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

Zhong, Lei; Liu, Changwen

doi:10.3390/en12203909

Cited by 7 publications

(5 citation statements)

References 52 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A few studies have attempted to examine how turbulence affects the intensity of the developing detonation. Wei et al (2016), Chen et al (2019 and Zhong and Liu (2019) used reduced-order turbulent models and found that increased turbulence intensity inhibits autoignition formation and reduced hot spot sizes, leading to different autoignition modes and knock intensities. Zhang et al (2019) studied the interaction of turbulent transport and low-temperature chemistry on knocking formation of an imposed hot spot.…”

Section: Introductionmentioning

confidence: 99%

Effects of Turbulence and Temperature Fluctuations on Knock Development in an Ethanol/Air Mixture

Luong

Pérez

Sankaran

et al. 2020

Flow Turbulence Combust

View full text Add to dashboard Cite

The effects of turbulence on knock development and intensity for a thermally inhomogeneous stoichiometric ethanol/air mixture at a representative end-gas autoignition condition in internal combustion engines are investigated using direct numerical simulations with a skeletal reaction mechanism. Two-and three-dimensional simulations are performed by varying the most energetic length scale of temperature, l T , and its relative ratio with the most energetic length scale of turbulence, l T ∕l e , together with two different levels of the turbulent velocity fluctuation, u ′ . It is found that l T /l e and the ratio of ignition delay time to eddy-turnover time, ig ∕ t , are the key parameters that control the detonation development. An increase in either l T or l e enhances the detonation propensity by allowing a longer run-up distance for the detonation development. The characteristic length scale of the temperature field, l T , is significantly modified by high turbulence intensity achieved by a large l e and u ′ . The intense turbulence mixing effectively distributes the initial temperature field to broader scales to support the developing detonation waves, thereby increasing the likelihood of the detonation formation. On the contrary, high turbulence intensity with a short mixing time scale, achieved by a small l e and a large u ′ , reduces the super-knock intensity attributed to the finer broken-up structures of detonation waves. Either ig ∕ t less than unity or l e = l T even with a large u ′ is found to have no significant effect on super-knock mitigation. Finally, high turbulent intensity may induce high-pressure spikes comparable to the von Neumann spike. Increased temperature and pressure by combustion heating, noticeably after the peak of heat release rate, significantly enhance the collision and interaction of multiple emerging autoignition fronts near the ending combustion process, resulting in localized high-pressure spikes.

show abstract

Section: Introductionmentioning

confidence: 99%

Effects of Turbulence and Temperature Fluctuations on Knock Development in an Ethanol/Air Mixture

Luong

Pérez

Sankaran

et al. 2020

Flow Turbulence Combust

View full text Add to dashboard Cite

show abstract

“…In our previous works [34][35][36], we have comprehensively validated the present models in terms of pressure profiles and heat release rate. The numerical pressure evolution agrees well with the experimental results, both in ST-10 case and ST-18 cases.…”

Section: Model Validationmentioning

confidence: 88%

“…The detailed numerical models can be found in Ref. [34][35][36]. The geometry model, which consists of a combustion chamber, an inlet port, and an outlet port, together with its grid splitting, can be found in Figure 2.…”

Section: Numerical Modelsmentioning

confidence: 99%

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

et al. 2020

View full text Add to dashboard Cite

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.

show abstract

“…Detonation should occur in the combustion chamber, which could cause serious damage to the piston. Compressed by the piston, the mixture rapidly reached a state of high temperature and high pressure [21]. Spontaneous ignition occurred at the TDC and, subsequently, the pressure profile deviated from the normal combustion, and jumped to the Pmax value.…”

Section: Super-knock In Misfired Cylindermentioning

confidence: 99%

Investigation into the Relationship between Super-Knock and Misfires in an SI GDI Engine

et al. 2021

View full text Add to dashboard Cite

The super-knock poses new challenges for further increasing the power density of spark ignition (SI) engines. The critical factors and mechanism connecting regarding the occurrence of super-knock are still unclear. Misfire is a common phenomenon in SI engines that the mixture in cylinder is not ignited normally, which is often caused by spark plug failure. However, the effect of misfire on engine combustion has not been paid enough attention to, particularly regarding connection to super-knock. The paper presents the results of experimental investigation into the relationship between super-knock and misfires at low speed and full load conditions. In this work, a boosted gasoline direct injection (GDI) engine with an exhaust manifold integrated in the cylinder head was employed. Four piezoelectric pressure transducers were used to acquire the data of a pressure trace in cylinder. The spark plugs of four cylinders were controlled manually, of which the ignition system could be cut off as demanded. In particular, a piezoelectric pressure transducer was installed at the exhaust pipe before the turbocharger to capture the pressure traces in the exhaust pipe. The results illustrated that misfires in one cylinder would cause super-knock in the other cylinders as well as the cylinder of itself. After one cylinder misfired, the unburned mixture would burn in the exhaust pipe to produce oscillating waves. The abnormal pressure fluctuation in the exhaust pipe was strongly correlated with the occurrence of super-knock. The sharper the pressure fluctuation, the greater the intensity of knock in the power cylinder. The cylinder whose exhaust valve overlapped with the exhaust valve of the misfired cylinder was prone to super-knock.

show abstract

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

Cited by 7 publications

References 52 publications

Effects of Turbulence and Temperature Fluctuations on Knock Development in an Ethanol/Air Mixture

Effects of Turbulence and Temperature Fluctuations on Knock Development in an Ethanol/Air Mixture

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

Investigation into the Relationship between Super-Knock and Misfires in an SI GDI Engine

Contact Info

Product

Resources

About