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Experimental study of stratified lean burn characteristics on a dual injection gasoline engine

Frontiers in Energy 2022年第6期16卷 900-915页

作者： Chun XIA Tingyu ZHAO Junhua FANG Lei ZHU Zhen HUANG Key Laboratory of Power Machinery and Engineering Shanghai Jiao Tong UniversityShanghai 200240China

Due to increasingly stringent fuel consumption and emission regulation,improving thermal efficiency and reducing particulate matter emissions are two main issues for next generation gasoline engine.Lean burn mode could greatly reduce pumping loss and decrease the fuel consumption of gasoline engines,although the burning rate is decreased by higher diluted intake air.In this study,dual injection stratified combustion mode is used to accelerate the burning rate of lean burn by increasing the fuel concentration near the spark plug.The effects of engine control parameters such as the excess air coefficient(Lambda),direct injection(DI)ratio,spark interval with DI,and DI timing on combustion,fuel consumption,gaseous emissions,and particulate emissions of a dual injection gasoline engine are studied.It is shown that the lean burn limit can be extended to Lambda=1.8 with a low compression ratio of 10,while the fuel consumption can be obviously improved at Lambda=1.4.There exists a spark window for dual injection stratified lean burn mode,in which the spark timing has a weak effect on combustion.With optimization of the control parameters,the brake specific fuel consumption(BSFC)decreases 9.05%more than that of original stoichiometric combustion with DI as 2 bar brake mean effective pressure(BMEP)at a 2000 r/min engine speed.The NO_(x) emissions before threeway catalyst(TWC)are 71.31%lower than that of the original engine while the particle number(PN)is 81.45%lower than the original engine.The dual injection stratified lean burn has a wide range of applications which can effectively reduce fuel consumption and particulate emissions.The BSFC reduction rate is higher than 5%and the PN reduction rate is more than 50%with the speed lower than 2400 r/min and the load lower than 5 bar.

关键词： dual injection stratified lean burn gasoline engine particulate matter emission combustion analysis

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A methodology for regulating fuel stratification and improving fuel economy of GCI mode via double main-injection strategy

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Frontiers in Energy 2023年第5期17卷 678-691页

作者： Haoqing WU Yaoyuan ZHANG Shijie MI Wenbin ZHAO Zhuoyao HE Yong QIAN Xingcai LU key laboratory for power machinery and engineering of the Ministry of Education Shanghai Jiao Tong UniversityShanghai 200240China

Gasoline compression ignition(GCI)combustion faces problems such as high maximum pressure rise rate(MPRR)and combustion deterioration at high loads.This paper aims to improve the engine performance of the GCI mode by regulating concentration stratification and promoting fuel-gas mixing by utilizing the double main-injection(DMI)strategy.Two direct injectors simultaneously injected gasoline with an octane number of 82.7 to investigate the energy ratio between the two main-injection and exhaust gas recirculation(EGR)on combustion and emissions.High-load experiments were conducted using the DMI strategy and compared with the single main-injection(SMI)strategy and conventional diesel combustion.The results indicate that the DMI strategy have a great potential to reduce the MPRR and improve the fuel economy of the GCI mode.At a 10 bar indicated mean effective pressure,increasing the main-injection-2 ratio(Rm-2)shortens the injection duration and increases the mean mixing time.Optimized Rm-2 could moderate the trade-off between the MPRR and the indicated specific fuel consumption with both reductions.An appropriate EGR should be adopted considering combustion and emissions.The DMI strategy achieves a highly efficient and stable combustion at high loads,with an indicated thermal efficiency(ITE)greater than 48%,CO and THC emissions at low levels,and MPRR within a reasonable range.Compared with the SMI strategy,the maximum improvement of the ITE is 1.5%,and the maximum reduction of MPRR is 1.5 bar/°CA.

关键词： gasoline compression ignition injection strategy fuel stratification high efficiency high load

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Combustion and emissions of RP-3 jet fuel and diesel fuel in a single-cylinder diesel engine

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Frontiers in Energy 2023年第5期17卷 664-677页

作者： Tongbin ZHAO Zhe REN Kai YANG Tao SUN Lei SHI Zhen HUANG Dong HAN key laboratory for power machinery and engineering of the Ministry of Education Shanghai Jiao Tong UniversityShanghai 200240China

The combustion characteristics and emission behaviors of RP-3 jet fuel were studied and compared to commercial diesel fuel in a single-cylinder compression ignition(CI)engine.Engine operational parameters,including engine load(0.6,0.7,and 0.8 MPa indicating the mean effective pressure(IMEP)),the exhaust gas recirculation(EGR)rate(0%,10%,20%,and 30%),and the fuel injection timing(–20,–15,–10,and–5°crank angle(CA)after top dead center(ATDC))were adjusted to evaluate the engine performances of RP-3 jet fuel under changed operation conditions.In comparison to diesel fuel,RP-3 jet fuel shows a retarded heat release and lagged combustion phase,which is more obvious under heavy EGR rate conditions.In addition,the higher premixed combustion fraction of RP-3 jet fuel leads to a higher first-stage heat release peak than diesel fuel under all testing conditions.As a result,RP-3 jet fuel features a longer ignition delay(ID)time,a shorter combustion duration(CD),and an earlier CA50 than diesel fuel.The experimental results manifest that RP-3 jet fuel has a slightly lower indicated thermal efficiency(ITE)compared to diesel fuel,but the ITE difference becomes less noticeable under large EGR rate conditions.Compared with diesel fuel,the nitrogen oxides(NOx)emissions of RP-3 jet fuel are higher while its soot emissions are lower.The NOx emissions of RP-3 can be effectively reduced with the increased EGR rate and delayed injection timing.

关键词： RP-3 jet fuel diesel engine combustion emissions

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Design and modeling of a free-piston engine generator

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Frontiers in Energy 2023年第6期17卷 811-821页

作者： Jinlong WANG Jin XIAO Yingdong CHENG Zhen HUANG key laboratory for power machinery and engineering(Ministry of Education) Shanghai Jiao Tong UniversityShanghai 200240China

Free-piston engine generators (FPEGs) can be applied as decarbonized range extenders for electric vehicles because of their high thermal efficiency, low friction loss, and ultimate fuel flexibility. In this paper, a parameter-decoupling approach is proposed to model the design of an FPEG. The parameter-decoupling approach first divides the FPEG into three parts: a two-stroke engine, an integrated scavenging pump, and a linear permanent magnet synchronous machine (LPMSM). Then, each of these is designed according to predefined specifications and performance targets. Using this decoupling approach, a numerical model of the FPEG, including the three aforementioned parts, was developed. Empirical equations were adopted to design the engine and scavenging pump, while special considerations were applied for the LPMSM. A finite element model with a multi-objective genetic algorithm was adopted for its design. The finite element model results were fed back to the numerical model to update the LPMSM with increased fidelity. The designed FPEG produced 10.2 kW of electric power with an overall system efficiency of 38.5% in a stable manner. The model provides a solid foundation for the manufacturing of related FPEG prototypes.

关键词： free-piston engine generator linear permanent magnet synchronous machine system design numerical model finite element method

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An experimental study of a single-piston free piston linear generator

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Frontiers in Energy 2022年第6期16卷 916-930页

作者： Jin XIAO Yingdong CHENG Jinlong WANG Chengwei ZHU Zhen HUANG key laboratory for power machinery and engineering of the Ministry of Education Shanghai Jiao Tong UniversityShanghai 200240China

Free piston linear generator(FPLG)is a promising range extender for the electrical vehicle with unparallel advantages,such as compact structure,higher system efficiency,and reduced maintenance cost.However,due to the lack of the mechanic crankshaft,the related piston motion control is a challenge for the FPLG which causes problems such as misfire and crash and limits its widespread commercialization.Aimed at resolving the problems as misfire,a single-piston FPLG prototype has been designed and manufactured at Shanghai Jiao Tong University(SJTU).In this paper,the development process and experimental validation of the related control strategies were detailed.From the experimental studies,significant misfires were observed at first,while the FPLG operated in natural-aspiration conditions.The root cause of this misfire was then identified as the poor scavenging process,and a compressed air source was leveraged to enhance the related scavenging pressure.Afterward,optimal control parameters,in terms of scavenging pressure,air-fuel equivalence ratio,and ignition position,were then calibrated in this charged-scavenging condition.Eventually,the FPLG prototype has achieved a continuous stable operation of over 1000 cycles with an ignition rate of 100%and a cycle-to-cycle variation of less than 0.8%,produced an indicated power of 2.8 kW with an indicated thermal efficiency of 26%and an electrical power of 2.5 kW with an overall efficiency of 23.2%.

关键词： free piston linear generator(FPLG) charged scavenging engine control misfire stable operation

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An assessment of surrogate fuel using Bayesian multiple kernel learning model in sight of sooting tendency

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Frontiers in Energy 2022年第2期16卷 277-291页

作者： Lei ZHU Zhan GAO Xiaogang CHENG Fei REN Zhen HUANG key laboratory for power machinery and engineering of the Ministry of Education Shanghai Jiao Tong UniversityShanghai 200030China

An integrated and systematic database of sooting tendency with more than 190 kinds of fuels was obtained through a series of experimental investigations. The laser-induced incandescence (LII) method was used to acquire the 2D distribution of soot volume fraction, and an apparatus-independent yield sooting index (YSI) was experimentally obtained. Based on the database, a novel predicting model of YSI values for surrogate fuels was proposed with the application of a machine learning method, named the Bayesian multiple kernel learning (BMKL) model. A high correlation coefficient (0.986) between measured YSIs and predicted values with the BMKL model was obtained, indicating that the BMKL model had a reliable and accurate predictive capacity for YSI values of surrogate fuels. The BMKL model provides an accurate and low-cost approach to assess surrogate performances of diesel, jet fuel, and biodiesel in terms of sooting tendency. Particularly, this model is one of the first attempts to predict the sooting tendencies of surrogate fuels that concurrently contain hydrocarbon and oxygenated components and shows a satisfying matching level. During surrogate formulation, the BMKL model can be used to shrink the surrogate candidate list in terms of sooting tendency and ensure the optimal surrogate has a satisfying matching level of soot behaviors. Due to the high accuracy and resolution of YSI prediction, the BMKL model is also capable of providing distinguishing information of sooting tendency for surrogate design.

关键词： sooting tendency yield sooting index Bayesian multiple kernel learning surrogate assessment surrogate formulation

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Experimental and kinetic study on the stabilities and gas generation of typical electrolyte solvent components under oxygen-lean oxidation and pyrolysis conditions

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Science China(Technological Sciences) 2022年第12期65卷 2883-2894页

作者： ZHANG JiaBo ZHONG AnHao HUANG Zhen HAN Dong key laboratory for power machinery and engineering Ministry of EducationShanghai Jiao Tong UniversityShanghai 200240China

The safety concerns of lithium-ion batteries(LIBs)due to thermal runaway hinder their broad applications.Flammable electrolytes are the major cause of gas venting and fire hazards of LIB,particularly when limited oxygen can be released because of the degradation of cathode materials.However,studies on the combustion characteristics of electrolytes under highly incomplete conditions,corresponding to thermal runaway scenarios,are limited.Therefore,a comprehensive experimental and kinetic study of three typical electrolyte solvents,namely,dimethyl carbonate(DMC),diethyl carbonate(DEC),and ethyl methyl carbonate(EMC),was performed under oxygen-lean and pyrolysis conditions.The experiments were conducted in a jet-stirred reactor with equivalence ratios of 2.5,5.0,and∞at atmospheric pressure,and the temperature ranged from 600 to 1100 K.Primary gas products,including H_(2),CH_(4),C_(2)H_(4),C_(2)H_(6),CH_(3)OH,C_(2)H_(5)OH,CO,and CO_(2),were quantified using gas chromatography.Results revealed that the consumption onset temperatures were in the order of DEC~EMC

关键词： lithium-ion battery thermal runaway carbonate electrolytes pyrolysis oxidation jet-stirred reactor

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Recent progress in electric-field assisted combustion: a brief review

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Frontiers in Energy 2022年第6期16卷 883-899页

作者： Hecong LIU Weiwei CAI key laboratory of the Ministry of Education for power machinery and engineering School of Mechanical EngineeringShanghai Jiao Tong UniversityShanghai 200240China

The control of combustion is a hot and classical topic.Among the combustion technologies,electric-field assisted combustion is an advanced technology that enjoys major advantages such as fast response and low power consumption compared with thermal power.However,its fundamental principle and impacts on the flames are complicated due to the coupling between physics,chemistry,and electromagnetics.In the last two decades,tremendous efforts have been made to understand electric-field assisted combustion.New observations have been reported based on different combustion systems and improved diagnostics.The main impacts,including flame stabilization,emission reduction,and flame propagation,have been revealed by both simulative and experimental studies.These findings significantly facilitate the application of electric-field assisted combustion.This brief review is intended to provide a comprehensive overview of the recent progress of this combustion technology and further point out research opportunities worth investigation.

关键词： electric field combustion flame stabilization emission reduction flame propagation

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High-quality quasi-monochromatic near-field radiative heat transfer designed by adaptive hybrid Bayesian optimization

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Science China(Technological Sciences) 2022年第12期65卷 2910-2920页

作者： ZHANG WenBin WANG BoXiang XU JianMing ZHAO ChangYing Institute of engineering Thermophysics MOE Key Laboratory for Power Machinery and EngineeringSchool of Mechanical EngineeringShanghai Jiao Tong UniversityShanghai 200240China State key laboratory of Space power-Sources Technology Shanghai Institute of Space Power-SourcesShanghai 200245China

The increasing demand for versatile and high-quality near-field radiative heat transfer(NFRHT) has created a critical need for a design approach that can handle numerous candidate structures. In this work, we employ and develop an adaptive hybrid Bayesian optimization(AHBO) algorithm to design the high-quality quasi-monochromatic NFRHT. The candidate materials include hexagonal boron nitride, silicon carbide, and doped silicon. The high-quality quasi-monochromatic NFRHT is optimized over 1.0 × 10^(8) candidate structures to maximize the evaluation factor. It is worth noting that only 2.6% of the candidate structures needed to be calculated to identify the optimal structure. The optimal structure of quasi-monochromatic NFRHT is an aperiodic multilayer metamaterial that differs from conventional periodic multilayer structures. Moreover, we investigate the robustness and mechanisms of the optimal quasi-monochromatic NFRHT with respect to the vacuum gap distance and the temperature difference between the emitter and receiver. In addition, the high-quality multi-peak NFRHT is designed using the AHBO algorithm by improving the definition of the evaluation factor. The results demonstrate that the AHBO algorithm is efficient in designing high-quality quasi-monochromatic and multi-peak NFRHT, and it can be further expanded to other structural designs in the field of energy conversion.

关键词： near-field radiative heat transfer adaptive hybrid Bayesian optimization quasi-monochromaticity evaluation factor inverse design

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Study on S-shaped region of pump turbine based on Omega vortex analysis method and entropy production theory

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International Journal of Agricultural and Biological engineering 2023年第3期16卷 102-109,F0003页

作者： Zhenggui Li Hongji Zeng Kun Wang Xiaodong Peng Shengnan Yan Qin Zhao key laboratory of Fluid and power machinery Ministry of Education(Xihua University)Chengdu 610039China key laboratory of Fluid machinery and engineering of Sichuan Province Xihua UniversityChengdu 610039China

In order to comprehensively analyze the operation instability of the pump turbine S-shaped region,this paper uses DDES turbulence model to calculate the model pump turbine from the perspective of the evolution law of runner vortex and draft tube vortex rope and entropy production rate,combined with experiments.The results show that the numerical simulation is in good agreement with the experiment.Omega vortex analysis method is more accurate than other vortex recognition methods because it is not affected by the threshold value.The vortices at the runner region under the runaway condition and the turbine brake condition develop towards the vaneless space and the blade pressure surface respectively,which will cause the flow obstruction and blade separation.The overall vorticity of the reverse pump condition is the largest.The vortex rope of the draft tube under runaway and turbine brake conditions is columnar in shape and has very high rotational strength.The vortex rope under reverse pump conditions is prone to fracture and form scattered vortices,impeding the normal movement of the fluid.The entropy production rate of the spanwise surface near the upper ring and the lower crown is greater than the middle spanwise surface due to the boundary layer effect.And the energy dissipation in the runner under reverse pump conditions is characterized by high at both ends of the runner and low in the middle.The energy dissipation near the wall of the straight cone section of the draft tube is large due to the squeezing effect of the vortex rope on the flow.

关键词： pump turbine S-shaped region vortex analysis method vortex evolution entropy production rate

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