Large-Eddy Simulation of a Scramjet Strut Injector with Pilot Injection

2016 ◽  
pp. 407-420
Author(s):  
Sebastian Eberhardt ◽  
Stefan Hickel
Keyword(s):  
Large Eddy Simulation ◽  
Pilot Injection ◽  
Eddy Simulation ◽  
Large Eddy

scholarly journals LARGE EDDY SIMULATION OF LEAN MIXED-MODE COMBUSTION ASSISTED BY PARTIAL FUEL STRATIFICATION IN A SPARK-IGNITION ENGINE

2021 ◽  
pp. 1-15
Author(s):  
Chao Xu ◽  
Sibendu Som ◽  
Magnus Sjoberg
Keyword(s):  
Large Eddy Simulation ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Mixed Mode ◽  
Spark Ignition ◽  
Pilot Injection ◽  
Eddy Simulation ◽  
Fuel Stratification ◽  
Large Eddy

Abstract Partial fuel stratification (PFS) is a promising fuel injection strategy to improve the stability of lean combustion by applying a small pilot injection near spark timing. Mixed-mode combustion, which makes use of end-gas autoignition following conventional deflagration-based combustion, can be further utilized to speed up the overall combustion. In this study, PFS assisted mixed-mode combustion in a lean-burn direct injection spark-ignition (DISI) engine is numerically investigated using multi-cycle large eddy simulation (LES). A previously developed hybrid G-equation/well-stirred reactor combustion model is extended to the PFS condition. The experimental spray morphology is employed to derive spray model parameters for the pilot injection. The LES based model is validated against experimental data and is further compared with the Reynolds-averaged Navier-Stokes (RANS) based model. Overall, both RANS and LES predict the mean pressure and heat release rate traces well, while LES outperforms RANS in capturing the CCV and the combustion phasing in the mass burned space. Liquid and vapor penetrations obtained from the simulations agree reasonably well with the experiment. Detailed flame structures predicted from the simulations reveal the transition from a sooting diffusion flame to a lean premixed flame, which is consistent with experimental findings. LES captures more wrinkled and stretched flames than RANS. Finally, the LES model is employed to investigate the impacts of fuel properties, including heat of vaporization (HoV) and laminar burning speed (SL). Combustion phasing is found more sensitive to SL than to HoV, with a larger fuel property sensitivity of the heat release rate from autoignition than that from deflagration. Moreover, the combustion phasing in the PFS-assisted operation is shown to be less sensitive to SL compared with the well-mixed operation.

scholarly journals Large Eddy Simulation of Lean Mixed-Mode Combustion Assisted by Partial Fuel Stratification in a Spark-Ignition Engine

2020 ◽  
Author(s):  
Chao Xu ◽  
Sibendu Som ◽  
Magnus Sjöberg
Keyword(s):  
Large Eddy Simulation ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Mixed Mode ◽  
Spark Ignition ◽  
Pilot Injection ◽  
Eddy Simulation ◽  
Fuel Stratification ◽  
Large Eddy

Abstract Lean operation is beneficial to spark-ignition engines due to the high thermal efficiency compared with conventional stoichiometric operation. Lean combustion can be significantly stabilized by the partial fuel stratification (PFS) strategy, in which a small amount of pilot injection is applied near the spark energizing timing in addition to main injections during intake. Furthermore, mixed-mode combustion, which makes use of end-gas autoignition following conventional deflagration-based combustion, can be further utilized to speed up the overall combustion. In this study, PFS-assisted mixed-mode combustion in a lean-burn direct injection spark-ignition (DISI) engine is numerically investigated using multi-cycle large eddy simulation (LES). To accurately represent the pilot injection characteristics, experimentally-derived spray morphology parameters are employed for spray modeling. A previously developed hybrid G-equation/well-stirred reactor model is extended to PFS conditions, to capture interactions of pilot injection, turbulent flame propagation and end-gas autoignition. The LES-based engine model is compared with Reynolds-averaged Navier-Stokes (RANS) based model, allowing an investigation of both mean and cycle-to-cycle variation (CCV) of combustion characteristics. Instantaneous spray and flame structures from simulations are compared with experiments. The LES-based model is finally leveraged to investigate impacts of fuel properties including heat of vaporization (HoV) and laminar flame speed (SL). It is shown that overall, the predicted mean pressure and heat release rate traces from both RANS and LES agree well with the experiment, while LES captures the CCV and the combustion phasing in the mass burned space much better than RANS. Predicted liquid fuel penetrations agree reasonably well with the experiment, both for RANS and LES. Detailed flame structures in the simulations also reveal the transition from a sooting flame to a lean premixed flame, which is consistent with experimental findings. LES is shown to capture more wrinkled and stretched flame fronts than RANS. Local sensitivity analysis further identifies the stronger combustion phasing sensitivity to SL compared with that to HoV, and the stronger sensitivity of autoignition heat release rate than deflagration. The results from this study demonstrate the high fidelity of the developed computational model based on LES, enabling future investigation of PFS-assisted mixed-mode combustion for different fuels and a wider range of operating conditions.

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