Temperature transients on engine combustion chamber walls—IV. Application of the finite-difference model to surface thermocouples and wall deposits

The FD computational code developed in Part I (Int. J. Mech. Sci. 33, 775 (1991) [1]) has the capability of handling composite walls having different material layers. This characteristic of the FD model is used to study the effects of thermocouple thickness and material type, as well as substrate material type on surface thermocuple readings. Later, the effects of wall deposits on surface thermocouple readings and engine heat transfer are explained.     

Fuel preparation and combustion in rocket and jet engines

A method is proposed for investigating the processes in the combustion chamber of chemical heat engines. In this method, the processes in the combustion chamber and the fuel injector are considered.     

Performance and emission characteristics of a low heat rejection spark ignited engine fuelled with E20

In internal combustion engines, the concept of low heat rejection (LHR) using thermal barrier coating on the surface of combustion chamber is gaining attention. Thermal barrier coating reduces the heat transfer to the cooling system, protects engine components from peak heat flux and fluctuating temperature produced during combustion and improves the performance of the engine. Information in the literature is plentiful for LHR diesel engine and only few studies exist on LHR spark ignited engine. The application of thermal barrier coating in spark ignited engine is limited by pre-ignition and knocking due to elevated combustion chamber temperature. A spark ignited engine with moderate insulation on the combustion chamber and higher octane fuel can overcome this difficulty. The objective of the present experimental study is to quantify the changes in performance and emission characteristics brought by partial thermal insulation on the combustion chamber of a four stroke spark ignited engine fueled with E20 blend. Partial thermal insulation was created by coating 0.3 mm thick Alumina (Al₂O₃) on the cylinder head, inlet and exhaust valves. The changes are quantified with respect to unmodified engine fueled with gasoline. The combustion parameters such as flame development and rapid burn duration are also estimated and compared. The results indicate that partially insulated SI engine when fueled with E20 improves performance and reduces emission. A maximum of 48% reduction in THC and 50% reduction in CO emission at part load was achieved.

     

船用柴油机燃烧室结构分析

为探索不同燃烧室结构对大缸径船用柴油机燃烧和排放的影响,基于原机燃烧室,新设计了6种不同形状的燃烧室,采用AVL Fire软件建立燃烧室仿真模型,并结合涡流数和均匀系数来对缸内流动、混合和燃烧过程进行数值模拟分析。结果表明：燃烧室直径和凹坑深度等参数会对缸内流动产生很大影响,凹坑深度较大的缩口燃烧室能产生较强的涡流从而改善燃烧,而浅坑的开口燃烧室的缸内燃烧状况较差。同时发现,只有在缸内涡流和湍动能都较大的情况下才能使燃烧更充分。从发动机性能和排放结果来看,缩口燃烧室G1的功率输出增加4.6%,排放与原机基本持平;直口燃烧室G4在略低于原机的功率输出下,NOx排放降低43.3%;开口燃烧室的做功能力较差。     

普通机床加工发动机缸盖球形燃烧室的工艺试验

发动机缸盖是发动机的关键零部件.发动机缸盖的燃烧室容积,直接影响到发动机的工作性能,所以在发动机缸盖制造过程中,最终必须保证发动机缸盖燃烧室的形状、表面粗糙度、尺寸精度、容积等一系列参数,从而保证发动机总机性能.     

A methodology for combustion detection in diesel engines through in-cylinder pressure derivative signal

In-cylinder pressure measurement has historically been used for off-line combustion diagnosis, but online application for real-time combustion control has become of great interest. This work considers low computing-cost methods for analysing the instant variation of the chamber pressure, directly obtained from the electric signal provided by a traditional piezoelectric sensor. Presented methods are based on the detection of sudden changes in the chamber pressure, which are amplified by the pressure derivative, and which are due to thermodynamic phenomena within the cylinder. Signal analysis tools both in time and in time-frequency domains are used for detecting the start of combustion, the end of combustion and the heat release peak. Results are compared with classical thermodynamic analysis and validated in several turbocharged diesel engines.     

Impact of the Oil Temperature on the Frictional Behavior of Laser-Structured Surfaces

This study investigates how the beneficial effects of laser-manufactured surface microstructures on friction vary with varying oil temperature. Laser surface texturing (LST) is a favorable method to optimize friction and wear, which have always been considerable obstacles against the performance improvement of combustion engines. The aim of this study is to detect correlations between the dimensional parameters of the laser-textured surfaces and tribological performance at varying temperatures. Although the experiments are on a fundamental level, the obvious application of combustion engines has been selected to align the material, processing, and test parameters. A wide range of micro indentations—henceforth called “dimples”—were fabricated onto honed flat aluminum samples by means of ultrashort pulse laser texturing and the frictional behavior at different lubricating oil temperatures (30 and 90?°C) was analyzed.     

Modeling and fuzzy control of the engine coolant conditioning system in an IC engine test bed

Mechanical and thermodynamical performance of internal combustion engines is significantly affected by the engine working temperature. In an engine test bed, the internal combustion engines are tested in different operating conditions using a dynamometer. It is required that the engine temperature be controlled precisely, particularly in transient states. This precise control can be achieved by an engine coolant conditioning system mainly consisting of a heat exchanger, a control valve, and a controller. In this study, constitutive equations of the system are derived first. These differential equations show the second-order nonlinear time-varying dynamics of the system. The model is validated with the experimental data providing satisfactory results. After presenting the dynamic equations of the system, a fuzzy controller is designed based on our prior knowledge of the system. The fuzzy rules and the membership functions are derived by a trial and error and heuristic method. Because of the nonlinear nature of the system the fuzzy rules are set to satisfy the requirements of the temperature control for different operating conditions of the engine. The performance of the fuzzy controller is compared with a PI one for different transient conditions. The results of the simulation show the better performance of the fuzzy controller. The main advantages of the fuzzy controller are the shorter settling time, smaller overshoot, and improved performance especially in the transient states of the system.     

Combustion and emission characteristics of HCNG in a constant volume chamber

Finding an alternative fuel and reducing environmental pollution are the main goals for future internal combustion engines. Hydrogenmethane (HCNG) is now considered an alternative fuel due to its low emission and high burning rate. An experimental study was carried out to obtain fundamental data for the combustion and emission characteristics of pre-mixed hydrogen and methane in a constant volume chamber (CVC) with various fractions of hydrogen-methane blends. A pre-mixed chamber was used to obtain a good mixture of these gases. Exhaust emissions were measured using a Horiba exhaust gas analyzer for various fractions of hydrogen-methane blends. The results showed that the rapid combustion duration was shortened, and the rate of heat release elevated as the hydrogen fraction in the fuel blend was increased. Moreover, the maximum mean gas temperature and the maximum rate of pressure rise also increased. These phenomena were attributed to the burning velocity, which increased exponentially with the increased hydrogen fraction in the fuel blend. Exhaust HC and CO₂ concentrations decreased, while NO_X emission increased with an increase in the hydrogen fraction in the fuel blend. Our results could facilitate the application of hydrogen and methane as a fuel in the current fossil hydrocarbon-based economy and the strict emission regulations in internal combustion engines.     

被动预燃室发动机低温冷起动及低负荷试验研究

预燃室射流点火是改善汽油发动机热效率的有效手段,为了研究和改善被动预燃室低温冷起动及低负荷时的燃烧稳定性,设计了不同容积、孔面积、材料、喷孔结构的被动预燃室装置,安装在一台涡轮增压汽油发动机上,进行了低温冷起动试验,以及低速、低负荷燃烧稳定性试验。研究结果表明,被动预燃室容积、孔面积、材料、喷孔结构对低温冷起动性能有显著影响。预燃室容积较小时,预燃室内部淬熄层占预燃室容积的比例大,预燃室内部混合气少。较小的孔径或孔面积减少了预燃室内残余废气的排出。旋转孔使得预燃室内部废气分层,火花塞附近废气比例大。较高的导热率使预燃室冷起动时预燃室散热较快。因此,小容积、小孔径、高导热率材料以及旋转喷孔等均不利于发动机冷起动。优化结构的被动预燃室在-20℃～-8℃的冷起动工况下能实现发动机稳定着火起动。点火角和排气VVT对发动机的燃烧稳定性影响较小。进气VVT对预燃室燃烧稳定性影响较大,进气门开起时刻推迟,着火上止点附近缸内湍动能变强;另一方面实际压缩比变大,主燃烧压入预燃室内部的新鲜混合气比例提高,预燃室点火燃烧稳定性显著改善。     

柴油机缸内辐射换热的多维数值模拟研究

对柴油机来说,辐射换热极为重要,在缸内总传热量中占有非常大的比重,直接关系到发动机热效率及因传热引起的各种热负荷、热强度问题,同时,辐射换热对燃烧系统的研究也十分重要,辐射热流量会深刻影响内燃机的燃烧性能,对发动机的各种燃烧产物的形成产生至关重要的影响。为此,利用离散传递法实现柴油机缸内辐射换热的多维数值模拟,通过多维模拟计算同时考察燃烧室部件表面发射率及喷雾提前角对柴油机缸内辐射换热的影响。结果表明：活塞的辐射热流量峰值高于缸盖的辐射热流;缸盖的辐射热流量的最大值并不在中心位置处,而是随时间变化;随着壁面辐射率的增加,缸内向燃烧室部件辐射换热量逐渐增大;喷雾提前角直接影响所有燃烧室部件表面的辐射热流密度。     

A study on the shaped combustion system using diesel spray impinged on a wall

In modern small compact combustion chambers of diesel engines with high speed injection spray, the wall impaction of spray is encountered. A number of combustion systems have been developed which deliberately employ wall impaction as a means of breaking up the fuel spray and/or directing it in a desired direction. As a link of this, in a further type of geometry, which has been presented by Park et al. cut-off pips were provided for a number of sprays directed not only straight down into combustion chamber centre but also across and down into the bowl in the normal radial direction. The sizes of the pips and their positions were tested for axisymmetrical shape, and their results were analyzed. The further type was simulated in here by using 3D non-orthogonal spray engine code. The simulation results show that the further type is much better than general conventional shapes, i.e. well mixing of fuel vapour and spray high qualified droplet atomization, etc. Thus the improvement of the engine performance is expected by the shaped engine.     

Hot-fire injector test for determination of combustion stability boundaries using model chamber

This study realizes the conceptual method to predict combustion instability in actual full-scale combustion chamber of rocket engines by experimental tests with model (sub-scale) chamber. The model chamber was designed based on the methodologies proposed in the previous work regarding geometrical dimensions and operating conditions, and hot-fire test procedures were followed to obtain stability boundaries. From the experimental tests, two instability regions are presented by the parameters of combustion-chamber pressure and mixture (oxidizer/fuel) ratio, which are customary for combustor designers. It is found that instability characteristics in the chamber with the adopted jet injectors can be explained by the correlation between the characteristic burning or mixing time and the characteristic acoustic time. In each instability region, dynamic behaviors of flames are investigated to verify the hydrodynamically-derived characteristic lengths of the jet injectors. Large-amplitude pressure oscillation observed in upper instability region is found to be generated by lifted-off flames.     

内燃机燃烧室芯头反求设计的CAD/CAM技术研究

以某发动机燃烧室铸造芯头为研究对象，采用非接触式光电测量技术获得了七万多个数据点，并对测量数据进行了预处理；运用CAD技术对散乱数据点进行了NURBS曲面拟合和光顺处理，生成了结构的三维实体模型；采用CAM技术对该芯头的数控加工技术进行了研究，编制了NC代码，加工出了符合要求的产品模型，成功的为某汽油机燃烧室的改进定型提供了技术指导。在此基础上生成的CAD／CAM软件系统可以应用于其它复杂曲面产品的反求工程。     

Performance and combustion characteristics of a diesel engine with titanium oxide coated piston using Pongamia methyl ester

Owing to the increasing cost of petroleum products, fast depletion of fossil fuel, environmental consideration and stringent emission norms, it is necessary to search for alternative fuels for diesel engines. The alternative fuel can be produced from materials available within the country. Though the vegetable oils can be fuelled for diesel engines, their high viscosities and low volatilities have led to the investigation of its various derivatives such as monoesters, known as bio diesel. It is derived from triglycerides (vegetable oil and animal fates) by transesterification process. It is biodegradable and renewable in nature. Biodiesel can be used more efficiently in semi adiabatic engines (Semi LHR), in which the temperature of the combustion chamber is increased by thermal barrier coating on the piston crown. In this study, the piston crown was coated with ceramic material (TiO₂) of about 0.5 mm, by plasma spray method. In this present work, the experiments were carried out with of Pongamia oil methyl (PME) ester and diesel blends (B20 & B100) in a four stroke direct injection diesel engine with and without coated piston at different load conditions. The results revealed 100% bio diesel, an improvement in brake thermal efficiency (BTE) and the brake specific fuel consumption decreased by about 10 % at full load. The exhaust emissions like carbon monoxide (CO) and hydrocarbon (HC) were decreased and the nitrogen oxide (NO) emission increased by 15% with coated engine compared with the uncoated engine with diesel fuel. The peak pressure and heat release rate were increased for the coated engine compared with the standard engine.     

A new approach to the prediction of heat flow and temperature in engine pistons with special reference to thermal barriers

Finite element techniques for the prediction of heat flow and temperature in pistons and other engine components are well established, although they rely invariably on initially assumed boundary conditions, particularly with respect to mean gas temperature during the cycle.Cycle analysis techniques for Diesel engines are equally well established, but these rely on much wider heat flow models for the combustion chamber walls, and generally are an assumed mean wall temperature.The paper describes a technique for one-dimensionalizing the results of finite element piston heat flow analysis and of incorporating this simplified piston model directly in the cycle analysis, using the concept of equivalent conductance.The two techniques are thus brought into much closer relationship than hitherto, allowing predictions of the effect of piston design changes on thermodynamic performance to be made much more readily.     

二冲程润滑油与发动机的排气系统堵塞

因二冲程润滑油直接参与燃烧，使发动机的燃烧室及排气系统产生大量沉积物。本文通过在不同排量发动机上的大量试验，研究了沉积物对发动机性能的影响，并提出了二冲程润滑油抗排气系统堵塞性能的评价方法。大量的试验表明该方法是准确可靠的。     

固体火箭发动机抗烧蚀防热涂层的研究

直径及开口都较大的固体火箭发动机燃烧室大都采用橡胶基绝热层,但是,对于长细比大,或者是开口较小的客体,采用橡胶基绝热层在工艺上难以实现.为了寻找同时具备隔热效果良好,且针对小口径壳体工艺可行性高的内防热材料,我们开展了以环氧树脂、橡胶为基体,云母粉等耐高温无机填料组成的防热材料.通过试件测试及产品验证,证明该防热涂层也是固发燃烧室一种较为适宜的烧蚀防热材料,它不受被保护产品的几何形状限制,烧蚀率较小.     

数控加工技术在活塞头制造中的应用

通过阐述数控加工技术在船用柴油机零部件——活塞头的制造中的具体应用,即加工活塞头顶部燃烧室及主螺孔,概述了数控加工技术相对于采用普通车床加工的优点。采用数控技术后,数控机床具有的曲面连续加工、重复定位、加工精度高和加工质量稳定的优点在活塞头的制造中得到充分发挥,同时采用数控加工技术后,生产效率和生产质量均获得了显著提升,生产成本也得到了有效控制。     

An experimentally based thermo-kinetic phase transformation model for multi-pass laser heat treatment by using high power direct diode laser

Laser-based phase transformation hardening (LPTH), based on rapid heating and cooling cycles produces hard and wear-resistant layers only at the selective region of the components. However, the bulk mass of the material’s core property is retained. The advantages of high power direct diode laser in comparison with other high power lasers (CO₂ and Nd:YAG) have put this type of laser as a main heat source for localized heat treatment. However, a tempered zone is formed in overlapping regions of a large heat-treated area during multi-pass laser heat treatment (MPLHT) that affects the uniformity of heat-treated depth of material. This study is focused on the development of a uniform hardness distribution model to minimize the tempering effect during the MPLHT process. A tool steel AISI S7 is heat treated by using different levels of laser power (1,400–1,800 W) and scanning speeds (15–25 mm/s). An experimentally based finite element (FE) thermal model is developed to predict the cross-sectional as well as surface temperature history of the MPLHT process. The temperature-dependent material properties and phase change kinetics are taken into account in the model. The laser beam is considered as a moving rectangular-shaped heat source (12 mm?×?1 mm) with a uniform distribution (top-hat) of laser power. The temperature history acquired from the FE thermal model is coupled with thermo-kinetic (TK) equations to determine the corresponding phase transformations and hardness. The tempering effect of MPLHT is studied for different sizes of overlap (1 mm–3 mm) and lengths of scan (10 mm–35 mm). The TK model results are verified with experimental ones to optimize the processing parameters. The optimized processing parameters, including laser power, scanning speed, size of overlap, and the length of scan are used to achieve a uniform hardness distribution and an even depth of heat treatment in the MPLHT area.