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14 pages, 26013 KiB

Open AccessArticle

Effects of Two Pilot Injection on Combustion and Emissions in a PCCI Diesel Engine

by Deqing Mei, Qisong Yu, Zhengjun Zhang, Shan Yue and Lizhi Tu

Energies 2021, 14(6), 1651; https://doi.org/10.3390/en14061651 - 16 Mar 2021

Cited by 8 | Viewed by 2010

The effects of two pilot injections on combustion and emissions were evaluated in a single−cylinder turbocharged diesel engine, which operated in premixed charge compression ignition (PCCI) modes with multiple injections and heavy exhaust gas recirculation under the low load by experiments and simulation. [...] Read more.

The effects of two pilot injections on combustion and emissions were evaluated in a single−cylinder turbocharged diesel engine, which operated in premixed charge compression ignition (PCCI) modes with multiple injections and heavy exhaust gas recirculation under the low load by experiments and simulation. It was revealed that with the delay of the start of the first pilot injection (SOI−P1) or the advance of the start of second pilot injection (SOI−P2), respectively, the pressure, heat release rate (HRR), and temperature peak were all increased. Analysis of the combustion process indicates that, during the two pilot injection periods, the ignition timing was mainly determined by the SOI−P2 while the first released heat peak was influenced by SOI−P1. With the delay of SOI−P1 or the advance of SOI−P2, nitrogen oxide (NOx) generation increased significantly while soot generation varied a little. In addition, increasing Q1 and decreasing the second pilot injection quantity (Q2) can manipulate the NOx and soot at a low level. The advance in SOI−P2 of 5 °CA couple with increasing Q1 and reducing Q2 was proposed, which can mitigate the compromise between emissions and thermal efficiency under the low load in the present PCCI mode. Full article

(This article belongs to the Special Issue Advanced Modeling and Experimental Methods for Engine Combustion Analysis)

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14 pages, 2986 KiB

Open AccessArticle

Analysis of the Ignition Behavior Based on Similarity Factor Method

by Weiwei Fan, Shengxiong Yang, Ke Xu, Mingdong Zhu and Jie Xu

Energies 2021, 14(4), 873; https://doi.org/10.3390/en14040873 - 7 Feb 2021

Cited by 1 | Viewed by 1559

Abstract

The chemical kinetics mechanism is an important factor to accurately predict the combustion characteristics of constant-volume bomb (CVB). In this study, an n-heptane oxidation mechanism constructed by Wang et al. is introduced to study the correlation of the ignition behaviors with the mechanism [...] Read more.

The chemical kinetics mechanism is an important factor to accurately predict the combustion characteristics of constant-volume bomb (CVB). In this study, an n-heptane oxidation mechanism constructed by Wang et al. is introduced to study the correlation of the ignition behaviors with the mechanism constructed by Chang et al. The effects of the similarity factor method in the analysis of ignition behaviors of fuel in CVB were repeatedly verified by changing the important spraying parameters: injection pressure and hole diameter. Through further verification, it was found that the combustion process was controlled at approximately 850 K and stoichiometric ratio mixture of fuel/air in CVB, which corresponds to the negative temperature coefficient region at stoichiometric ratio mixture in shock tube (ST). The mechanism verified by the experiment under the condition in ST can reflect the chemical ignition in CVB. In addition, the similarity factor method was less dependent on the chemical reaction mechanism and boundary conditions. Full article

(This article belongs to the Special Issue Advanced Modeling and Experimental Methods for Engine Combustion Analysis)

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18 pages, 6180 KiB

Open AccessArticle

The Role of Multiple Injections on Combustion in a Light-Duty PPC Engine

by Rickard Solsjö, Mehdi Jangi, Bengt Johansson and Xue-Song Bai

Energies 2020, 13(21), 5535; https://doi.org/10.3390/en13215535 - 22 Oct 2020

Viewed by 1977

Abstract

This paper presents a numerical investigation of the ignition and combustion process of a primary reference fuel in a partially premixed light-duty internal combustion (PPC) engine. Partially pre-mixed combustion is achieved by employing a multiple injection strategy with three short injection events of [...] Read more.

This paper presents a numerical investigation of the ignition and combustion process of a primary reference fuel in a partially premixed light-duty internal combustion (PPC) engine. Partially pre-mixed combustion is achieved by employing a multiple injection strategy with three short injection events of fuel pulses. The timing of the first two fuel pulses, 48 and 22 crank angle degrees before top dead center, are chosen with the purpose to stratify the fuel and air charge, whereas the third injection, at five crank angle degrees before top dead center, serves as an actuator of the main heat release. In addition to this baseline injection, three alternative injection strategies are studied, including a split-fuel two-injection strategy and modified triple-injection strategies. Large eddy simulations are employed utilizing a skeletal chemical kinetic mechanism for primary reference fuel capable of capturing the low-temperature ignition and the high temperature combustion. The large eddy simulation (LES) results are compared with experiments in an optical accessible engine. The results indicate that the first ignition sites are in the bowl region where the temperature is relatively higher, and the reaction fronts thereafter propagate in the swirl direction and towards the centerline of the cylinder. The charge from the first two injections initially undergoes low-temperature reactions and thereafter high-temperature reservoirs are formed in the bowl region. The main heat-release is initiated in the engine when the fuel from the third injection reaches the high-temperature reservoirs. Finally, the remaining fuel in the lean mixtures from the first two injections is oxidized. By variation of the injection strategy, two trends are identified: (1) by removing the second injection a higher intake temperature is required to enable the ignition of the charge, and (2) by retarding second injection, a longer ignition delay is identified. Both can be explained by the stratification of fuel and air mixture, and the resulting reactivity in various equivalence ratio and temperature ranges. The LES results reveal the details of the charge stratification and the subsequent heat release process. The present results indicate a rather high sensitivity of partially premixed combustion process to the injection strategies. Full article

(This article belongs to the Special Issue Advanced Modeling and Experimental Methods for Engine Combustion Analysis)

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24 pages, 4755 KiB

Open AccessArticle

Comparative Study of Physics-Based Modeling and Neural Network Approach to Predict Cooling in Vehicle Integrated Thermal Management System

by Duwon Choi, Youngkuk An, Nankyu Lee, Jinil Park and Jonghwa Lee

Energies 2020, 13(20), 5301; https://doi.org/10.3390/en13205301 - 12 Oct 2020

Cited by 7 | Viewed by 3090

Abstract

Vehicle integrated thermal management system (VTMS) is an important technology used for improving the energy efficiency of vehicles. Physics-based modeling is widely used to predict the energy flow in such systems. However, physics-based modeling requires several experimental approaches to get the required parameters. [...] Read more.

Vehicle integrated thermal management system (VTMS) is an important technology used for improving the energy efficiency of vehicles. Physics-based modeling is widely used to predict the energy flow in such systems. However, physics-based modeling requires several experimental approaches to get the required parameters. The experimental approach to obtain these parameters is expensive and requires great effort to configure a separate experimental device and conduct the experiment. Therefore, in this study, a neural network (NN) approach is applied to reduce the cost and effort necessary to develop a VTMS. The physics-based modeling is also analyzed and compared with recent NN techniques, such as ConvLSTM and temporal convolutional network (TCN), to confirm the feasibility of the NN approach at EPA Federal Test Procedure (FTP-75), Highway Fuel Economy Test cycle (HWFET), Worldwide harmonized Light duty driving Test Cycle (WLTC) and actual on-road driving conditions. TCN performed the best among the tested models and was easier to build than physics-based modeling. For validating the two different approaches, the physical properties of a 1 L class passenger car with an electric control valve are measured. The NN model proved to be effective in predicting the characteristics of a vehicle cooling system. The proposed method will reduce research costs in the field of predictive control and VTMS design. Full article

(This article belongs to the Special Issue Advanced Modeling and Experimental Methods for Engine Combustion Analysis)

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24 pages, 7206 KiB

Open AccessArticle

Effect of Spark Ignition Timing and Water Injection Temperature on the Knock Combustion of a GDI Engine

by Aqian Li and Zhaolei Zheng

Energies 2020, 13(18), 4931; https://doi.org/10.3390/en13184931 - 20 Sep 2020

Cited by 14 | Viewed by 3559

Abstract

A turbocharged downsizing spark ignition (SI) engine cooperating with an in-cylinder direct injection technology is one of the most effective ways to improve the power and economy of gasoline engines. However, engine knock has limited the application and development of the downsizing of [...] Read more.

A turbocharged downsizing spark ignition (SI) engine cooperating with an in-cylinder direct injection technology is one of the most effective ways to improve the power and economy of gasoline engines. However, engine knock has limited the application and development of the downsizing of gasoline engines. Water injection technology can effectively suppress the knock. In this study, a method of numerical simulation was used to explore the effect of the water injection temperature on the combustion and suppression of the knock. First of all, the knock of the gasoline engine was induced by advancing the spark timing. Then, when the other conditions were the same, different water injection temperatures were set. The results show that lowering the water injection temperature reduced the knock intensity in the cylinder, but increasing the water injection temperature made the water distribution more uniform, and the peak values of each monitoring point were more consistent. The circulating work power increased with the increase of the water injection temperature. For emissions, as the temperature of the water injection increased, the emissions of soot and unburned hydrocarbons (UHCs) decreased, and NO_x slightly increased. Full article

(This article belongs to the Special Issue Advanced Modeling and Experimental Methods for Engine Combustion Analysis)

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22 pages, 4286 KiB

Open AccessArticle

Analysis of the Influence of Diesel Spray Injection on the Ignition and Soot Formation in Multiple Injection Strategy

by Raul Payri, José M. García-Oliver, Victor Mendoza and Alberto Viera

Energies 2020, 13(13), 3505; https://doi.org/10.3390/en13133505 - 7 Jul 2020

Cited by 11 | Viewed by 2362

Abstract

Multiple injection strategies have increased their capabilities along with the evolution of injection system technologies up to the point that nowadays it is possible to inject eight different pulses, permitting to improve the engine performance, and consequently, emissions. The present work was realized [...] Read more.

Multiple injection strategies have increased their capabilities along with the evolution of injection system technologies up to the point that nowadays it is possible to inject eight different pulses, permitting to improve the engine performance, and consequently, emissions. The present work was realized for two simplified strategies: a pilot-main and a main-post, in order to analyze the influence of an auxiliary pulse on the main and otherwise, in reactive conditions for two pilot/post quantities and four hydraulic dwell times. The study was carried out by employing two optical techniques: diffused back-illumination with flame bandpass chemiluminescence for measuring soot, represented by soot-maps distribution, and single-pass schlieren for ignition delay (ID). Furthermore, a novel methodology for decoupling the start of combustion (SOC) of the second pulse was developed and successfully validated. From the ignition delay results, it was found for all test points that the pilot injection enhanced conditions, which promote a faster ignition of the main pulse, also at higher chamber temperatures, all conditions presented a separate combustion event for each injection. In emission terms, soot increased in the pilot-main strategies compared to its single injection case, as well as, in conditions that promote faster-premixed combustion. Full article

(This article belongs to the Special Issue Advanced Modeling and Experimental Methods for Engine Combustion Analysis)

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24 pages, 3642 KiB

Open AccessArticle

Large-Eddy Simulation of ECN Spray A: Sensitivity Study on Modeling Assumptions

by Mahmoud Gadalla, Jeevananthan Kannan, Bulut Tekgül, Shervin Karimkashi, Ossi Kaario and Ville Vuorinen

Energies 2020, 13(13), 3360; https://doi.org/10.3390/en13133360 - 1 Jul 2020

Cited by 17 | Viewed by 4752

Abstract

In this study, various mixing and evaporation modeling assumptions typically considered for large-eddy simulation (LES) of the well-established Engine Combustion Network (ECN) Spray A are explored. A coupling between LES and Lagrangian particle tracking (LPT) is employed to simulate liquid n-dodecane spray [...] Read more.

In this study, various mixing and evaporation modeling assumptions typically considered for large-eddy simulation (LES) of the well-established Engine Combustion Network (ECN) Spray A are explored. A coupling between LES and Lagrangian particle tracking (LPT) is employed to simulate liquid n-dodecane spray injection into hot inert gaseous environment, wherein Lagrangian droplets are introduced from a small cylindrical injection volume while larger length scales within the nozzle diameter are resolved. This LES/LPT approach involves various modeling assumptions concerning the unresolved near-nozzle region, droplet breakup, and LES subgrid scales (SGS) in which their impact on common spray metrics is usually left unexplored despite frequent utilization. Here, multi-parametric analysis is performed on the effects of (i) cylindrical injection volume dimensions, (ii) secondary breakup model, particularly Kelvin–Helmholtz Rayleigh–Taylor (KHRT) against a no-breakup model approach, and (iii) LES SGS models, particularly Smagorinsky and one-equation models against implicit LES. The analysis indicates the following findings: (i) global spray characteristics are sensitive to radial dimension of the cylindrical injection volume, (ii) the no-breakup model approach performs equally well, in terms of spray penetration and mixture formation, compared with KHRT, and (iii) the no-breakup model is generally insensitive to the chosen SGS model for the utilized grid resolution. Full article

(This article belongs to the Special Issue Advanced Modeling and Experimental Methods for Engine Combustion Analysis)

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26 pages, 9312 KiB

Open AccessArticle

High-Speed Imaging of Spray Formation and Combustion in an Optical Engine: Effects of Injector Aging and TPGME as a Fuel Additive

by Xinda Zhu, Manu Mannazhi, Natascia Palazzo, Per-Erik Bengtsson and Öivind Andersson

Energies 2020, 13(12), 3105; https://doi.org/10.3390/en13123105 - 16 Jun 2020

Cited by 1 | Viewed by 3148

Abstract

High-speed imaging of fuel sprays and combustion is conducted on a light-duty optical engine to investigate the effects of injector aging, with a focus on soot. The spray behaviors of one new and one aged injector are compared using Mie-scattering. In addition to [...] Read more.

High-speed imaging of fuel sprays and combustion is conducted on a light-duty optical engine to investigate the effects of injector aging, with a focus on soot. The spray behaviors of one new and one aged injector are compared using Mie-scattering. In addition to this, the combustion process of a baseline diesel fuel and a blend with TPGME (tripropylene glycol monomethyl ether) are compared using natural luminosity (NL) imaging. TPGME is an oxygenated additive which can be used to reduce soot emissions. X-ray tomography of the two injectors demonstrates that the aging does not lead to significant geometry differences, nor to formation of dense internal nozzle deposits. Both injectors show similar liquid penetration and spreading angle. However, the aged injector shows a prolonged injection and more fuel dribbling after the injection events, leading to a higher injection quantity. The fuel quantity difference shows a larger impact on the NL at low load than the TPGME additive, indicating that the in-cylinder temperature is more important for soot oxidation than oxygen concentration under these conditions. At medium load, the NL is much less sensitive to small temperature variations, while the TPGME is more effective for soot reduction. Full article

(This article belongs to the Special Issue Advanced Modeling and Experimental Methods for Engine Combustion Analysis)

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23 pages, 14930 KiB

Open AccessArticle

The Flex-OeCoS—a Novel Optically Accessible Test Rig for the Investigation of Advanced Combustion Processes under Engine-Like Conditions

by Bruno Schneider, Christian Schürch, Konstantinos Boulouchos, Stefan Herzig, Marc Hangartner, David Humair, Silas Wüthrich, Christoph Gossweiler and Kai Herrmann

Energies 2020, 13(7), 1794; https://doi.org/10.3390/en13071794 - 8 Apr 2020

Cited by 7 | Viewed by 3462

Abstract

A new test rig has been designed, built and commissioned, and is now jointly pursued to facilitate experimental investigations into advanced combustion processes (i.e., dual fuel, multi-mode) under turbulent conditions at high, engine-like temperature and pressure levels. Based on a standard diesel engine [...] Read more.

A new test rig has been designed, built and commissioned, and is now jointly pursued to facilitate experimental investigations into advanced combustion processes (i.e., dual fuel, multi-mode) under turbulent conditions at high, engine-like temperature and pressure levels. Based on a standard diesel engine block, it offers much improved optical access to the in-cylinder processes due to its separated and rotated arrangement of the compression volume and combustion chamber, respectively. A fully variable pneumatic valve train and the appropriate preconditioning of the intake air allows it to represent a wide range of engine-like in-cylinder conditions regarding pressures, temperatures and turbulence levels. The modular design of the test rig facilitates easy optimizations of the combustion chamber/cylinder head design regarding different experimental requirements. The name of the new test rig, Flex-OeCoS, denotes its Flexibility regarding Optical engine Combustion diagnostics and/or the development of corresponding Sensing devices and applications. Measurements regarding in-cylinder gas pressures, temperatures and the flow field under typical operating conditions are presented to complete the description and assessment of the new test rig. Full article

(This article belongs to the Special Issue Advanced Modeling and Experimental Methods for Engine Combustion Analysis)

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