research engine with two different stroke-to-bore ratios (1.2 and 1.5) and a constant bore. In addition, two compression ratios (CRs) were investigated on each setup: CR = 10.8 using RON95 E10 gasoline fuel and a higher CR = 15 using neat methanol. In contrast to previous studies of stroke-to-bore ratio influences on SI combustion, this article aims at demonstrating how the advantages of a high stroke-to-bore ratio can be exploited by combining a long-stroke engine with increased compression ratios and methanol. The increased stroke enhances the tumble motion due to a higher piston speed and a larger compression volume which improves the mixture homogenization and combustion velocity. Moreover, the lower surface/volume ratio results in a reduced heat transfer. When using RON95E10 gasoline fuel and CR = 10.8, an efficiency gain of up to 1.6% could be achieved with the long-stroke compared to the short-stroke especially at lower engine loads. With methanol and CR = 15, an efficiency gain of up to 1.6% could be achieved with the long-stroke setup compared to the short-stroke engine. Subsequently, lean burn conditions were experimentally investigated with methanol and CR = 15. The longer stroke allowed the lean burn limit to be extended from λ = 1.9 to λ = 2.0 with an efficiency gain of up to 2.2%. A maximum indicated efficiency of 47.4% could be achieved at λ = 1.9 with methanol on the long-stroke engine with CR = 15.

Development of hydraulic cylinder diagnostic methods by modeling methods

The hydraulic drive of a construction machine is a complex dynamic system that is subjected to many dynamic loads of a variable nature and operates under conditions of variable external influences caused by various factors. During operation, these loads cause failure of the hydraulic transmission elements. To prevent these malfunctions, technical diagnostics should be applied by determining their current technical condition and remaining service life. The article assesses the working condition of hydraulic cylinders using a mathematical model. Using matlab/simulink software to simulate the hydraulic cylinder and hydraulic piston speed when changing the hydraulic cylinder clearance. The simulation results are presented. Keywords: diagnostic, hydraulic cylinder, simulation, development

Optimization Modeling of Irreversible Carnot Engine from the Perspective of Combining Finite Speed and Finite Time Analysis

An irreversible Carnot cycle engine operating as a closed system is modeled using the Direct Method and the First Law of Thermodynamics for processes with Finite Speed. Several models considering the effect on the engine performance of external and internal irreversibilities expressed as a function of the piston speed are presented. External irreversibilities are due to heat transfer at temperature gradient between the cycle and heat reservoirs, while internal ones are represented by pressure losses due to the finite speed of the piston and friction. Moreover, a method for optimizing the temperature of the cycle fluid with respect to the temperature of source and sink and the piston speed is provided. The optimization results predict distinct maximums for the thermal efficiency and power output, as well as different behavior of the entropy generation per cycle and per time. The results obtained in this optimization, which is based on piston speed, and the Curzon–Ahlborn optimization, which is based on time duration, are compared and are found to differ significantly. Correction have been proposed in order to include internal irreversibility in the externally irreversible Carnot cycle from Curzon–Ahlborn optimization, which would be equivalent to a unification attempt of the two optimization analyses.

Multi-Response Optimization of Magnetic Abrasive Flow Finishing Process on Aluminum (6061-T6) Using Utility Concept Embedded Firefly’s Algorithm

Surface finish is the most desired properties of any sophisticated machinery parts for its proper functioning and long endurance. The surface finish must be in the order of micrometer to nanometer for most of the machinery parts. The nontraditional surface finish processes prepare these parts; in these processes, the uses of electromagnet play a vital role in the surface finishing mechanism. Magnetic abrasive flow finishing (MAFF) is such a hybrid process, which gives a combined effect of abrasive flow finishing (AFF) and magnetic abrasive finishing (MAF). In this method, a pair of electromagnets are attached to the AFF setup. By using electromagnet in the AFF process, it enhanced material removal and surface finishing. The main process parameters selected in the MAFF process were magnetic flux density, number of cycles, percentage abrasive content, piston speed, and corresponding responses selected were material removal, percentage improvement in surface finish. In this research paper, the responses were optimized by a combination of utility theory and meta-heuristic firefly’s algorithm. The utility theory based-firefly algorithm’s predicted global optimum parameters set, which was more suitable for reducing the finishing time and required surface finish. The confirmatory test validated this optimized parameter set and it was revealed that the meta-heuristic firefly algorithm embedded with utility theory had given optimized results in the MAFF process.

Investigation of Multistage Combustion Inside a Heavy-Duty Natural-Gas Spark-Ignition Engine Using Three-Dimensional Computational Fluid Dynamics Simulations and the Wiebe-Function Combustion Model

The conversion of existing heavy-duty diesel engines to lean natural-gas (NG) spark ignition can be achieved by replacing the diesel injector with a spark plug and fumigating the NG into the intake manifold. While the original fast-burn diesel chamber will offset the lower NG flame speed, it will result in a two-stage combustion process (a stage inside and another outside the bowl). However, experimental data at more advanced spark timing, equivalence ratio of 0.8, and mean piston speed of 6.5 m/s suggested an additional combustion stage (i.e., three combustion stages). A three-dimensional (3D) computational fluid dynamics (CFD) simulation and a zero-dimensional triple Wiebe-function model were used to better understand the phenomena. While 78% fuel burned inside the bowl, burning rate reduced significantly when the flame approached the squish entrance and the bowl bottom. Moreover, the triple Wiebe-function indicated that the burn inside the squish was also divided into two separate combustion stages, due to the particularities of in-cylinder flow before and after top dead center. The first stage was fast and took place inside the compression stroke. The second took place in the expansion stroke and produced a short-lived increase in the burning rate, probably due to the increasing squish height during the expansion stroke and the increased combustion-induced turbulence, hence the third heat-release peak. Overall, these findings support the need for further investigations of combustion characteristics in such converted engines, to benefit their efficiency and emissions.

Volumetric hydraulic drive with series connection of hydraulic actuators

The aim of the proposed work is theoretical and experimental studies of the performance of a single-channel hydraulic drive with a series connection of executive hydraulic cylinders and the de-velopment of recommendations for predicting their characteristics. The authors of the paper carried out a set of experimental studies and obtained the numerical kinematic, speed and power characteristics of a single-channel hydraulic drive with five hydraulic cylinders connected in series. It is shown that the nature of the kinematic connection is determined by the differentiation of the hydraulic cylinders. The speed of advancement of the piston of an indi-vidual hydraulic cylinder is determined by its serial number in the chain of hydraulic cylinders, while the highest speed of the piston movement is developed by the first hydraulic cylinder. The relative unevenness of the piston movement in comparison with the speed of the piston movement of the first hydraulic cylinder is determined by the differentiation of the hydraulic cylinder, while the hydraulic drive with the differentiation D = 2 has the greatest unevenness. It is shown that by the selection of the differentiation of the hydraulic cylinders, their stepwise arrangement and the displacement of the location of the bottom of the hydraulic cylinder, that it is possible to realize complex forms of the total trajectory of the points of attachment of the hydraulic cylinder rods. In the hydrostatic (power) hydraulic drive in the rod cavities of the hydraulic cylinders, depend-ing on the serial number of the hydraulic cylinder, the thrust on its rod and the differentiation set different pressure levels, and the lowest pressure will be in the piston cavity of the last hydraulic cylinder. With uniformly loaded hydraulic cylinders, the pressure in the piston cavities depends only on the number of the hydraulic cylinder and its differentiation. In a hydraulic drive with hydraulic cylinders of equal power, the last hydraulic cylinder will develop the greatest force at the lowest piston speed. In addition, the work also shows that the reproducibility of the positions of unloaded rods of hy-draulic cylinders of equal differentiation is not less than 1%. As a result of the experimental studies, a method was developed for the design of a volumetric hydraulic drive with sequential switching on of executive hydraulic cylinders, which can be used to solve the problems of hydrofication of me-chanical engineering production (bending presses, sheet stamping), in shipbuilding (ship slipways), in flexible production systems, industrial and warehouse logistics.

Simulation Fluidity Test for Semisolid Squeeze Casting

The paper deals with semi solid squeeze casting technology. Fluidity tests were designed for the selected technology. The shape of the test casting was designed in the shape of test bars with different thicknesses and also in the shape of a stepped casting. The thickness of the individual elements was chosen on the basis of a selected / preferred numbers R10 EN STN 17. As a result, the thickness of the elements was 2.0, 2.5, 3.15, 4.0, 5.0 and 6.3 mm. Designed fluidity tests were verified by using ProCast simulation software. The selected process parameters were: operating pressure 80 MPa, mold temperature 200 °C, piston speed 30 mm.s-1. The experimental material was an AlSi7Mg0.3 alloy with a different solid phase content. The initial solid amount were 50, 55 and 60 %. The effect of solidus and liquidus, temperature distribution and pressure was monitored during the evaluation of fluidity.

A Fundamental Thermodynamic Study on the Effects of Engine Scale in Diesel Engines

The Navy has a wide range of diesel engines with bore sizes varying by a factor of four. In general, diesel engines can have bore scaling over a full order of magnitude. As an engine cylinder gets larger its surface area to volume ratio reduces significantly, which in turn affects in-cylinder heat transfer. In this study, a fundamental generalized thermodynamic model of diesel engines was developed. The various key model effects were systematically analyzed along with engine bore size. Further, cylinder wall temperature was varied across a range of cold start to stabilized operating temperatures. The results of this study show that smaller bore diesel engines are always more sensitive to cold start conditions. The effect is reduced with increasing wall temperature yet smaller diesel engines have cooler end-of-compression temperatures as comparted to larger engines. The effects of engine speed, in which mean piston speed is held constant, tend to modestly reduce the differences between various size diesel engines due to non-linear heat transfer effects. When variable specific heat effects are correctly considered, end-of-compression air charge temperatures are only modestly different as a function of engine bore size. The most significant difference is the overall reduced heat transfer in larger engines due to the surface area to volume effect. A difference of a factor of three for in cylinder heat transfer relative to in-cylinder inducted air mass is predicted being much greater for the smaller engines. Higher exhaust temperatures are also characteristic of the larger bore engines. This allows more combustion work to be delivered to the piston with a correspondingly higher thermal efficiency for larger diesel engines. Future work will evaluate fuel effects on varying bore size.