Bottom Dead Center Research Articles

Force and energy analysis of single-piston free-piston expander—linear generator

The movement of piston in free-piston expander-linear generator (FPE-LG) mainly depends on the dynamic force balance among four kinds of forces (air impetus, air resistance, electromagnetic resistance and frictional resistance). In this paper, the Newton's Second Law and the first law of thermodynamics are used to analyze the single-piston FPE-LG, the change of four kinds of forces and work produced by the four kinds of forces are analyzed. Nominal work-electricity conversion loss coefficient is proposed for the firs time to represent the energy loss. The experiment results show that the work produced by four forces from top dead center (TDC) to bottom dead center (BDC) are higher than those from BDC to TDC. The minimum proportion of air resistance energy consumption is also more than 50%, the proportion of electromagnetic resistance energy consumption is less than 20%, and the proportion of frictional resistance energy consumption is more than 20%. Therefore, the total nominal work-electricity conversion loss can be effectively reduced by increasing intake time or intake pressure.

Parametric Optimization of Producer Gas fuelled Spark Ignition Engine through Thermodynamic Modelling

Development of alternative fuel has become a necessity to quench the current/rising future energy demands and alarming environmental pollution. Producer gas/syngas has potential to be most favorite alternative fuel substitution whose performance characteristics are lower whereas emission characteristics of carbon monoxide (CO), carbon dioxide (CO 2 ) and hydrocarbons are better than petrol/diesel. Looking at these facts, the present work focuses on thermodynamic modelling and parametric studies on a real-life engine using producer gas as fuel to study its performance and emission characteristics. Simulated program is validated with published literature and results are found within ± 9% in terms of power and efficiency. The model is then used to study the effect of Spark advance (10°–30°), valve timing and combustion duration (40°–80°), fuel-air ratio, stroke to bore ratio and connecting rod length to crank radius to study their impact on emission and performance of real-life engine. The optimum engine performance parameters while also considering emission of nitric oxide (NO) and CO operated at stoichiometric fuel-air ratio turns out to be L/D as 1.0, Spark advance as 20° BTDC (before top dead center), combustion duration as 50°, inlet valve closing as 30° ATDC and exhaust valve opening as 10° BBDC (before bottom dead center). The efficiency, specific fuel consumption, power, CO and NO with these optimal parameters are of the order of 19.58%, 1.23 kg/kWh, 67.0 kW, 0.65 ppm and 0.017 ppb, respectively. It is believed that present work offers optimal design and operating parameters through actual thermodynamic cycle analysis which may be used as a reference for design and development of producer gas-fuelled Spark Ignition (SI) engines.

Reduced Flow Fluctuation of Radial Piston Pump with Silencing Groove Valve Plate

The theoretical study and numerical analysis have been carried out on the valve plate geometry of the radial piston pump to reduce the flow and pressure fluctuation. The radial piston pump is widely used in industrial applications as a hydraulic power source. The pressure and flow fluctuation of pump produce an adverse effect for the hydraulic system. The geometries of valve plate are studies for the analyses of pressure and flow fluctuation of the pump. The explicit area calculation of the piston kidney over the manifold is carried out to simulate the main flow in between piston chamber and manifold in vale plate configurations of with silencing groove, without silencing groove and with silencing groove cum damping orifice. The analyses of cross-port leakage is done at transition zone near at top dead centre (TDC) and bottom dead centre (BDC) of the valve plate, study the effects of cross-port leakage on pressure and flow fluctuation with volumetric efficiency of the pump. Studies the pump pressure and flow build up characteristic under varying load and validated with existing pump performance. The simulation results suggest that the silencing groove valve plate model is better perform than other configurations in terms of high flow rate, low pressure and flow fluctuation with less cross port leakage and more volumetric efficiency.

Analysis of a tumbling motion using a clustering algorithm on dual-piv measurements: application to the in-cylinder flow of a miller cycle engine

This paper aims to study the internal aerodynamics of a Miller cycle gasoline engine. This cycle uses an over-expanded stroke to recover more work, for the same amount of fuel, than the classical Otto cycle. To achieve this, the effective compression stroke is made smaller than the expansion one by closing the intake valves prematurely. The in-cylinder tumble flow then stops being driven by the valve jet before the piston reaches the bottom dead center, which disturbs the movement. The flow is observed here on a motored single-cylinder transparent engine coupled to a dual-PIV system. This system allows two velocity fields per engine cycle to be measured. The temporal evolution of the flow structures could thus be followed, while keeping the high number of instantaneous fields measured by the traditional PIV systems. The data are then well adapted to statistical analysis. A clustering analysis method, using the k-means algorithm and adapted to dual-PIV data, is described here. The first part presents a method defining a criterion on the instantaneous center of rotation of the tumble motion that can improve the rotation rates by 17%. A second analysis classifies the velocity fields into three groups of strong, medium and weak rotation intensity. The evolution of the characteristic quantities of each group shows that the movements with high rotation rates, created upstream of the compression phase, can give high turbulence rates close to the top dead center of the piston.Graphical abstract

Investigation of force-assisted suction reed valves in hermetic reciprocating compressors

Reed valves are widely used in hermetic reciprocating compressors and are responsible for a major share of thermodynamic losses. The suction valve in particular, which is opened for almost the entire suction phase, has a very significant improvement potential. Suction valves in hermetic reciprocating compressors are usually opened only by the pressure difference created by the moving piston and should be closed before the compression phase starts, in order to avoid a reversed mass-flow through the valve. The valves are thus preloaded, which, on the other hand, results in a higher flow resistance. In this work, a force-assisted suction valve is investigated. An electromagnetically actuated spring generates an additional force acting on the conventional suction reed valve. This force leads to a completely different valve movement and a significant reduction of the losses caused by the suction valve. A conventional suction valve flutters during the suction phase. Thus, it hits the valve seat several times which has, beside an increased flow resistance, negative influences on the reliability of the reed valve and noise emissions. With the help of the additional force, it is able to overcome the opening delay due to the preload and the oil ‘stiction’ effect. Furthermore, the suction valve can be held open during the whole suction phase, and it closes smoothly in time near the bottom dead centre of the piston. The investigation of the force-assisted suction valve is done by numerical simulations as well as by experiments. Results show an improvement of the coefficient of performance by approximately 0.7%–1.6% depending on the operating conditions.

Experimental Investigation of the Dynamics of a Slider-Crank Mechanism With Local Linear Force Input

Abstract Conventional implementation of slider-crank mechanisms result in high loads transmitted through the mechanical structure, inhibiting the design of compact and oil-free machines. Therefore, this research proposes to step away from the conventional, i.e., rotative, actuation and to investigate local linear actuation on the slider-component directly, while maintaining the kinematic link of the slider-crank configuration. In this work, the local linear actuating principle is evaluated experimentally where the goal is to obtain a continuous movement of the slider mechanism where Top Dead Center & Bottom Dead Center are reached and to minimize the loads transmitted through the mechanical structure. The non-isochronous transient behavior of a slider-crank mechanism loaded with a spring-damper element is detailed as well as the optimal working conditions at steady-state to achieve a reduced loading of the kinematic structure. By matching the operating frequency and resonance frequency of the system, a reduction of the loads transmitted through the system by 63% of the nominal spring load can be achieved. Further experimental (and multibody mechanical) investigation on the influence of flywheel exposes a clear trade-off between the sensitivity of the system and the transmission of the actuation force through the kinematic link.

Perbandingan Kinerja Motor Bakar 6-Langkah dengan Power-Ekspansi sampai Titik Mati Bawah Menggunakan Bahan Bakar Pertalite dan Etanol

This paper describes compare the performance and emissions of a 6-stroke engine with power-expansion up to BDC (bottom dead center) using pertalite fuel (non-renewable) and 99.7% ethanol (renewable alternative) with performance parameters including (effective power , fuel consumption, Combustion Efficiency , thermal efficiency , fuel efficiency  and emission parameters including (HC, CO and CO2). The method used is a real experimental method, with the independent variables being throttle openings of 35%, 40% , 45%, and 50% with loading on the prony disk brake of 10kg, 20kg, 30kg, 40kg, 50kg. The results of the research on the performance parameters of the magnitude of the effective power of ethanol is 17.5% less than pertalite, The rate of consumption of ethanol fuel 1,61 seconds/10ml lower than pertalite by 2,9 seconds/10ml, For the magnitude of the combustion efficiency (Combustion Efficiency) pertalite is 0.3% greater than ethanol, For the magnitude of the thermal efficiency p there is a 6-stroke engine with power-expansion up to BDC with ethanol fuel tends to be almost the same with 0.29% greater pertalite compared to ethanol, for the magnitude of pertalite fuel efficiency is 4% higher than ethanol. Then the emission parameters for the CO2 value of 80% pertalite tend to have a higher value than ethanol, the HC value is 21.7% higher in ethanol, for the higher CO2 content is dominated by 51.8% ethanol than pertalite.

Analysis of the Tribological and Dynamic Characteristics of the Piston Compression Ring Under Different Engine Operating Conditions

In this investigation, a study of the tribological and dynamic characteristics present in the compression ring is executed for different engine conditions. A series of numerical simulations has been carried out using the OpenFOAM software for the study. The simulation conditions have been based on the parameters measured on a diesel engine test bench. Different ranges of rotation speed, load, and lubrication oil temperature have been established for the analysis. The results show that the parameters of rotation speed and engine load significantly influence the tribological and dynamic conditions of the piston compression ring. An increase of 425 rpm and 136 Nm in the rotational speed and load of the engine causes an increase of 13% and 34% in the power loss due to friction. The Top Dead Center and the Bottom Dead Center are the locations most prone to experience critical wear and tear. Increasing the lubricating oil temperature increases the maximum friction force by 9%. In general, the proposed methodology allows for establishing a direct relationship between the operating conditions and the tribological characteristics in the compression ring that directly affect the efficiency and useful life of the engine.

Study on shape memory effect of hot deep-drawn NI-TI shape memory alloy sheet part

This study investigates the properties of Ni-rich Ni-Ti shape memory alloy sheet parts during and after deep drawing process at an elevated temperature, which is under a plane tensile-compressive stress state. According to the results, the sheet metal shows superelasticity and ductility at 500°C, 550°C, and 600°C. In the hot deep drawing process, the working parameters affect the result. The higher the forming temperature and the longer the holding time at the bottom dead center of the punch or the longer the ageing shape memory treatment, the greater the height of the drawn part and the lesser the springback. The results of the subsequent free recovery experiment show that the deep drawn sheet part without ageing treatment still possesses the shape memory effect. It also shows in the further constraint recovery experiment that in a wide temperature span the deep drawn sheet part possesses a different recovery load when reacting to the phase transformation of the shape memory alloy. Furthermore, the higher the forming temperature and the shorter the ageing treatment, the greater the part recovery load.

Performa pada Motor Bakar 6-Langkah dengan Langkah Power Ekspansi sampai Titik Mati Bawah

This study aims are to observe the performance of a six-stroke combustion motor and to analyze the thermodynamics of a six-stroke combustion engine with a power expansion step to the bottom dead center. The fuel used in this observation is pertalite with a RON 90 value. The method used is a true experimental method, with independent variables, namely 35%, 40%, 45%, and 50% throttle openings with loading on the prony disc brake of 10 kg, 20kg, 30kg, 40kg, and 50kg. In the torque data, each throttle opening shows the highest number of 7.26 (Nm) with a load of 50kg and the lowest value of 2.01 (Nm) with a load of 10kg, for effective power the highest value is 8.47 (kW) at 50% throttle opening with load is 40kg and the lowest value is 2.49 (kW) at 35% throttle opening with a load of 10kg, while for the specific fuel consumption (SFC) the highest value is 4.28 (kg/Hp.h) at 40% throttle opening with a load of 10kg and the lowest value is 0.77 (kg/Hp.h) at 50% throttle openings with a load of 50kg, and for the thermal efficiency of the six-stroke motor, which means an average increase of 14.58% compared to the thermal efficiency of the conventional 4-stroke internal combustion engine.

Free Stream Behavior of Hydrogen Released from a Fluidic Oscillating Nozzle

The H2 internal combustion engine (ICE) is a key technology for complete decarbonization of the transport sector. To match or exceed the power density of conventional combustion engines, H2 direct injection (DI) is essential. Therefore, new injector concepts that meet the requirements of a H2 operation have to be developed. The macroscopic free stream behavior of H2 released from an innovative fluidic oscillating nozzle is investigated and compared with that of a conventional multi-hole nozzle. This work consists of H2 flow measurements and injection tests in a constant volume chamber using the Schlieren method and is accompanied by a LES simulation. The results show that an oscillating H2 free stream has a higher penetration velocity than the individual jets of a multi-hole nozzle. This behavior can be used to inject H2 far into the combustion chamber in the vertical direction while the piston is still near bottom dead center. As soon as the oscillation of the H2 free stream starts, the spray angle increases and therefore H2 is also distributed in the horizontal direction. In this phase of the injection process, spray angles comparable to those of a multi-hole nozzle are achieved. This behavior has a positive effect on H2 homogenization, which is desirable for the combustion process.

Analysis on the influence of sinusoidal wind on the structure of pumping unit based on dynamics of solid-fluid interaction

China National Petroleum Corporation Dingbian oilfield is located in the wind field area of the beam pumping unit affected by the wind load, occurred several pumping unit bracket bending, beam fracturing, horsehead off and horsehead drop and other serious accidents, endanger the equipment and personnel safety. However, there is little research on the influence of beam pumping unit under wind load. Based on the dynamics of solid-fluid interaction theory and the standard k- turbulence model, this paper calculated the polished rod load range of the pumping unit according to the actual working condition of Dingbian oilfield, and established the CYJ10-4.2-53 numerical model of wind field. Under the sinusoidal variable wind speed conditions, the stress and deformation of the beam loader with different sizes of wind load on the beam loader were compared to those of the different sorts. The stress and deformation of the two different types of pumping unit were compared under the wind load. The results show that under the influence of wind load, the rig of the pumping unit bracket has a serious bending deformation, and the safety risk of the front end of the horsehead along the wind load is deformed. When the wind speed reaches 24.48m/s, the horsehead and barcket’s offset is the largest to the top dead point by the wind load, The minimum impact is affected by the wind load at the bottom dead center, The maximum offset of the horsehead and the bracket reached 8.5 mm and 2.16 mm. The research work of this paper provides a scientific basis for the improvement of safety structure for pumping unit in the wind field area.

Analysis on dynamic precision degradation mechanism of high-speed precision press

With the increase of service time, the dynamic precision of high-speed precision press is getting lower and lower. In order to study the precision degradation mechanism, a dynamic model of main transmission system of high-speed precision press was established based on ADAMS, and the influence of different bearing clearance on the dynamic precision was studied. The simulation results show that the dynamic precision of bottom dead center (BDC) decreases with the increase of joint clearance. And the increase of the joint clearance between main linkage and main slider has the greatest impact on the dynamic accuracy of BDC, the impact of the joint clearance between crankshaft and major linkage is smaller, and the impact of the joint clearance between crank shaft and bearing is the smallest. Finally, the field test was carried out. The analysis of the test data shows that the wear of the bearings in the main drive system leads to the increase of the clearance, which leads to the degradation of the dynamic precision.

Stainless Steel Thermal Spray Coating of Cylinder Bores for VC-Turbo Engine

<div class="section abstract"><div class="htmlview paragraph">Nissan’s variable compression turbo (VC-Turbo) engine has a multilink mechanism that continuously adjusts the top and bottom dead centers of the piston to change the compression ratio and achieve both fuel economy and high power performance. Increasing the exhaust gas recirculation (EGR) rate is an effective way to further reduce the fuel consumption, although this increases the exhaust gas condensation in the cylinder bores, causing a more corrosive environment. When the EGR rate is increased in a VC-Turbo engine, the combined effect of piston sliding and exhaust gas condensation at the top dead center accelerates the corrosive wear of the thermal spray coating. Stainless steel coating is used to improve the corrosion resistance, but the adhesion strength between the coating and the cylinder bores is reduced. Trial production of the coatings with different linear expansion coefficients was conducted, and the sensitivity of the linear expansion coefficient and adhesion strength was obtained. Consequently, the adhesion strength was found to have a maximum value with respect to the linear expansion coefficient. By contrast, the surface observation of this coating after the honing process showed an increase in surface porosity. The martensitic content in the coating was reduced, and the appropriate martensitic content and chemical composition with the optimal corrosion resistance, adhesion strength, and surface porosity were found. Using this coating (0.01C-12Cr-0.22Ni-0.35Mn), the corrosive wear at the top dead center was resolved. Consequently, the fuel economy was improved by more than 4% compared with that of the current VC-Turbo engine, which has already adopted a carbon-steel-based coating.</div></div>

Design and Verification Test of the Primary and Secondary Stage Compression Gap Size of Miniature High Pressure Air Compressor

Aiming at the prominent problem of the primary and secondary pistons hitting the cylinder head in the current miniature high-pressure three-stage air compressor, a design study on the size of the primary and secondary compression gap is carried out. Through the theoretical force analysis of the connecting rod, the force situation of the connecting rod at the top and bottom dead centers is obtained. The three-dimensional models of connecting rod and cylinder are established based on SolidWorks software, and the three-dimensional models are simplified. Based on Ansys Workbench software, the connecting rod and cylinder models are pre-processed, model discretized and post-processed. The structural statics and steady-state thermal comprehensive analysis of the connecting rod at the upper and lower dead points and the steady-state thermal analysis of the cylinder under working conditions are completed. Through analysis, the total axial deformation of the connecting rod and the total axial deformation of the cylinder under high temperature and high speed working conditions are obtained. According to the simulation analysis results, the first and second compression gap size is designed. Based on the design results, ten sets of air compressors are tested for dimensional design verification. The test results show that the air compressors of each test group can complete the charging requirements within the specified time, and there is no phenomenon of piston hitting the cylinder head, indicating the size design reliability.

Analysis of the dynamics of a slider-crank mechanism locally actuated with an act-and-wait controller

Traditional use of slider-crank mechanisms result in high loads transmitted through the mechanical structure, inhibiting the design of a compact machine. Therefore, this paper proposes to step away from the conventional, i.e. rotative, actuation and to investigate local linear actuation of the slider-component directly, while maintaining the kinematic link. In this work the equation of motion and corresponding non-isochronous movement are derived for the proposed system, loaded with a linear spring-damper element. Afterwards the focus shifts towards the evaluation of the local linear actuating principle by implementing an act-and-wait control strategy in a multibody model in Simscape. The obtained configuration results both in a continuous movement of the slider mechanism where Top Dead Centre & Bottom Dead Centre are reached and in a minimisation of the loads transmitted through the mechanical structure. Further investigation of one of the most determining parameters, i.e. the operating frequency, proves that operating at the resonance frequency of the system, yields optimal results. This configuration allows for the reduction of the loads transmitted through the system by 90% of the nominal spring-damper load.

Kinematic synthesis method and eccentricity effects of a Stephenson mechanism

Abstract. When implementing the technological process on crank presses, it is necessary to provide a predetermined working cycle of the slider motion: fast lifting, dwell, and slow lowering. The cycle cannot be realized without controlling the motor. In addition, using controllable motors increases the manufacturing cost. Due to the geometric and kinematic capabilities of the mechanism, changing the kinematics of the working link is the best choice. Thanks to the use of the Stephenson II mechanism, the slider skew is eliminated due to the parallel connecting rods and the increased area of slider contact. This study presents a numerical method for kinematic synthesis of the Stephenson mechanism that has kinematic advantages. The method is based on mean square deviation which is the minimizing of an objective function. Thanks to the proposed synthesis method, approximate dwell movement can be performed when the slider is on the bottom dead center. In this study, values of the crank length and parallel connecting rods' lengths, angular coordinates of the crank and connecting rods, and the eccentricity of the guide slider relative to the crank rotation axis were obtained. It is observed that eccentricity affects the lower forward and higher backward speed of the slider. The kinematic results of the slider movement are comparatively presented in this article.

Experimental study on the performance of single-piston free-piston expander—linear generator

In this study, a single-piston free-piston expander—linear generator test system for the power-electricity conversion is presented using compressed air as the working fluid. This study investigated the effect of intake time and intake pressure on the performance of the test system. Examples include the following: in-cylinder pressure, bias displacement, one-way time, indicated work, output electric energy, and work-electricity conversion efficiency in a single cycle using the position-time control method with the intake position of 21and 45 mm. Result shows that: in the operational process of the test system, all values obtained when the piston runs from top dead center to bottom dead center are all different compared with those obtained when the piston runs from bottom dead center to top dead center. When the test system operates with low intake pressure and short intake time, the working chamber without a piston rod will over-expand. With the increase of intake time or intake pressure, the bias displacement, indicated work, and one-way output electric energy show an increasing trend. Moreover, the one-way time shows a decreasing trend and eventually tends to a fixed value, and the one-way work-electricity conversion efficiency initially increases and then decreases.

Decomposition analysis and peak stagger design for Crank-triangular linkage-elbow mechanism of mechanical servo presses

High mechanical advantage as well as low and steady slide speed within the working stroke Sn are the fundamental requirements for the working mechanism of servo-mechanical press. Currently, the Crank-Triangular Linkage-Elbow (CTLE) mechanism has attracted more and more attention from researchers and manufacturers of servo presses. This paper presents a new analysis and design method of CTLE. The mechanism is decomposed into two sub-units: crank and triangular-linkage elbow, followed by the kinematic and force analysis of each sub-unit. The influences of each structural parameter on the working performance are obtained and can be used as the basis for preliminary design. Through the offset design, the mechanical advantage peaks of the two units, MA1max and MA2max, do not occur at the same time: MA1max is located near Sn, while MA2max is just at BDC (Bottom Dead Center). Because the mechanical advantage of the whole mechanism is the product of the two subunits, the designed mechanism can obtain high and steady mechanical advantage together with low and steady slide speed within Sn. After preliminary design, the scheme can be further modified by numerical simulation and optimization. Hence the design efficiency can be improved.

System construction of a four-side primary permanent-magnet linear motor drive mechanical press

A primary permanent-magnet linear motor (PPMLM) has a robust secondary structure and high force density and is appropriate for direct-drive mechanical press. The structure of a four-side PPMLM drive press is presented based on our previous research. The entire press control system is constructed to realize various flexible forming processes. The control system scheme is determined in accordance with the mathematical model of PPMLM, and active disturbance rejection control is implemented in the servo controller. Field-circuit coupling simulation is applied to estimate the system’s performance. Then, a press prototype with 6 kN nominal force is fabricated, and the hardware platform of the control system is constructed for experimental study. Punch strokes with 0.06 m displacement are implemented at trapezoidal speeds of 0.1 and 0.2 m/s; the dynamic position tracking errors are less than 0.45 and 0.82 mm, respectively. Afterward, continuous reciprocating strokes are performed, and the positioning errors at the bottom dead center are less than 0.015 mm. Complex pulse trajectories are also achieved. The proposed PPMLM drive press exhibits a fast dynamic response and favorable tracking precision and is suitable for various forming processes.