某款GDI汽油发动机烧机油现象的研究

烧机油是发动机常见的试验现象之一,尤其是增压缸内直喷汽油发动机,承受较高工作温度和燃烧压力,烧机油现象相对较普遍。机油的额外消耗会减少发动机正常换油里程,导致机燃比失调、加剧运动副磨损,破坏零部件使用功能、影响排放及后处理系统,严重情况下还会导致发动机发生爆燃,发动机动力下降甚至报废。主要分析一款2.0L GDI增压缸内直喷发动机烧机油的影响因素,从一环环高、油环结构、发动机回油结构、增压器机油损耗、气门密封性及活塞环岸结构、缸体网纹参数、配缸间隙、机油温度稳定性方面进行试验分析和验证。结果表明,增加一环环高、改变油环结构、改善回油不畅、优化活塞环岸和环槽结构、机油温度稳定控制、减小网纹参数Rvk均能够改善GDI发动机烧机油现象。     

增压直喷汽油机超级爆震研究进展

缸内直喷和增压已成为当今汽油机技术的主流方向,然而,随着发动机小型化和动力性的提高,增压汽油直喷发动机出现了一种新的异常燃烧现象——超级爆震,严重影响着发动机性能和使用寿命。本文根据国内外超级爆震的研究现状,阐述了超级爆震的产生机理和检测方法,从发动机及其零部件设计参数、运行参数、控制参数以及燃油和机油品质等方面,分析了影响超级爆震的因素,给出了缓解和抑制超级爆震的措施。     

增压直喷汽油发动机早燃现象改善的研究

低速大负荷早燃现象是制约增压直喷汽油发动机低速性能提升的主要因素之一,早燃易导致发动机火花塞烧蚀、活塞熔顶等质量问题,所以在发动机设计开发过程中必须对早燃问题加以优化改善。阐述了早燃产生的机理,更换不同机油、改变压缩比以及空燃比进行试验,结果表明：更换机油以及改变空燃比能够降低早燃频次,改变压缩比对早燃无影响。     

增压发动机取消机油冷却器的研究

随着国家对油耗法规的逐步加严,现代社会对传统汽车的动力性、燃油经济性以及排放性能要求越来越高,发动机小型化、增压化已成为发动机发展的方向,强化的发动机会引起发动机油温度过高,因此增压发动机普遍装有机油冷却器。本文通过对增压发动机取消机油冷却器前后对发动机各维度的影响进行研究,重点探讨机油冷却器取消对发动机热管理、热怠速、爆震、油耗排放的综合影响。通过试验发现:取消机油冷却器后,发动机整体水温有3℃的降低;带机油冷却器的热怠速机油压力与取消机油冷却器后的机油压力基本持平;取消油冷器后发动机爆震有所增强,油耗排放均有所劣化。我们为增压发动机油冷却器的开发提供支持。     

直喷汽油机缸内喷雾湿壁问题研究

直喷汽油机的湿壁问题会导致机油稀释,燃油经济性下降及尾气排放增加。但通过喷雾、燃烧室及缸内流场三者合理匹配与优化可以大大减少燃油湿壁。利用激光诊断技术对某直喷喷油器的喷雾特性进行全面测试,然后标定三维CFD软件中的喷雾模型,对缸内喷雾和混合气形成过程进行仿真计算,并研究了燃油喷射策略对燃油湿壁的影响。研究结果表明:采用两段喷射策略可以降低15%的碰壁量,混合气均匀程度基本不变;采用三段喷射可以降低27%的碰壁量,并可明显改善混合气浓度分布。     

二次喷射对增压直喷汽油机颗粒物排放的影响

基于某款增压直喷汽油机分别采用燃油单次喷射策略和二次喷射策略,利用DMS500颗粒分析仪对颗粒物数量浓度和粒径分布进行测试,研究不同工况下采用单次喷射和二次喷射策略后的发动机经济性和颗粒物排放的变化,选取二次喷射策略的适用工况.研究表明:当二次喷射策略运用于增压直喷发动机,二次喷射比例和二次喷射相位的合理优化能有效降低燃油消耗率和颗粒物排放;比较单次喷射和二次喷射策略,两种喷射策略颗粒物粒径分布均呈核态与积聚态的双峰分布,而在转速小于3 000 r/min、转矩大于105 N·m的工况条件下,运用二次喷射策略后燃油消耗率和颗粒物数量浓度相对于单次喷射均有明显降低,其中核态颗粒物占比增大,颗粒物平均几何粒径减小;其他工况下采用单次喷射策略的发动机经济性和排放性能更佳.     

增压直喷汽油机超级爆燃研究

缸内直喷和增压已成为当今汽油机技术的主流方向,然而,随着发动机小型化和动力性的提高,增压直喷汽油发动机出现了一种新的异常燃烧现象——超级爆燃,其严重影响着发动机性能和使用寿命。根据国内外超级爆燃的研究现状,在典型增压直喷汽油机上对不同的超级爆燃抑制方法进行了研究。结果表明:加浓、二次喷射、冷型火花塞都能够抑制超级爆燃。     

基于远后喷的DPF再生技术对发动机机油及抗拉缸性能研究

采用缸内远后喷技术进行柴油机颗粒过滤器(diesel particulate filter,DPF)再生。通过配制不同质量比的柴油和机油,分析机油黏度和闪点的变化趋势。采用特定循环进行机油老化验证和机油稀释试验,利用热重分析仪研究柴油和机油的挥发特性,并在机油黏度下限进行极限拉缸和高温拉缸试验。试验结果表明:随着燃油稀释率的增加,机油黏度和闪点呈下降趋势,且黏度到达下限值时,燃油稀释率为7%左右。远后喷不会引起柴油的不完全燃烧,也不会导致机油中烟炱(soot)的增加。随着再生次数的增加,机油黏度下降较快,至再生50次后,黏度未达到下限值。热重曲线可以看出柴油和机油的挥发温度差别较大,含7%柴油的机油在120℃会有少量挥发。最小间隙拉缸和高温拉缸试验完成后拆检缸套、活塞环、活塞等主要摩擦副,未出现异常磨损,发动机出现拉缸的风险较小。     

直喷汽油机气门积碳的成因与对策研究

针对在用汽油直喷发动机出现的气门积碳现象,对比缸内直喷汽油机与进气道喷射汽油机气门积碳组分与成因的差异,分析了缸内直喷汽油机进气门积碳的主要形成机理、影响因素和生成途径,其中气门表面温度、机油的物理和化学性能起了关键作用。在上述分析基础上,探讨了在发动机设计与应用层面减少进气门积碳的措施。     

增压直喷乙醇-汽油发动机超级爆震模拟

采用在压缩行程上止点前向燃烧室内直接喷入一定量机油液滴,模拟了悬浮在燃烧室内的机油液滴引燃可燃混合气诱发低速早燃(LSPI)现象的过程.试验验证了选用的计算模型及计算方法的可行性后,数值模拟了不同低速运转条件下、不同乙醇掺混比(体积分数)的乙醇-汽油混合燃料时,小缸径增压直喷发动机燃烧室内由机油液滴引发的低速早燃现象以及后续的超级爆震过程.结果表明:乙醇掺混比分别为10%和20%(E10、E20)时,发动机缸内依次发生了超级爆震燃烧;当乙醇掺混比为30%(E30)时,即使发生了早燃现象(1 200 r/min)并导致随后的爆震燃烧,但压力升高幅度明显降低,此时没有发生超级爆震燃烧;随着发动机转速提高(1 600 r/min),使用E30燃料时发动机缸内也仅发生了早燃现象,而没有发生爆震燃烧;当乙醇掺混比高于50%(E50)后,不同工况条件下发动机缸内已经没有低速早燃现象.使用乙醇-汽油混合燃料的小缸径增压直喷发动机在超级爆震发生前一定有低速早燃现象发生,但低速早燃现象不一定导致超级爆震过程.     

Oil strategies benefits over different driving cycles using numerical simulation

95 g/kin is the allowed quantity of CO2 emission normalized to NEDC to be set in 2020.In addition,NEDC will be replaced by more severe driving cycles and will be united worldwide.To respond to those criteria,automotive industries are working on every possible field.Thermal management has been proved to be effective in reducing fuel consumption.Cold start is a primordial reason of overconsumption,as the engine highest efficiency is at its optimal temperature.At cold start,the engine's oil is at its lowest temperature and thus its higher viscosity level.A high viscosity oil generates more friction,which is one of the most important heat losses in the engine.In this paper,hot oil storage is studied.Numerical simulations on GT-suite model were done.The model consists of a 4-cylinder turbocharged Diesel engine using a storage volume of 1 liter of hot oil.Ambient temperature variation were taken into consideration as well as different driving cycles.Furthermore,different configurations of the thermal strategy (multifunction oil sump) were proposed and evaluated.Lubricant temperature and viscosity profiles are presented in the article as well as fuel consumption savings for different configurations,driving cycles and ambient temperatures.     

棉籽油及其甲酯作柴油机燃料的试验研究

本文就棉籽油及其甲酯的燃料特性、相应的柴油机性能以及植物油酯的制备等进行了研究。研究表明棉籽油甲酯是一种比棉籽油更好的柴油机代用燃料。     

The effect of elevated fuel inlet temperature on performance of diesel engine running on neat vegetable oil at constant speed conditions

The concept that engine design is all important in the use of vegetable oils as a diesel fuel has been pointed out by many researchers. One hundred percent of vegetable oil can be used safely in an indirect injection engine, but not in a direct injection engine due to the high degree of atomization required for this type. This problem is related to increasing droplet size on injection into the cylinder that results in poor combustion. This in turn, causes the formation of deposits in the combustion chamber, together with oil dilution due to introduction of unburnt fuel into the crankcase. The objective of this work was to evaluate the effect of increasing fuel inlet temperature on viscosity and performance of a single cylinder, unmodified diesel engine. The overall results showed that fuel heating increased peak cylinder pressure and was also beneficial at low speed and under part-load operation. The high combustion temperature at high engine speed becomes the dominant factor, making both heated and unheated fuel to acquire the same temperature before fuel injection.     

二甲醚与重油复合燃料的燃烧与排放特性试验研究

由于具有较高的十六烷值,相对简单的化学结构、无碳烟排放以及易于与运送的特点,二甲醚被公认是最有发展潜力的柴油机代用燃料之一。而重油作为海洋运输中最主要的燃料,燃油品质低劣。在此项研究中,我们通过试验,在一台直燃式柴油机上燃用二甲醚和重油混合燃料,观察并测量排放情况。结果发现:二甲醚和重油复合燃料是一种有效的清洁代用燃料,能有效降低柴油机废弃物CO、HC和烟度的排放。     

乳化燃料油在船舶柴油机上的应用研究

为了实现乳化燃料油在船舶上的应用,研发了一套重油在线乳化装置,并在以G6300ZC18B型柴油机为动力的宁大6号运输船上进行实船试验.试验结果表明:当掺水率在16％-24％时,乳化质量好,可作为船舶燃料使用;乳化燃料油燃烧时,柴油机爆发压力在1 ～2 MPa间波动,排气温度平均下降12℃,冷却水出口温度略有下降,参数变化都处于正常范围内;平均节油率为9.7％,NOx、CO、碳烟排放平均分别降低19.6％、20％、35％.     

植物油发动机在JS6608汽车上应用的试验研究

柴油机直接燃用植物油燃料,存在启动困难、在怠速、低转速和小负荷等工况时燃烧排放性能差等问题。本文对原车柴油机燃料供给系统进行改进设计,应用控制单元对燃油供给系统进行控制,在启动、怠速、低转速和小负荷时给发动机供柴油,中高负荷时给发动机供植物油,实现柴油和植物油燃料的双供给。改装后整车道路试验表明,燃用植物油汽车运行可靠,动力性、经济性与原车相当,在中高负荷时燃烧和排放特性优于柴油车。     

油冷,轴针喷嘴直喷式柴油机燃烧系统分析

本文论述了采用机油高温冷却的轴针喷油器的直喷式柴油机燃烧过程的特点，对燃烧系统的布置，油束的雾化特性等参数进行了分析。     

Performance of direct-injection off-road diesel engine on rapeseed oil

This article presents the comparative bench testing results of a naturally aspirated, four stroke, four cylinder, water cooled, direct injection Diesel engine operating on Diesel fuel and cold pressed rapeseed oil. The purpose of this research is to study rapeseed oil flow through the fuelling system, the effect of oil as renewable fuel on a high speed Diesel engine performance efficiency and injector coking under various loading conditions.Test results show that when fuelling a fully loaded engine with rapeseed oil, the brake specific fuel consumption at the maximum torque and rated power is correspondingly higher by 12.2 and 12.8% than that for Diesel fuel. However, the brake thermal efficiency of both fuels does not differ greatly and its maximum values remain equal to 0.37–0.38 for Diesel fuel and 0.38–0.39 for rapeseed oil. The smoke opacity at a fully opened throttle for rapeseed oil is lower by about 27–35%, however, at the easy loads its characteristics can be affected by white coloured vapours.Oil heating to the temperature of 60 °C diminishes its viscosity to 19.5 mm² s⁻¹ ensuring a smooth oil flow through the fuel filter and reducing the brake specific energy consumption at light loads by 11.7–7.4%. Further heating to the temperature of 90 °C offers no advantages in terms of performance. Special tests conducted with modified fuel injection pump revealed that coking of the injector nozzles depends on the engine performance mode. The first and second injector nozzles that operated on pure oil were more coated by carbonaceous deposits than control injector nozzles that operated simultaneously on Diesel fuel.     

Performance and emission study of preheated Jatropha oil on medium capacity diesel engine

Diesel engines have proved its utility in transport, agriculture and power sector. Environmental norms and scared fossil fuel have attracted the attention to switch the energy demand to alternative energy source. Oil derived from Jatropha curcas plant has been considered as a sustainable substitute to diesel fuel. However, use of straight vegetable oil has encountered problem due to its high viscosity. The aim of present work is to reduce the viscosity of oil by heating from exhaust gases before fed to the engine, the study of effects of FIT (fuel inlet temperature) on engine performance and emissions using a dual fuel engine test rig with an appropriately designed shell and tube heat exchanger (with exhaust bypass arrangement). Heat exchanger was operated in such a way that it could give desired FIT. Results show that BTE (brake thermal efficiency) of engine was lower and BSEC (brake specific energy consumption) was higher when the engine was fueled with Jatropha oil as compared to diesel fuel. Increase in fuel inlet temperature resulted in increase of BTE and reduction in BSEC. Emissions of NO_x from Jatropha oil during the experimental range were lower than diesel fuel and it increases with increase in FIT. CO (carbon monoxide), HC (hydrocarbon), CO₂ (carbon dioxide) emissions from Jatropha oil were found higher than diesel fuel. However, with increase in FIT, a downward trend was observed. Thus, by using heat exchanger preheated Jatropha oil can be a good substitute fuel for diesel engine in the near future. Optimal fuel inlet temperature was found to be 80 °C considering the BTE, BSEC and gaseous emissions.     

Performance characteristics of a low heat rejection diesel engine operating with biodiesel

Vegetable oils are a promising alternative among the different diesel fuel alternatives. However, the high viscosity, poor volatility and cold flow characteristics of vegetable oils can cause some problems such as injector coking, severe engine deposits, filter gumming, piston ring sticking and thickening of lubrication oil from long-term use in diesel engines. These problems can be eliminated or minimized by transesterification of the vegetable oils to form monoesters. These monoesters are known as biodiesel. The important advantages of biodiesel are lower exhaust gas emissions and its biodegradability and renewability compared with petroleum-based diesel fuel. Although the transesterification improves the fuel properties of vegetable oil, the viscosity and volatility of biodiesel are still worse than that of petroleum diesel fuel. The energy of the biodiesel can be released more efficiently with the concept of low heat rejection (LHR) engine. The aim of this study is to apply LHR engine for improving engine performance when biodiesel is used as an alternative fuel. For this purpose, a turbocharged direct injection (DI) diesel engine was converted to a LHR engine and the effects of biodiesel (produced from sunflower oil) usage in the LHR engine on its performance characteristics have been investigated experimentally. The results showed that specific fuel consumption and the brake thermal efficiency were improved and exhaust gas temperature before the turbine inlet was increased for both fuels in the LHR engine.