Combustion stability analysis during engine stop and restart in a hybrid powertrain

A cycle-resolved analysis system was designed with the specified measurement instruments to investigate the characteristics of combustion stability in a mild gasoline hybrid powertrain. A Fast Response Flame Ionization Detector (FFID), cylinder pressure transducer and engine torque transducer were used to observe both the engine-out THC emissions and engine performance during a brief moment of engine restart. This research aimed to improve combustion stability and was performed by varying the battery State Of Charge (SOC), injection duration and ignition timing. The results indicate that engine combustion tends to be more stable with longer fuel injection durations and advanced ignition timing, while the effect of the battery SOC is negligible. Also, peculiar differences in the catalyst conversion efficiency at the front and rear of the catalyst during engine restart and deceleration were revealed, with the degree of HC oxidation being the suspected cause. This study not only analyzed the engine control and engine-out total hydrocarbon (THC) emission characteristics, but also implemented control strategies that allowed for combustion stability during engine stop and restart operation.     

Emissions simulation in a 7000 kg-grade diesel hybrid electric vehicle

Hybrids combine a combustion engine with an electric motor and battery. The two technologies can be combined to reduce fuel consumption and exhaust emissions. This paper presents the concept of hybrid electric vehicles (HEVs) applied to truck or van vehicles with diesel engines. The simulation results from the advanced vehicle simulator (ADVISOR) demonstrate that the required power may be properly shared between the internal combustion engine and electric motor. The simulation can also be used to prove that the technique is useful for improvements in driving performance; additionally, the technique is suitable for hybrid electric vehicles, allowing for good fuel economy and low emissions performance.     

Optimal fuel-cut driving method for better fuel economy

Eco-drive methods are being applied in modern passenger cars in the form of LCD displays showing real-time fuel consumption rates. The eco-drive is one of the most promising methods to enhance the fuel economy of vehicles. The ecodrive method can be made more effective by using the fuel-cut function. The fuel is not injected when the driver does not depress the gas pedal of a vehicle with engine speeds higher than approximately 1,500 rpm above the mid-vehicle speed range. This function is known as the fuel-cut function, and almost every modern vehicle is equipped with this function. The fuel-cut is most frequently activated on downhill sections of highway. Therefore, the CO₂ exhausted from the vehicle can be zero in this downhill section. In this study, the fuel-cut function is simulated with CRUISE of AVL to find the most effective driving pattern in downhill sections. Simulations with the CRUISE software showed that the lower limit of the vehicle speed for fuelcut should be raised to improve fuel economy on steeper downhill sections. The fuel economy can be optimized when the fuelcut coasting and reacceleration is completed in the downhill part of the road. The simulation result was also compared to previous test results. Fuel consumption was reduced by approximately 4% in both the experimental and simulated results for the West Coast Highway in South Korea.     

高原环境对缸内燃烧及壁面油膜的影响研究

为了分析高原环境下缸内燃烧过程及壁面油膜生成规律,采用 CFD 方法对不同海拔条件下柴油机燃烧过程进行了三维仿真计算,着重分析了海拔对壁面油膜的影响。结果表明：随海拔升高,过量空气系数降低,滞燃期延长,着火推迟,燃烧恶化,柴油机性能下降;高原条件对壁面油膜生成有较大影响,壁面累计油膜质量随海拔升高而增大,4500 m 海拔下壁面油膜累计质量最大可达19 mg ,约占总油量的8％;壁面油膜在燃油喷射弹着点处形成,随着时间推移,油膜向活塞边缘扩散,在高海拔条件下,燃烧结束时活塞边缘仍有油膜残留。     

Operating strategy for gasoline/diesel dual-fuel premixed compression ignition in a light-duty diesel engine

Environmental problems have become a major issue for diesel engine development. Although emission aftertreatment systems such as DPFs (diesel particulate filters), LNTs (lean NOx traps) and SCR (selective catalytic reduction) have been used in diesel vehicles, the manufacturing cost increase caused by this equipment can be hard to be control. Thus, it is better for engine emissions to be reduced by improving the combustion system. A dual-fuel combustion concept is a recommended method to improve a combustion system and effectively reduce emissions. Low reactivity fuel including gasoline and natural gas, which was supplied to the intake port by the FPI (port fuel injector), improved the premixed air-fuel mixture conditions before ignition. Additionally, a small amount of high reactivity fuel, in this case diesel, was injected into the cylinder directly as an ignition source. This dual-fuel combustion promises lower levels of NOx (nitrogen oxide) and PM (particulate matter) emissions due to the elimination of local rich regions in the cylinder. However, it is challenging to control the dual-fuel combustion because the combustion stability and efficiency deteriorate due to the lack of ignition source and reactivity. Thus, it is important to establish an appropriate dual-fuel operating strategy to achieve stable, high efficiency and low emission operation. As a result of this research, a detailed operating method of dual-fuel PCI (premixed compression ignition) was introduced in detail at a low speed and low load condition by using a single cylinder diesel engine. Engine operating parameters including the gasoline ratio, a diesel injection strategy consisting of multiple injectors and timing, the EGR (exhaust gas recirculation) rate and the intake pressure were controlled to satisfy the low ISNOx (indicated specific NOx) and PM emissions levels (0.21 g/kWh and 0.1 FSN, 0.040 g/kWh, respectively) as per the EURO-6 regulation without any after-treatment systems. The results emphasized that a well-constructed dual-fuel PCI operating strategy showed low NOx and PM emissions and high GIE (gross indicated fuel conversion efficiency) with excellent combustion stability.     

进气门关闭状态下喷油时刻对汽油机性能的影响

为了改善进气道喷射式发动机性能,采用台架试验和数值计算的方法对喷油时刻与进气道喷射式汽油机性能之间的关系进行了研究。研究结果表明：在进气门关闭状态下进行燃油喷射,发动机运行工况不同,喷油时刻对发动机性能的影响规律不同,小节气门开度时推迟喷油时刻会导致 HC 排放升高和发动机动力性下降,大节气门开度时喷油时刻的改变对发动机性能的影响可以忽略。通过数值计算分析发现该变化规律与附壁油膜挥发速率有直接关系,在小节气门开度条件下,附壁油膜无法完全挥发,会增加燃油以液态形式进入气缸的量,从而使发动机性能下降,而处于大节气门条件下,较高的机体温度使得附壁油膜挥发速率加快,降低液态燃油的量,从而改善发动机性能。因此,进气道喷射发动机可以在小节气门开度时采用两次燃油喷射方式提升发动机性能,而在大节气门开度下则无需考虑喷油时刻的影响。     

PFI汽油机空燃比控制仿真及试验研究

基于发动机台架试验,建立并标定了进气道燃油喷射单缸汽油机一维仿真模型,探索了空燃比控制的新方法。依据经典控制理论,通过所建空燃比PID控制器与参数整定,实现了稳态空燃比控制。基于x-τ油膜模型,提出了其代数控制X-Y油膜方程,分析了进气道燃油传输过程对空燃比控制的影响;通过燃油阶跃扰动法,对X,Y参数进行识别,获得了X,Y参数MAP图,构建了离散化燃油动态补偿器,实现了空燃比在瞬态工况下的前馈控制。     

汽油喷雾碰壁和油膜形成的可视化试验与数值模拟

进气道喷射汽油机混合气形成对燃烧和排放起着重要的作用。为了研究汽油喷雾碰壁过程,利用定容燃烧弹进行了汽油喷雾碰壁直接高速摄影,研究了不同倾斜角度壁面、不同壁面粗糙度和碰壁距离等对喷雾碰壁和油膜形成的影响。在此基础上,利用CFD软件建立了定容燃烧弹内汽油喷雾碰壁和油膜形成过程的三维数值模型。测量了定容燃烧弹内的压力,并与理论值进行了对比分析。研究结果为汽油机进气道喷射系统的设计提供了参考。     

Reduction of engine emissions via a real-time engine combustion control with an egr rate estimation model

Vehicle emissions regulations are becoming increasingly severe and remain a principal issue for vehicle manufacturers. Since, WLTP (Worldwide harmonized Light vehicles Test Procedures) and RDE (real driving emission) regulations have been recently introduced, the engine operating conditions have been rapidly changed during the emission tests. Significantly more emissions are emitted during transient operation conditions compared to those at steady state operation conditions. For a diesel engine, combustion control is one of the most effective approaches to reduce engine exhaust emissions, particularly during the transient operation. The concern of this paper is about reducing emissions using a closed loop combustion control system which includes a EGR rate estimation model. The combustion control system calculates the angular position where 50 % of the injected fuel mass is burned (MFB50) using in-cylinder pressure for every cycle. In addition, the fuel injection timing is changed to make current MFB50 follow the target values. The EGR rate can be estimated by using trapped air mass and in-cylinder pressure when the intake valves are closed. When the EGR rate is different from the normal steady conditions, the target of MFB50 and the fuel injection timing are changed. The accuracy of the model is verified through engine tests, as well as the effect of combustion control. The peaks in NO level was decreased during transient conditions after adoption of the EGR model-based closed loop combustion control system.     

涡轮增压气道喷射汽油机工作过程性能优化

本文对某涡轮增压气道喷射汽油机进行了工作过程性能优化。首先根据实验结果,进行了同系列自然吸气汽油机工作数值模拟模型的标定;然后以该标定后模型为基础,建立了涡轮增压气道喷射汽油机工作过程数值模拟模型;再利用此模型进行了7种涡轮增压器的选型和匹配计算,确定了合适的涡轮增压器;最后分析了压缩比、进排气歧管结构、凸轮升程与配气相位等对该汽油机动力性、经济性的影响,并进行了相应的汽油机参数和结构优化。     

Topological analysis of powertrains for refuse-collecting vehicles based on real routes–Part II: Hybrid electric powertrain

In this two-part paper, a topological analysis of powertrains for refuse-collecting vehicles (RCVs) based on simulation of different architectures (internal combustion engine, hybrid electric, and hybrid hydraulic) on real routes is proposed. In this second part, three different hybrid electric powertrain architectures are proposed and modeled. These architectures are based on the use of fuel cells, ultracapacitors, and batteries. A calculation engine, which is specifically designed to estimate energy consumption, respecting the original performance as the original internal combustion engine (ICE), is presented and used for simulations and component sizing. Finally, the overall performance of the different architectures (hybrid hydraulic, taken from the first paper part, and hybrid electric, estimated in this second part) and control strategies are summarized in a fuel and energy consumption table. Based on this table, an analysis of the different architecture performance results is carried out. From this analysis, a technological evolution of these vehicles in the medium- and long terms is proposed.     

Transient characteristics of emissions during engine start/stop operation employing a conventional gasoline engine for HEV application

In this paper, we investigate the transient characteristics of combustion and emissions during engine start/stop operations in hybrid electric vehicle (HEV) applications. Hydrocarbon (HC) emissions during the initial 2^nd∼9^th cycles are found to be significantly greater when the engine is quickly started under the original engine calibration mode. Lower intake manifold absolute pressure (MAP) was also found to cause larger residual gas dilution and poor combustion, resulting in a higher HC concentration when the cranking speed was increased. The post-catalyst HC concentration was found in the way of initially decrease and then to increase again as the cranking speed was increased. A lowest concentration value was achieved at a cranking speed of 1000 r/min. Engine shut-down by fuel cut-off was shown to produce lower emissions than shut-down by ignition cut-off as one can avoid misfire of the last fuel injection cycle. The fuel deposited during the stop process seems to impact engine restart enrichment mostly during the initial 0.7 s for this engine, whose performance is dominated by the MAP transition characteristic and the time coefficient for fuel vaporization in this time period     

Exhaust nanoparticle emissions from internal combustion engines: A review

This paper reviews the particle emissions formed during the combustion process in spark ignition and diesel engine. Proposed legislation in Europe and California will impose a particle number requirement for GDI (gasoline direct injection) vehicles and will introduce the Euro 6 and LEV-III emission standards. More careful optimization for reducing particulate emission on engine hardware, fuel system, and control strategy to reduce particulate emissions will be required during cold start and warm-up phases. Because The diesel combustion inherently produces significant amounts of PM as a result of incomplete combustion around individual fuel droplets in the combustion zone, much attention has been paid to reducing particle emissions through electronic engine control, high pressure injection systems, combustion chamber design, and exhaust after-treatment technologies. In this paper, recent research and development trends to reduce the particle emissions from internal combustion engines are summarized, with a focus on PMP activity in EU, CARB and SAE papers and including both state-of-the-art light-duty vehicles and heavy-duty engines.     

Effect of fuel injection strategies on the combustion process in a PFI boosted SI engine

A low-cost solution based on fuel injection strategies was investigated to optimize the combustion process in a boosted port fuel injection spark ignition (PFI SI) engine. The goal was to reduce the fuel consumption and pollutant emissions while maintaining performance. The effect of fuel injection was analyzed for the closed and open valve conditions, and the multiple injection strategies (MIS) based on double and triple fuel injection in the open-valve condition. The tests were performed on an optical accessible single-cylinder PFI SI engine equipped with an external boost device. The engine was operated at full load and with a stoichiometric ratio equivalent to that of commercial gasolines. Optical techniques based on 2D-digital imaging were used to follow the flame propagation from the flame kernel to late combustion phase. In particular, the diffusion-controlled flames near the valves and cylinder walls, due to fuel deposition, were studied. In these conditions, the presence of soot was measured by two-color pyrometry, and correlated with engine parameters and exhaust emissions measured by conventional methods. The open valve fuel injection strategies demonstrated better combustion process efficiency than the closed ones. They provided very low soot levels in the combustion chamber and engine exhaust, and a reduction in specific fuel consumption. The multiple injection strategies proved to be the best solution in terms of performance, soot concentration, and fuel consumption.     

换气与压缩过程对汽油机燃烧特性的影响研究

针对增压气道喷射汽油机进行了发动机换气与压缩过程对燃烧特性的影响研究,对比了两种状态下的气门升程与配气正时,基于发动机试验台架测试数据,重点分析了发动机动力性、经济性和燃烧特性。试验数据表明了配气相位的改变对燃烧有较大的影响,可使燃烧效率大幅度提高,爆震倾向减小。同时基于AVL-fire软件进行发动机进气与压缩过程三维CFD分析,分析结果表明:对燃烧特性的影响不能仅靠瞬态滚流比和缸内平均湍动能进行判断,真正影响燃烧的是火花塞附近湍动能的变化,即发动机换气与压缩过程对燃烧特性的影响来自压缩上止点火花塞附近的湍动能。     

Topological analysis of powertrains for refuse-collecting vehicles based on real routes–Part I: Hybrid hydraulic powertrain

In this two-part paper, a topological analysis of powertrains for refuse-collecting vehicles (RCVs) based on the simulation of different architectures (internal combustion engine, hybrid electric, and hybrid hydraulic) on real routes is proposed. In this first part, a characterization of a standard route is performed, analyzing the average power consumption and the most frequent working points of an internal combustion engine (ICE) in real routes. This information is used to define alternative powertrain architectures. A hybrid hydraulic powertrain architecture is proposed and modelled. The proposed powertrain model is executed using two different control algorithms, with and without predictive strategies, with data obtained from real routes. A calculation engine (an algorithm which runs the vehicle models on real routes), is presented and used for simulations. This calculation engine has been specifically designed to analyze if the different alternative powertrain delivers the same performance of the original ICE. Finally, the overall performance of the different architectures and control strategies are summarized into a fuel and energy consumption table, which will be used in the second part of this paper to compare with the different architectures based on hybrid electric powertrain. The overall performance of the different architectures indicates that the use of a hybrid hydraulic powertrain with simple control laws can reduce the fuel consumption up to a 14 %.     

基于多维模型的电喷汽油机MAP图的数值生成

将DPIK点火模型和单步燃烧模型集成在K IVA-3V中,构建汽油机MAP研究的多维模型。对汽油机工作过程进行数值模拟,并以动力性、经济性和指示功为控制条件,结合试验数据对点火提前角和喷油脉宽进行优化。研究表明:用多维模型模拟的方法生成的MAP可以作为电喷汽油机的初始MAP。     

螺旋气门的结构优化及对无节气门汽油机燃烧性能的影响

由于进气方式的改变,气道喷射式无节气门汽油机中小负荷时泵气损失显著降低,但燃烧性能却明显恶化.为改善其燃烧性能,本文中设计了一种在进气过程中能产生较强进气涡流的螺旋气门,并使用仿真软件STAR-CCM+对螺旋气门的主要结构参数进行了优化.在稳流气道试验台上测量其进气涡流比和流量系数,证明该螺旋气门在开启升程较小时能产生...     

发动机采用BOOST建模和与CRUISE联合仿真的研究

利用AVL公司开发的BOOST软件可宏观地描述发动机的热力学过程且优化发动机的性能,而AVL的CRUISE软件可调用BOOST建立的发动机模型.在进行道路循环工况的仿真时,须对发动机全部工况点进行准确的标定.文中采用BOOST开发了发动机的仿真模型.通过调整节气门开度和燃烧模型参数,标定了发动机在多个转速和负荷点的转矩、功率和油耗,较好地模拟了发动机的动力性和经济性.最后基于ECE循环工况,将此模型与CRUISE进行联合仿真,分析了发动机瞬态工况的动力性、油耗和NO_x排放等参数.     

车用汽油机稀薄燃烧的实现及排放特征分析

研究了车用465汽油机稀薄燃烧的实现与机内净化策略,借助于缸内存在的滚流运动,采用适当的气道内喷射方式,实现了均质稀薄燃烧,不同负荷时的稀燃极限可达21~22,分析了汽油机稀燃排放的特征,NOx排放先升高后降低,HC和CO排放明显降低,合理控制稀燃空燃比,可降低NOx排放。