scholarly journals Effects of Flame Propagation Velocity and Turbulence Intensity on End-Gas Auto-Ignition in a Spark Ignition Gasoline Engine

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5039
Author(s):  
Lei Zhou ◽  
Xiaojun Zhang ◽  
Lijia Zhong ◽  
Jie Yu
Keyword(s):  
Flame Propagation ◽  
Turbulence Intensity ◽  
Propagation Velocity ◽  
Gasoline Engine ◽  
Pressure Oscillation ◽  
Spark Ignition ◽  
Flame Propagation Velocity ◽  
Eddy Simulation ◽  
Auto Ignition ◽  
Large Eddy

Knocking is a destructive and abnormal combustion phenomenon that hinders modern spark ignition (SI) engine technologies. However, the in-depth mechanism of a single-factor influence on knocking has not been well studied. Thus, the major aim of the present study is to study the effects of flame propagation velocity and turbulence intensity on end-gas auto-ignition through a large eddy simulation (LES) and a decoupling methodology in a downsized gasoline engine. The mechanisms of end-gas auto-ignition as well as strong pressure oscillation are qualitatively analyzed. It is observed that both flame propagation velocity and turbulence have a non-monotonic effect on knocking intensity. The competitive relationship between flame propagation velocity and ignition delay of the end gas is the primary reason responding to this phenomenon. A higher flame speed leads to an increase in the heat release rate in the cylinder, and consequently, quicker increases in the temperature and pressure of the unburned end-gas mixture are obtained, leading to end-gas auto-ignition. Further, the coupling of a pressure wave and an auto-ignition flame front results in super-knocking with a maximum peak of pressure of 31 MPa. Although the turbulence indirectly influences the end-gas auto-ignition by affecting the flame propagation velocity, it can accelerate the dissipation of radicals and heat in the end gas, which significantly influences knocking intensity. Moreover, it is found that the effect of turbulence is more pronounced than that of flame propagation velocity in inhibiting knocking. It can be concluded that the intensity of the pressure oscillation depends on the unburned mixture mass as well as the local thermodynamic state induced by flame propagation and turbulence, with mutual interactions. The present work is expected to provide valuable perspective for inhibiting super-knocking of an SI gasoline engine.

scholarly journals Numerical Analysis of End-Gas Autoignition and Pressure Oscillation in a Downsized SI Engine Using Large Eddy Simulation

Energies ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3909 ◽  
Author(s):  
Zhong ◽  
Liu
Keyword(s):  
Large Eddy Simulation ◽  
Gasoline Engine ◽  
Numerical Models ◽  
Pressure Oscillation ◽  
Spark Ignition ◽  
Gasoline Engines ◽  
Eddy Simulation ◽  
Auto Ignition ◽  
Large Eddy ◽  
Primary Reference

Knock and super-knock are abnormal combustion phenomena in engines, however, they are hard to study comprehensively through optical experimental methods due to their inherent destructive nature. In present work, the methodology of large eddy simulation (LES) coupled with G equations and a detailed mechanism of primary reference fuel (PRF) combustion is utilized to address the mechanisms of knock and super-knock phenomena in a downsized spark ignition gasoline engine. The knock and super-knock with pressure oscillation are qualitatively duplicated through present numerical models. As a result, the combustion and onset of autoignition is more likely to occur at top dead center (TDC), which causes end gas at a higher temperature and pressure. It is reasonable to conclude that the intensity of knock is not only proportional to the mass fraction of mixtures burned by the autoignition flame but the thermodynamics of the unburned end-gas mixture, and the effect of thermodynamics is more important. It also turns out that two auto-ignitions occur in conventional knock conditions, while only one auto-ignition takes place in super-knock conditions. However, the single autoignition couples with the pressure wave and they reinforce each other, which eventually evolves into detonation combustion. This work gives the valuable insights into knock phenomena in spark ignition gasoline engines.

Impact of Wall Temperature in Large Eddy Simulation of Light-Round in an Annular Liquid Fueled Combustor and Assessment of Wall Models

2019 ◽  
Author(s):  
S. Puggelli ◽  
T. Lancien ◽  
K. Prieur ◽  
D. Durox ◽  
S. Candel ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Flame Propagation ◽  
A Priori ◽  
Heat Losses ◽  
Wall Region ◽  
Fixed Temperature ◽  
Flame Propagation Velocity ◽  
Eddy Simulation ◽  
Spray Flames ◽  
Large Eddy

Abstract The process of ignition in aero-engines raises many practical issues that need to be faced during the design process. Recent experiments and simulations have provided detailed insights on ignition in single-injector configurations and on the light-round sequence in annular combustors. It was shown that Large Eddy Simulation (LES) was able to reliably reproduce the physical phenomena involved in the ignition of both perfectly premixed and liquid spray flames. The present study aims at further extending the knowledge on flame propagation during the ignition of annular multiple injector combustors by focusing the attention on the effects of heat losses, which have not been accounted for in numerical calculations before. This problem is examined by developing Large Eddy Simulations of the light-round process with a fixed temperature at the solid boundaries. Calculations are carried out for a laboratory-scale annular system. Results are compared in terms of flame shape and light-round duration with available experiments and with an adiabatic LES serving as a reference. Wall heat losses lead to a significant reduction in the flame propagation velocity as observed experimentally. However, the LES underestimates this effect and leads to a globally shorter light-round. To better understand this discrepancy, the study focuses then on the analysis of the near wall region where the velocity and temperature boundary layers must be carefully described. An a-priori analysis underlines the shortcomings associated to the chosen wall law by considering a more advanced wall model that fully accounts for variable thermophysical properties and for the unsteadiness of the boundary layer.

scholarly journals The technologies of improving the process of air-fuel mixture combustion in spark ignition engines

2020 ◽  
pp. 51-57
Author(s):  
A. P. Shaikin ◽  
◽  
I. R. Galiev ◽  
D. A. Pavlov ◽  
M. V. Sazonov ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Internal Combustion Engine ◽  
Flame Propagation ◽  
Turbulence Intensity ◽  
Propagation Velocity ◽  
Combustion Engine ◽  
Combustion Process ◽  
Fuel Mixture ◽  
Flame Propagation Velocity ◽  
Combustion Phase

The paper considers the turbulence intensity and the fuel chemical composition impact on the flame propagation velocity at the initial and main combustion phases when changing the air-fuel mixture composition. The relevance of the study is caused by the fact that currently, the improvement of conventional engine operation characteristics is mainly achieved through the improvement of the fuel mixture combustion process. However, there are no data on the influence of chemical and gas-dynamic factors on the peculiarities of flame propagation at the initial and main combustion phases. The gas reciprocating internal combustion engine was the object of the research, and the subject of the study was the fuel combustion process. Fuel chemical composition changed due to the promoting addition of hydrogen to the natural gas and variations of the excess-air coefficient. The experiments carried out on the UIT-85 power plant (i.e. under the simulated internal combustion engine conditions) show that the promoting addition of hydrogen stronger influences the flame velocity in the initial combustion phase compared to the second combustion phase, as a combustion source in the first phase is a laminar flame bent front and depends only on chemical and thermo-physical properties of the fuel-air mixture. The analysis of experimental data showed the dual impact of turbulence intensity on the flame propagation velocity. In particular, at the beginning of the combustion process, the fluctuating velocity scarcely influences the flame propagation velocity, as opposed to the main combustion phase, where the flame propagation velocity increases at the increase of turbulence intensity.

Impact of Wall Temperature in Large Eddy Simulation of Light-Round in an Annular Liquid Fueled Combustor and Assessment of Wall Models

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
S. Puggelli ◽  
T. Lancien ◽  
K. Prieur ◽  
D. Durox ◽  
S. Candel ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Flame Propagation ◽  
A Priori ◽  
Heat Losses ◽  
Wall Region ◽  
Fixed Temperature ◽  
Flame Propagation Velocity ◽  
Eddy Simulation ◽  
Spray Flames ◽  
Large Eddy

Abstract The process of ignition in aero-engines raises many practical issues that need to be faced during the design process. Recent experiments and simulations have provided detailed insights into ignition in single-injector configurations and on the light-round sequence in annular combustors. It was shown that large eddy simulation (LES) was able to reliably reproduce the physical phenomena involved in the ignition of both perfectly premixed and liquid spray flames. This study aims at further extending the knowledge on flame propagation during the ignition of annular multiple injector combustors by focusing the attention on the effects of heat losses, which have not been accounted for in numerical calculations before. This problem is examined by developing LESs of the light-round process with a fixed temperature at the solid boundaries. Calculations are carried out for a laboratory-scale annular system. Results are compared in terms of flame shape and light-round duration with available experiments and with an adiabatic LES serving as a reference. Wall heat losses lead to a significant reduction in the flame propagation velocity as observed experimentally. However, the LES underestimates this effect and leads to a globally shorter light-round. To better understand this discrepancy, the study focuses then on the analysis of the near wall region. An a priori analysis underlines the shortcomings associated with the chosen wall law by considering a more advanced wall model that fully accounts for variable thermophysical properties and for the unsteadiness of the boundary layer.

Numerical Simulation of Flame Propagation in a Staged Combustor

2002 ◽  
Author(s):  
Tomoko Tsuru ◽  
Akira Imamura ◽  
Yasuhiro Kinoshita ◽  
Yoshiharu Nonaka ◽  
Yuichi Itoh ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Flame Propagation ◽  
Turbulence Intensity ◽  
Turbulence Models ◽  
Numerical Code ◽  
Velocity Fluctuations ◽  
Flamelet Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Conventional Numerical Method

Highly unsteady flow fields are generated in recent low-emissions gas turbine combustors. Numerical simulation of such flows using conventional numerical code using a time-averaged turbulence model is difficult and time-accurate LES (Large Eddy Simulation) is expected to predict them. Calculation of turbulent combusting and non-combusting flow field in a staged combustor were conducted using LES. To validate the LES calculation, a prediction of time-averaged velocity field is compared with those by an experiment and a conventional numerical method based on RANS model. Turbulence intensity affects flame speed so much that velocity fluctuations were measured to obtain turbulence intensity in the non-combustion test. Strongly turbulent regions between the pilot and main stages, which are important for the flame propagation, were simulated. The combustion was calculated using a laminar flamelet model and the flame propagating phenomenon was simulated properly, which is impractical by the conventional simulations using time-averaged turbulence models. The feasibility of the LES calculation is discussed.

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