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Effects of Direct Injection Timing and Air Dilution on the Combustion and Emissions Characteristics of Stratified Flame Ignited (SFI) Hybrid Combustion in a 4-Stroke PFI/DI Gasoline Engine

Tianjin University-Bang-Quan He, Hongtao Li, Tao Chen
Tianjin University; CATARC-Xue-Qing Fu
  • Technical Paper
  • 2020-01-1139
To be published on 2020-04-14 by SAE International in United States
Controlled Auto-Ignition (CAI) combustion can effectively improve the thermal efficiency of conventional spark ignition (SI) gasoline engines, due to shortened combustion processes caused by multi-point auto-ignition. However, its commercial application is limited by the difficulties in controlling ignition timing and violent heat release process at high loads. Stratified flame ignited (SFI) hybrid combustion, a concept in which rich mixture around spark plug is consumed by flame propagation after spark ignition and the unburned lean mixture closing to cylinder wall auto-ignites in the increasing in-cylinder temperature during flame propagation, was proposed to overcome these challenges. The combustion and emissions characteristics in the SFI hybrid combustion were experimentally investigated in a single-cylinder 4-stroke gasoline engine operating at medium to high loads when direct injection timing was retarded from -100 °CA to -40 °CA after top dead center (ATDC) and excess air coefficient was increased from 1.0 to 1.2 at the direct injection ratio of 30%. The experimental results show that direct injection timing and excess air coefficient control the ignition timing and combustion duration. Ignition timing advances…
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Effect of Split Injection and Intake Air Humidification on Combustion and Emission Characteristics of a Marine Diesel Engine in Partially Premixed Low-Temperature Combustion Mode

Tianjin University-Yujie Cai, Ke Wang, Shiru Kong, Zhishang Bian
  • Technical Paper
  • 2020-01-0298
To be published on 2020-04-14 by SAE International in United States
The objective of this study was to investigate combined effects of split injection strategies and intake air humidification on combustion and emissions of a partially premixed charge compression ignition (PCCI) marine diesel engine. In this research, a three-dimensional numerical model was established by a commercial code AVL-Fire to explore in-cylinder combustion process and pollutant formation factors in a four-stoke supercharged intercooled marine diesel engine under partial load at 1350 r/min. The novelty of this study is to combine different water-fuel ratios and fuel injection parameters (pilot injection timing and main injection timing) to find the optimized way to improve engine performance as well as NOx-soot emissions, thus meeting the increasingly stringent emissions restriction. The results indicate that as the main injection timing advances (-14°CA to -20°CA aTDC), the in-cylinder peak pressure increases by about 10%, the main injection ignition delay (MI ignition delay) becomes longer, the CA50 is advanced near the top dead center (TDC), which is effective to improve the indicated thermal efficiency (ITE). Meanwhile, soot emissions are reduced by about 50% compared with…
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Numerical investigations on strong knocking combustion under compression ignition conditions

Tianjin University-Lin Chen, Jianfu Zhao
State Key Lab of Engines-Jiaying Pan
  • Technical Paper
  • 2020-01-1137
To be published on 2020-04-14 by SAE International in United States
Homogeneous charge compression ignition (HCCI) combined with high compression ratio is an effective way to improve engines’ thermal efficiency. However, the severe thermodynamic conditions at high load may induce knocking combustion thus damage engine body. In this study, compression ignition knocking characteristics were parametrically investigated through RCM experiments and simulation analysis. First, the knocking characteristics were optically investigated. The experimental results show that there even exists detonation when the knock occurs thus the combustion chamber is damaged. Considering both safety and costs, the effects of different initial conditions were numerically investigated and the results show that knocking characteristics is more related to initial pressure other than initial temperature. The initial pressure have a great influence on peak pressure and knock intensity while initial temperature on knock onset. Further analysis shows that knock intensity is mainly related to the energy density of the in-cylinder mixture and energy density is higher under higher pressure conditions. Then the effects of different cylinder wall temperature on the local auto-ignition thus knocking characteristics were further discussed. The results show that…
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Numerical Investigation of the Combustion Kinetics of Partially Premixed Combustion (PPC) Fueled with Primary Reference Fuel

Tianjin University-Yuanyuan Zhao, Hu Wang, Daojian Liu, Wang Chen, Hongyan Zhu, Mingfa Yao
King Abdullah University of Science & Technology-Xinlei Liu
  • Technical Paper
  • 2020-01-0554
To be published on 2020-04-14 by SAE International in United States
This work numerically investigates the detailed combustion kinetics in a gasoline compression ignition (GCI) engine using three fuel injection strategies, including single-injection, double-injection, port fuel injection and direct injection (PFI+DI). A reduced Primary Reference Fuel (PRF) chemical kinetics mechanism was coupled with CONVERGE-SAGE CFD model to predict GCI combustion under various operating conditions. To provide insight into key reaction pathways, a post-process tool was used. The validated Converge CFD code with the PRF chemistry and the post-process tool was applied to investigate how the ignition occurs during the low-to high-temperature reaction transition and how it varies due to single- and double-injection and PFI+DI injection strategies. Three characteristic GCI combustion features were selected: (1) initial low temperature heat release (LTHR); (2) intense LTHR, where both iso-octane and n-heptane were converted to intermediates through oxygen-related reactions; (3) early stage high temperature heat release (HTHR) with CH2O as the core source species. It is found that the heat release was primarily dominated by the reaction H+O2 (+M)=HO2 (+M) and AC8H¬17+O2=AC8H17O2 during LTHR. For single- and double-injection, the high…
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Large-Scale Simulation of PEM Fuel Cell Using a “3D+1D” Model

Tianjin University-Biao Xie, Guobin Zhang, Yan Yin, Qing Du, Kui Jiao
Imperial College London-Yang Jiang
  • Technical Paper
  • 2020-01-0860
To be published on 2020-04-14 by SAE International in United States
Nowadays, proton exchange membrane (PEM) fuel cell is widely seen as a promising energy conversion device especially for transportation application scenario because of its high efficiency, low operation temperature and nearly-zero road emission. Extensive modeling work have been done based on different dimensions during the past decades, including one-dimensional (1D), two-dimensional (2D), three-dimensional (3D) and intermediate combinations in between (e.g. “1+1D”). 1D model benefits from a rationally-chosen set of assumptions to obtain excellent calculation efficiency, yet at the cost of accuracy to some extent. In contrast, 3D model has great advantage over 1D model on acquiring more comprehensive information inside the fuel cell. For macro-scale modeling work, one compromise aiming to realize both acceptable computation speed and reasonable reflection of cell operation state is to simplify the membrane electrode assembly (MEA). Therefore in this study, a “3D+1D” model is developed in which the 3D domain contains flow field and gas diffusion layer (GDL) of cathode side. The remaining part of MEA and the anode side are treated as 1D domain. The model considers two-phase flow…
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Study on Combustion Information Feedback Based on the Combination of Virtual Model and Actual Angular Velocity Measurement

Tianjin University-lichun Shi, Tao Chen
  • Technical Paper
  • 2020-01-1151
To be published on 2020-04-14 by SAE International in United States
Combustion closed-loop control is now being studied intensively for engineering applications to improve fuel economy. Currently, combustion closed-loop feedback control is usually based on the cylinder pressure signal, which is the most direct and exact signal that reflects engine working process. Although there were some relatively cheap types of in-cylinder pressure sensors, cylinder pressure sensors have not been widely applied because of their high price now. Moreover, the combustion analysis based on cylinder pressure imposes high requirements on the information acquisition capability of the current ECU, such as high acquisition and analog-digital conversion frequency and so on. For developing a low price and feasible technology, a new engine information feedback method based on model calculation and crank angular velocity measurement was proposed. A simplified combustion model was operated in ECU for the real-time calculation of cylinder pressure and combustion parameters. At the same time, the angular velocity of the crankshaft was measured by the crankshaft flywheel end sensor for the indication of real-time cylinder pressure. The first derivative can indicate the peak phase of cylinder…
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Effect of Injection Strategy on the Combustion and Knock in a Downsized Gasoline Engine with Large Eddy Simulation

Tianjin University-Ying Wang, Haiqiao Wei, Lei Zhou
BAIC Motor Powertrain Co., Ltd.-Yan Li, Junjie Liang
  • Technical Paper
  • 2020-01-0244
To be published on 2020-04-14 by SAE International in United States
Strategies to suppress knock have been extensively investigated to pursue thermal efficiency limits in downsized engines with a direct-injection spark ignition. Comprehensive considerations were given in this work, including the effects of second injection timing and injector location on knock combustion in a downsized gasoline engine by large eddy simulation. The turbulent flame propagation is determined by an improved G-equation turbulent combustion model, and the detailed chemistry mechanism of a primary reference fuel is employed to observe the detailed reaction process in the end-gas auto-ignition process. The conclusions were obtained by comparing the data to the baseline single-injection case with moderate knock intensity. Results reveal that for both arrangements of injectors, turbulence intensity is improved as the injecting timing is retarded, increasing the flame propagation speed. It can be found that knock intensity is greatly affected by the location of the injector since the distribution of the end gas is determined by the direction of the fuel injection. In present study, when injector is mounted on the opposite side as the spark plug, double injection…
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Noise Source Identification of a Gasoline Engine Based on Parameters Optimized Variational Mode Decomposition and Robust Independent Component Analysis

Tianjin University-Xiao Yang, Fengrong Bi, Lipeng Zhang, Xiaobo Bi, Teng Ma, Daijie Tang
  • Technical Paper
  • 2020-01-0425
To be published on 2020-04-14 by SAE International in United States
Noise source identification and separation of internal combustion engines is an effective tool for engine NVH (noise, vibration and harshness) development. Among various experimental approaches, noise source identification using signal processing has attracted extensive attention because of that the signal can be easily acquired and the requirements for equipment is relatively low. In this paper, variational mode decomposition (VMD) combined with independent component analysis (ICA) is used for noise source identification of a turbo-charged gasoline engine. Existing algorithms have been proved to be effective to extract signal features but also have disadvantages. One of the key problems in presently used method is that the main components of the signal, i.e. the main source of the noise, are unknown in advance. Thus the parameters selection of signal processing algorithms, which has a significance influence on the identification result, has no uniform criterion. To solve this problem, a parameter selection method using Kurtosis index is developed to optimize the decomposition level and the quadratic penalty of VMD. After the signal is decomposed into several relevant intrinsic mode…
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Effect of Supercharging on the Intake Flow Characteristics of a Swirl-Supported Engine

Tianjin University-Yizhuo Feng, Zhen Lu, Tianyou Wang, Junqian Cai, Pengfei Wei
China North Engine Research Institute-Yufeng Li
  • Technical Paper
  • 2020-01-0794
To be published on 2020-04-14 by SAE International in United States
Although supercharged system has been widely employed in downsized engines, the effect of supercharging on the intake flow characteristics remains inadequately understood. Therefore, it is worthwhile to investigate intake flow characteristics under high intake pressure. In this study, the supercharged intake flow is studied by experiment using steady flow test bench with supercharged system and transient flow simulation. For the steady flow condition, gas compressibility effect is found to significantly affect the flow coefficient (Cf), as Cf decreases with increasing intake pressure drop, if the compressibility effect is neglected in calculation by the typical evaluation method; while Cf has no significant change if the compressibility effect is included. Compared with the two methods, the deviation of the theoretical intake velocity and the density of the intake flow is the reason for Cf calculation error. For the transient intake condition, such increase of intake flow velocity with increasing intake pressure was found to be valid only at low engine speeds (2000 rpm). At high engine speeds (4000 rpm), however, flow velocity remains almost unchanged regardless of…
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Study on dynamic characteristics of droplet impact on wet wall

Tianjin University-Yuqian Wang, Yiqiang Pei, Jing Qin, Lili Lu, Xiang Li, Zhenshan Peng
  • Technical Paper
  • 2020-01-1429
To be published on 2020-04-14 by SAE International in United States
To better understand the spray impingement on oil substrate and the interaction of the two in a gasoline direct injection engine.It's important to understand the behavior of single droplet impinge on the oil film and composition of the coronal formed by fuel and oil.In this paper, laser induced fluorescence method was used to observe the phenomenon of ethanol droplets impinging on the liquid film of glycerol aqueous solution. The We number of incident droplets, the dynamic viscosity of the liquid film and the dimensionless liquid film thickness were studied. The relationship of fluorescence intensity and coronal composition and the formation mechanisms of coronal and splash were built. Tests have shown that We number have a major promoting effect on crown splash. High liquid film dynamic viscosity and dimensionless liquid film thickness have an inhibitory effect on coronal formation and splash. Under the condition that the We number of incident droplets is equal, the composition of the liquid film in the crown decreases as the dynamic viscosity of the liquid film increases. The proportion of the…