Experimental evaluation of local instantaneous heat transfer characteristics in the combustion chamber of air-cooled direct injection diesel engine

An experimental analysis is conducted investigating the differences between the variations of overall and local instantaneous heat transfer coefficients, during the engine cycle, in the combustion chamber walls of a direct injection (DI), air-cooled diesel engine located at the authors’ laboratory. For this purpose, a novel experimental installation is developed, which separates the engine transient temperature signals into two parts, namely the long- and the short-term response ones, processed in two independent data acquisition systems. Moreover, a new pre-amplification unit for fast response thermocouples, appropriate heat flux sensors and an object-oriented control code for fast data acquisition have been designed and applied. Experimentally obtained cylinder pressure diagrams are used as a basis for the calculation of the overall heat transfer coefficients, whereas one-dimensional heat conduction theory with Fourier analysis techniques, combined with an iterative procedure between calculated and measured temperature data, are implemented in order to calculate the instantaneous local heat transfer coefficients in the engine cylinder. Analysis of the experimental results reveals interesting aspects of transient engine heat transfer. Significant differences are disclosed between the overall and local heat transfer coefficient variations, with the importance of the latter one on engine design being emphasized. The local heat transfer coefficient on the cylinder head is quantified based on the experimental data. The effect of engine speed and load as well as of the air swirling motion on the heat transfer variations are presented. From the analysis results it is concluded that the instantaneous heat transfer variation is non-uniform, unlike its values calculated from standard correlations that assume spatial uniformity, noting that such information, especially for air-cooled diesel engines, seems to be very scarce in the open literature.     

Analysis of local convective heat transfer in a spark ignition engine

A computational fluid dynamics (CFD) code is applied to simulate fluid flow, heat transfer and combustion in a four-stroke single cylinder engine with pent roof combustion chamber geometry, having two inlet valves and two exhaust valves. Heat flux and heat transfer coefficient on the cylinder head, cylinder wall, piston, intake and exhaust valves are determined with respect to crank angle position. Results for a certain condition are compared for total heat transfer coefficient of the cylinder engine with available correlation proposed by experimental measurement in the literature and close agreement are observed. It was found that the local value of heat transfer coefficient varies considerably in different parts of the cylinder, but they have equivalent trend with crank angle. Based on the results, new correlations are suggested to predict maximum and minimum convective heat transfer coefficient in the combustion chamber of a SI engine.     

风冷汽油机缸盖瞬态传热研究

本文介绍了作者在风冷汽油机上所进行的瞬态温度场测量及用表面温度法理论计算的研究结果。作者选 用的实验机型为１６５Ｆ－Ⅲ型风冷汽油机，通过在其缸盖在布置多支ＴＣＳ－Ｋ型薄膜热电偶，利用自行开发的测量系统，实测了在不同运转工况下的温度场。同时，还研究了沉积物对温度测量的影响。在此基础上，运用表面温度法，进行了局部瞬态换热系数的计算，并对结果进行了理论分析。     

Experiments on the influence of intake conditions on local instantaneous heat flux in reciprocating internal combustion engines

The present study tries to be a contribution for the development of more precise theoretical models for predicting the dissipation of heat through the combustion chamber walls of reciprocating (internal combustion) IC engines. A fast response thermocouple was embedded in the combustion chamber of a single cylinder engine to measure instantaneous wall temperatures. The heat flux was obtained by solving the one-dimensional transient energy equation with transient boundary conditions using the Fast Fourier Transform. The engine was tested under different operating conditions to evaluate the sensitivity of the measurement procedure to variations of three relevant combustion parameters: injection pressure, air temperature and oxygen concentration at the intake. The local heat flux obtained was compared with other relevant parameters that characterize the thermal behaviour of engines, showing, in most of the cases, correlation among them. The results showed that the instantaneous heat flux through the walls and hence the local wall temperatures are strongly affected by the ignition delay and the start of combustion.     

Heat transfer model for small-scale spark-ignition engines

A heat transfer model for small-scale spark-ignition engines has been proposed by authors in previous study. However, that model was developed based on experimental data of one engine, it may not be so accurate for others. In order to improve the accuracy of predicted heat transfer rate for different engines, a modified heat transfer model using Stanton number based on two engines is proposed. Prediction results of instantaneous heat flux, global heat transfer, heat release rate, and cylinder pressure based on the proposed model are compared with the experimental results of three engines and prediction results of previous model. It is found that the proposed model has prediction results closer to the measured data than the previous models at the most engine operation conditions.     

Heat transfer model for small-scale air-cooled spark-ignition four-stroke engines

The heat transfer models proposed in previous studies are not suitable for small-scale spark-ignition engines, because they were developed primarily for large-scale engines. In order to improve the accuracy of the predicted heat transfer rate for small-scale engines, a heat transfer model using the Stanton number is proposed in this paper. Prediction results of instantaneous heat flux, global engine heat transfer, and cylinder pressure based on the proposed model are compared with the experimental results and prediction results of previous models. It is found that the proposed model has prediction results closer to the measured data than the previous models at most engine operating conditions.     

某4缸乘用车柴油机冷却水套的设计优化

介绍了长城汽车研发的一款高性能"2.0VGT"柴油发动机冷却水套的设计优化过程,该发动机在进行可靠性试验过程中发现缸盖第1缸鼻梁区存在裂纹,导致冷却水渗入燃烧室发生失火。经过CFD模拟分析,采用优化垫片水孔结构,调整水孔上水量,得到优化后方案整体压力场,局部速度、对流传热系数、温度场的分布等均比优化前有明显改善。特别是优化后方案提高了缸盖第1缸鼻梁区(排气道与喷油器之间水路)冷却水的流速,避免了鼻梁区由于热负荷较大而导致的结构断裂问题。     

Evaluation of heat transfer correlations for HCCI engine modeling

Combustion in HCCI engines is a controlled auto-ignition of well-mixed fuel, air and residual gas. The thermal conditions of the combustion chamber are governed by chemical kinetics strongly coupled with heat transfer from the hot gas to the walls. The heat losses have a critical effect on HCCI ignition timing and burning rate, so it is essential to understand heat transfer process in the combustion chamber in the modeling of HCCI engines. In the present paper, a comparative analysis is performed to investigate the performance of well-known heat transfer correlations in an HCCI engine. The results from the existing correlations are compared with the experimental results obtained in a single-cylinder engine. Significant differences are observed between the heat transfer results obtained by using Woschni, Assanis and Hohenberg correlations.     

Measurements and analysis of load and speed effects on the instantaneous wall heat fluxes in a direct injection air‐cooled diesel engine

This work presents an experimental analysis which is carried out to study the instantaneous heat fluxes, during the engine cycle, in the cylinder head and exhaust manifold of a direct injection, air‐cooled, four‐stroke diesel engine. For temperature measurements, a new pre‐amplification unit for fast response thermocouples, appropriate heat flux sensors and an innovative, object‐oriented, control code for fast data acquisition have been designed and developed at the authors' laboratory. The experimental installation separates the engine transient temperature signals into two parts; namely the ‘long’‐ and the ‘short’‐term response ones; followed by their discrete processing in two independent data acquisition systems. One‐dimensional heat conduction with Fourier analysis of the raw temperature data are implemented in order to calculate the instantaneous engine combustion chamber and exhaust pipe heat fluxes. This study concentrates on the correct interpretation of the measured temporal variations of heat fluxes and the examination of the effect of engine load and speed on the cylinder head and exhaust manifold heat flux losses. Many interesting aspects of transient engine heat transfer are revealed. The simultaneous presentation of heat fluxes on the cylinder head and exhaust manifold, together with the engine indicator diagram, sheds light into the mechanisms governing transient heat transfer during an engine cycle. Copyright © 2000 John Wiley & Sons, Ltd.     

耦合法在柴油机传热研究中的应用

利用流固耦合的分析方法,将柴油机气缸盖、气缸垫、气缸体、气缸套等柴油机主要零部件以及缸内气体、冷却介质作为一个耦合体,进行燃烧室部件的传热数值模拟实验。其中,冷却水侧的对流换热系数和温度由CFD软件Star-CD对整个水路进行模拟计算获得;底板火力面侧燃气的对流换热系数和温度由GT-POWER软件对缸内工作过程进行模拟获得;缸套燃气侧温度由活塞组——气缸套耦合传热模拟获得。最终的计算结果与实验数据较吻合,可以为柴油机热负荷分析和柴油机设计提供理论依据。     

内燃机传热全仿真模拟研究进展综述

概述了内燃机传热研究的意义和发展;对内燃机传热研究的新领域－缸内气体的流动、燃烧、对流传热、辐射传热等模型与燃烧室部件整体导热模型耦合的计算机模拟,进行了全面综述,并指出了下一步应着重解决的问题。     

火花点火发动机碗形燃烧室的设计与研究

本文介绍了在同一台单缸汽油试验机上分别采用浴盆形和压缩比不同的碗形燃烧室进行动力性、经济性、排放指标和燃烧过程分析的对比试验研究。结果表明，采用碗形燃烧室，发动机的总燃烧期缩短，循环变动下降，适合采用较高的压缩比。在排放指标大致相当的条件下，动力性改善，节油效果达１０％以上，具有良好的实际应用价值。在国产汽车发动机向小缸径、高转速、高压缩比的方向发展时，采用碗形燃烧室将会取得良好的效果     

Numerical study of heat transfer of hydrogen combustion in noble gases atmosphere in compression ignition engine

The high energy content of hydrogen and zero carbon emission from hydrogen combustion is very important for compression ignition engine development. Hydrogen requires a very high auto-ignition temperature, which encourages replacing nitrogen with noble gases with higher specific heat ratio during compression process. In noble gases-hydrogen combustion, higher combustion temperature potentially leading to a higher heat loss. This paper aims to investigate the effect of hydrogen combustion in various noble gases on heat distribution and heat transfer on the cylinder wall. Converge CFD software was used to simulate a Yanmar NF19SK direct injection compression ignition engine. The local heat flux was measured at different locations of cylinder wall and piston head. The heat transfer of hydrogen combustion in various noble gases at different intake temperatures was studied using the numerical approach. As a result, hydrogen combustion in light noble gases such as helium produces faster combustion progress and higher heat temperature. The hydrogen combustion that experienced detonation, which happened in neon at 340 K and argon at 380 K, recorded a very high local heat flux at the cylinder head and piston due to the rapid combustion, which should be avoided in the engine operation. At a higher intake temperature, the rate of heat transfer on the cylinder wall is increased. In conclusion, helium was found as the best working gas for controlling combustion and heat transfer. Overall, the heat transfer data gained in this paper can be used to construct the future engine hydrogen in noble gases.     

一种计算火焰与燃烧室之间几何关系的新模型

建立了一种用于计算火焰与各种几何形状的点燃式发动机燃烧室之间相互关系的计算模型，应用在发动机准维模型中能很好地满足火焰形状椭球化、火焰中心飘移等计算要求。能计算火焰前锋面积，已、未燃区体积和已、未燃区与燃烧室之间的传热面积等参数。通过有效性讨论，认为模型具有较好的精确性和适应性。     

基于集总参数法的坦克发动机热性能模型

发展了一个基于集总参数法的坦克发动机热性能模型，考虑了发动机燃烧室的传热、发动机主要部件的传热、冷却系统和润滑系统的工作及坦克动力舱内的空气流动，建立了燃烧气体与发动机部件、各部件之间、部件与冷却液、部件与润滑油、部件与动力舱空气之间的热耦合计算公式．对一台坦克涡轮增压柴油机的热性能进行了实例计算，结果证实这个模型可以用于坦克发动机热性能的研究．     

汽油机非稳定加速工况燃烧放热率计算模型的修正

要对发动机非稳定工况实施最优控制,就应对其在非稳定工况下的工作过程做深入的研究。求取燃烧放热率是进行燃烧过程优化研究的基本手段,但在迄今为止的各种燃烧分析仪中,给出的多为稳定工况分析结果。作依据４９２Ｑ汽油机加速过程的试验结果,修正了汽油机燃烧放热率计算的热力学模型,使之适用于非稳定工况最后,通过实测示功图分析了４９２Ｑ汽油机沿外特性加速过程的放热特性和指示效率。     

6110A柴油机绝热性能的预测

本文建立了计算直喷式柴油机气缸内热力过程、气缸周壁传热和气缸盖排气道传热的数学模型,并编制了计算机程序。采用解析法处理气缸周壁传热,特别是应用二维解析法建立活塞顶传热,将气缸周璧传热计算与柴油机气缸内热力过程计算相结合,互为边界条件,因此能模拟计算绝热机工作过程。在几种气缸周壁绝热层布置形式下,以6110A柴油机为例进行了非增压、增压和增压带动力涡轮在标定工况下的模拟计算,并分析了绝热对发动机性能,燃烧过程以及热平衡的影响。为研制绝热发动机提供了预测数据。     

Experimental study of the interactions between long and short-term unsteady heat transfer responses on the in-cylinder and exhaust manifold diesel engine surfaces

The paper presents the results from the analysis of an experimental investigation with the aim to provide insight to the cyclic, instantaneous heat transfer phenomena occurring in both the cylinder head and exhaust manifold wall surfaces of a direct injection (DI), air-cooled diesel engine. The mechanism of cyclic heat transfer is investigated during engine transient events, viz. after a sudden change in engine speed and/or load, both for the combustion chamber and exhaust manifold surfaces. These results are then compared with relevant experimental data from steady state operation which in the present case are used as reference helping to reveal any potential influences of each transient event on cyclic heat transfer. The experimental installation allowed both long- and short-term signal types to be recorded on a common time reference base during the transient event. Processing of experimental data was accomplished using a modified version of one-dimensional heat conduction theory with Fourier analysis, capable to cater for the special characteristics of transient engine operation. Based on this model, the evolution of local surface heat flux during a transient event was calculated. Two engine transient events are examined, which present a key difference in the way the load and speed changes are imposed on each one of them. From the analysis of experimental results it is confirmed that each thermal transient event consists of two distinguished phases the “thermodynamic” and the “structural” one which are appropriately configured and analyzed. In the case of a severe variation, in the first 20 cycles after the beginning of the transient event, the wall surface temperature amplitude on cylinder head was almost three times higher than the one observed at the “normal” temperature oscillations occurring during the steady state operation. At the same time, peak pressure values in the same cycles are increased by almost 15% above their corresponding values at the final steady state. The same phenomena are valid for the exhaust manifold surfaces but on a moderated scale.     

Effect of wall proximity on forced convection in a plane channel with a built-in triangular cylinder

A numerical investigation has been carried out to analyze the effect of wall proximity of a triangular cylinder on the heat transfer and flow field in a horizontal channel. Computations have been carried out for Reynolds numbers (based on triangle width) range of 100–450 and gap widths (a/h) 0.5, 0.75 and 1. Results are presented in the form of instantaneous contours of temperature, vorticity, with some characteristics of fluid flow and heat transfer; such as time-averaged and instantaneous local Nusselt number, skin friction coefficient along bottom channel's wall, and drag coefficient. Results show that approaching triangular cylinder in the wall, removes vortex shedding and subsequently the heat transfer rate decreases at low Reynolds number. By decreasing the vortex shedding, drag coefficient decrease as triangular cylinder approaches the wall of the channel. The variation of vortex formation has a more significant suppression effect on the skin friction coefficient than the Nusselt number.     

Coupling conjugate heat transfer with in-cylinder combustion modeling for engine simulation

A conjugate formulation to predict heat conduction in the solid domain and spray combustion in the fluid domain was developed for multidimensional engine simulation. Heat transfer through the wall affects the combustion process in the cylinder and the thermal loading on the combustion chamber surface. To account for the temporal and spatial variations of temperature on the chamber surface, a fully coupled numerical procedure was developed to simulate in-cylinder flow and solid heat conduction simultaneously. Temperature fields in both the fluid and the solid domains were coupled by imposing equal heat flux and equal temperature at the fluid–solid interface. The formulation was first validated against analytical solutions. The formulation was then applied to simulate the in-cylinder combustion process and the solid heat conduction in a diesel engine under different operating conditions. Results show that the present model is able to predict unsteady and non-uniform temperature distributions on the chamber surface, which can fluctuate by nearly 100 K during combustion. The highest temperature on the piston surface occurs at the bowl edge along the spray axis. Predicted global engine parameters agree well with the experimental data. The present approach can be used to improve engine design for optimal combustion and reduced thermal loading.