预喷射对柴油机瞬态工况燃烧噪声控制策略的试验研究

通过瞬态与稳态工况燃烧噪声测试试验,开展预喷射对柴油机瞬态工况燃烧噪声控制的研究。从缸内压力升高率最大值来分析预喷射对瞬态与稳态工况燃烧噪声不同的影响机理。通过分析预喷射对瞬态工况与稳态工况燃烧噪声的控制差异,得出预喷射同样能够降低瞬态工况燃烧噪声,但控制效果低于稳态工况。在此基础上,得出预喷射控制瞬态工况燃烧噪声的策略:相对于稳态工况,瞬态工况下应取较大的预喷量和与主预喷间隔,并得到试验的验证。     

增压前后柴油机燃烧噪声的对比分析

通过测量稳态和恒转速增扭矩瞬态工况增压前后影响燃烧噪声的参数,对比分析得出增压前后柴油机燃烧噪声的变化规律.结果表明:增压后燃烧噪声降低,增压对稳态工况燃烧噪声的降低比对恒转速增扭矩瞬态工况明显,增压在中速中负荷工况下,对燃烧噪声的控制效果较好.并从压力高频振荡、气体动力载荷和燃烧室壁面温度对试验结果进行了分析,证明了增压前后燃烧室壁面温度的差异影响增压前后柴油机燃烧噪声.     

直喷式柴油机瞬态工况燃烧噪声的试验研究与分析

研究直喷式柴油机瞬态工况对燃烧噪声影响机理。开展内燃机瞬态工况测试技术和测试方法研究，找出瞬态工况下燃烧噪声相对于同转速、同负荷的稳态工况燃烧噪声差异的规律，并从瞬念与稳态工况下燃烧过程的差异对试验结果进行分析。瞬态工况擘面温度、喷油爪力、针阀升程最大值和针阀外启持续时问均高于同负荷同转速的稳态工况，导致瞬态工况滞燃期、燃烧始点和喷油最与稳态工况相比产生差异。结果表明，瞬态工况下动力负荷和压力高频振荡相对于同负荷同转速的稳态工况发生改变是引起燃烧噪声产生差异的根本原因。     

柴油机恒转矩增转速瞬态工况的烟度及燃烧特性分析

采用自行设计的瞬态工况控制及测量系统对增压中冷柴油机进行了恒转矩增转速瞬态工况下发动机的空燃比、消光烟度及示功图参数的测试，并与稳态数据进行了对比。试验结果表明：在瞬态工况下，发动机的外部参数及燃烧过程参数与稳态过程存在很大的差异，其差异程度随工况瞬变性加剧而增加。随转速增加率的上升空燃比减小，燃烧持续期延长，扩散燃烧比增加，导致排气烟度上升。     

EGR对直喷式柴油机瞬态工况燃烧噪声影响的试验研究

设计了合适的废气再循环(EGR)系统和试验方案,通过测量引入EGR前后影响燃烧噪声的参数,开展EGR对直喷式柴油机瞬态工况燃烧噪声影响的研究.研究结果表明:引入合适的EGR量,可以降低柴油机瞬态工况燃烧噪声,使大部分负荷工况的柴油机瞬态工况辐射噪声降低1dB以上,且对动力性能影响不大.针对试验结果的分析表明:合适的EGR率使得瞬态工况过程的压力升高率降低,压力高频振荡幅值减小,从而引起相应的燃烧噪声的降低.     

柴油机瞬态工况烟度排放特性及分析

为了研究车用柴油机瞬态工况中,燃烧边界条件对燃烧过程的影响,在试验台上针对增压中冷柴油机在恒转速增转矩瞬态工况下的烟度排放特性进行了试验,并用商业计算软件STAR-CD对此瞬态工况下柴油机的燃烧过程进行了数值模拟分析。针对增压柴油机低转速大负荷排烟较差的特点,试验中发动机转速定为1000r／min,以3种不同的转矩变化率来考察柴油机瞬态工况下的排烟特性。结果表明,柴油机瞬态工况下和稳态工况下的燃烧边界条件有很大的差别,这种差别导致了柴油机瞬态工况下的烟度排放值要明显高于其相应的稳态工况。计算结果表明,随着转矩变化率的升高,最大初始放热率升高及燃烧持续期延长,这些差异同样导致排气烟度值增加。     

直喷式柴油机瞬态工况燃烧噪声二级影响机理研究

研究直喷式柴油机瞬态工况燃烧噪声二级影响机理。设计瞬态与稳态工况燃烧噪声试验，测量燃烧噪声二级影响因素，分析瞬态工况下壁面温度、油管压力和针阀升程等间接因素影响动力负荷与压力高频振荡，从而影响燃烧噪声的二级影响机理，并对不同供油提前角瞬态工况燃烧噪声二级影响机理进行了研究。结果表明，瞬态工况壁面温度、油管压力、针阀升程及针阀开启时间均高于同负荷同转速的稳态工况，影响到瞬态工况滞燃期以及滞燃期的喷油量，进而影响动力负荷和压力高频振荡，使得瞬态与稳态工况燃烧噪声产生差异。     

直喷式柴油机瞬态工况燃烧噪声机理

通过测量瞬态工况与稳态工况燃烧噪声的各种影响参数,研究气体动力载荷及燃烧压力高频振荡对燃烧噪声的影响机理．瞬态工况的壁面温度、喷油压力、针阀升程最大值和针阀开启持续时间均高于同负荷、同转速的稳态工况,导致瞬态工况滞燃期、燃烧始点和喷油量与稳态工况相比产生差异,引起燃烧压力、庄力升高率及高频压力振荡频率和幅值发生变化．结果表明,瞬态工况与同负荷、同转速的稳态工况相比,着火延迟期缩短,但每循环喷油量增大,燃烧噪声增大．     

高压中冷EGR对直喷增压发动机油耗影响的试验研究

基于某一直喷增压发动机,研究了EGR对发动机小负荷油耗的影响。结果表明：在改善油耗方面,原发动机使用进气门晚关策略优于使用内部EGR策略;在低转速小负荷工作区域,外部中冷EGR对油耗的贡献主要来自于降低了泵气功,但是过多的EGR气体引入容易导致燃烧不稳;使用高压EGR时,最佳的进排气VVT角度与无EGR时相同。     

瞬态工况对内燃机燃烧噪声的影响研究

研究了内燃机瞬态工况对燃烧噪声影响机理,开展了内燃机瞬态工况测试技术和测试方法研究,通过对瞬态与稳态过程的缸内压力、缸内压力最大值、压力升高率、压力升高率最大值、压力高频振荡以及气缸压力级等参数在不同频率范围的差异的研究分析,从气体动力载荷和高频压力振荡两方面分析研究瞬态噪声与稳态噪声产生差异的机理.瞬态与稳态工况压力升高率变化趋势与两种工况下燃烧噪声变化趋势基本相似,但在一些工况上存在差异,这是由于受到了缸内压力高频振荡对燃烧噪声影响的结果.结果表明：瞬态与稳态工况燃烧噪声的差异是由压力动力载荷与压力高频振荡共同影响的结果.     

内燃机燃烧噪声的研究与发展

本文概述了内燃机燃烧噪声的特性及其研究与发展，阐述了燃烧过程参数、结构参数、工况参数以及其它参数影响燃烧噪声的机理，论述了近年来降低燃烧噪声、内燃机燃烧噪声机理和内燃机瞬态工况燃烧噪声的研究状况。通过对燃烧噪声与内燃机工作过程中激发燃烧噪声特征因素关系的描述，为了解燃烧噪声特性和降低燃烧噪声提供全面的技术支撑。     

汽油机非稳定加速工况燃烧放热率计算模型的修正

要对发动机非稳定工况实施最优控制,就应对其在非稳定工况下的工作过程做深入的研究。求取燃烧放热率是进行燃烧过程优化研究的基本手段,但在迄今为止的各种燃烧分析仪中,给出的多为稳定工况分析结果。作依据４９２Ｑ汽油机加速过程的试验结果,修正了汽油机燃烧放热率计算的热力学模型,使之适用于非稳定工况最后,通过实测示功图分析了４９２Ｑ汽油机沿外特性加速过程的放热特性和指示效率。     

Knocking combustion in spark-ignition engines

Knocking combustion research is crucially important because it determines engine durability, fuel consumption, and power density, as well as noise and emission performance. Current spark ignition (SI) engines suffer from both conventional knock and super-knock. Conventional knock limits raising the compression ratio to improve thermal efficiency due to end-gas auto-ignition, while super-knock limits the desired boost to improve the power density of modern gasoline engines due to detonation. Conventional combustion has been widely studied for many years. Although the basic characteristics are clear, the correlation between the knock index and fuel chemistry, pressure oscillations and heat transfer, and auto-ignition front propagation, are still in early stages of understanding. Super-knock combustion in highly boosted spark ignition engines with random pre-ignition events has been intensively studied in the past decade in both academia and industry. These works have mainly focused on the relationship between pre-ignition and super-knock, source analyses of pre-ignition, and the effects of oil/fuel properties on super-knock. The mechanism of super-knock has been recently revealed in rapid compression machines (RCM) under engine-like conditions. It was found that detonation can occur in modern internal combustion engines under high energy density conditions. Thermodynamic conditions and shock waves influence the combustion wave and detonation initiation modes. Three combustion wave modes in the end gas have been visualized as deflagration, sequential auto-ignition and detonation. The most frequently observed detonation initiation mode is shock wave reflection-induced detonation (SWRID). Compared to the effect of shock compression and negative temperature coefficient (NTC) combustion on ignition delay, shock wave reflection is the main cause of near-wall auto-ignition/detonation. Finally, suppression methods for conventional knock and super-knock in SI engines are reviewed, including use of exhaust gas recirculation (EGR), the injection strategy, and the integration of a high tumble - high EGR-Atkinson/Miller cycle. This paper provides deep insights into the processes occurring during knocking combustion in spark ignition engines. Furthermore, knock control strategies and combustion wave modes are summarized, and future research directions, such as turbulence-shock-reaction interaction theory, detonation suppression and utilization, and super-knock solutions, are also discussed.     

Experiments on the influence of intake conditions on local instantaneous heat flux in reciprocating internal combustion engines

The present study tries to be a contribution for the development of more precise theoretical models for predicting the dissipation of heat through the combustion chamber walls of reciprocating (internal combustion) IC engines. A fast response thermocouple was embedded in the combustion chamber of a single cylinder engine to measure instantaneous wall temperatures. The heat flux was obtained by solving the one-dimensional transient energy equation with transient boundary conditions using the Fast Fourier Transform. The engine was tested under different operating conditions to evaluate the sensitivity of the measurement procedure to variations of three relevant combustion parameters: injection pressure, air temperature and oxygen concentration at the intake. The local heat flux obtained was compared with other relevant parameters that characterize the thermal behaviour of engines, showing, in most of the cases, correlation among them. The results showed that the instantaneous heat flux through the walls and hence the local wall temperatures are strongly affected by the ignition delay and the start of combustion.