scholarly journals Large-Eddy Simulations of Spray Variability Effects on Flow Variability in a Direct-Injection Spark-Ignition Engine Under Non-Combusting Operating Conditions

2018 ◽  
Author(s):  
Noah Van Dam ◽  
Magnus Sjöberg ◽  
Sibendu Som
Keyword(s):  
Direct Injection ◽  
Spark Ignition ◽  
Operating Conditions ◽  
Large Eddy Simulations ◽  
Spark Ignition Engine ◽  
Flow Variability ◽  
Large Eddy ◽  
Direct Injection Spark Ignition

scholarly journals Large-eddy spray simulation under direct-injection spark-ignition engine-like conditions with an integrated atomization/breakup model

2020 ◽  
pp. 146808741988186
Author(s):  
Hongjiang Li ◽  
Christopher J Rutland ◽  
Francisco E Hernández Pérez ◽  
Hong G Im
Keyword(s):  
Direct Injection ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Computational Domain ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Hybrid Breakup Model ◽  
Direct Injection Spark Ignition ◽  
Breakup Model ◽  
The Given

In this work, a hybrid breakup model tailored for direct-injection spark-ignition engine sprays is developed and implemented in the OpenFOAM CFD code. The model uses the Lagrangian–Eulerian approach whereby parcels of liquid fuel are injected into the computational domain. Atomization and breakup of the liquid parcels are described by two sub-models based on the breakup mechanisms reported in the literature. Evaluation of the model has been carried out by comparing large-eddy simulation results with experimental measurements under multiple direct-injection spark-ignition engine-like conditions. Spray characteristics including liquid and vapor penetration curves, droplet velocities, and Sauter mean diameter distributions are examined in detail. The model has been found to perform well for the spray conditions considered in this work. Results also show that after the end of injection, most of the residual droplets that are still in the breakup process are driven by the bag and bag–stamen breakup mechanisms. Finally, an effort to unify the breakup length parameter is made, and the given value is tested under various ambient density and temperature conditions. The predicted trends follow the measured data closely for the penetration rates, even though the model is not specifically tuned for individual cases.

Large-eddy simulation analysis of knock in a direct injection spark ignition engine

2018 ◽  
Vol 20 (7) ◽  
pp. 765-776 ◽  
Author(s):  
Anthony Robert ◽  
Karine Truffin ◽  
Nicolas Iafrate ◽  
Stephane Jay ◽  
Olivier Colin ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Simulation Analysis ◽  
Direct Injection ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Eddy Simulation ◽  
Oscillation Analysis ◽  
Spark Timing ◽  
Large Eddy ◽  
Direct Injection Spark Ignition

Downsized spark ignition engines running under high loads have become more and more attractive for car manufacturers because of their increased thermal efficiency and lower CO2 emissions. However, the occurrence of abnormal combustions promoted by the thermodynamic conditions encountered in such engines limits their practical operating range, especially in high efficiency and low fuel consumption regions. One of the main abnormal combustion is knock, which corresponds to an auto-ignition of end gases during the flame propagation initiated by the spark plug. Knock generates pressure waves which can have long-term damages on the engine, that is why the aim for car manufacturers is to better understand and predict knock appearance. However, an experimental study of such recurrent but non-cyclic phenomena is very complex, and these difficulties motivate the use of computational fluid dynamics for better understanding them. In the present article, large-eddy simulation (LES) is used as it is able to represent the instantaneous engine behavior and thus to quantitatively capture cyclic variability and knock. The proposed study focuses on the large-eddy simulation analysis of knock for a direct injection spark ignition engine. A spark timing sweep available in the experimental database is simulated, and 15 LES cycles were performed for each spark timing. Wall temperatures, which are a first-order parameter for knock prediction, are obtained using a conjugate heat transfer study. Present work points out that LES is able to describe the in-cylinder pressure envelope whatever the spark timing, even if the sample of LES cycles is limited compared to the 500 cycles recorded in the engine test bench. The influence of direct injection and equivalence ratio stratifications on combustion is also (MAPO) analyzed. Finally, focusing on knock, a Maximum Amplitude Pressure Oscillation analysis (MAPO) is conducted for both experimental and numerical pressure traces pointing out that LES well reproduces experimental knock tendencies.

CFD modeling of pre-spark heat release in a boosted direct-injection spark-ignition engine

2021 ◽  
pp. 146808742110441
Author(s):  
Hengjie Guo ◽  
Roberto Torelli ◽  
James P Szybist ◽  
Sibendu Som
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Chemical Kinetics ◽  
Ignition Delay ◽  
Direct Injection ◽  
Spark Ignition ◽  
Operating Conditions ◽  
Spark Ignition Engine ◽  
Detailed Chemistry ◽  
Direct Injection Spark Ignition

Accurate predictions of low-temperature heat release (LTHR) are critical for modeling auto-ignition processes in internal combustion engines. While LTHR is typically obscured by deflagration, extremely late ignition phasing can lead to LTHR prior to the spark, a behavior known as pre-spark heat release (PSHR). In this research, PSHR in a boosted direct-injection spark-ignition engine was studied using 3-D computational fluid dynamics (CFD) and detailed chemical kinetics. The turbulent combustion was modeled via a hybrid approach that incorporates the G-equation model for tracking the turbulent flame front, and the well-stirred reactor model with detailed chemistry for assessing the low-temperature reactions in unburnt gas. Simulations were conducted using Co-Optima alkylate and E30 fuels at operating conditions characterized by different PSHR intensities. The predicted in-cylinder pressure and heat release rate were found to agree well with experiments. It was found the estimate of previous-cycle trapped residuals is of utmost importance for capturing PSHR correctly. A simulation best practice was developed which keeps the detailed chemistry solver active throughout the entire simulation, allowing to track the evolution of intermediate species from one cycle to the next. Following the validation, the dynamics of PSHR were analyzed in detail employing the pressure-temperature (P-T) trajectory framework. It was shown that PSHR correlated with the first-stage ignition delay of the fuel, hence showing close relation to the in-cylinder P-T trajectory and the chemical kinetics. Besides, it was indicated that LTHR is a self-limiting process that has the effect of attenuating the thermal stratification in the combustion chamber. Furthermore, it was observed the occurrence of PSHR caused the P-T trajectory of end-gas to overlap with the negative temperature coefficient region of the fuel’s ignition-delay maps. This effect was more significant in the fuel-rich regions where engine knock tendency would be generally higher, with potential implications on knock control and mitigation.

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