Insights into engine autoignition: Combining engine thermodynamic trajectory and fuel ignition delay iso-contour

Tao, Mingyuan; Zhao, Peng; Szybist, James P.; Lynch, Patrick T.; Ge, Haiwen

doi:10.1016/j.combustflame.2018.11.025

Cited by 30 publications

(3 citation statements)

References 64 publications

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“…The engine thermodynamic conditions are selected from the previous 0D kinetic study of fuel metric under ACI conditions along the combustion phasing iso-contour. 40,41,45 Detailed in-cylinder flow, spray dynamics and mixing are systematically considered in the current computational study. The results are further compared with the 0D kinetic study without considering stratification and charge cooling.…”

Section: Introductionmentioning

confidence: 99%

Effects of stratification and charge cooling on combustion in a gasoline direct-injection compression ignition (GDCI) engine

Zhao

2022

International Journal of Engine Research

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With the development of low temperature engine combustion strategies, performance of gasoline-type fuels under compression ignition conditions has attracted extensive research interest. Meanwhile, for the sake of co-optimization of engines and fuels for future ground transportation, identification and evaluation of general fuel properties should be a core research priority instead of endless testing of specific fuels. In this study, the roles of fuel octane sensitivity in characterizing the ignition performance of gasoline surrogates have been systematically investigated under typical gasoline direct ignition compression ignition (GDCI) engine conditions using 3D combustion CFD simulation, especially considering the subsequent in-cylinder charge stratification and charge cooling. Two different operating conditions, high boost pressure low boost temperature (beyond-RON) case and low boost pressure high boost temperature (beyond-MON) case, were considered. By comparing with our previous zero-dimensional chemical kinetic study of gasoline surrogates in advanced compression ignition (ACI) engines, the effects of stratification and charge cooling on the combustion processes are investigated. It is found that different fuel octane sensitivities lead to slight difference in equivalence ratio stratification and charge cooling due to differences in volatility. However, fuel reactivity is still the more dominant factor than the stratification and charge cooling effects in determining combustion phasing. The present results help to justify the P-T domain framework for engine autoignition analysis of overlapping pressure-temperature trajectory with ignition delay iso-contour. The results also provide useful guidance to the understanding of GCI combustion process, and to the evaluation of controlling fuel properties and the selection of alternative fuels in GCI engines

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Section: Introductionmentioning

confidence: 99%

Effects of stratification and charge cooling on combustion in a gasoline direct-injection compression ignition (GDCI) engine

Zhao

2022

International Journal of Engine Research

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“…OI is calculated from RON, MON, and K, a variable that describes the engine operating conditions. An increasing body of research has found that the knocking and autoignition tendency of fuels predicted by the OI can be explained by the pressure temperature (PT) trajectory history experienced by the cylinder contents during compression and up to combustion [21][22][23][24][25]. However, Szybist et al [25] found that the OI correlation broke down with ACI operation.…”

Section: Introductionmentioning

confidence: 99%

Octane Index Applicability over the Pressure-Temperature Domain

et al. 2021

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Modern boosted spark-ignition (SI) engines and emerging advanced compression ignition (ACI) engines operate under conditions that deviate substantially from the conditions of conventional autoignition metrics, namely the research and motor octane numbers (RON and MON). The octane index (OI) is an emerging autoignition metric based on RON and MON which was developed to better describe fuel knock resistance over a broader range of engine conditions. Prior research at Oak Ridge National Laboratory (ORNL) identified that OI performs reasonably well under stoichiometric boosted conditions, but inconsistencies exist in the ability of OI to predict autoignition behavior under ACI strategies. Instead, the autoignition behavior under ACI operation was found to correlate more closely to fuel composition, suggesting fuel chemistry differences that are insensitive to the conditions of the RON and MON tests may become the dominant factor under these high efficiency operating conditions. This investigation builds on earlier work to study autoignition behavior over six pressure-temperature (PT) trajectories that correspond to a wide range of operating conditions, including boosted SI operation, partial fuel stratification (PFS), and spark-assisted compression ignition (SACI). A total of 12 different fuels were investigated, including the Co-Optima core fuels and five fuels that represent refinery-relevant blending streams. It was found that, for the ACI operating modes investigated here, the low temperature reactions dominate reactivity, similar to boosted SI operating conditions because their PT trajectories lay close to the RON trajectory. Additionally, the OI metric was found to adequately predict autoignition resistance over the PT domain, for the ACI conditions investigated here, and for fuels from different chemical families. This finding is in contrast with the prior study using a different type of ACI operation with different thermodynamic conditions, specifically a significantly higher temperature at the start of compression, illustrating that fuel response depends highly on the ACI strategy being used.

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“…Recently, a framework by overlapping the engine thermodynamic pressure-temperature trajectory and the fuel ignition delay iso-contour has been developed, aiming to provide general insights on the knock in spark-ignition (SI) engines and bulk combustion phasing in ACI engines Tao et al, 2019). Manifested by the changes in fuel ignition delay iso-contour and engine thermodynamic trajectory, this framework can qualitatively show the effects of conventional fuel reactivity metrics such as research and motor octane numbers (RON and MON) and octane sensitivity (OS), as well as the effects of engine operating condition, e.g., intake conditions, global equivalence ratio and level of exhaust gas recirculation (EGR).…”

Section: Introductionmentioning

confidence: 99%

Auto-Ignition and Reaction Front Dynamics in Mixtures With Temperature and Concentration Stratification

et al. 2020

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In-cylinder thermal and concentration stratification is omnipresent in the operation of internal combustion engines, especially for various types of direct injection engines. Meanwhile, mixture stratification and φ-sensitivity is frequently adopted in advanced compression ignition strategies to modulate heat release profile and control combustion phasing, such as homogeneous charge compression ignition (HCCI) with partial fuel stratification (PFS), and premixed charge compression ignition (PCCI). Hence, ignition and combustion mode evolution in a stratified charge is of substantial significance in the understanding and prediction of combustion in advanced compression ignition engines. To probe complex combustion in a stratified charge, we have performed one-dimensional direct numerical simulations with detailed chemistry and transport, using a recently developed open source reacting flow CFD platform based on OpenFOAM 6.0. N-heptane is adopted in this work as a typical fuel exhibiting low temperature chemistry. Temperature and equivalence ratio gradient are varied among the simulations to observe ignition and the subsequent combustion development. Three stages of heat release are identified, including the low temperature chemistry chain branching, H 2 O 2 chain branching and CO oxidation, consistent with the recent ignition experiment for lean n-heptane air mixture in a rapid compression machine (RCM). Reaction fronts induced by these oxidation stages are found to be unaffected by diffusion process and exhibit unique propagation features. The results provide useful guidance to the understanding of combustion in a stratified charge and shed light on the development of novel low temperature combustion strategy for advanced compression ignition engines.

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Insights into engine autoignition: Combining engine thermodynamic trajectory and fuel ignition delay iso-contour

Cited by 30 publications

References 64 publications

Effects of stratification and charge cooling on combustion in a gasoline direct-injection compression ignition (GDCI) engine

Effects of stratification and charge cooling on combustion in a gasoline direct-injection compression ignition (GDCI) engine

Octane Index Applicability over the Pressure-Temperature Domain

Auto-Ignition and Reaction Front Dynamics in Mixtures With Temperature and Concentration Stratification

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