内燃机动力特性的一个新评价指标

本文通过对车用（包括工程机械）活塞式内燃机动力储备性能评价指标──扭矩适应系数Km和转速适应系数Kn及现有的扭矩曲线拟合公式分析,指出了它们所存在的不足,推导出了拟合精度较高的扭矩曲线经验方程,并以此为依据推导出了动力储备性能综合指标──理想功率特性系数KN计算式,为正确评价内燃机的动力储备性能提供了理论依据。     

内燃机零部件动态特性结构动力修改技术的研究开发

本文简要介绍了结构动力修改技术的基本原理及系统配置。通过对该系统灵敏度分析及结构修改正反问题的介绍,说明系统的特点及功能。应用该系统对SD1105机体进行了结构修改,取得了显著的效果。     

内燃机理想油耗率特性系数及求解

提出了内燃机外特性理想油耗率特性曲线。根据实际内燃机油耗率曲线与理想油耗率曲线的逼近程度,引入并导出一个新的评价指标－理想油耗率特性系数Ｋａ及其计算公式,用以评价外特性油耗率曲线的变化平坦程度,为正确评价内燃机工作转速范围内的燃油经济性好坏提供了理论依据。     

多缸内燃机缸体瞬态动力分析

建立了某4缸内燃机缸体的有限元模型,运用完全矩阵法进行了缸体的模态分析及瞬态动力分析。分析中考虑了缸套所受的缸套-活塞间的润滑油膜力、曲轴主轴承处所受的油膜动压作用、燃烧室内气体压力的作用以及缸盖对缸体的作用力。缸套活塞间的油膜力通过求解平均雷诺方程得到。曲轴主轴承处所受的油膜力由主轴承油膜润滑与活塞-连杆-曲轴系统动力学的耦合分析得到。瞬态动力学分析表明：该型号的内燃机在工作过程中,缸体的受迫振动主要是弯曲振动及沿缸套轴向的伸缩振动。缸体的振动会对缸套-活塞间的油膜润滑产生很大影响。     

用神经网络模拟内燃机万有特性

提出了以神经网络模拟万有特性的新方法，并将神经网络的拟合结果与人工样条拟合的结果进行了比较。同时也介绍了有关神经网络应用的基本方法。     

内燃机特性曲线的数字拟合方法

以四种柴油机扭矩试验曲线＾「１」为例,介绍了可以根据试验所测定的数据曲线推导其参数间数学近似表达式的对数校直法的基本原理和计算程序。     

内燃机消声器特性试验装置的研制及应用

研制了一种用于消声器声学性能研究的试验装置，该装置可研究在气流条件下内燃机进气消声器和在热气流条件下排气消声器的声学性能，为研究和分析消声器声学性能提供了坚实的试验基础。初步的试验结果表明：该装置能向试验管道内提供稳定的流动气体，对管内气流的加热温度能达到设计要求，能很好地模拟内燃机消声器内的声学条件。     

内燃机曲轴轴系动态特性优化修改的研究

本文根据结构动态系统状态空间敏感度分析提出了一种内燃机轴系扭振特性修改的优化方法，并介绍了一种动态特性优化计算和重分析的计算机通用程序，文中附有曲轴轴系扭振特性优化分析的结论以及计算机仿真和实测分析的实例。     

重心位移法在研究内燃机平衡性能中的应用

本文以１６Ｖ２４０ＺＪＢ型柴油机的参数为例介绍了用重心位移法来研究内燃机振动力平衡的方法,通过数据计算,说明该方法的可行性     

Towards a detailed soot model for internal combustion engines

In this work, we present a detailed model for the formation of soot in internal combustion engines describing not only bulk quantities such as soot mass, number density, volume fraction, and surface area but also the morphology and chemical composition of soot aggregates. The new model is based on the Stochastic Reactor Model (SRM) engine code, which uses detailed chemistry and takes into account convective heat transfer and turbulent mixing, and the soot formation is accounted for by SWEEP, a population balance solver based on a Monte Carlo method. In order to couple the gas-phase to the particulate phase, a detailed chemical kinetic mechanism describing the combustion of Primary Reference Fuels (PRFs) is extended to include small Polycyclic Aromatic Hydrocarbons (PAHs) such as pyrene, which function as soot precursor species for particle inception in the soot model. Apart from providing averaged quantities as functions of crank angle like soot mass, volume fraction, aggregate diameter, and the number of primary particles per aggregate for example, the integrated model also gives detailed information such as aggregate and primary particle size distribution functions. In addition, specifics about aggregate structure and composition, including C/H ratio and PAH ring count distributions, and images similar to those produced with Transmission Electron Microscopes (TEMs), can be obtained. The new model is applied to simulate an n-heptane fuelled Homogeneous Charge Compression Ignition (HCCI) engine which is operated at an equivalence ratio of 1.93. In-cylinder pressure and heat release predictions show satisfactory agreement with measurements. Furthermore, simulated aggregate size distributions as well as their time evolution are found to qualitatively agree with those obtained experimentally through snatch sampling. It is also observed both in the experiment as well as in the simulation that aggregates in the trapped residual gases play a vital role in the soot formation process.     

Experimental results of hydrogen enrichment of ethanol in an ultra-lean internal combustion engine

An investigation was made to determine the effects of hydrogen enrichment of ethanol at ultra-lean operating regimes utilizing an experimental method. A 0.745 L 2-cylinder SI engine was modified to operate on both hydrogen and ethanol fuels. The study looked at part throttle, fixed RPM operation of 0%, 15%, and 30% hydrogen fuel mixtures operating in ultra-lean operating regimes. Data was collected to calculate NO and HC emissions, power, exhaust gas temperature, thermal efficiency, volumetric efficiency, brake-specific fuel consumption, and Wiebe burn fraction curves.     

Analytical study to minimise the heat losses from a propane powered 4-stroke spark ignition engine

The alarming rate at which the Earth’s atmosphere is getting polluted, the increased impact of global warming on the weather conditions on Earth and the stringent anti-pollution laws imposed in certain countries are among the main reasons for the search for alternatives to gasoline. Liquefied Petroleum Gas (LPG) (mainly propane) is among the many alternatives proposed to replace gasoline in the short term due to its excellent characteristics as a fuel for spark ignition (SI) engines. This paper presents a discussion on the parameters that affect the engine’s heat losses mainly during power stroke, with suggestions to minimise it. The effect of the equivalence ratio, compression ratio, spark plug location, and combustion duration at different speeds on the heat losses has been studied.     

A novel internal combustion engine utilizing internal hydrogen production for improved efficiency – A theoretical concept

Starting from the baseline of a Diesel engine, we show that with a suitable in-cylinder catalyst and well controlled injection of fuel and steam mixture during a certain period in the compression stage, a significant increase in the ideal cycle efficiency is achievable (from 67% to 78% for an initial compression ratio of 25). In such an arrangement, the fuel injection session comprises a two-stage process. In the first stage, fuel and water are injected into the hot previously compressed cylinder charge over the catalyst. Residual heat is absorbed due to a steam reforming process to produce hydrogen. The heat absorption cools the compressed mixture and enables a higher compression ratio up to the maximum allowed pressure, while the temperature of the cylinder charge remains constant. In the second stage, only fuel is injected to initiate combustion while the absorbed heat (of the first stage) is released through the hydrogen oxidation. Essentially, the absorbed heat is exploited to produce extra hydrogen fuel, which increases the cycle efficiency.     

Large eddy simulation of highly turbulent under-expanded hydrogen and methane jets for gaseous-fuelled internal combustion engines

Burning hydrogen in conventional internal combustion (IC) engines is associated with zero carbon-based tailpipe exhaust emissions. In order to obtain high volumetric efficiency and eliminate abnormal combustion modes such as preignition and backfire, in-cylinder direct injection (DI) of hydrogen is considered preferable for a future generation of hydrogen IC engines. However, hydrogen's low density requires high injection pressures for fast hydrogen penetration and sufficient in-cylinder mixing. Such pressures lead to chocked flow conditions during the injection process which result in the formation of turbulent under-expanded hydrogen jets. In this context, fundamental understanding of the under-expansion process and turbulent mixing just after the nozzle exit is necessary for the successful design of an efficient hydrogen injection system and associated injection strategies. The current study used large eddy simulation (LES) to investigate the characteristics of hydrogen under-expanded jets with different nozzle pressure ratios (NPR), namely 8.5, 10, 30 and 70. A test case of methane injection with NPR = 8.5 was also simulated for direct comparison with the hydrogen jetting under the same NPR. The near-nozzle shock structure, the geometry of the Mach disk and reflected shock angle, as well as the turbulent shear layer were all captured in very good agreement with data available in the literature. Direct comparison between hydrogen and methane fuelling showed that the ratio of the specific heats had a noticeable effect on the near-nozzle shock structure and dimensions of the Mach disk. It was observed that with methane, mixing did not occur before the Mach disk, whereas with hydrogen high levels of momentum exchange and mixing appeared at the boundary of the intercepting shock. This was believed to be the effect of the high turbulence fluctuations at the nozzle exit of the hydrogen jet which triggered Gortler vortices. Generally, the primary mixing was observed to occur after the location of the Mach disk and particularly close to the jet boundaries where large-scale turbulence played a dominant role. It was also found that NPR had significant effect on the mixture's local fuel richness. Finally, it was noted that applying higher injection pressure did not essentially increase the penetration length of the hydrogen jets and that there could be an optimum NPR that would introduce more enhanced mixing whilst delivering sufficient fuel in less time. Such an optimum NPR could be in the region of 100 based on the geometry and observations of the current study.     

Detailed numerical simulation of syngas combustion under partially premixed combustion engine conditions

Two-dimensional detailed numerical simulation is performed to study syngas/air combustion under partially premixed combustion (PPC) engine conditions. Detailed chemical kinetics and transport properties are employed in the study. The fuel, a mixture of CO and H₂ with a 1:1 molar ratio, is introduced to the domain at two different instances of time, corresponding to the multiple injection strategy of fuel used in PPC engines. It is found that the ratio of the fuel mass between the second injection and the first injection affects the combustion and emission process greatly; there is a tradeoff between NO emission and CO emission when varying the fuel mass ratio. The ignition zone structures under various fuel mass ratios are examined. A premixed burn region and a diffusion burn region are identified. The premixed burn region ignites first, followed by the ignition of mixtures at the diffusion burn region, and finally a thin diffusion flame is formed to burn out the remaining fuel. NO is produced mainly in the premixed burn region, and later from the diffusion burn region in mixtures close to stoichiometry, whereas unburned CO emission is mainly from the diffusion burn region. An optimization of the fuel mass in the two regions can offer a better tradeoff between NO emission and CO emission. The effects of initial temperature and turbulence on the premixed burn and diffusion burn regions are investigated.     

Second-law analyses applied to internal combustion engines operation

This paper surveys the publications available in the literature concerning the application of the second-law of thermodynamics to internal combustion engines. The availability (exergy) balance equations of the engine cylinder and subsystems are reviewed in detail providing also relations concerning the definition of state properties, chemical availability, flow and fuel availability, and dead state. Special attention is given to identification and quantification of second-law efficiencies and the irreversibilities of various processes and subsystems. The latter being particularly important since they are not identified in traditional first-law analysis. In identifying these processes and subsystems, the main differences between second- and first-law analyses are also highlighted. A detailed reference is made to the findings of various researchers in the field over the last 40 years concerning all types of internal combustion engines, i.e. spark ignition, compression ignition (direct or indirect injection), turbocharged or naturally aspirated, during steady-state and transient operation. All of the subsystems (compressor, aftercooler, inlet manifold, cylinder, exhaust manifold, turbine), are also covered. Explicit comparative diagrams, as well as tabulation of typical energy and exergy balances, are presented. The survey extends to the various parametric studies conducted, including among other aspects the very interesting cases of low heat rejection engines, the use of alternative fuels and transient operation. Thus, the main differences between the results of second- and first-law analyses are highlighted and discussed.     

一种新的燃烧方式--均匀充量压缩着火的研究进展

分析均质充量压缩着火的特点,国外将均质充量压缩着火方式应用于往复式发动机中的研究现状,阐述燃料系统的设计,并探讨在我国开展均质充量压缩着火研究工作的必要性和方案。