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.     

方箱炉旋流燃烧技术研究与应用

旋流燃烧可以提高火焰速度,从而强化传热、提高燃烧效率,采用多个同旋向喷嘴形成旋流燃烧器,或者通过喷口不同方向的倾斜排列形成两排燃烧器,可以实现很好的方箱炉旋流速度场。通过冷态流场数值模拟和试验分析,验证了旋流燃烧能加强炉子流场的均匀性,热态试验和工业应用结果表明,炉膛下部燃烧和传热得到强化,烟气出口烟温下降,方箱炉热效率显著提高。     

An experimental study on the evaporation of freely falling droplet under high temperature and high pressure gas stream

An experimental apparatuses and measuring system have been made to obtain characteristics connected with evaporation, ignition delay, combustion of a freely falling liquid fuel droplet in high temperature and high pressure gas stream. In this study some systematic experiments were performed to test the utility of the system. The newly devised apparatus was ensured reliability and utility from the tentative experimental results.     

An experimental study on spray and combustion characteristics based on fuel temperature of direct injection bio-ethanol-gasoline blending fuel

This study investigated the spray and combustion characteristics of a direct injection spark ignition type system based on the changes in the temperature of the blended fuel (with bio-ethanol and gasoline). The test was performed in a chamber with a constant volume. The diameter and width of the chamber were 86 mm and 39 mm, respectively. The bio-ethanol test fuel was blended at volume ratios of 0 %, 10 %, 20 % and 100 %. The temperature of the fuel was set as −7, 25 and 35 °C. The fuel injection pressure and ambient pressure were set as 4.5 and 0.5 MPa, respectively. The shape and characteristics of the spray were investigated through a spray experiment. The increase in the fuel temperature changed its density and viscosity; this in turn increased spray penetration and spray area and increased the bio-ethanol blending ratio. The combustion visualization and experimental analysis indicated that the decrease in the fuel temperature and the increase in the bio-ethanol blending ratio led to the high viscosity and low heating value. This resulted in an increase in the ignition delay and a decrease in the rate of heat release. It is necessary to adjust the spray strategy and ignition timing to adopt bio-ethanol blended fuel as an alternative fuel.

     

柴油机燃烧室匹配参数对撞壁喷雾特性的影响

利用高速纹影摄像技术,研究了喷油器喷孔角度、喷孔与活塞顶面间的撞壁距离、燃烧室缩口半径和凸台夹角对柴油撞击燃烧室壁面后喷雾特性的影响。研究结果表明,试验条件下适宜的喷孔角度为75°,增大喷孔角度可以促进喷雾撞壁后的油气混合,但是喷孔角度过大会增加油束撞击气缸盖和气缸套的风险;适宜的撞壁距离为4.2mm,即压缩上止点前15°CA（CA指曲轴转角）,较小的撞壁距离会促进喷雾液滴在凹坑区域的碰撞与黏结,而较大的撞壁距离不利于燃烧室中心区域的空气利用;此外,适当增大缩口半径可以促进燃油与空气的混合,减小燃烧室壁面的燃油湿壁面积;改变凸台夹角可以控制撞壁后喷雾在燃烧室中心区域的扩散速度。     

Numerical study on no emission with flue gas dilution in air and fuel sides

Flue gas recirculation (FGR) is widely adopted to control NO emission in combustion systems. Recirculated flue gas decreases flame temperature and reaction rate, resulting in the decrease in thermal NO production. Recently, it has been demonstrated that the recirculated flue gas in fuel stream, that is, the fuel induced recirculation (FIR), could enhance much improved reduction in NO per unit mass of recirculated gas, as compared to conventional FGR in air. In the present study, the effect of dilution methods in air and fuel sides on NO reduction has been investigated numerically by using N3 and CO2 as diluent gases to simulate flue gases. Counterflow diffusion flames were studied in conjunction with the laminar flamelet model of turbulent flames. Results showed that CO2 dilution was more effective in NO reduction because of large temperature drop due to the larger specific heat of CO2 compared to N₂. Fuel dilution was more effective in reducing NO emission than air dilution when the same recirculation ratio of dilution gas was used by the increase in the nozzle exit velocity, thereby the stretch rate, with dilution gas added to fuel side.     

不同温度气体喷射特性的PIV试验研究

研究气体的喷射特性,用于指导发动机燃油供给系统的设计和燃烧室有效组织燃烧。基于粒子图像测速技术(PIV),对不同温度、不同压差下气体喷射的特性进行了对比研究。通过试验分析和图像处理等手段对射流流场及涡结构、气体射流边界扩展、喷嘴轴向流速衰减规律、断面流速分布等进行了总结。试验表明:射流边界呈线性扩展,可用锥角大小来表征其特性,锥角随压差的减小而增大,且增幅明显,温度对其也有一定影响。喷嘴射流的轴向速度与射流距离成反比,而速度的影响面积随射流距离的增大而增大,温度的增大使得相同压差下的轴向速度相应增大,断面流速的分布存在很大的相似性。     

Performance simulation of a turboprop engine for basic trainer

A performance simulation program for the turboprop engine (PT6A-62), which is the power plant of the first Korean indigenous basic trainer KT-1, was developed for performance prediction, development of an EHMS (Engine Health Monitoring System) and the flight simulator. Characteristics of components including compressors, turbines, power turbines and the constant speed propeller were required for the steady state and transient performance analysis with on and off design point analysis. In most cases, these were substituted for what scaled from similar engine components’ characteristics with the scaling law. The developed program was evaluated with the performance data provided by the engine manufacturer and with analysis results of GASTURB program, which is well known for the performance simulation of gas turbines. Performance parameters such as mass flow rate, compressor pressure ratio, fuel flow rate, specific fuel consumption and turbine inlet temperature were discussed to evaluate validity of the developed program at various cases. The first case was the sea level static standard condition and other cases were considered with various altitudes, flight velocities and part loads with the range between idle and 105% rotational speed of the gas generator. In the transient analysis, the Continuity of Mass Flow Method was utilized under the condition that mass stored between components is ignored and the flow compatibility is satisfied, and the Modified Euler Method was used for integration of the surplus torque. The transient performance analysis for various fuel schedules was performed. When the fuel step increase was considered, the overshoot of the turbine inlet temperature occurred. However, in case of ramp increase of the fuel longer than step increase of the fuel, the overshoot of the turbine inlet temperature was effectively reduced.     

一种船用液体燃料蜗壳旋流器的数值研究与性能验证

为实现船用液体燃料蜗壳旋流器的可靠性点火,提高其燃烧的稳定性和燃烧效率,采用RNG k-ε双方程湍流模型,设计出一种满足船用特殊需要的蜗壳旋流器,列举了7组不同戊烷和空气进口流量,对该具体尺寸的蜗壳旋流器的液雾燃烧过程进行了数值模拟和试验验证,得到了蜗壳旋流器内部流场以及出口处的烟气温度场和燃烧产物的组分浓度分布。分析对比这7组进口流量对该蜗壳旋流器的出口温度和出口气体组分的影响,找到了满足船用需要的该具体尺寸蜗壳旋流器对应的最佳燃料进口流量。该模拟和试验结果为蜗壳旋流器的结构设计提供了理论依据。     

Experimental study on the icing characteristics of LPLi injectors under various injection conditions

Development of alternative fuels has been increasing to replace conventional fuels because of severe environmental pollution from the exhaust emissions of ground vehicles and the depletion of fossil fuels. LPG (Liquefied petroleum gas) fuel provides clean energy for gasoline-fueled engines and LPG fuel R&D (Research & development) has actively progressed in reaching the application stage. However, the icing phenomenon in liquid-phase LPG injection systems remains a major problem. The purpose of this study was therefore to investigate the temperature distribution on the icing protection tip and icing formation characteristics under various test conditions (i.e. injection pressure, injection frequency, injection duty). The results showed that increasing the injection frequency induced a big the temperature drop, whereas increasing the injection duty decreased the temperature drop under the same test conditions. Increasing the injection pressure caused a small temperature drop because of an increase in the injection velocity, which meant that much of the injected LPG evaporated at a region distant from the nozzle tip. The protection tip with a double-hollow structure had a smaller the temperature drop than the all-in-one type protection tip made of the same material (copper).

     

Research on effects of key influencing factors upon fuel injection characteristics of the combination electronic unit pump for diesel engines

A numerical model of the combination electronic unit pump (CEUP) fuel injection system was developed in AMESim environment. The effects of five key influencing factors, including cam profile velocity, plunger diameter, length of high pressure fuel pipe, inner diameter of high pressure fuel pipe and nozzle flow rate on injection characteristic parameters, were analyzed by using the developed numerical model. On the basis, a correlation analysis between the influencing factors and injection characteristics was performed by using the design of experiments (DoE) method, and the influences of these factors were quantized accordingly. Relevant results show that both the single influencing factor and the interaction among these factors correlates with the injection characteristics, and the correlation represents a complex law with the cam rotational speed. The effect of plunger diameter on the injection pressure, cycle fuel injection quantity and injection duration is the most obvious, especially at a cam rotational speed of 500 r/min and the correlation coefficient is up to 0.82. The length of high-pressure pipe (HP pipe) has the most obvious influence on the coefficient of fuel feeding at cam rotational speed of 500 r/min and 800 r/min, and the correlation coefficient is negative. Overall, the independent influence of the factors is more significant than the combined influence of various factors. The CEUP fuel injection system is a complicated multi-input multi-output (MIMO) nonlinear system in fact.     

Combustion behaviors of wood pellet fuel and its co-firing with different coals

Biomass resources, which are carbon-neutral and sustainable, may help to address climate change and reduce greenhouse gas emissions. This study was performed to examine the effects of wood pellet (WP) particle size, environmental conditions (stoichiometric ratio; SR), and blending ratio on the combustion characteristics of single fuels and blends using a thermogravimetric analyzer and drop tube furnace (DTF). The results indicate that WP demonstrated a higher mass reduction in the devolatilization region and a faster reaction rate compared with coal. Blends tested in the analyzer showed the expected profiles for devolatilization and char oxidation without the presence of non-additive effects. However, the DTF results showed that simultaneous reactive and non-reactive phenomena occurred with increasing biomass-blending ratios. When WP fuel containing fine particles (< 200 μm) was blended with coal under low SR conditions, early-stage oxygen deficiency was caused by rapid combustion. WP fuel containing coarse particles (> 600 μm) showed that unburned carbon (UBC) increased owing to slower reactivity. WP fuel containing particles of 400 μm or less in size demonstrated superior UBC performance, indicating that biomass-coal blends were significantly affected by blending ratio, particle size, and the surrounding environment.

     

An experiment analysis of MILD combustion with liquid fuel spray in a combustion vessel

Mild combustion is characterized by its distinguished features, such as suppressed pollutant emission, homogeneous temperature distribution, reduced noise, and thermal stress. Recently, many studies have revealed the potential of MILD combustion in various power systems but most studies have been focused on gas phase fuel MILD combustion. Therefore, further study on MILD combustion using liquid fuel is needed for the application to a liquid-fueled gas turbine especially. In this work, we studied experimentally on the formation of liquid fuel MILD combustion under the condition of high dilution by burnt gas generated from a first premixed flame in two stages combustor which consists of the first premixed burner and secondary combustor. In particular, the effects of burnt gas velocity and oxygen level of burnt gas on the formation of liquid fuel MILD combustion were investigated. The results show that as the burnt gas velocity through the nozzle becomes higher, the color of flames was changed from yellow to pale blue and flames became very short. The OH radical measured by ICCD camera was uniformly distributed on the pale blue flame surface and its intensity was very low compared to conventional liquid diffusion flame. As burnt gas velocity is increased, local high-temperature region appeared to be diminished and the flame temperature became spatially uniform. And CO emission was sampled around 1 ppm and NOx emission was measured around 10 ppm under the overall equivalence ratio of 0.8 to 0.98 for 40 mm or less diameter of velocity control nozzle. This low NOx emission seems to be attributed to maintaining the average temperature in secondary combustor below the threshold temperature of thermal NOx formation. In view of the uniform temperature distribution, low OH radical intensity and low NOx emission data in the secondary combustor, formation of stable MILD combustion using kerosene liquid fuel could be verified at high burnt gas velocity.

     

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。     

Prediction of flame formation in highly preheated air combustion

Fundamental information about the ignition position and shape of a flame in highly preheated air combustion was obtained, and the suitability of the suggested reduced kinetic mechanism that reflects the characteristics of the highly preheated air combustion was demonstrated. Flame lift height and flame length with variations of premixed air temperature and oxygen concentration were measured by CH* chemiluminescence intensity, and were computed with a reduced kinetic mechanism. Flame attached near a fuel nozzle started to lift when preheated air temperature became close to auto-ignition temperature and/or oxygen concentration reduced. The flame lift height increased but the flame length decreased with decreasing preheated air temperature and flame length reversed after a minimum value. Calculated results showed good agreement with those of experiment within tolerable error. Flame shape shifted from diffusion flame shape to partial premixed flame shape with increasing lift height and this tendency was also observed in the computation results. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Gyung-Min Choi studied the areas of combustion engineering, heat recirculating combustion, and solid fuel gasification, receiving his Ph.D. degree in engineering from Osaka University in 2001. He served as a researcher at Japan Aerospace Exploration Agency and is now an associate professor in the School of Mechanical Engineering at Pusan National University.     

不同燃油温度下柴油机喷嘴空穴流动特性试验研究

作为喷射系统的终端,喷油器内部的空穴流动对燃油雾化具有重要影响。采用比例放大透明喷嘴,研究不同燃油温度对喷嘴内空穴流动及其对近场喷雾的影响。引入无单位参数空穴数表征喷油器内燃油空化程度,研究发现燃油温度升高,其空穴初生时的压力减小,同一空穴数下,空穴程度更强烈。同时,试验观察到喷嘴内空穴区域的不对称性,喷孔管壁下壁面的空穴分布远大于上壁面的空穴分布;发生超空穴之后,随着空穴数的增加,试验结果中喷嘴内部的空穴流动变化不太明显,但仿真结果中看出喷孔出口流速减小。相同燃油温度下,随着空穴数增加,体积流量增加,流量系数减小,空穴相对面积增加,近场喷雾锥角增大;相同空穴数下,燃油温度增加使体积流量和流量系数都增加,空穴相对面积逐渐增大,近场雾化效果更好。     

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。     

汽车喷油嘴加热模块的实验研究

乙醇燃料是含氧燃料,无毒且对环境无危害,蒸发潜热高,发动机燃用乙醇可以实现无烟排放,并能大幅度降低CO排放。乙醇的汽化潜热大,理论空燃比下的蒸发温度大于常规汽油,但乙醇汽车存在启动难的问题。针对以乙醇为燃料的汽车难以启动的问题,提出了一种体积小、控制精确、制造成本低的汽车喷油嘴加热模块,并详细介绍了该汽车喷油嘴加热模块的工作原理,利用TestStand软件测试了喷油嘴加热模块的输入电流、输入端与输出端的频率和占空比、Feedback端与Heater端的电压等,模拟了乙醇汽车喷油嘴加热助启动实验。实验研究结果表明:喷油嘴加热模块能有效地帮助乙醇汽车启动,并且具有广阔的推广应用前景。     

基于黑箱模型和RBF-PID的HCCI发动机燃烧正时控制

由于均质充气压缩点燃(HCCI)发动机缺少直接控制其燃烧的手段,导致HCCI发动机的燃烧正时控制成为HCCI发动机的研究热点。以HCCI发动机进气歧管的温度和压力、燃油当量比、转速以及进气门关闭正时为输入,利用BP神经网络建立用于估计HCCI发动机燃烧正时的黑箱模型。在此模型基础上,以进气门关闭正时为控制量设计了PID控制器,并利用径向基神经网络对其参数进行整定,以实现对燃烧正时的反馈控制。实验结果表明,BP神经网络估计模型对HCCI发动机燃烧正时的估计误差小于0.4(CAD),能实现准确的估计;此外,与传统的PID控制器相比,设计的RBF-PID控制器在超调量、调节时间以及抗干扰性等性能方面均有改善。     

射弹打击下油箱燃油泄露研究

为了确定射弹击穿飞机油箱后附近干舱的引燃和燃烧,需要对燃油通过穿孔泄露过程中燃油的泄露质量及雾化液滴的数目和尺寸进行定量计算分析。该文建立了用于模拟高速射弹击穿油箱后燃油泄露过程的解析模型,给出了燃油初始泄露速度的定量计算方法,利用最大熵原理和质量守恒定律,推出了弹丸撞击条件下泄露燃油液滴尺寸数目分布函数和索特尔平均直径SMD的计算公式,并采用Harmon液滴索特尔平均直径经验计算公式定量计算泄露燃油的平均直径。研究结果表明燃油的初始泄露速度随射弹速度的增加而呈线性增加,液滴索特尔平均直径随穿孔直径的增加而增加,随射弹速度的增加而呈线性减小。研究结果为下一步进行油箱附近干舱引燃和燃烧提供理论基础。