Piston Trajectory Research Articles

Numerical Analysis of Piston's Trajectory for a New Kind Engine

Kinematic analysis method is used to verify the feasibility of a new kind rotary engine which is proposed recently. Firstly, a coordinate system and relevant parameters are presented for the engine, and then the kinematic theory model of key components in system are built, based on this model, the law of pistons motion is studied at last. The results could provide an effective reference to the study on design and manufacture of this engine.

Ecological performance improved by controlling piston motion: linear phenomenological system bimolecular, light driven engine

The ecological criterion is introduced into the optimal configuation problem of an irreversible light driven engine with a working fluid composed of the bimolecular reacting system , in which the heat transfer between the working fluid and the environment obeys linear phenomenological heat transfer law []. Piston trajectory for maximum ecological performance is determined with rate dependent loss mechanisms of friction and heat leakage. Numerical examples of optimal configurations for maximum ecological performance are provided. The obtained results are not only compared with those for maximum work output and minimum entropy generation with linear phenomenological heat transfer law but also compared with those for maximum ecological performance with Newton’s heat transfer law. The results indicate that taking maximum ecological criterion as the objective makes larger improvement of the reduction in the entropy generation with the cost of a little decrease in the work output.

Hydraulic Free Piston Engine Enabled by Active Motion Control

This article explores various functional aspects of hydraulic free piston engine (FPE) enabled by action motion control. Given the potential for high efficiency and flexibility, the FPE is well suited for mobile applications such as on-road vehicles and off-road heavy machinery. The advantage of the active motion controller lies in its ability to precisely track and shape the piston trajectory. FPE has a great potential for energy saving and emission control, but its reliable operation is limited by the complex dynamic coupling among the engine subsystems and the lack of the crankshaft. This inherent technical barrier for FPE could be overcome by active control with today’s sensing, actuation and computing technologies. A prototype hydraulic FPE is used to demonstrate the capabilities of active piston motion control. Experimental results demonstrate the feasibility and promise of the technology. Engine power control will be combined with piston motion control in the future to achieve a wider range of engine operation and higher engine efficiency.

Optimal Configuration of a Bimolecular, Light-Driven Engine for Maximum Ecological Performance

An irreversible light-driven engine with a working fluid composed of the bimolecular reacting system \({2{SO}_3{\rm F} \rightleftarrows {S}_2{O}_6{F}_2}\) is studied in this paper. It is assumed that the heat transfer between the working fluid and the environment obeys Newton’s heat transfer law \({[q\propto \Delta T].}\) Piston trajectory for maximum ecological performance is determined for such an engine with rate-dependent loss mechanisms of friction and heat leakage. Optimal control theory is applied to determine the optimal configurations of piston motion trajectory and the fluid temperature. Numerical examples of optimal configuration for maximum ecological performance are provided, and the obtained results are compared with those for maximum work output and minimum entropy generation. The results show that taking maximum ecological optimization criterion as the objective makes larger improvement of the reduction of the entropy generation with the cost of a little decrease in the work output. Along the optimal path for maximum ecological performance, the time-parametrized piston velocity, temperature of the working fluid, piston position and area enveloped by the curves of temperature against piston position all lie between those along the optimal path for maximum work output and those along the optimal path for minimum entropy generation. This work can provide some guidelines for the optimal design and operation of practical light-driven engines and enriches our knowledge of finite time thermodynamic theory.

Optimal path of piston motion of irreversible Otto cycle for minimum entropy generation with radiative heat transfer law

AbstractThe performance of an Otto cycle heat engine with internal and external irreversibilities of heat transfer and friction, in which the heat transfer between the working fluid and the environment obeys radiative heat transfer law [q∝Δ(T4)], is studied in this paper using finite time thermodynamics. The optimal piston motion trajectory for minimising entropy generation per cycle is derived for the fixed total cycle time and fuel consumed per cycle. Optimal control theory is applied to determine the optimal piston trajectories for the cases with and without piston acceleration constraint on each stroke and the optimal distribution of the total cycle time among the strokes. The optimal piston motion with acceleration constraint for each stroke consists of three segments, including initial maximum acceleration and final maximum deceleration boundary segments respectively. Numerical examples for optimal configuration are provided, and the obtained results are compared with those obtained with Newton’s he...

Improving reciprocating compressor performance using a hybrid two‐level optimisation approach

Purpose – This paper seeks to describe a design approach which can be used to manufacture better‐performing reciprocating compressors. This design approach relates the drive kinematic characteristics to the thermodynamic performance of the compressor.Design/methodology/approach – The presented approach is based on employing a stochastic optimisation algorithm to find the best piston trajectory within one cycle of operation and couple that with a gradient‐based technique to find the best dimensions of the mechanism which can realise this trajectory.Findings – The mathematical models presented to implement the proposed design approach have been coded in a computer program which has been employed for simulation purposes. A case study given at the end of the paper asserts the usefulness of the proposed method and proves that a few percentage points increase in a defined set of performance indices has been gained from the optimisation exercise.Research limitations/implications – The presented models are only r...

The Novel Design of Full-Balancing Mechanism for Single-Cylinder Diesel Engine

One new sliding-block balancing mechanism is proposed for the single-cylinder diesel engine. In the new mechanism, the sliding block is installed against the engine piston. The reciprocation trajectory of sliding block is collinear with the piston trajectory, while sliding block and piston move in the opposite direction, just like two opposite crank connecting rods. The new mechanism includes the crankshaft, connecting rod ring, the slider and the guide components. Through the bearing, connecting rod is installed in the eccentric journal of the crankshaft. The circular connecting rod is in the accurate guiding surface of the slider; and the guide pins are in the guide groove. Guide rod connects with supporting shaft through the guide hole of the slide. The optimized parameters for the sliding block show that the ratio of eccentric distance of the eccentric journal to the length of the connecting rod is equal to the ratio of crank radius to connecting rod length. The appropriate results can balance both the centrifugal inertia force and the reciprocating inertia force generated by piston group. Even the complete balance of the first and second-order reciprocating inertia forces can be obtained, which can reduce the vibration and noise of diesel engine.

Optimal paths for a light-driven engine with a linear phenomenological heat transfer law

An irreversible light-driven engine is described in this paper, in which the heat transfer between the working fluid and the environment obeys a linear phenomenological heat transfer law [q ∝ Δ(T−1)], with a working fluid composed of the bimolecular reacting system 2SO3FaiS2O6F2. Piston trajectories maximizing work output and minimizing entropy generation are determined for such an engine with rate-dependent loss mechanisms of friction and heat leakage. The optimal control theory is applied to determine the optimal configurations of the piston motion trajectory and the fluid temperature. Numerical examples for the optimal configuration are provided, and the obtained results are compared with those derived with Newtonian heat transfer law [q ∝ Δ(T)].

The optimal path of piston motion for Otto cycle with linear phenomenological heat transfer law

An Otto cycle engine with internal and external irreversibilities of friction and heat leakage, in which the heat transfer between the working fluid and the environment obeys linear phenomenological heat transfer law [q ∝ Δ(T −1)], is studied in this paper. The optimal piston motion trajectory for maximizing the work output per cycle is derived for the fixed total cycle time and fuel consumed per cycle. Optimal control theory is applied to determine the optimal piston trajectories for the cases of with and without piston acceleration constraint on each stroke and the optimal distribution of the total cycle time among the strokes. The optimal piston motion with acceleration constraint for each stroke consists of three segments, including initial maximum acceleration and final maximum deceleration boundary segments, respectively. Numerical examples for optimal configuration are provided, and the obtained results are compared with those obtained with Newton’s heat transfer law [q ∝ Δ(T)]. The results also show that optimizing the piston motion can improve power and efficiency of the engine by more than 9%. This is primarily due to the decrease in heat leakage loss on the initial portion of the power stroke.

Optimal piston trajectories for adiabatic processes in the presence of friction

Optimal piston motion is derived for adiabatic processes in the presence of different types of friction and with frictional energy dissipated externally as well as internally. The assumed model for the frictional dissipation affects the optimal motion. We consider a piston fitted in a cylinder containing an ideal gas as the working fluid. The gas starts from a given initial temperature and is assumed to complete the process in a prescribed finite time. The effect of the working gas temperature (or equivalently internal energy) on the viscosity leads to a temperature dependence of the frictional losses. The optimal piston motion then is no longer constant speed, as was concluded previously for the externally dissipative case. In the current study two objectives are considered: maximizing power output and minimizing frictional losses. It is shown that in the externally dissipative mode optimizing power or frictional losses are equivalent, while in the internally dissipative mode the optimal motions are different.

Lubrication in refrigeration systems: Numerical model for piston dynamics considering oil-refrigerant interaction

Piston dynamics plays a fundamental role in several processes related to the operation of hermetic reciprocating compressors used in refrigeration. For example, the refrigerant leakage through the radial clearance between piston and cylinder, which reduces compressor pumping efficiency, and also the viscous friction associated with the lubricant film in the radial clearance, which is related to energy consumption. It is important to optimize such variables, ensuring at the same time smooth operation of the piston in its reciprocating motion, minimizing wear and increasing lifetime. In this context, numerical models studying piston dynamics provide a useful tool for engineering design. These models usually consider an oil film filling the piston-cylinder clearance and operating in the hydrodynamic regime. Determining cavitation conditions occurring along the ringless piston represents an additional difficulty in modelling. As refrigerant is present in the compressor environment, it inevitably interacts with the oil, changing lubricant characteristics. The refrigerant can dissolve in the oil at higher pressures, reducing viscosity, and can be released at lower pressures, leading to a two-phase flow. This work explores how the interaction of oil and refrigerant affects piston dynamics, using a numerical model that considers as the lubricant a mixture of oil and refrigerant with variable properties. Comparing the results with simulations where pure oil is considered as the lubricant and a cavitation criterion is adopted, significant differences were observed in predicting piston trajectory and power consumption along the cycle.

Numerical analysis of the piston secondary dynamics in reciprocating compressors

In this study, a numerical analysis for the piston secondary dynamics of small refrigeration reciprocating compressors is performed. In general, the length of cylinder in this class of compressors is shortened to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder wall is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the piston dynamics, the variation in bearing length of the piston and all corresponding forces and moments are considered in order to determine the piston trajectory, velocity and acceleration at each step. A Newton-Raphson procedure was employed in solving the secondary dynamic equations of the piston. The developed computer program can be used to calculate the entire piston trajectory and the lubrication characteristics as functions of crank angle under compressor running conditions. The results explored the effects of some design parameters and operating conditions on the stability of the piston, the oil leakage, and friction losses.

PISTON LUBRICATION IN RECIPROCATING COMPRESSORS

Piston dynamics plays a fundamental role in two critical processes related to fluid flow in reciprocating compressors. The first is the refrigerant leakage through the radial clearance, which may cause considerable loss in the pumping efficiency of the compressor. The second process is the viscous friction associated with the lubricant film in the radial clearance; certainly a significant factor in the compressor energy consumption. In the present contribution a numerical simulation of the piston movement inside the cylinder of a reciprocating compressor is performed. The compressor considered here is a small hermetic compressor employed in domestic refrigerators. For the problem formulation both the axial and the radial piston motion is considered. In operation, the piston moves up and down along the axis of the cylinder, but the radial oscillatory motion in the cylinder bore, despite being usually small, plays a very important role on the compressor performance and reliability. The compromise between sealing of the gas leakage through the piston-cylinder clearance and the friction losses requires a detailed analysis of the oscillatory motion for a good design. The forces acting on the piston are the hydrodynamic force due to the pressure build up in the oil film (lubrication effects), the force due to the connecting rod, the viscous force associated with the relative motion between the piston and oil, and the force exerted by the gas on the top of the piston. All corresponding moments are also included in the problem formulation of the piston dynamics, in order to determine the piston trajectory, velocity and acceleration at each time step. The hydrodynamic force is obtained from the integration of the pressure distribution on the piston skirt, which, in turn, is determined from a finite volume solution of the time dependent equation that governs the oil flow. A Newton-Raphson procedure was employed in solving the equations of the piston dynamics. The results explored the effects of some design parameters and operating conditions on the stability of the piston, its sealing performance and friction losses. Emphasis was placed on investigating the influence of the pin location, radial clearance and oil viscosity on the piston dynamics. The complexity of the piston movement in reciprocating compressors was demonstrated and the detailed model presented can be employed as an useful tool for engineering design.

PISTON LUBRICATION IN RECIPROCATING COMPRESSORS

Piston dynamics plays a fundamental role in two critical processes related to fluid flow in reciprocating compressors. The first is the refrigerant leakage through the radial clearance, which may cause considerable loss in the pumping efficiency of the compressor. The second process is the viscous friction associated with the lubricant film in the radial clearance; certainly a significant factor in the compressor energy consumption. In the present contribution a numerical simulation of the piston movement inside the cylinder of a reciprocating compressor is performed. The compressor considered here is a small hermetic compressor employed in domestic refrigerators. For the problem formulation both the axial and the radial piston motion is considered. In operation, the piston moves up and down along the axis of the cylinder, but the radial oscillatory motion in the cylinder bore, despite being usually small, plays a very important role on the compressor performance and reliability. The compromise between sealing of the gas leakage through the piston-cylinder clearance and the friction losses requires a detailed analysis of the oscillatory motion for a good design. The forces acting on the piston are the hydrodynamic force due to the pressure build up in the oil film (lubrication effects), the force due to the connecting rod, the viscous force associated with the relative motion between the piston and oil, and the force exerted by the gas on the top of the piston. All corresponding moments are also included in the problem formulation of the piston dynamics, in order to determine the piston trajectory, velocity and acceleration at each time step. The hydrodynamic force is obtained from the integration of the pressure distribution on the piston skirt, which, in turn, is determined from a finite volume solution of the time dependent equation that governs the oil flow. A Newton-Raphson procedure was employed in solving the equations of the piston dynamics. The results explored the effects of some design parameters and operating conditions on the stability of the piston, its sealing performance and friction losses. Emphasis was placed on investigating the influence of the pin location, radial clearance and oil viscosity on the piston dynamics. The complexity of the piston movement in reciprocating compressors was demonstrated and the detailed model presented can be employed as an useful tool for engineering design.

Dynamic Analysis of Piston Secondary Motion for Small Reciprocating Compressors

Piston dynamics plays a fundamental role in two critical processes related to fluid flow in reciprocating compressors. The first is the gas leakage through the radial clearance, which may cause considerable loss in the pumping efficiency of the compressor. The second process is the viscous friction associated with the lubricant film in the radial clearance. In the present contribution a numerical simulation is performed for a ringless piston inside the cylinder of a reciprocating compressor, including both the axial and the radial piston motion. The compressor considered here is a small hermetic compressor employed in domestic refrigerators, with the radial clearance between piston and cylinder filled with lubricant oil. In operation, the piston moves up and down along the axis of the cylinder, but the radial oscillatory motion in the cylinder bore, despite being usually small, plays a very important role on the compressor performance and reliability. The compromise between oil leakage through the piston-cylinder clearance and the friction losses requires a detailed analysis of the oscillatory motion for a good design. All corresponding forces and moments are included in the problem formulation of the piston dynamics in order to determine the piston trajectory, velocity and acceleration at each time step. The hydrodynamic force is obtained from the integration of the pressure distribution on the piston skirt, which, in turn, is determined from a finite volume solution of the time dependent equation that governs the oil flow. A Newton-Raphson procedure was employed in solving the equations of the piston dynamics. The results explored the effects of some design parameters and operating conditions on the stability of the piston, the oil leakage, and friction losses. Emphasis was placed on investigating the influence of the pin location, radial clearance and oil viscosity on the piston dynamics. [S0742-4787(11)00301-8]

Construction of piecewise-analytical gas flows joined through shock waves near the axis or center of symmetry

Analytical solutions of a quasilinear system of equations with partial derivatives are constructed in the case where the initial data for different functions are specified on different surfaces and the resultant problem has singularities of the form u/x and w/x. Conditions for existence and uniqueness of a solution in the form of formal power series for the problem posed and sufficient conditions for convergence of the series are indicated. A generalization of the problem considered is given. Results of the study are used to solve the problem of the focussing of a compression wave generated by a piston moving smoothly in a quiescent gas: a solution for t=0, including determination of the piston trajectory, and a solution for t 0. The solution of this problem is a generalization to the case of two independent variable self-similar Sedov's solutions.

Dynamic Analysis of Gas Lubricated Reciprocating Ringless Pistons—Basic Modeling

A mathematical model is developed for analyzing the dynamics of gas lubricated ringless pistons. It takes into account the effects of piston-cylinder geometry, dynamic properties of piston and connecting rod, and operating conditions. A corresponding computer program is described which enables to obtain the piston trajectory and evaluate its stability. Preliminary results are presented for a reference case of a cryocooler which uses a stirling cycle design where helium gas is compressed by a motor driven piston. It is found that the connecting rod inertia plays an important role in stabilizing the piston motion. It is also found that the stability of piston motion strongly depends on the thermohydrodynamic condition of operation. Under isothermal condition the piston can be stable while under adiabatic condition its dynamic equilibrium may be unstable.

A Numerical Analysis for Piston Skirts in Mixed Lubrication: Part II—Deformation Considerations

This paper presents a mathematical model for piston skirts in mixed lubrication. It takes into account the effects of surface waviness, roughness, piston skirt surface profile, bulk elastic deformation and thermal distortion of both piston skirts and cylinder bore on piston motion, lubrication and friction. The corresponding computer program developed can be used to calculate the entire piston trajectory and the hydrodynamic and contact friction forces as functions of crank angle under engine running conditions. Complete distributions of the oil film thickness and elastic deformation as well as the hydrodynamic and contact pressures can also be given at any crank angle if needed. This paper is the second part of a series of two papers. The first part (Basic Modeling), presented earlier by Zhu et al. (1991), gave the basic formulation and some preliminary results without bulk deformation considerations. In the present part, the three-dimensional finite element method is used to calculate so-called influence coefficient matrices. These matrices are repeatedly used to compute bulk elastic deformations of piston skirts. Results for 12 different cases are presented, and discussions are given focusing on the influences of elastic and thermal deformations on piston motion, lubrication and friction. An attempt to compare the calculated friction with experimental data is made, and agreement appears good for the two available cases. The computer program presented should be a useful tool for piston design and development.

A Numerical Analysis for Piston Skirts in Mixed Lubrication—Part I: Basic Modeling

This paper presents a mathematical model for piston skirts in mixed lubrication. It takes into account the effects of surface waviness, roughness, piston skirt surface profile, bulk elastic deformation and thermal distortion of both piston skirts and cylinder bore on piston motion, lubrication and friction. The corresponding computer program developed can be used to calculate the entire piston trajectory and the hydrodynamic and contact friction forces as functions of crack angle under engine running conditions. This paper is the first part of a series of two papers. It gives basic information and some preliminary results. The second part will include the major results and discussions, focused on the influences of elastic and thermal deformations.

Optimal paths for a bimolecular, light-driven engine

We examine a light-driven dissipative engine, which must necessarily operate far from equilibrium and at a nonzero rate to be capable of providing power and work. The engine’s working fluid consists of a buffer gas and the reacting system 2SO3F⇄S2O6F2. We model the concentrations of the reacting system as functions of both temperature and pressure. Piston trajectories maximizing work output and minimizing entropy production are determined for such an engine with the rate-dependent loss mechanisms of friction and heat conduction.