The 3-D In-Cylinder Charge Motion of a Four-Valve SI Engine under Stroke, Speed, and Load Variation

Meeting the increasingly stringent emission and fuel efficiency standards is the primary objective of the automotive research. Lean/diluted combustion is a promising avenue to realize high-efficiency combustion and reduce emissions in SI engines. Under the diluted conditions, the flame propagation speed is reduced because of the reduced charge reactivity. Enhancing the in-cylinder charge motion and turbulence, and thereby increasing the flame speed, is a possible way to harness the combustion process in SI engines. However, the charge motion can have a significant effect on the spark ignition process because of the reduced discharge duration and frequent restrikes. A longer discharge duration can aid in the formation of the self-sustained flame kernel and subsequent stable ignition. Therefore, an empirical study is undertaken to investigate the effect of the discharge duration and ignition timing on the ignition and early combustion in a port fueled SI engine, operated under lean conditions. The discharge duration is modulated from 1 ms to 8 ms through a continuous discharge strategy. The discharge current and voltage measurements are recorded during the engine operation to characterize the discharge process. The in-cylinder charge is diluted using fresh air to achieve lean combustion. The in-cylinder pressure measurement and heat release analysis are used to investigate the ignition and combustion characteristics of the engine. Preliminary results indicate that while the discharge duration has a marginal effect on the ignition delay, cyclic variations are notably impacted.

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Evaluation of the Predictive Capabilities of a Phenomenological Combustion Model for Natural Gas SI Engine

Journal of Middle European Construction and Design of Cars ◽

10.1515/mecdc-2017-0007 ◽

2017 ◽

Vol 15 (2) ◽

pp. 37-48 ◽

Cited By ~ 1

Author(s):

Rastislav Toman ◽

Jan Macek

Keyword(s):

Natural Gas ◽

Laminar Flame ◽

Computational Effort ◽

Combustion Model ◽

Charge Motion ◽

Si Engine ◽

Engine Operation ◽

Calibration Methods ◽

Sensitivity Studies ◽

Cylinder Flow

Abstract The current study evaluates the predictive capabilities of a new phenomenological combustion model, available as a part of the GT-Suite software package. It is comprised of two main sub-models: 0D model of in-cylinder flow and turbulence, and turbulent SI combustion model. The 0D in-cylinder flow model (EngCylFlow) uses a combined K-k-ε kinetic energy cascade approach to predict the evolution of the in-cylinder charge motion and turbulence, where K and k are the mean and turbulent kinetic energies, and ε is the turbulent dissipation rate. The subsequent turbulent combustion model (EngCylCombSITurb) gives the in-cylinder burn rate; based on the calculation of flame speeds and flame kernel development. This phenomenological approach reduces significantly the overall computational effort compared to the 3D-CFD, thus allowing the computation of full engine operating map and the vehicle driving cycles. Model was calibrated using a full map measurement from a turbocharged natural gas SI engine, with swirl intake ports. Sensitivity studies on different calibration methods, and laminar flame speed sub-models were conducted. Validation process for both the calibration and sensitivity studies was concerning the in-cylinder pressure traces and burn rates for several engine operation points achieving good overall results.

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