Visualisation of fuel-lubricant interaction on the cylinder surface in the combustion chamber of SI engines

Visualisation of fuel component penetration and release into the lubricating oil layer covering the combustion chamber wall has been achieved, using a laser-induced fluorescence (LIF) test technique. Experimental data show that fuel component penetration into the oil layer contributes not only to unburnt hydrocarbon emissions in spark ignition (SI) engines, but also to engine oil degradation. Fuel components accumulated in the oil layer are transferred to the bulk in ring belt zones, after a measurable residence time. A significant difference in film thickness between the oil layer on the combustion-chamber wall during the intake/compression sequence, as against the expansion/exhaust sequence, indicates that in the ring belt zones and above, engine oil viscosity, and hence load-carrying capacity, is influenced by fuel absorption/desorption in the engine oil.     

Flow direction characteristics in the vicinity of the spark plug in an S. I. Engine

The flame speed may be decomposed into the burning speed and the flame transport speed. The flame transport speed is affected considerably by the flow direction, variation rate of flow direction, and flow speed in the combustion chamber. Especially, the flow direction and the variation rate of flow direction at the spark plug location during the ignition period have an important effect on the ignition process and the early flame propagation process. We measured the flow direction component and the variation rate of flow direction with a hot wire probe at the spark plug location. It was shown that the representative flow direction of ignition period is the right-vertical direction of crank shaft and it was used to investigate the variation rate of flow direction.     

An in situ set up for the detection of CO2 from catalytic CO oxidation by using planar laser-induced fluorescence

We report the first experiment carried out on an in situ setup, which allows for detection of CO(2) from catalytic CO oxidation close to a model catalyst under realistic reaction conditions by the means of planar laser-induced fluorescence (PLIF) in the mid-infrared spectral range. The onset of the catalytic reaction as a function of temperature was followed by PLIF in a steady state flow reactor. After taking into account the self-absorption of CO(2), a good agreement between the detected CO(2) fluorescence signal and the CO(2) mass spectrometry signal was shown. The observed difference to previously measured onset temperatures for the catalytic ignition is discussed and the potential impact of IR-PLIF as a detection technique in catalysis is outlined.     

民用飞机热气候燃油试验适航试飞技术研究

热气候燃油试验是飞机燃油系统适航取证中的重要内容。飞机燃油系统在热气候条件下运行时,易在燃油管路和燃油泵叶轮附近出现气塞和气蚀,造成发动机供油故障,从而导致飞行事故。本文结合已进行的某型民用飞机热气候燃油试验,对民机热气候燃油试验中的试验设备、试验方法和程序进行了分析和研究。     

A study on fuel spray of spark-ignited direct injection engine using laser image technology

One of the important research for developing a spark-ignited direct injection engine is optimization of the fuel spray distribution and air flow field in the cylinder. Therefore, spray pattern and mean fuel droplet size of swirl injector were investigated using Laser Light Sheet Photography and PDPA' respectively. And, for the formation of stratified mixture with adequate strength near a spark plug at injection mode in compression stroke, spray distribution after impingement on flat piston or bowl piston in a transparent motoring engine was visualized for the three different injector positions. KIA Motors Corp.     

Experimental study on axial stratification process and its effects (I)-Stratification in Engine-

This paper is the first of several companion papers, which investigate axial stratification process and its effects in an SI engine. The axial stratification is very sophisticate phenomenon, which results from combination of fuel injection, port and in-cylinder flow and mixing. Because of the inherent unsteady condition in the reciprocating engine, it is impossible to understand the mechanism through the analytical method. In this paper, the ports were characterized by swirl and tumble number in steady flow bench test. After this, lean misfire limit of the engines, which had different port characteristic, were investigated as a function of swirl ratio and injection timing for confirming the existence of stratification. In addition, gas fuel was used for verifying whether this phenomenon depends on bulk air motion of cylinder or on evaporation of fuel. High-speed gas sampling and analysis was also performed to estimate stratification charging effect. The results show that the AFR at the spark plug and LML are very closely related and the AFR is the results of bulk air motion.     

Size distributions and number concentrations of particles from the DOC and CDPF

Particulate matters (PM) from diesel combustion comprise the major portion of harmful components of air in urban areas. In this study, the effects of DOC and/or CDPF on the size distributions and catalytic reactions of these nano-sized particles were investigated to clarify the exhaust mechanism and to minimize the emission of the nano-sized PM. Parameters of interest in the investigation included sulfur content of the fuels used, air-fuel equivalence ratio, fuel injection pressure, and the engine speed. The number concentration of the particles in diluted exhaust gas was measured by a SMPS in the diametric range of 10–385 nm. The number of nanometer-sized particles increased when the engine was operated at high equivalence ratio with diesel fuel that contained 500 ppm of sulfur. As the sulfur concentration in the fuel increased, the number of the particles smaller than 30 nm increased upon passing DOC and CDPF in the exhaust system of the common-rail diesel engine.     

Control of cold start hydrocarbon emissions of motor bike engine by gasoline-ethanol blends and intake air heating

Two wheeled motor bikes are playing an important role in urban passenger transportation owing to ease of handling and affordable cost. Maximum amount of unburnt hydrocarbons (HC) and carbon monoxide (CO) are emitted during cold start of spark ignition engines. The current work presents the possible reduction of cold start HC emissions of 150 CC motorbike spark ignition (SI) engine with ethanolgasoline blends and/or with intake air heating by glow plug. Anhydrous ethanol was blended with unleaded gasoline in the range of 0% (E0) to 20% (E20) by volume to be used as fuel. The experimented parameters were intake air temperature, exhaust gas temperature, fuel consumption and exhaust gas emissions. Without intake air heating, E10 was found to be the optimum to reduce the cold start HC emissions by 23%. With intake air heating in the range of 40°C to 70°C, maximum HC emissions reduction was 23.8% for neat gasoline at 50°C and 33.6% for E10 blend at 60°C.     

Experimental study of fine center electrode spark plug in bi-fuel engines

In the present work, the erosion of platinum fine center electrode spark plugs and conventional nickel plugs are investigated in a gasoline and natural gas bi-fuel engine. The effect of electrode erosion is evaluated by comparing the required ignition voltage and cold start ability of the different plug designs. After durability tests, platinum fine center electrode plug had insignificant electrode erosion and negligible gap growth; whereas the nickel plug had notable erosion and gap growth. There was no detectable side sparking for fine center electrode plugs. In terms of performance, the required ignition voltage of fine center electrode plug was lower than conventional spark plug. Also, results of a cold start test demonstrated that the starting time of the engine with fine electrode plugs was lower than conventional spark plugs. The surface of electrodes was studied by the scanning electron microscope and the energy dispersive X-ray spectroscopy techniques. Cracking and peeling was observed on the surface of the nickel conventional electrodes, but not on the surface of the platinum fine electrodes. These tests show that platinum fine center electrodes could be suitable for gasoline/natural gas bi-fuel engines to meet long lifetime demand.     

应用火花塞式传感器测量增压汽油机缸内压力

气缸压力是发动机的一个重要的指标,通过选举火花塞式传感器测量增压汽油机缸内压力,得出增压后发动机的工作状态及其增压效果。该传感器由一个小型点火电极和一压力传感件构成,其接收气缸压力的表面尽可能接近燃烧室,同时易受热影响的压电陶瓷传感元件尽可能近地置于火花塞温度最低的塞柱底座。避免了燃烧气体的纵向共振和热传递的影响。     

Cycle-to-cycle variations under cylinder-pressure-based combustion analysis in spark ignition engines

Combustion analysis based on cylinder-pressure provides a mechanism through which a combustion researcher can understand the combustion process. The objective of this paper was to identify the most significant sources of cycle-to-cycle combustion variability in a spark ignition engine at idle. To analyse the cyclic variation in a test engine, the burn parameters are determined on a cycle-to-cycle basis through the analysis of the engine pressure data. The burn rate analysis program was used here and the burn parameters were used to determine the variations in the input parameter—i, e,, fuel, air, and residual mass. In this study, we investigated the relationship of indicated mean effective pressure (IMEP), coefficient of variation (COV) of IMEP, burn angles, and lowest normalized value (LNV) in a spark ignition engine in a view of cyclic variations.     

Effect of engine variables on the turbulent flow of a spark ignition engine

The turbulent flow in a spark ignition engine plays an important role in determining its combustion characteristics and thermal efficiency. In order to analyse the combustion process, the turbulent flow and its turbulence intensity must be studied. To study the turbulent flow as varying various factors in a combustion chamber of a spark ignition engine, the L-head with or without squish area are selected. The turbulent as varying flow on the piston speed, inlet flow velocity, and squish velocity are measured by using hot wire anemometer. To examine the characteristics of turbulent flow, the ensemble averaged mean velocity, turbulence intensity, turbulence intensity decrease ratio, production rate of turbulence intensity, production coefficient of turbulence intensity are analysied.     

点燃式天然气发动机燃烧室结构优化的仿真与试验研究

利用三维数值仿真的方法,对带有浴盆形燃烧室的天然气发动机缸内流动和燃烧特性进行分析,提出了两种燃烧室结构优化设计方案,试验对比了采用原燃烧室和挤气喷射燃烧室时的发动机性能。结果表明:在不改变压缩比情况下,通过改变活塞头部凸起形状和位置,能够实现浴盆形燃烧室内的挤流与滚流有效耦合;控制点火时刻的火花塞附近气体流速,能提高缸内平均湍动能,加大快速燃烧期内火焰前封面的面积,改善燃烧质量。发动机采用优化的2号挤气喷射燃烧室,能够明显加快发动机燃烧进程,提高发动机的动力性和经济性,发动机功率从75kW提高到78.7kW,最低比气耗降低4.4%,HC和CO排放略有降低。     

预燃室射流点火对汽油机性能影响研究

通过试验手段对比分析了预燃室射流点火模式及火花塞点火模式 （SI）对燃烧性能的影响,结果表明:SI点火模式的发动机受高负荷爆震的限制,仅在中等负荷达到最佳的油耗率和热效率。压缩比（CR）的增加仅在中小负荷对油耗率和热效率有改善效果;相比于SI点火模式,预燃室射流点火模式可实现更快的燃烧速度和火焰传播速度,对SI发动机的爆震有较好的抑制效果,在中等负荷具有更低的油耗率和更高的热效率,但在低负荷及高负荷阶段,油耗率和热效率恶化;采用预燃室射流点火模式,能有效增加缸内燃烧速率,减轻CA50推迟对油耗率恶化的效果,通过提高压缩比实现降低油耗率的潜力和效果更好。     

An experimental investigation of the engine operating limit and combustion characteristics of the RI-CNG engine

In this paper, the radical induced (RI) ignition method was applied into a compressed natural gas (CNG) engine to achieve rapid bulk combustion. The experimental RI-CNG engine was modified from a diesel engine. The combustion chamber of the modified diesel engine was divided into a sub-chamber and a main-chamber. The sub-chamber is physically separated from the main-chamber above the piston and is connected to the main-chamber via several passage holes. CNG is injected into the sub-chamber during the intake stroke and then ignited before the top dead center (TDC) by a spark plug. As the ignition occurs in the sub-chamber, the pressure rises, forcing the gases which contain a number of active radicals out into the main-chamber to ignite the unburned mixture. The purpose of this paper is to study the engine operating limit and the combustion characteristics of the RI-CNG engine. The engine operating limit was accessed with different engine speeds and injection timings. The obtained data including the coefficient of variation (COV), brake specific fuel consumption (BSFC), mass fraction burned and emissions were analyzed.     

A mathematical model for the prediction of the injected mass diagram of a S.I. engine gas injector

A mathematical model of gaseous fuel solenoid injector for spark ignition engine has been realized and validated through experimental data. The gas injector was studied with particular reference to the complex needle motion during the opening and closing phases, which strongly affects the amount of fuel injected. As is known, in fact, when the injector nozzle is widely open, the mass flow depends only on the fluid pressure and temperature upstream the injector: this allows one to control the injected fuel mass acting on the “injection time” (the period during which the injector solenoid is energized). This makes the correlation between the injected fuel mass and the injection time linear, except for the lower injection times, where we experimentally observed strong nonlinearities. These nonlinearities arise by the injector outflow area variation caused by the needle bounces due to impacts during the opening and closing transients [1] and may seriously compromise the mixture quality control, thus increasing both fuel consumption and pollutant emissions, above all because the S.I. catalytic conversion system has a very low efficiency for non-stoichiometric mixtures. Moreover, in recent works [2, 3] we tested the simultaneous combustion of a gaseous fuel (compressed natural gas, CNG, or liquefied petroleum gas, LPG) and gasoline in a spark ignition engine obtaining great improvement both in engine efficiency and pollutant emissions with respect to pure gasoline operation mode; this third operating mode of bi-fuel engines, called “double fuel” combustion, requires small amounts of gaseous fuel, hence forcing the injectors to work in the non-monotonic zone of the injected mass diagram, where the control on air-fuel ratio is poor. Starting from these considerations we investigated the fuel injector dynamics with the aim to improve its performance in the low injection times range. The first part of this paper deals with the realization of a mathematical model for the prediction of both the needle motion and the injected mass for choked flow condition, while the second part presents the model calibration and validation, performed by means of experimental data obtained on the engine test bed of the internal combustion engine laboratory of the University of Palermo.     

二冲程煤油发动机整机建模与初始点火提前角计算分析

针对二冲程汽油发动机改燃烧航空煤油后,初始点火提前角需重新标定的问题,利用GT-Power对以煤油为燃料的二冲程发动机进行整机建模。通过数值计算分析了转速、负荷、进气压力、进气温度和空燃比对点火提前角的影响,得出除转速和负荷外,进气温度对点火提前角的大小影响明显。针对不同的工况条件,充分考虑动力性而忽略经济性与排放性的前提下,通过计算获取了发动机初始点火提前角;通过仿真数据与实验结果对比验证了其一致性。     

火花塞电磁兼容性能的提升对策

近年来,乘用车辆采用了越来越多的电子设备,需要系统考虑车辆上所有电器件的电磁兼容性能;同时发动机技术的提升也对电磁兼容性能提出了更高的要求。火花塞作为发动机点火系列中的点火执行器,其单体不具备辐射电磁波的能力。但火花塞点火时,释放点火线圈储存的能量,在间隙击穿的瞬间,其周围的电场会发生急剧变化,从而产生电磁波。可以通过减小间隙、使用贵金属尖端中心电极等手段,降低点火电压,从而降低电磁波的频率和能量;同时采用合适的包边口尺寸和合适的接线端子位置,采用屏蔽型等手段,来减短和缩小电磁波传播的路径,达到良好的火花塞电磁兼容性能。采用电阻型、电感型、磁阻型的火花塞结构是抑制电磁波常用和主要的手段,通过不同的组合可以实现更好的火花塞电磁兼容性能。     

The experimental study of atomization characteristics of gasoline spray impinging on glow plug

In order to reduce the exhaust emissions of a spark ignition engine, it is important not only to improve the catalyst conversion efficiency, but also to directly reduce the engine-out exhaust emissions during a cold starting of the engine and warm up periods. The purpose of this study is to evaluate feasibility of a glow plug for an early fuel evaporator. In order to promote atomization, gasoline is injected on the glow plug with room temperature (20°C) and high temperature (250°C). To analyze the spray behavior characteristics, a PMAS is used to measure the SMD and the dropsize distribution of an impinging spray and a free spray. Results show that the evaporation rate of the impinging spray on the high temperature surface of the glow plug was higher than that of the free spray on the room temperature surface.     

A study on the effect of operating conditions for the stability at idle

A gasoline engine with an electronically controlled fuel injection system has substantially better fuel economy and lower emissions than a carburetted engine. In general, the stability of engine operation is improved with fuel injector, but the stability of engine operation at idle is not improved compared with a carburetted gasoline engine. In addition, the increase in time that an engine is at idle due to traffic congestion has an effect on the engine stability and vehicle reliability. Therefore, in this research, we will study the influence of fuel injection timing, spark timing, dwell angle, and air-fuel ratio on engine stability at idle.