Test Research on the Knock of a Common-Rail Diesel Engine Fueled with Diesel-Methanol Dual-Fuel

Experiments were conducted on a diesel-methanol dual-fuel(DMDF)engine modified by a six-cylinder,turbocharged,inter-cooled diesel engine.According to the number of diesel injection,the experiments are divided to two parts:the single injectionmode and double injectionmode.The results show that,at the double injectionmode,themaximumof pressure rise rate is small and the engine runs smoothly,however,knock still occurswhen the cocombustion ratio(CCR)is big enough.Under knock status,the power density of the block vibration concentrating at some special frequencies rises dramatically,and the special frequency of single injection mode(about 4.1 kHz)is lower than that of double injection mode(7–9 kHz).The cylinder pressure oscillations of knock status are very different fromthe non-knock status.Under knock status,cylinder pressure oscillations become more concentrated and fiercer at some special frequencies,and the same as the block vibration.The special frequency of single injection mode(3–6 kHz)is lower than that of double injection mode(above 9 kHz).

STRATEGY FOR DIESEL ROTARY ENGINE WITH COMMON RAIL INJECTION SYSTEM

A direct injection low compression ratios diesel rotary engine is designed and studied to find the appropriate application of the electronic controlled high pressure common rail injection system. Current development focuses on the applied fuel injection and ignition strategies, especially concerning the combustion configurations of injectors, ignition source, and combustion chamber. The prototype engine, equipped with Bosch common rail system and high performance electronic control unit （ECU）, is designed correspondingly. Studies show that the integration of a common rail injection system and the main and pilot duel injectors configurations, assisted with glow plug ignition device and flexible ECU, represents a promising approach to improve the potential of the low compression ratios diesel rotary engine. Currently the engine can run at 6 kr · min^-1 steadily and the power is about 68 kW/（4 kr ·min^- 1）.

Elimination of Fuel Pressure Fluctuation and Multi-injection Fuel Mass Deviation of High Pressure Common-rail Fuel Injection System

The influence of fuel pressure fluctuation on multi-injection fuel mass deviation has been studied a lot,but the fuel pressure fluctuation at injector inlet is still not eliminated efficiently.In this paper,a new type of hydraulic filter consisting of a damping hole and a chamber is developed for elimination of fuel pressure fluctuation and multi-injection fuel mass deviation.Linear model of the improved high pressure common-rail system（HPCRS）including injector,the pipe connecting common-rail with injector and the hydraulic filter is built.Fuel pressure fluctuation at injector inlet,on which frequency domain analysis is conducted through fast Fourier transformation,is acquired at different target pressure and different damping hole diameter experimentally.The linear model is validated and can predict the natural frequencies of the system.Influence of damping hole diameter on fuel pressure fluctuation is analyzed qualitatively based on the linear model,and it can be inferred that an optimal diameter of the damping hole for elimination of fuel pressure fluctuation exists.Fuel pressure fluctuation and fuel mass deviation under different damping hole diameters are measured experimentally,and it is testified that the amplitude of both fuel pressure fluctuation and fuel mass deviation decreases first and then increases with the increasing of damping hole diameter.The amplitude of main injection fuel mass deviation can be reduced by 73%at most under pilot-main injection mode,and the amplitude of post injection fuel mass deviation can be reduced by 92%at most under main-post injection mode.Fuel mass of a single injection increases with the increasing of the damping hole diameter.The hydraulic filter proposed by this research can be potentially used to eliminate fuel pressure fluctuation at injector inlet and improve the stability of HPCRS fuel injection.

Characteristics of Diesel/N-Butanol Blend on a Common Rail Diesel Engine with Exhaust Gas Recirculation

20%n-butanol is blended in diesel by volume(noted as D80B20)and experiment has been carried out to study the effect on the combustion and emission characteristics based on a common rail diesel engine with exhaust gas recirculation(EGR)system.The results reveal thatD80B20 has longer ignition delay,shorter combustion duration and higher maximumin-cylinder temperature than pure diesel(noted as D100).Further,the number concentration and volume concentration of ultrafine particles decrease significantly while NO_(X) emissions increase a little with the addition of n-butanol.When the exhaust gas is induced into cylinder,NO_(X) emissions significantly decrease and ultrafine particles emissions increase.The number geometric mean diameters and volume geometricmean diameters of ultrafine particles increase withEGR ratio.Compared toD100 without EGR,D80B20 with 20%EGR ratio can reduce both NO_(X) and ultrafine particles emissions at 0.14MPa BMEP and 0.56MPa BMEP.

Frequency compensation control method for opposedpiston two-stroke folded-cranktrain engine's common rail system by loop-shaping theory

A frequency compensation control method for the opposed-piston two-stroke folded-cranktrain（ OPFC） diesel engine＇s common rail system is presented as a result of the study of the loop-shaping theory. A common rail working process and the classical frequency control theory are combined to construct a frequency restriction of common rail pressure. A frequency compensator is utilized to improve the robustness of multiplicative perturbations and disturbance. The loop-shaping method has been applied to design the common rail pressure controller of the OPFC diesel engine. Simulation and bench test results show that in the condition of perturbation that comes from the effect of injection,multi-injection,fuel pumping of a pre-cylinder,and instantaneous pressure fluctuation,the controller indicates high precision. Compared with the original controller,this method improves the control precision by 67. 3%.

EFFECTS OF INJECTION STRATEGY ON D.I. DIESEL ENGINE COMBUSTION

Experiments are conducted to develop an understanding of how split injections can affect the combustion and emission characteristics of a D.I. diesel engine with a common-rail injection system. The ratio of the amount of fuel injected between two injection pulses and the injection interval is varied keeping the injected fuel quantity constant. Results show that under the 70D90-10 injection pattern, the engine achieves the lower NOx-smoke emissions and BSFC compared with the single injection pattern. The heat release rate and the temperature show that the split injections increase the initial premixed burn and retards the diffusion burn. With the balance of these two effects, the maximum in-cylinder temperature decreases while the 50% heat release point is held at almost the same crank angle. Therefore, both NOx emission and BSFC are improved while keeping the smoke emission at the same level.

An experimental study on RP-3 jet fuel injection on a common rail injection system

RP-3 jet fuel could be an alternative fuel for diesel engines.In this study,the injection characteristics of RP-3jet fuel under single and split injection strategies were investigated and compared with diesel fuel.The experimental results indicate that RP-3 jet fuel has slightly shorter injection delay time than diesel fuel,but this difference is negligible in actual engine operations.Further,although the lower density and viscosity of RP-3 jet fuel lead to higher volumetric injection rates and cycle-based injection quantities,the cycle-based injection mass and the mass injection rates at the stable injection stage of RP-3 jet fuel are close to or slightly lower than those of diesel fuel.Based on these experimental observations,it could be concluded that fuel physical properties are the secondary factor influencing the injection characteristics in both single and split injection strategies,as RP-3 jet fuel and diesel fuel are taken for comparison.

国六柴油机轨压和喷油正时对柴油机性能的影响

为优化柴油机性能,基于一台配备了完整国Ⅵ后处理系统的高压共轨直列4缸柴油机,开展了柴油机负荷特性研究,在此基础上研究轨压和喷油正时对柴油机性能的影响。研究结果表明:以适当较小的轨压配合较为提前的喷油正时可以达到较为理想的柴油机油耗及排放;轨压和喷油正时对HC排放的影响较小;轨压对柴油机油耗、排温、NOx排放、CO排放的影响较大,且在中等偏高负荷时更为敏感,随着轨压增加了57 MPa,柴油机油耗、排温分别下降了16.1 g/(kW·h)、63℃,NOx排放上升了663×10^(-6),CO排放下降了785×10^(-6);喷油正时对烟度及柴油机氧化催化器前端温度T4、柴油机颗粒捕集器前端温度T5、选择性催化还原系统前端温度T6的影响较大,且在低负荷时更为敏感。随着喷油正时提前6.0°,烟度下降了0.43%,T4、T5、T6峰值出现在轨压为76 MPa且喷油正时为上止点前7.5°时,温度分别为315.3、338.4、329.3℃。

高压共轨柴油机国产芯片控制系统研究

针对现有高压共轨柴油机电控单元高度依赖进口芯片、自主不足的问题,提出了基于全国产芯片的高压共轨柴油机电控单元方案。所设计的国产控制单元选用兆易创新的GD32F450芯片为控制核心,承担发动机数据采样、处理、存储与控制任务。首先,采用Boost升压电路提供喷油器峰值电流,利用分立器件设计双边驱动与电流反馈电路,在不依赖进口专用芯片的条件下,对喷油器驱动电流进行闭环控制;然后,基于FreeRTOS操作系统,开发高压共轨柴油机底层驱动软件,实现对不同任务调度周期的精准控制;最后,对所设计的电控单元进行了实验验证。结果表明,所设计的国产高压共轨柴油机电控单元功能齐全、工作稳定,双边驱动电路典型峰值电流为22 A,维持电流为10 A,最小喷射间隔时间为200μs,多次喷射性能与Bosch系统相当。发动机不同转速条件下任务调度周期精准、实时性好,研究证实了高压共轨柴油机电控单元全国产化方案的可行性,对推动发动机电控技术自主可控提供了有益参考。

引燃柴油量对双燃料发动机循环变动的影响

为了降低重型高压共轨柴油机燃用LNG-柴油的燃烧循环变动,优化引燃柴油量控制,通过双燃料发动机试验台架,研究了在最大转矩转速1600r/min,功率输出为73kW工况下,随引燃柴油喷油量的增加,峰值压力、峰值压力升高率、平均指示压力循环变动的变化趋势。研究结果表明,随引燃柴油量的增加,双燃料发动机的峰值压力、峰值压力升高率和平均指示压力的循环变动趋势相同,它们的均值均增大,标准差减小,循环分布集中,循环变动系数降低。在不导致爆震燃烧的前提下,适当增大引燃柴油量,能够改善双燃料发动机的燃烧稳定性。

喷油器柱塞副动态泄漏及特性

为了研究高压共轨喷油器柱塞副的动态泄漏特性,建立了柱塞副间隙燃油流动的数学模型,通过有限差分法对数学模型进行数值计算,研究了不同轨压下柱塞副燃油的平均动态泄漏率的变化趋势,与试验值进行对比,验证该数学模型的有效性,并分析了轨压、进口燃油温度、柱塞最大升程和喷射脉宽四种因素对柱塞副动态泄漏量的影响及在不同柱塞速度下,油膜压力、厚度和温度参数的变化趋势。结果表明,在一个喷油循环内,动态泄漏率的变化曲线与控制腔油压变化曲线相似,平均动态泄漏率随着喷油器的轨压、入口燃油温度和柱塞最大升程的增加而增加,但随着喷射脉宽的增加而减小;随着柱塞速度由正速度到负速度的过程,油膜的厚度逐渐变薄,油膜的温度整体上升,油膜的压力变小。

高压油泵阻尼孔对燃油系统压力特性的影响研究

为实现更高的热效率和更优的排放,柴油机的喷射压力不断提高。阻尼孔作为高压油泵等压出油阀的关键结构,对燃油系统的压力特性有重要影响。本文研究了阻尼孔大小对喷油器的喷射特性以及高压油管压力波动特性的影响,结果表明:随着阻尼孔由0.1 mm增大至2.0 mm,喷油器喷油持续期相对缩短,循环喷油量减小,这是不同阻尼孔对应的高压油管残余压力大小不同,以及不同阻尼孔大小对系统压力调节的速度不同的结果;此外,阻尼孔较小(0.1 mm)时,燃油系统存在二次喷射现象,而阻尼孔过大(3 mm)时,系统内还会存在零压区,即存在穴蚀的风险;对高压油管残余压力的频谱分析发现,阻尼孔较小时,高压油管内压力脉动与出油阀的运动存在较强的相关性,而阻尼孔较大时,压力脉动与回油阀的运动相关,即供油系统中多种阀件的运动是高压油管压力脉动的主要原因。

汽车发动机高压共轨系统轨压特性分析与优化

基于关键零/部件参数,建立了汽车发动机高压共轨喷射系统的数学模型,使用AMESim软件进行仿真模拟,并通过试验分析验证了该仿真模型的准确性。通过对系统轨压波动和压力特性进行仿真分析,得出共轨管长度、内径和高压油管内径是影响系统轨压特性的重要参数。针对原始共轨管和高压油管模型,利用响应曲面法对共轨管和高压油管参数进行优化分析,并得出以平均轨压设定值为目标的共轨管和高压油管的最佳结构参数。经过优化后,汽车发动机高压共轨喷射系统的平均轨压提高了0.65%,整体轨压波动平均值降低了79.48%,单次喷射过程中轨压波动平均值降低了27.89%,平均喷油压力提高了0.63%,其喷油特性得到明显的改善。

非道路柴油机冷却水套流动传热分析与优化

冷却水套作为柴油机的核心结构,其流动与传热特性直接影响着柴油机的可靠性和使用寿命。以某两缸高压共轨柴油机为研究对象,为了解该发动机冷却水套流动与传热性能,以水套速度场、温度场、换热系数等空间分布参数为判据,重点对冷却水套关键区域的流动和传热特性进行分析,同时提出优化方案。仿真结果表明:发动机整体冷却液流动性差,平均流速低于0.5m/s,缸体进气侧冷却水套上部出现了流动死区;通过对冷却系统性能参数和冷却水套结构进行优化,冷却水套进出口压力损失减小,整体冷却液平均流速较原方案提高了173.91%,整体平均换热系数较原方案提高了41.93%,整体冷却水套流动均匀性得到改善。

双升程电控喷油器多次喷射油量波动特性研究

为实现船用柴油机高压共轨系统喷射的柔性和稳定控制,提出一种双升程电控喷油器,基于搭建的喷油器AMESim仿真模型,探究了喷油器不同多次喷射模式下的油量波动特性.结果表明:大升程预喷模式下的主喷量标准差随预喷量的增加先上升后下降,而小升程预喷模式下的主喷量标准差随预喷量呈幅值逐渐降低的波动变化趋势.总体上,在预喷量为161~660 mm^(3)范围,小升程预喷模式在降低主喷量波动程度方面比大升程预喷模式更占优势.预喷射采用小升程喷射模式且预喷量一定时,升程切换延迟为0.2 ms的靴形主喷模式在降低主喷量波动程度方面略优于相同主喷脉宽或相同单次喷射油量的大升程主喷模式.大升程和小升程后喷模式下的后喷量标准差随主喷脉宽和目标后喷量均呈波动变化趋势,且小升程后喷模式下的后喷量标准差波动程度更小.与大升程后喷模式相比,小升程后喷模式在降低后喷量波动程度方面更占优势.

基于堆叠稀疏自编码器的多缸喷油器堵塞定位算法

燃油喷射系统的工作质量直接影响柴油机工作过程及性能,针对多缸机不同喷油器发生堵塞故障且故障程度不一时,传统故障诊断方法难以精准定位故障喷油器的问题,提出一种基于堆叠稀疏自编码器(Stacked Sparse Autoencoder,SSAE)的故障定位算法。通过SSAE提取不同喷油器发生堵塞故障时轨压信号的深层特征,以softmax网络实现故障部件定位。以一维轨压信号为输入,故障喷油器定位为输出,并研究算法超参数对算法精度的影响。研究结果表明,此算法能精准定位发生堵塞故障的喷油器,且精度不受堵塞程度的影响,故障诊断正确率可达96.7%。

EEMD—模糊聚类在共轨系统故障诊断上的应用研究

高压共轨柴油机作为一种往复式运行的机械,其故障的发生是一个具有模糊性的渐变过程。针对高压共轨柴油机供油系统故障程度诊断中出现的特征值识别困难,分类界限模糊等问题,提出了一种基于EEMD(集合经验模态分解)—模糊聚类的故障诊断方法。通过EEMD将供油系统轨压信号分解为一系列的IMF(固有模态函数),利用过零率曲线确定的特征提取准则并提取本征模态函数中的特征值,建立模糊聚类模型进行故障程度的诊断。在此基础上通过台架实验获得轨压信号,提取了相关特征值进行识别,分析了诊断结果,验证了该方法的正确性。

回油背压对高压共轨喷油器喷油特性影响的研究

高压共轨喷油器是柴油机高压共轨电控系统中最重要的一个部件,其喷油特性(如喷油器量)的优劣将直接影响发动机的性能表现。喷油器的喷射特性不仅受到喷油器的结构参数的影响,同时在喷射过程中还受到外界工作环境的影响,比如喷油器喷射时发动机缸内的背压,以及喷油器工作时的回油通道中的背压。本文主要对某高压共轨喷油器进行台架试验测试,研究喷油器回油背压对喷油特性的影响,并分析产生影响的原因,为开发新型的燃油喷射系统提供试验数据。

叉车柴油机加速工况声品质改进试验研究

为降低某叉车柴油机加速过程中的噪声,试验分析柴油机加速异响产生的原因,研究喷油规律对加速噪声的影响,分析声品质参数,并提出改进方案。试验结果表明:柴油机急加速“嘎嘎”声是由燃烧过程缸内压力升高率过大导致,增加预喷量可以在一定程度上降低噪声水平,但对加速异响几乎没有影响;减小喷油提前角可以轻微降低加速异响;降低轨压上升率可以明显降低加速异响,轨压上升率由150 MPa/s降低至100 MPa/s,柴油机加速时异响消失,响度的变化趋势与声压级基本一致,尖锐度和粗糙度降低,声品质明显提升。

基于LabVIEW的比例压力控制阀自动测试系统

根据某公司比例压力控制阀的出厂测试要求,本文设计了一套比例控制阀自动测试系统。该系统基于LabVIEW编程和PLC控制,可实现共轨管稳定的超高压供给,并自动实现比例压力控制阀的耐久测试、流量滞环测试及压力-流量测试,且操作简便,满足企业需求。