Temperature Field Of Piston Research Articles

Effect of knock on piston thermal load of a high compression ratio natural gas engine based on stepwise decoupling calculation

High compression ratio natural gas engine (NGE) is prone to knock at high load, which aggravates the thermal load of piston. Therefore, accurately evaluating the piston thermal load in the practical design is essential to enhance engine reliability and improve performance. The typical piston thermal load simulation adopts uniform wall boundary conditions, making it difficult to reveal the influence of turbulent flame and knock on the piston thermal load. In this paper, a stepwise decoupling method is applied to calculate the piston thermal load. The advancement of this method lies in its integration of chemical reaction mechanism with computational fluid dynamics (CFD) to calculate the spatial variations in heat transfer coefficient (HTC) and near-wall gas temperature at the piston top. Moreover, the conjugate heat transfer (CHT) method is adopted to solve the piston thermal load by coupling the thermal boundary conditions (TBC) obtained in the first step with the cooling oil boundary conditions. Based on this method, the effect of knock on piston thermal load of a high compression ratio NGE under different knock intensities is explored in this paper. It is found that turbulent combustion causes uneven distribution of thermal load at piston top. The decrease in knock intensity significantly reduces the gas temperature, heat flux and thermal load at piston top. Particularly under severe knock, the average temperature of piston is 22.9 K and 32.4 K higher than that of light knock and normal combustion, respectively. Furthermore, the main factor affecting the piston temperature field distribution is the gas temperature rather than the HTC. The gas temperature at piston top is overall the highest on the side near the inlet valve pit, which leads to a higher temperature on this side. Compared to light knock and normal combustion, when severe knock occurs, the thermal load on the exhaust valve pit increases significantly. This study provides an effective method for analyzing the heat transfer of the piston under knocking combustion, which is of guiding significance for controlling the thermal load of the high-temperature components in the combustion chamber.

Study on transient thermal state of steel piston in diesel engine under cold start condition

The thermal load issue of pistons remains a topic of active research, especially the transient thermal state of steel pistons in diesel engines under cold start conditions has not been studied in depth. In this paper, a new steel piston power assembly was designed and developed on the basis of a small-bore diesel engine. A real-time temperature test system for the steel piston temperature field was developed to address the problem of the inability to obtain real-time temperature data. The test system was applied to the steel piston to investigate the transient variations in temperature field, thermal stress, and thermal deformation at different starting temperatures. The results show that the temperature field of steel pistons exhibits exponential growth in the early stage of cold start and then tends to stabilize after about 44 s. The lower the cold start temperature and the closer the monitoring points are to the high-temperature combustion gas, the faster the rate of temperature rise. The thermal stress of the steel piston initially increases rapidly, then decreases, and subsequently increases again until reaching a stable level. The lower the starting temperature, the longer the thermal stress inflection point of the monitoring point will be. The variation of thermal deformation of the steel piston follows the same trend as that of the temperature field.

Oil jets piston cooling: A numerical methodology for the estimation of heat transfer coefficients and optimization of the piston temperature field through a genetic algorithm

High-efficiency internal combustion engines need specific methodologies to be developed for the design improvement of the components. Predicting and reducing the thermal loadings on the parts are critical tasks to be addressed. This contribution focuses on the thermal management of the piston through oil jets. The operating temperature of the piston deeply affects its thermo-mechanical behavior, thus possibly jeopardizing the structural integrity of the component. The design of piston cooling jets is usually addressed through Computational Fluid Dynamics, which can guarantee accurate results, usually at a high computational cost. In this contribution, a faster tool is derived to grasp the effect of the cooling jets on the temperature of the piston. Empirical correlations are applied to predict the instantaneous heat transfer coefficients on the piston. The reciprocating motion of the piston is considered since it affects the interaction between the surface and the oil jets. Instantaneous coefficients are cycle-averaged and used to estimate the temperature of the piston through a Finite Element thermal analysis. Finally, an optimization code is developed to find the best jet configuration capable to minimize the temperature of the piston. This methodology is a powerful tool to select the optimal oil jet nozzles for piston cooling.

A transient numerical study for heat transfer and flow characteristics of dimpled piston cooling gallery of a diesel engine

Piston cooling gallery is an effective cooling method to achieve an acceptable piston temperature field. This paper aims to analyze the effects of teardrop dimples size and dimple head-and-tail orientation on flow and heat transfer inside the cooling gallery. To do so, the computational fluid dynamics model for galleries with different teardrop dimples were established. The results indicate that the local oil flow patterns in the axial and circumferential directions are affected by the dimples. Compared with smooth gallery, the presence of dimple enlarges the fluid charge ratio (FCR). Specifically, when radius of teardrop shaped dimples are R2 and R3 respectively, their corresponding gallery FCRs achieve 55% and 58%. Further, the variation in FCR makes a difference in the distribution of heat transfer, an in-depth analysis finds the dimples increase the heat transfer area between the gallery surface and the oil and simultaneously reduce the space of oil suspending in the gallery. Therefore, the heat transfer coefficient of a dimpled gallery is always greater than that of the smooth gallery, with the maximum improvement of 2.42%. Moreover, the change of heat transfer distribution reconstructs the heat transfer uniformity of the cooling gallery, with the maximum improvement of 24.25%.

Finite element analysis and structural optimization of piston temperature field of a type of aviation piston engine

Finite element analysis and structural optimization of piston temperature field of a type of aviation piston engine

Experimental and simulation study on aluminium alloy piston based on thermal barrier coating

Thermal barrier coatings (TBCs) have low thermal conductivity, effectively reducing the temperature of the metal matrix and improving thermal performance, knock resistance, and combustion performance of the piston. In this study, an off-road high-pressure common-rail diesel engine was chosen as the research object. Combined with the test results of the piston temperature field under the rated power and maximum torque conditions, a finite element simulation model of the thermal barrier coating piston was established. This model enabled the distribution characteristics and variation laws of the temperature field, stress, and deformation of the thermal barrier coating on the piston matrix to be analysed. The results show that the maximum temperature of the TBC piston is 12.2% and 13.73% lower than that of the aluminium alloy piston under the rated power and maximum torque conditions, respectively. The thermal stresses of the TBC piston at the top of the cavity were 25.9% and 26.8% lower than those of the aluminium piston, while the thermo-mechanical coupling stress of the TBC piston was slightly higher than that of the aluminium piston—1.2 MPa and 3.7 MPa in the bottom of the combustion chamber with geometric mutation, respectively. The radial thermal deformation of the TBC piston was 0.067 mm and 0.073 mm lower than that of the aluminium piston, with the radial thermo-mechanical coupling deformation also decreasing by 0.069 mm and 0.075 mm, respectively. The radial thermal deformation of the piston in the direction parallel to the pinhole axis was greater than that in the direction perpendicular to the pinhole axis; the difference in the magnitude of the change results in uneven thermal deformation of the piston.

Oil Jets Piston Cooling: A Numerical Methodology for the Estimation of Heat Transfer Coefficients and Optimization of the Piston Temperature Field Through an Ai-Guided Genetic Algorithm

Oil Jets Piston Cooling: A Numerical Methodology for the Estimation of Heat Transfer Coefficients and Optimization of the Piston Temperature Field Through an Ai-Guided Genetic Algorithm

Thermal load analysis and control of four-stroke high speed diesel engine

Aiming at the thermal load problem of the four-stroke high-speed Diesel engine piston, a piston thermal fluid-solid coupling model based on the combustion thermal boundary and the two-phase flow oscillation cooling thermal boundary is established. The model considers the problem that the piston cannot fill the cooling cavity due to the reciprocating motion. The effects of different engine speeds and the injection speed on the filling rate are studied. The variation curves of the filling rate of the oil in the cooling cavity are simulated, and the transient heat transfer coefficient and temperature of each crank angle are obtained. The average value is then analyzed by thermal flow-solid coupling method, and the influence of the filling rate of the piston cavity on the temperature field of the piston is obtained. Through the comparison of the experimental results of the hardness plug measurement method, the calculation of the model is accurate and can be well used for the simulation of the piston temperature field and the evaluation of the thermal load at the critical position. Based on this model, the regularity analysis of the influencing factors of the piston thermal load is carried out. The influencing factors include the filling rate of the cavity, the air-fuel ratio, the injection timing, etc., and finally the engine operating range that meets the heat load requirements is obtained.

Research On Thermal Load Characteristics Of Piston Based On Fluid-Structure Coupled Heat Transfer

In order to study the thermal load characteristics of piston, the temperature field of piston is predicted based on fluid solid coupling heat transfer numerical simulation. A numerical model for the coupled heat transfer of a piston is established. The top surface of the piston, the bottom of the combustion chamber, is used as the coupling surface of the fluid and the solid, and the fluid mechanics software FLUENT is used to simulate the heat transfer. By comparing the calculated cylinder pressure with the experimental data, the correctness of the spray combustion simulation is verified. Comparing the temperature distribution of piston at different time, the results show that the transient temperature field of piston can be obtained directly by the fluid solid coupling method, which reflects the transient change of the temperature field of the piston. For the whole piston, the temperature fluctuation of the coupling surface defined in this paper is larger, the temperature fluctuation in other places is smaller. The flow field in the combustion chamber has a certain effect on the temperature field of the piston, where the direct contact with the gas has a greater impact, and the place where it does not directly contact with the gas has less influence.

Fluid-structure interaction heat transfer of piston with consideration of oil oscillating cooling and in-cylinder local heat transfer

Taking the piston of heavy commercial vehicle as an example, in-cylinder local heat transfer boundary condition is obtained through the calculation of intake, spray, combustion and exhaust process; the heat transfer boundaries of the inner oil gallery and the bottom of the piston are obtained by the transient piston injection cooling calculation; the numerical simulation of temperature field of piston is realized by the coupling of gas side, lubrication oil side and structure with consideration of the temperature’s influence on the thermal conductivity of the piston. Furthermore, the thermal deformation of the piston is analysed. Results show that the calculated values are in agreement with the experimental temperature values of the piston measuring points; The highest temperature appears at the junction of the bowl and the top surface of the piston at the exhaust valve side; The heat transfer coefficient and gas temperature at the junction of the bowl and the top surface of the piston are in high value, the in-cylinder local heat transfer is significant ; In the straight inlet pipe of the inner oil gallery, the temperature of the lube oil is the lowest while heat transfer coefficient is the highest, so the cooling effect is the most obvious; The radial expansion deformation is large at the top and bottom of the piston skirt while small at the middle.

Analysis of thermal temperature fields and thermal stress under steady temperature field of diesel engine piston

With the improvement of the diesel engine power and performance, the piston in the combustion chamber is subjected to higher thermal load and the thermal stress decreases its working life. Therefore, it is necessary to analyze the subsequent thermal stress on the piston during design process to reach the optimum one. This paper tries to present a new calculation method for the theoretical design of the piston. In this study, the 3D solid model of piston in 16V280 diesel engine was developed and the simulation calculation of the steady-state and the transient-state temperature field is carried out. Based on calculation results, the maximum temperature fluctuation of the piston temperature field is less than 20°, so the steady-state temperature field was used as boundary condition for the thermal stress calculation and the thermal mechanical decoupling method was used to calculate the thermal stress caused only by the uneven temperature distribution. The results show that the maximum temperature is 354°C, which appears at the edge of the combustion chamber. The steady-state temperature field of finite element simulation shows a good agreement with the experimental results. The thermal stress obtained from thermal mechanical decoupling method was within the allowable range, since the maximum value is 270MPa. Danger zone appears at the combustion chamber throat, the contact area of piston head and skirt.

Thermal Load Simulation and Structure Improvement of High Speed Diesel Engine Piston

In order to solve cylinder-scraping of a four-cylinder high speed diesel engine, based on the measurement of piston temperature, the piston temperature field was numerically simulated by using temperature fitting method, the calculation results were well consistent with the measured temperature. By finite element analysis of piston thermal load based on the calculation results as temperature load, enlarging oil cooling cavity in the piston head was proposed to enhance cooling locally, which could effectively reduce temperature of the piston head and the first ring groove and avoid the occurrence of cylinder-scraping.

The Experimental and Simulation Analysis of Steel Piston Temperature Field and Deformation Based on Finite Element Method

The traditional aluminum piston, the can not meet the engine development to the high power density direction, so the higher strength steel piston designed. The temperature filed and deformation was calculated and analyzed by finite element method with finite element software MSC.NASTRAN. The results can provide theoretical foundation for the promotion of the all-steel piston.

Study on Key Factors in Piston Transient Temperature Field

By means of ANSYS, piston finite element model is constructed to attain transient numerical simulation and explore the characteristics of surface temperature. On the basis of experimental design, the correlation is analyzed between major boundary conditions and temperature of feature points, thus revealing the corresponding correlation of quantity. Transient calculation method is proved to be scientific and paves way to defining boundary conditions. And furthermore there forms a theoretical foundation for positioning test point in piston temperature field.

Study on Structural Design and Optimization Analysis for 2V80 Engine Piston Based on Finite Element Analysis

According to the experiment of engine bench test and piston's temperature field, the thermal boundary conditions and the mechanical conditions of piston are obtained. Under the condition of mechanical load and thermal load playing, the stress and strain of original engine is simulated and analyzed. Stress concentration and weak structure of original engine is found. The parameter of piston structure is optimized and the optimizations are put forward and analyzed to verify the optimizations' effectiveness. These provide a reference for the digital modeling and numerical analysis to solver engineering problems.

The Effects of the Cooling Gallery Position on the Piston Temperature Field and Thermal Stress

The effects of cooling gallery position on the piston temperature field and thermal stress are studied. A finite element model of 1015 engine piston is developed using Pro/E software and finite element analyses are achieved through ANSYS code. Numerical simulations are performed to find the temperature and thermal stress change rules with regard to the cooling gallery position. The results demonstrate that the axial direction position of cooling gallery has obvious effects on the piston temperature while the radial direction position of cooling gallery affects the piston thermal stress a lot. The highest position of cooling gallery should be as the same line as the top of the first ring groove. The distance between cooling gallery and piston radial edge should be more than a certain value to decrease the temperature gradient and thermal stress concentration.