Research

12 pages, 4286 KiB

Open AccessArticle

Probing the Pre-Ignition Behavior of Negative Temperature Coefficient Fuels at Low to High Temperatures: A Case Study of Dimethyl Ether

by Wenlin Huang, Honghuan Wu, Wuchuan Sun, Congjie Hong, Zemin Tian, Yingwen Yan, Zuohua Huang and Yingjia Zhang

Energies 2023, 16(5), 2118; https://doi.org/10.3390/en16052118 - 22 Feb 2023

Cited by 1 | Viewed by 998

Abstract

Pre-ignition, involving complex interactions of physical and chemical processes, occurs not only in actual combustion engines but also in fundamental research equipment such as rapid compression machines and shock tubes. Thus, identifying the combustion conditions prone to pre-ignition is critical for the interpretation [...] Read more.

Pre-ignition, involving complex interactions of physical and chemical processes, occurs not only in actual combustion engines but also in fundamental research equipment such as rapid compression machines and shock tubes. Thus, identifying the combustion conditions prone to pre-ignition is critical for the interpretation of ignition data and fuel design. Shock tube experiments with dimethyl ether (DME) were carried out in this study to investigate the pre-ignition behavior during fuel auto-ignition. The experimental conditions included a wide range of temperatures (620–1370 K), pressures (1–9 atm), and equivalence ratios (0.5–5.0). The results indicate that pre-ignition of DME is prone to occur in the transition region from a high temperature to an intermediate temperature (~1000 K), and the decrease in pressure and equivalency ratio will aggravate the pre-ignition behavior. Theoretical analysis was then performed using four physical-based criteria: temperature perturbation sensitivity of ignition delay times, thermal diffusivity, a dimensionless parameter analogous to the Damköhler number, and the Sankaran number. According to experimental observations and theoretical analysis, it was found that the temperature sensitivity (S_tp = 75 μs/K) and Sankaran number (Sa_p = 1) are the best available criteria for predicting the pre-ignition behavior of negative temperature coefficient (NTC) fuels. The pre-ignition region of non-NTC fuels can be accurately predicted by thermal diffusivity and the Damköhler number, but they deviate greatly when predicting the pre-ignition of NTC fuels. This strategy is expected to provide a feasible method for identifying the critical conditions under which pre-ignition may occur and for revealing the pre-ignition mechanisms for other NTC fuels. Full article

(This article belongs to the Special Issue Trends and Prospects in Engine Combustion)

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19 pages, 3933 KiB

Open AccessArticle

An Experimental Analysis and ANN Based Parameter Optimization of the Influence of Microalgae Spirulina Blends on CI Engine Attributes

by S. Charan Kumar, Amit Kumar Thakur, J. Ronald Aseer, Sendhil Kumar Natarajan, Rajesh Singh, Neeraj Priyadarshi and Bhekisipho Twala

Energies 2022, 15(17), 6158; https://doi.org/10.3390/en15176158 - 24 Aug 2022

Cited by 2 | Viewed by 1304

Abstract

In this present investigation, emittance and performance attributes of a diesel engine using micro-algae spirulina blended biodiesel mixtures of various concentrations (20%, 35%, 50%, 65%, 80%, and 100%) were evaluated. An optimization model was also developed using an Artificial Neural Network (ANN) to [...] Read more.

In this present investigation, emittance and performance attributes of a diesel engine using micro-algae spirulina blended biodiesel mixtures of various concentrations (20%, 35%, 50%, 65%, 80%, and 100%) were evaluated. An optimization model was also developed using an Artificial Neural Network (ANN) to characterize the experimental parameters. Experimental findings demonstrated significant improvement in brake specific fuel consumption (BSFC) using varied blends. Furthermore, brake thermal efficiency (BTE) is decreased gradually for biodiesel blends as compared to diesel. Micro-algae spirulina blends have shown lower concentrations of NO_X and HC while increasing CO₂ relative to pure diesel. To develop the model, three sets of optimizers, namely, adam, nadam, and adagrad, along with activation functions, such as sigmoid, softmax, and relu, were selected. The results revealed that sigmoid activation function with adam learning optimizer by using 32 hidden layer neurons has given the least value of mean squared error (MSE). Hence, the ANN approach was proven to be capable of predicting engine attributes with a least mean squared error of 0.00013, 0.00060, 0.00021, 0.00011, and 0.00104 for NO_X, HC, CO₂, brake thermal efficiency, and brake specific fuel consumption, respectively. The Artificial Neural Network approach is capable of predicting CI engine attributes with accuracy and ease of investigation. Full article

(This article belongs to the Special Issue Trends and Prospects in Engine Combustion)

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18 pages, 9576 KiB

Open AccessArticle

Numerical Study of Knocking Combustion in a Heavy-Duty Engine under Plateau Conditions

by Haiying Li, Xiaoqin Zhang, Chaofan Li, Rulou Cao, Weiqing Zhu, Yaozong Li, Fengchun Liu and Yufeng Li

Energies 2022, 15(9), 3083; https://doi.org/10.3390/en15093083 - 22 Apr 2022

Cited by 3 | Viewed by 979

Abstract

Diesel engine combustion becomes very rough and can lead even lead to deflagration under high altitude conditions, which is harmful to component durability. In this study, the effects of altitude on the main combustion characteristics—in-cylinder fluid flow, spray behavior, and pressure and temperature [...] Read more.

Diesel engine combustion becomes very rough and can lead even lead to deflagration under high altitude conditions, which is harmful to component durability. In this study, the effects of altitude on the main combustion characteristics—in-cylinder fluid flow, spray behavior, and pressure and temperature distribution—were analyzed with CFD. A numerical model was built on the CONVERGE platform and validated with the optical spray behavior and pressure trace measured by the test bench. The simulation results indicated that the decreases in compression pressure and temperature at 4.5 km led to an over 4 °CA longer ignition delay than those of 1 and 3 km. The combustion efficiency decreased from 90% to 47% when the combustion changed from normal combustion to knocking combustion due to severe spray impingement. The processes of end-gas ignition, sequential combustion, and pressure oscillation in knocking combustion were revealed by the numerical modeling results. These results indicate that super-knocking combustion exists in both spark-ignition (SI) engines and compression-ignition (CI) engines. Full article

(This article belongs to the Special Issue Trends and Prospects in Engine Combustion)

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13 pages, 1648 KiB

Open AccessArticle

Experimental Investigation on the Heat Flux Distribution and Pollutant Emissions of Slot LPG/Air Premixed Impinging Flame Array

by Haisheng Zhen, Baodong Du, Xiaoyu Liu, Zihao Liu and Zhilong Wei

Energies 2021, 14(19), 6255; https://doi.org/10.3390/en14196255 - 01 Oct 2021

Cited by 2 | Viewed by 1323

Abstract

Experiments were carried out to investigate the heat transfer and pollutants emission characteristics of a slot LPG premixed flame array impinging normally onto a flat plate. The effects of jet-to-jet spacing (S/de), nozzle-to-plate distance (H/de), [...] Read more.

Experiments were carried out to investigate the heat transfer and pollutants emission characteristics of a slot LPG premixed flame array impinging normally onto a flat plate. The effects of jet-to-jet spacing (S/de), nozzle-to-plate distance (H/de), and jet Reynolds number (Re) on the heat flux and emission index of CO, CO₂, and NO_x/NO₂ were examined. In addition, the thermal and emission characteristics between slot jets and circular jets were compared under identical experimental conditions. The results show that the more uniform heat flux distribution and higher total heat flux can be obtained at moderate jet-to-jet spacing, large jet-to-plate distance, and higher Reynolds number. EICO emissions can be influenced by the combined effects of jet-to-jet spacing, jet-to-plate distance, and higher Reynolds number. For the sake of the better combustion efficiency and lower EICO emission, the moderate jet-to-jet spacing (S/de = 2.5), larger jet-to-plate distance (H/de = 4), and relatively higher Reynolds number (Re = 1500) are preferred for the slot jet flame array. Furthermore, it is found that there exists a trade-off between the EICO and EINOx of the slot LPG flame array. Compared with multiple circular flame jets, multiple slot flames jets have the higher area-averaged heat flux due to the larger heating area and more uniform heat flux distribution, while the higher EICO emission and lower EINO_x emission are due to the greater jet interaction suppressing the air entrainment. Thus, it is known that the slot flame array has a better heating performance but relatively higher pollutant emissions than the circular flame array. Full article

(This article belongs to the Special Issue Trends and Prospects in Engine Combustion)

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26 pages, 7330 KiB

Open AccessArticle

Simulation Study on the Effect of Flue Gas on Flow Field and Rotor Stress in Gas Turbines

by Guangkui Liu, Sicong Sun, Kui Liang, Xisheng Yang, Dong An, Qi Wen and Xiaohan Ren

Energies 2021, 14(19), 6135; https://doi.org/10.3390/en14196135 - 26 Sep 2021

Cited by 5 | Viewed by 1739

Abstract

A flue gas turbine is the main energy recovery equipment in a heavy oil catalytic cracking unit. Blade erosion and fracture are the main reasons for gas turbine failure. In this study, the characteristics of the flow field and rotor stress in the [...] Read more.

A flue gas turbine is the main energy recovery equipment in a heavy oil catalytic cracking unit. Blade erosion and fracture are the main reasons for gas turbine failure. In this study, the characteristics of the flow field and rotor stress in the gas turbine under different fume volumes are simulated and analyzed by simulation software (ANSYS). The influences of fume volume on the high-temperature fume flow field, temperature, velocity, catalyst particle movement rotor stress in the gas turbine, as well as the influence law of flue gas flow on temperature gradient, pressure gradient, velocity distribution, and the main position of blade erosion were studied. The stress distribution and maximum stress position of the impeller were also determined. It was found that the variation trends of the pressure gradient in the calculation domain of the gas turbine under different fume volumes are similar. The pressure on the working face of the rotor blade decreases gradually along the flow direction of the high-temperature fume. The highest pressure appears near the sharp corner with the large radius of the front edge of the rotor blade. The variation of the fume flow rate has little influence on the temperature field of the entire machine. The erosion wear of the rotor blade mainly occurs in the leading edge and tail. The maximum stress point of the blade is located at the large fillet of the first pair of tenon teeth. The maximum stress point of the disc is located at the large fillet of the third pair of tenon teeth. It is believed that these research results have reference help for analyzing the typical failure causes of flue gas turbine, optimizing the actual operating conditions and the reconstruction design of flue gas turbine. Full article

(This article belongs to the Special Issue Trends and Prospects in Engine Combustion)

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31 pages, 9861 KiB

Open AccessArticle

Hierarchical Auto-Ignition and Structure-Reactivity Trends of C₂–C₄ 1-Alkenes

by Wuchuan Sun, Yingjia Zhang, Yang Li and Zuohua Huang

Energies 2021, 14(18), 5797; https://doi.org/10.3390/en14185797 - 14 Sep 2021

Cited by 2 | Viewed by 1965

Abstract

Ignition delay times of small alkenes are a valuable constraint for the refinement of the core kinetic mechanism of hydrocarbons used in representing combustion properties of real fuels. Moreover, the chemical reactivity comparison of those small alkenes provides a reference in object-oriented fuel [...] Read more.

Ignition delay times of small alkenes are a valuable constraint for the refinement of the core kinetic mechanism of hydrocarbons used in representing combustion properties of real fuels. Moreover, the chemical reactivity comparison of those small alkenes provides a reference in object-oriented fuel design and logical combustion utilization. In this study, the ignition delay times of C₂–C₄ alkenes (ethylene, propene and 1-butene) were measured behind reflected shock waves first, with a fixed oxygen concentration (X_O2 = 6%) and equivalence ratio (φ = 1.0) at various pressures of 1.2, 4.0 and 16.0 atm, in order to facilitate the comparison. Three chemical-based-Arrhenius-type correlations covering a wide range of temperature, pressure, equivalence ratio, and dilution were proposed. The simplified reaction network for pyrolysis and oxidation of 1-alkenes was depicted relying on the reaction classes of alkenes. Nine generally accepted mechanisms were used to simulate the ignition delay times measured by this study as well as literature. All the kinetic models show reasonable structure-reactivity trends for all of the three alkenes, but only NUIGMech 1.1 is capable of representing quantificationally the chemical reactivity at all tested conditions. Generally, ethylene exhibits the highest reactivity while propene presents the lowest at high temperatures. Analyses of sensitivity and flux indicate that the main oxidation pathway of ethylene is chain-branching, which accelerates the accumulation of free radical pools, especially for the Ḣ atom, Ȯ atom and ȮH radical, which results in the highest reactivity of ethylene. For propene and 1-butene, due to the presence of the allylic site, consumption of allylic radicals becomes the decisive step of oxidation and allylic radicals are mostly consumed by the HȮ₂ radical. However, there are no such efficient reaction pathways for the formation of HȮ₂ radicals during the propene oxidation process, while reaction pathways for HȮ₂ formation in 1-butene are efficient. Thus, 1-butene presents higher reactivity compared to propene. Full article

(This article belongs to the Special Issue Trends and Prospects in Engine Combustion)

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14 pages, 3406 KiB

Open AccessArticle

Research on Optical Diagnostic Method of PDE Working Status Based on Visible and Near-Infrared Radiation Characteristics

by Xiaolong Huang, Ning Li and Yang Kang

Energies 2021, 14(18), 5703; https://doi.org/10.3390/en14185703 - 10 Sep 2021

Viewed by 1257

Abstract

Fill fraction not only has a profound impact on the process of deflagration to detonation in pulsed detonation engine, but also affects the propulsion performance in both flight and ground tests. In this paper, a novel optical diagnostic method based on detonation exhaust [...] Read more.

Fill fraction not only has a profound impact on the process of deflagration to detonation in pulsed detonation engine, but also affects the propulsion performance in both flight and ground tests. In this paper, a novel optical diagnostic method based on detonation exhaust radiation in visible and near-infrared region within 300–2600 nm is developed to determine the current working state in the gas–liquid two-phase pulsed detonation cycle. The results show that the radiation characteristic in each stage of detonation cycle is unique and can be a good indicator to infer the fill fraction. This is verified experimentally by comparison with the laser absorption spectroscopy method, which utilizes a DFB laser driven by ramp injection current to scan H₂O transition of 1391.67 nm at a frequency of 20 kHz. Due to concentrated radiation intensity, time duration reaching accumulated radiant energy ratio of 50% in detonation status would be smaller than 1.2 ms, and detonation status would be easily distinguished from deflagration with this critical condition. In addition, the variation of important intermediates OH, CH, and C₂ radicals during detonation combustion are obtained according to the analysis of detonation spectrum, which can also be proposed as a helpful optical diagnostics method for the combustion condition based on C radical concentration. The study demonstrates the feasibility of optical diagnostics based on radiation in visible and near-infrared regions, which could provide an alternative means to diagnose and improve pulsed detonation engine performance. Full article

(This article belongs to the Special Issue Trends and Prospects in Engine Combustion)

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17 pages, 7307 KiB

Open AccessArticle

Effect of Temperature Conditions on Flame Evolutions of Turbulent Jet Ignition

by Jiaying Pan, Yu He, Tao Li, Haiqiao Wei, Lei Wang and Gequn Shu

Energies 2021, 14(8), 2226; https://doi.org/10.3390/en14082226 - 16 Apr 2021

Cited by 6 | Viewed by 1822

Abstract

Turbulent jet ignition technology can significantly improve lean combustion stability and suppress engine knocking. However, the narrow jet channel between the pre-chamber and the main chamber leads to some difficulties in heat exchange, which significantly affects combustion performance and mechanical component lifetime. To [...] Read more.

Turbulent jet ignition technology can significantly improve lean combustion stability and suppress engine knocking. However, the narrow jet channel between the pre-chamber and the main chamber leads to some difficulties in heat exchange, which significantly affects combustion performance and mechanical component lifetime. To clarify the effect of temperature conditions on combustion evolutions of turbulent jet ignition, direct numerical simulations with detailed chemical kinetics were employed under engine-relevant conditions. The flame propagation in the pre-chamber and the early-stage turbulent jet ignition in the main chamber were investigated. The results show that depending on temperature conditions, two types of flame configuration can be identified in the main chamber, i.e., the normal turbulent jet flame propagation and the spherical flame propagation, and the latter is closely associated with pressure wave disturbance. Under low-temperature conditions, the cold jet stoichiometric mixtures and the vortexes induced by the jet flow determine the early-stage flame development in the main chamber. Under intermediate temperature conditions, pre-flame heat release and leading pressure waves are induced in the jet channel, which can be regarded as a transition of different combustion modes. Whereas under high-temperature conditions, irregular auto-ignition events start to occur, and spherical flame fronts are induced in the main chamber, behaving faster flame propagation. Full article

(This article belongs to the Special Issue Trends and Prospects in Engine Combustion)

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18 pages, 5091 KiB

Open AccessArticle

Combustion Characteristics of Small Laminar Flames in an Upward Decreasing Magnetic Field

by Yu Xie, Zhilong Wei, Teng Zhou, Haishen Zhen, Zihao Liu and Zuohuang Huang

Energies 2021, 14(7), 1969; https://doi.org/10.3390/en14071969 - 02 Apr 2021

Cited by 4 | Viewed by 2405

Abstract

The combustion characteristics of laminar biogas premixed and diffusion flames in the presence of upward decreasing magnetic fields have been investigated in this study. The mechanism of magnet–flame interaction in the literature, in which magnetic fields change the behaviors of laminar flames due [...] Read more.

The combustion characteristics of laminar biogas premixed and diffusion flames in the presence of upward decreasing magnetic fields have been investigated in this study. The mechanism of magnet–flame interaction in the literature, in which magnetic fields change the behaviors of laminar flames due to the paramagnetic and diamagnetic properties of the constituent gases, is examined and the results are as follows. The magnetic field has no noticeable effect on premixed flames due to low oxygen concentration of the mixed gas at the injection and the relatively high flow momentum. However, due to the diffusion nature of diffusion flames and paramagnetic property of oxygen in ambient air, oxygen distributions are subjected to the gradient of magnetic flux, thus shortening the height of diffusion flames. Results also show that the flame volume is more strongly varied than flame height. Altered oxygen distributions result in improved combustion and higher flame temperature. In the case of current magnet–flame interaction, the magnetic driving force is combined with gravitational force, and a modified gravity g* as well as gravity modification factor G are derived to characterize the paramagnetism theory of oxygen. Full article

(This article belongs to the Special Issue Trends and Prospects in Engine Combustion)

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