A statistical analysis of developing knock intensity in a mixture with temperature inhomogeneities

Luong, Minh Bau; Pérez, Francisco E. Hernández; Sankaran, Ramanan; Johansson, Bengt

doi:10.1016/j.proci.2020.05.044

Cited by 32 publications

(39 citation statements)

References 35 publications

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“…In our previous study (Luong et al 2020b) without turbulence effects, no detonation was observed with l T as small as 1 mm for T ′ over a wide range from 0.5 to 20 K. Therefore, it was believed that a minimum size of l T was needed so that a sufficient amount of unburned reactants allows a sufficient run-up of detonation development (Towery et al 2020). As shown in Fig.…”

Section: Effect Of L T : Baseline Casesmentioning

confidence: 84%

“…Three metrics are adopted to assess the knock intensity, which are defined as follows (Luong et al 2020b):…”

Section: Quantitative Analysismentioning

confidence: 99%

“…F H , F CJ , and F VN of all the cases from the previous study without turbulence (Luong et al 2020b), as well as those from this study are compiled and plotted in Fig. 13.…”

Section: Fig 11mentioning

confidence: 99%

“…Recently, Towery and coauthors (2020) proposed a statistical model to predict the detonability degree of an autoignitive gas with the thermodynamic gradients induced by compressible homogeneous isotropic turbulence (HIT) fluctuations, and validated the model with the DNS results, showing a good agreement. Our recent DNS study (Luong et al 2020b) with varying l T and the root-mean-square temperature fluctuation levels, T ′ , found that l T is the key factor affecting the knock intensity, i.e., increasing l T significantly increases the peak pressure by allowing a longer run-up time. As a first attempt, however, the effects of different scales of temperature fluctuations were investigated without an additional turbulence mixing.…”

Section: Introductionmentioning

confidence: 99%

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

Luong

Pérez

Sankaran

et al. 2020

Flow Turbulence Combust

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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.

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Section: Effect Of L T : Baseline Casesmentioning

confidence: 84%

“…Three metrics are adopted to assess the knock intensity, which are defined as follows (Luong et al 2020b):…”

Section: Quantitative Analysismentioning

confidence: 99%

“…F H , F CJ , and F VN of all the cases from the previous study without turbulence (Luong et al 2020b), as well as those from this study are compiled and plotted in Fig. 13.…”

Section: Fig 11mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

Luong

Pérez

Sankaran

et al. 2020

Flow Turbulence Combust

Self Cite

View full text Add to dashboard Cite

show abstract

“…by decreasing SOI and BMEP increased and BSFC and exhaust gas temperature decreased significantly; also, the emissions of carbon dioxide and unburned hydrocarbons were significantly reduced. Long et al [23] conducted a study on knock intensity due to non-uniform temperature distribution in the engine in the form of two and three-dimensional simulations with regular temperature changes. Gikwad et al [24], in the form of an experimental and numerical study of a piston engine, investigated the effects of peak pressure on the occurrence of knock in the engine.…”

Section: Introductionmentioning

confidence: 99%