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.

     

Investigation of heat transfer in an oil cooled piston with and without ceramic insulation on crown face

A numerical method is presented for calculating the temperature fields in a semi-adiabatic diesel engine piston having a cooling oil canal. The crown face of the piston is coated by a 2 mm thick oxide based ceramic insulating material. The non-ideal thermal contacts between the piston circumference and cylinder wall are also considered. A detailed analysis has been given for estimating the boundary conditions of the cylinder-piston assembly of an internal combustion engine. The isothermic distribution in the piston body and the heat flow rate through the different cooling media at four different engine loads have been depicted both for the cases with and without insulation coating. The results indicate a reduction (12–30%) in heat loss through the piston by use of an insulation coating at the piston crown face, assuming that both the heat transfer process from and the temperature of the combustion products remain unchanged.     

ZAV40S柴油发电机组旋阀机构的改进

旋阀机构是保证中速柴油机进、排气阀正常工作的重要装置。本文介绍的改进型旋阀机构不仅保证气阀在开启过程中能不断转动,而且使气阀在落座过程中亦能保持这种转动,从而进一步改善气阀的工作条件,延长气阀的使用寿命。     

船用柴油机排气阀锥面激光融覆Stellite合金分析

采用激光熔覆表面技术,在6250系列船用四冲程中速柴油机排气阀锥面熔覆Stellite 6钴基合金粉末制备涂层,通过对熔覆层进行试验分析,得出Stellite 6钴基合金涂层的熔覆对船用柴油机排气阀锥面材料的组织结构、抗热腐蚀、耐磨性能等都有很大的提升。     

Data-driven modeling of truck engine exhaust valve failures: A case study

Exhaust valve is an essential part of truck engine. Dynamic and unpredictable thermal and mechanical stress cause valves to wear prematurely, leading to increased maintenance costs. In this paper, a data-driven approach is presented to predict failures of exhaust valves of truck engines. The failure datasets of exhaust valves recorded from 13 truck engines are divided into three groups: First failure, second failure, and third or more failures. The Kaplan-Meier estimator is selected to express the distribution of survival probability of the three groups of failures. In order to find the hazard indicator, two data-mining algorithms, a wrapper and a boosting tree are applied to select parameters highly relevant to the hazard rate. A Cox proportional hazard model is used to conduct regression analysis on each selected parameter. Based on the derived hazard ratio, the time-dependent baseline hazard rate is computed. Five parametric reliability models are selected to capture the baseline hazard rate for the three groups. The value-at-risk for each group of failures is computed to express the risk at different confidence levels. Life circle of truck engine exhaust valves can be estimated.     

气动发动机排气冷量在内燃机冷却系统中的回收利用研究

针对气动发动机排气的低温特性,提出了利用气动发动机排气冷却内燃机散热器的技术方案。通过初步试验,获得了气动发动机在不同转速下的排气流量和温度特性。基于初步试验结果,建立了气动发动机排气与内燃机冷却水的热交换模型,并进行了仿真计算,得到了不同水泵流量下,热水流经换热器的进出口温差以及换热量。研究结果表明,换热器进出口热水温差、换热量随着气动发动机转速的升高而增大;随水泵流量的增加,热水流经换热器进出口的温差逐渐减小,换热量增大,但各个水泵流量下的换热量相差较小,当发动机转速为700r／min时,温差增加值及换热量的增加值均为最小;随着气动发动机转速增加,气动发动机排气的冷量炯变化范围很小,回收指数逐渐上升,冷量回收效果变好。     

Introductory measurements of in-cylinder flow past intake valve ports with a film split-fiber probe

A new steady flow test bench test facility has been designed and fabricated for exploration of complex three-dimensional flowfields inside a cylinder of an internal combustion engine. An engine cylinder head of a currently produced car engine with four head valves is utilized as an inlet section of the newly built test bench test. No piston is located in the cylinder and the intake valves are not periodically operated. They remain open during the test periods. An extensive set of initial experimental data has been acquired for both open intake valves and for the location of the probes at two different axial stations in the engine cylinder. The experimental technique of thermo-anemometer split-fiber probes is employed in this research work, which is a novelty never applied before to this class of flows. The probe properties are explained in the paper with emphasis on the probe directional characteristics. The verification tests proved the operational readiness of the new test bench to acquire reliable experimental data at a range of flow conditions simulating real engine settings. The acquired data set base will be used for validations of improved CFD engine design codes. An analysis of the initial set of experimental data clearly indicates that two vortices, or more likely down-flowing spiral flow structures. are present side by side in the cylinder. Mutual interaction of these two flow structures and the ability to generate faithful numerical simulation of this flow pattern for additional planes of measurement and various valve openings will be reported separately.     

P-V图和阀片运动图在冰箱压缩机性能评价中的应用

通过建立新的实验平台,准确测量压缩机各腔体内的气体压力和吸排气阀片的升程量,获取真实的P-V图和阀片运动图。对压缩机P-V图和阀片运动图进行同步研究和分析,得到阀片动作与压缩机内部工作过程的耦合关系,从而为压缩机优化提供方法。实验数据表明：在ASHRAE工况下,该款压缩机循环功耗为66.825W,其中排气压力损失功耗占比为4.254%,吸气压力损失功耗占比为1.2%,吸气阀片位移为2.148mm,排气阀片位移为0.825mm。对压缩机吸排气阀片延时现象进行了分析。     

Steady and non-steady flow through an i.c. engine inlet valve with heat transfer

Two methods are described for predicting flow conditions through an internal combustion engine inlet valve with heat transfer. Calculations using these methods show that the heat transfer effects may have a significant influence on the mass flow rate through the valve, the trapped mass in the cylinder and the trapped pressure and temperature.     

全可变气门机构闭环控制试验研究

为进行均质充量压缩燃烧的研究,开发一套进气门升程和相位、排气门升程和相位等4个参数均可独立自由控制的全可变气门机构。同时为研究可变气门技术的控制策略,开发一套全可变气门机构控制策略研究试验平台,包括一台变频调速电动机、液压及润滑系统、全可变气门机构控制单元及其试验管理系统,该平台可在模拟发动机运行的条件下进行气门机构控制策略研究和评价。对可变升程和可变相位闭环控制策略的试验研究结果表明,整套策略可以实现进排气门升程在0～9.7 mm之间、相位在60°范围内连续、快速、稳定的调节,为提高汽油机的效率和实现均质充量压缩燃烧发动机的运行控制奠定了基础。     

浅谈发动机配气机构优化改进设计

配气机构是发动机重要的组成,配气机构功能要按照发动机各气缸工作循环与发火次序要求对进、排气门进行定时开启与关闭。发动机动力和经济的性能是不是具有优越性和可靠性,将噪声和振动控制到较低限度内,这都与配气机构的设计有着直接的关系。配气机构要具备良好换气性能和良好运动学、动力学的性能,保持平稳工作和低振动,小噪声。本文通过对配气机构的研究与优化改进设计,将理论与实际应用结合,为发动机配气机构的设计积累经验。     

A study on characteristics and control strategies of cold start operation for improvement of harmful exhaust emissions in SI engines

Emission regulations for automobiles have become more stringent and the improvement of emission during cold start has been a major key issue to meet these regulations. Among many kinds of factors that affect cold start operation, ignition timing is crucial to improve emission characteristics due to the influence on exhaust gas temperature. Recent progress in variable valve timing allows optimized valve event strategies under various ranges of engine operating conditions including cold start. This study investigates effects of ignition and exhaust valve timing on exhaust gas temperature, combustion stability and emission characteristics through cold start bench tests of an SI engine. Experimental results show that exhaust valve timings and ignition timings significantly affect exhaust gas temperature and stability of engine operation under cold start condition. Exhaust valve timing also affects CO and NO_x emission due to changes in residual gas fraction of the combustion chamber. Ignition timing mainly affects exhaust gas temperature and HC emission. A control strategy, advanced exhaust valve timing and retarded ignition, is plausible in order to achieve reduction of exhaust emission while maintaining stability under cold start operation of SI engines.     

气动发动机的试验研究

为优化气动发动机的设计,提高气动发动机的工作性能,在一台由R175柴油机改装的二冲程气动发动机上进行详细的台架试验研究,并提出两个评价气动发动机性能的新指标--比质量流量和总能量效率.采用变压器机油、冷冻油和特制机油等三种不同的润滑油进行气动发动机的润滑油试验,试验结果表明润滑油对气动发动机的经济性和动力性影响很大.针对水套中无水、注入常温水和开水等三种不同换热条件进行气动发动机的换热试验,试验结果表明加强换热条件对气动发动机的经济性和动力性帮助有限,但多级利用压缩空气可以提高气动发动机的总能量效率.利用三种不同进气提前角的进气凸轮,进行三种不同配气相位的速度特性和负荷特性试验.试验表明:气动发动机在低速阶段拥有较好的经济性和动力性,进气提前角为10 ℃A时,气动发动机性能最好.     

Fabrication of Metal Matrix Composite Automotive Parts

Driven by the need to build lighter weight, quieter and more fuel-efficient engines, the automotive industry has recognised the need for materials substitution, offering outstanding proper-ties in a number of engine components, including engine poppet valves. Since the valves control the gas flow, valve size, timing and overlap, they all influence volumetric efficiency. The valve train is designed to achieve maximum volumetric efficiency at the desired level of engine performance. Also engine valves are subjected to high operating temperatures and stress con-ditions which affect durability. The application of finite element analysis resulting in a Weibull failure theory analysis is a valid tool in predicting the probability of failure of the valves. The present work envisages carrying out some studies on Al-SiC and Al-TiC composites as possible alternative materials for engine poppet valves. The present trend to make parts at or near net shape has brought powder metallurgy (PM) to the forefront and is being vigorously pursued by automotive design and materials engin-eers who are finding an increased application for this energy-and cost-saving process. Mixtures of four different compositions (15, 20, 25, 30% by weight) of SiC were prepared. By the PM technique, valves were fabricated by placing these powder mixtures in layers (one weight per cent along the stem and one along the base) in a die. Specimens ( φ15 × 30) were also prepared by the PM technique so that properties like compressive, tensile strength, etc. could be studied. A die was fabricated to cast valves through a liquid metallurgy route.     

柴油机气门导管润滑与密封性研究

针对柴油机气门导管的漏油与磨损问题，设计了高性能粉末冶金材料和三种不同的密封结构，并从理论上对这些结构的流体动力润滑特性进行了分析计算；然后通过对材料改进前后的摩擦磨损试验、不同结构的漏油量对比试验和整机排放试验，证实材料设计和理论计算是合理的，同时也证实气门导管只加工凹槽而不安装密封圈的结构既可以润滑又可以密封．此结构不仅节省密封圈、简化装配工艺．而且减少进入进、排气道的机油量，降低颗粒排放，还减轻了气门副的磨损，从而在实际机型中得到应用。     

密封面作用长度的快速测量原理及专用检测装置

本文介绍了密封面作用长度的快速检测装置，此装置适用于发动机中进排气门的在线检测。文章阐述了检具的工作原理和结构特点，并对检测结果作了误差分析，分析表明其测量精度完全能满足需要。     

发动机排气阀温度场试验方法和结果

通过试验得到45Cr9Si3材料回火温度和硬度对应曲线,通过排气阀温度场试验,可以确定排气阀在实际工作中的最高温度以及排气阀各部分工作温度分布情况。为制造排气阀选用正确材料和排气阀的研发、设计提供数据参考。     

Experimental and analytical investigation of the heat transfer and thermal stresses in a cylinder head of a diesel engine

An experimental and theoretical study has been carried out to investigate the mechanism of crack development in cylinder heads of two-stroke diesel engines. The cracks initiate in the valve bridge region, between a pair of exhaust valves, where high temperatures exist during operation of the engine. The experiments included steady state and transient modes (cold start, loading and shut off), and temperature distributions were measured in the metal and the cooling water. The hot surface temperature as well as the maximum stresses are estimated using an analytical model. It is concluded that the dominant process of cracking is low cycle thermal fatigue and residual tensile stresses which appear after engine shut off.     

发动机辅助制动性能仿真研究

通过对发动机辅助制动工作过程进行理论分析,建立了发动机辅助制动计算模型,根据辅助制动相关参数（包括排气门开度、发动机转速和排气背压等）,对发动机辅助制动进行了单因素和多因素条件下的仿真研究及试验验证。结果表明：随着发动机转速的升高,缸内压力增大,且压力峰值更靠近上止点;制动扭矩随转速的升高而增大,减压制动时制动扭矩最大,发动机制动时制动扭矩最小;发动机转速一定时,泄漏制动和减压制动分别有一对应的最佳排气门开度值,并且转速越高,排气门开度最佳值越大,排气背压越高,制动扭矩越大。     

乳化液泵配流机理的试验研究

乳化液泵属于多柱塞阀配流往复式容积泵,以进、排液阀完成配流任务,实践中为了达到流量调节目的往往采用变频驱动技术。采用线性可变差动变压器（Linear Variable Differential Transformer,LVDT）位移传感器测量了进、排液阀阀芯和柱塞位移规律,并同步采集了泵出口处的压力数据。试验结果显示：排液阀阀芯在不同曲轴转速下的行程是变化的,且均未达到由限位结构决定的限位高度;排液阀阀芯在开启过程中存在着抖动,这种开启行程中的反向运动是由泵出口处的压力脉动导致;进、排液阀开启过程均存在滞后,而排液阀关闭滞后不明显,进液阀关闭滞后随着曲轴转速的下降而缓解。为了降低这类泵曲轴转速降低时引发的压力脉动加剧现象,可考虑采用主动控制进液阀启闭时刻的方式实现流量调节目的。