Influence of the Local Mixture Characteristics on the
Combustion Process in a CAI™ Engine

Knop, Vincent; Thirouard, Benoist; Cherel, J.

doi:10.4271/2008-01-1671

Cited by 11 publications

(9 citation statements)

References 22 publications

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“…The analysis of mixture stratification in CAI engines requires either optical diagnostic methods 6,7,12 or 3D CFD modelling. [3][4][5]7,8,12 The numerical approach has the advantage of simultaneously providing insights about all species as well as temperature field, allowing for a combined analysis of the influence of temperature, dilution rate and fuel/air equivalence ratio on combustion initiation and progress. However, gaining confidence into numerical results first requires a detailed validation with optical diagnostic methods.…”

Section: Existing Knowledge On Mixture Stratification In Cai Enginesmentioning

confidence: 99%

“…However, gaining confidence into numerical results first requires a detailed validation with optical diagnostic methods. 4,5,7,12 Babajimopoulos et al 3 numerically compared on a single operating point CAI combustion mode obtained through burnt gas trapping with negative valve overlap (NVO) with gasoline HCCI obtained through intake air heating. They were the first to correlate the statistics of temperature and fuel/air equivalence ratio fields with combustion onset, emphasising the central role of the temperature field.…”

Section: Existing Knowledge On Mixture Stratification In Cai Enginesmentioning

confidence: 99%

“…Knop et al 7 went further along this path thanks to a numerical tool simultaneously describing mixture formation and heat release. Similarly to Koopmans et al 4 and Mori et al, 5 the validation of the numerical approach relied on a direct comparison with optical diagnostics results, the key difference being that the numerical quantity to be compared with experimental observation of combustion is numerical heat release.…”

Section: Existing Knowledge On Mixture Stratification In Cai Enginesmentioning

confidence: 99%

“…12,41,47 Control over the amount of burnt gases is a key for successful implementation of CAI combustion in an engine. Two valve lift strategies are possible: NVO 4,7,41,53,54 and EGRB. 12,47,55 In the present study, we considered the NVO strategy (Figure 4), which relies on an early exhaust valve closure and a low peak valve lift to restrict the exhaust blow-down efficiency and, therefore, to directly trap the desired amount of burnt gases.…”

Section: Engine Set-up and Selected Conditionsmentioning

confidence: 99%

“…Although homogeneous charge compression ignition (HCCI) name presupposes a perfect mixture homogeneity, it is today commonly acknowledged that some degree of mixture heterogeneity survives in actual HCCI engines. [1][2][3][4][5][6][7][8] Published research on mixture heterogeneity quantification generally highlighted the central role of temperature stratification, either as the unique driving force or as an important quantity competing with others (generally dilution rate and/or mixture strength). Yet, to the best of author's knowledge, previous research works concentrated on isolated operating point(s), so that the variation of the stratification amplitude over a complete HCCI operating map remains unknown.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of mixture structure and of its influence on combustion in a CAI engine

Knop

2017

International Journal of Engine Research

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Homogeneous Charge Compression Ignition (HCCI) combustion mode theoretically relies on a perfectly homogeneous air/fuel mixture simultaneously releasing heat across the whole combustion chamber. However, practical implementation always leads to a staged combustion process that is still significantly quicker than conventional sparkignition or compression-ignition combustion modes. The degree of combustion staging is central to the limitation of combustion-induced noise, to cycle efficiency, as well as to combustion stability and completion. The present study numerically explored on the whole operating map the mixture structure at ignition for a specific type of HCCI combustion, namely the Controlled Auto-Ignition (CAI) combustion mode attained through burnt gas trapping with negative valve overlap. The analysis of the complete CAI operating map outlined the similarity of mixture structure for any operating condition and the mixture/chemistry interactions depending on the end-of-compression temperature domain. Temperature stratification appeared as the key input defining combustion-induced noise and combustion stability but mean in-cylinder temperature and dilution combine with temperature stratification to define operating map limitations.

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Section: Existing Knowledge On Mixture Stratification In Cai Enginesmentioning

confidence: 99%

Section: Existing Knowledge On Mixture Stratification In Cai Enginesmentioning

confidence: 99%

Section: Existing Knowledge On Mixture Stratification In Cai Enginesmentioning

confidence: 99%

Section: Engine Set-up and Selected Conditionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Analysis of mixture structure and of its influence on combustion in a CAI engine

Knop

2017

International Journal of Engine Research

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Investigation of Engine Combustion and Auto-ignition of a Multicomponent Surrogate Fuel with NTC Behavior Under Knocking Conditions

Kircher

Popp

Gierth

et al. 2022

Flow Turbulence Combust

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The occurrence of knocking combustion is limiting the efficiency of modern spark ignition engine operation. Thus, an understanding of the processes at the knock limit is required for further optimization of the combustion process. In this work, the combustion of a multicomponent Toluene Reference Fuel (TRF) in a single-cylinder research engine is investigated under knocking conditions. The fuel exhibits a negative temperature coefficient (NTC) regime for thermodynamic conditions relevant to the engine operation. A precursor model is used to capture the auto-ignition process. Under homogeneous conditions, a two-stage auto-ignition is observed. Inside the NTC regime, the temperature affects both first-stage and second-stage auto-ignition delay times. With a subsequently conducted multi-cycle engine LES, the effects of temperature stratification and turbulent flame propagation on the local auto-ignition process are investigated. It is observed, that the NTC behavior leads to a widespread two-stage auto-ignition. The knock intensity observed in the experiments is directly related to the mass consumed by auto-ignition. This is due to the fast consumption of the auto-ignited mass by the flame front. With that, the NTC behavior affects the local auto-ignition process in the unburned mixture while the flame propagation determines the knock intensity for the operating conditions at the knock limit.

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On the use of a tabulation approach to model auto-ignition during flame propagation in SI engines

2011

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Influence of the Local Mixture Characteristics on the Combustion Process in a CAI™ Engine

Cited by 11 publications

References 22 publications

Analysis of mixture structure and of its influence on combustion in a CAI engine

Analysis of mixture structure and of its influence on combustion in a CAI engine

Investigation of Engine Combustion and Auto-ignition of a Multicomponent Surrogate Fuel with NTC Behavior Under Knocking Conditions

On the use of a tabulation approach to model auto-ignition during flame propagation in SI engines

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