Paolo Tamburrano

Fluid-dynamic design optimization of hydraulic proportional directional valves

This article proposes an effective methodology for the fluid-dynamic design optimization of the sliding spool of a hydraulic proportional directional valve: the goal is the minimization of the flow force at a prescribed flow rate, so as to reduce the required opening force while keeping the operation features unchanged. A full three-dimensional model of the flow field within the valve is employed to accurately predict the flow force acting on the spool. A theoretical analysis, based on both the axial momentum equation and flow simulations, is conducted to define the design parameters, which need to be properly selected in order to reduce the flow force without significantly affecting the flow rate. A genetic algorithm, coupled with a computational fluid dynamics flow solver, is employed to minimize the flow force acting on the valve spool at the maximum opening. A comparison with a typical single-objective optimization algorithm is performed to evaluate performance and effectiveness of the employed genetic algorithm. The optimized spool develops a maximum flow force which is smaller than that produced by the commercially available valve, mainly due to some major modifications occurring in the discharge section. Reducing the flow force and thus the electromagnetic force exerted by the solenoid actuators allows the operational range of direct (single-stage) driven valves to be enlarged.

The importance of a full 3D fluid dynamic analysis to evaluate the flow forces in a hydraulic directional proportional valve

Purpose – The purpose of this paper is to present a full 3D Computational Fluid Dynamics (CFD) analysis of the flow field through hydraulic directional proportional valves, in order to accurately predict the flow forces acting on the spool and to overcome the limitations of two-dimensional (2D) and simplified three-dimensional (3D) models. Design/methodology/approach – A full 3D CAD representation is proposed as a general approach to reproduce the geometry of an existing valve in full detail; then, unstructured computational grids, which identify peculiar positions of the spool travel, are generated by means of the mesh generation tool Gambit. The computational grids are imported into the commercial CFD code Fluent, where the flow equations are solved assuming that the flow is steady and incompressible. To validate the proposed computational procedure, the predicted flow rates and flow forces are compared with the corresponding experimental data. Findings – The superposition between numerical and experime...

High Temperature Gas-to-Gas Heat Exchanger Based on a Solid Intermediate Medium

This paper proposes the design of an innovative high temperature gas-to-gas heat exchanger based on solid particles as intermediate medium, with application in medium and large scale externally fired combined power plants fed by alternative and dirty fuels, such as biomass and coal. An optimization procedure, performed by means of a genetic algorithm combined with computational fluid dynamics (CFD) analysis, is employed for the design of the heat exchanger: the goal is the minimization of its size for an assigned heat exchanger efficiency. Two cases, corresponding to efficiencies equal to 80% and 90%, are considered. The scientific and technical difficulties for the realization of the heat exchanger are also faced up; in particular, this work focuses on the development both of a pressurization device, which is needed to move the solid particles within the heat exchanger, and of a pneumatic conveyor, which is required to deliver back the particles from the bottom to the top of the plant in order to realize a continuous operation mode. An analytical approach and a thorough experimental campaign are proposed to analyze the proposed systems and to evaluate the associated energy losses.

Thrust Control of Small Turbojet Engines Using Fuzzy Logic: Design and Experimental Validation

The aim of this paper is to propose an effective technique which employs a proportional-integral Fuzzy logic controller for the thrust regulation of small scale turbojet engines, capable of ensuring high performance in terms of response speed, precision and stability. Fuzzy rules have been chosen by logical deduction and some specific parameters of the closed loop control have been optimized using a numerical simulator, so as to achieve rapidity and stability of response, as well as absence of overshoots. The proposed Fuzzy logic controller has been tested on the Pegasus MK3 microturbine: the high response speed and precision of the proposed thrust control, revealed by the simulations, have been confirmed by several experimental tests with step response. Its stability has been demonstrated by means of the frequency response analysis of the system. The proposed thrust control technique has general validity and can be applied to any small-scale turbojet engine, as well as to microturbines for electricity production, provided that thrust being substituted with the net mechanical power.

Laminar flame speed correlations for methane, ethane, propane and their mixtures, and natural gas and gasoline for spark-ignition engine simulations

The laminar flame speed plays an important role in spark-ignition engines, as well as in many other combustion applications, such as in designing burners and predicting explosions. For this reason, it has been object of extensive research. Analytical correlations that allow it to be calculated have been developed and are used in engine simulations. They are usually preferred to detailed chemical kinetic models for saving computational time. Therefore, an accurate as possible formulation for such expressions is needed for successful simulations. However, many previous empirical correlations have been based on a limited set of experimental measurements, which have been often carried out over a limited range of operating conditions. Thus, it can result in low accuracy and usability. In this study, measurements of laminar flame speeds obtained by several workers are collected, compared and critically analyzed with the aim to develop more accurate empirical correlations for laminar flame speeds as a function of equivalence ratio and unburned mixture temperature and pressure over a wide range of operating conditions, namely ϕ = 0 . 6 - 1 . 7 , p u = 1 - 50 atm and T u = 298 - 800 K . The purpose is to provide simple and workable expressions for modeling the laminar flame speed of practical fuels used in spark-ignition engines. Pure compounds, such as methane and propane and binary mixtures of methane/ethane and methane/propane, as well as more complex fuels including natural gas and gasoline, are considered. A comparison with available empirical correlations in the literature is also provided.

Effects of lubricant oil on particulate emissions from port-fuel and direct-injection spark-ignition engines:

This work presents experimental tests where lubricant oil was added to the engine in order to highlight its contribution to particle emissions from both gasoline and compressed natural gas spark-ignition engines. Three different ways of feeding the extra lubricant oil and two fuel-injection modes—port fuel injection and direct injection—were investigated to mimic the different ways by which lubricant may reach the combustion chamber. In particular, in the tests using compressed natural gas, the oil was injected either into the intake manifold or directly into the combustion chamber, whereas in both the port-fuel-injection and direct-injection tests using gasoline, the oil was premixed with the fuel. The experiments were performed on a single-cylinder, optically accessible spark-ignition engine, running at 2000 r/min under stoichiometric and full-load conditions, and requiring no lubrication. Particle size distribution functions were measured in the range from 5.6 to 560 nm by means of an engine exhaust particle sizer. Particle samples were taken directly from the exhaust flow, just downstream of the valves. Opacity was measured by an AVL 439 opacimeter, and gaseous emissions were measured by means of an exhaust gas analyzer in order to globally monitor the combustion process. Detailed analysis of the recorded total particulate number and particle size distributions allowed to determine the size ranges and relative amounts associated with the lubricant-oil-derived particles. Oil addition produced a significant increase in the particles emitted in the lowest range size, independent of the way lubricant was added. Only when lubricant was injected directly into the combustion chamber (either blended with the fuel or by itself), an increase in the number of particles with sizes larger than 50 nm was recorded.

Tangential inlet cyclone separators with low solid loading: Design by means of 3D fluid dynamic optimization

Purpose The purpose of this paper is to propose an effective methodology for the industrial design of tangential inlet cyclone separators that is based on the fully three-dimensional (3D) simulation of the flow field within the cyclone coupled with an effective genetic algorithm. Design/methodology/approach The proposed fully 3D computational fluid dynamics (CFD) model makes use of the Reynold stress model for the accurate prediction of turbulence, while the particle trajectories are simulated using the one-way coupling discrete phase, which is a model particularly effective in case of low concentration of dust. To validate the CFD model, the numerical predictions are compared with experimental data available in the scientific literature. Eight design parameters were chosen, with the two objectives being the minimization of the pressure drop and the maximization of the collection efficiency. Findings The optimization procedure allows the determination of the Pareto Front, which represents the set of the best geometries and can be instrumental in taking an optimal decision in the presence of such a trade-off between the two conflicting objectives. The comparison among the individuals belonging to the Pareto Front with a more standard cyclone geometry shows that such a CFD global search is very effective. Practical implications The proposed procedure is tested for specific values of the operating conditions; however, it has general validity and can be used in place of typical procedures based on empirical models or engineers’ experience for the industrial design of tangential inlet cyclone separators with low solid loading. Originality/value Such an optimization process has never been proposed before for the design of cyclone separators; it has been developed with the aim of being both highly accurate and compatible with the industrial design time.

An Adaptive Fuzzy Logic Algorithm for the Thrust Control of a Small Turbojet Engine

ABSTRACT This paper proposes a Fuzzy technique for the thrust control of small-scale turbo-jet engines, as an effective alternative to conventional PID techniques. Fuzzy rules have been preliminarly chosen and tuned so as to achieve rapidity and stability of response, as well as absence of overshoots, by simulating the transient operation of the Pegasus MK3 small-scale turbo-jet. Three experimental tests with large increases or decreases of set thrust have been carried out on the same engine: excellent results in terms of response speed, stability and absence of overshoots have been achieved. The proposed thrust control technique has general validity and can be applied to any small-scale turbojet engine, as well as to microturbines for electricity production, provided that thrust being substituted with the net mechanical power. INTRODUCTION Recently, the development of unmanned aerial vehicles (UAVs) has increased the interest for small turbojet engines [1,2,3,4] derived from turbocharger rotor components. A small-scale turbojet engine can also be employed as gas generator core for small ramjet engines, powering supersonic UAVs. For both applications, i.e., for small portable power generation systems and for mini or micro UAVs, the potentially very high power density of the gas turbine allows a strong reduction in battery, and thus of the overall system weight [5,6,7,8,9,10,11]. Such a rapid development makes it crucial to develop a fast and reliable thrust control system for these small-scale turbojet engines. Most of the automatic controls employed in industrial application are based on PID (Proportional, Integral, Derivative) algorithms, which are the most common and studied controllers. In addition to PID controllers, research is studying alternatives such as control systems based on Fuzzy logic: several authors report theoretical studies of Fuzzy controllers and applications to real systems [12-22]. Fuzzy logic is much closer to human reasoning than conventional algorithms: it is mainly based on the employment of degrees of partial truth, which allows to study a physical phenomenon thoroughly. For these reasons Fuzzy logic fits very well to nonlinear systems and to systems whose mathematical model is not known [12,15]. As for the conventional controllers, the controllers based on Fuzzy logic may have a proportional action (P), a proportional-integral action (PI) or a proportional-integral-derivative action (PID). This paper describes the application of a PI Fuzzy controller for the automatic control of the axial thrust of a turbojet engine, namely “Pegasus MK3”. The paper will first propose a brief description of the Pegasus small-scale turbojet engine and of the experimental rig employed to test the turbojet engine. Then, characteristics of the closed-loop control are described and parameters of the Fuzzy controller are reported in detail. Some experimental tests will be finally presented to validate the proposed thrust control technique.

A Review of Direct Drive Proportional Electrohydraulic Spool Valves: Industrial State-of-the-Art and Research Advancements

This paper reviews the state of the art of directly driven proportional directional hydraulic spool valves, which are widely used hydraulic components in the industrial and transportation sectors. Firstly, the construction and performance of commercially available units are discussed, together with simple models of the main characteristics. The review of published research focusses on two key areas: investigations that analyse and optimize valves from a fluid dynamic point of view, and then studies on spool position control systems. Mathematical modelling is a very active area of research, including Computational Fluid Dynamics (CFD) for spool geometry optimisation, and dynamic spool actuation and motion modelling to inform controller design. Drawbacks and advantages of new designs and concepts are described in the paper.