Abstract
To reduce emissions and fuel consumption, the current generation of gasoline engines uses technologies such as direct injection, downsizing and supercharging. All of them require a strong vortical in-cylinder charge motion, usually described as “tumble”, to improve fuel-air mixing and enhance flame propagation. The tumble development strongly depends on the flow field during the intake stroke. This flow field is dominated by the intake jet, which has to be captured well in the simulation. This work investigates the intake jet on a steady-state flow bench, especially in the vicinity of the intake valve. At first, the general flow dynamics of the intake jet for three different valve lifts and three different mass flows were investigated experimentally. For the smallest valve lift (3 mm), flow-field measurements using Particle Image Velocimetry (PIV) show that the orientation of the intake jet significantly depends on the air flow rate, attaching to the pent roof for low flow rates. This phenomenon is less pronounced for higher valve lifts. An intermediate valve lift and flow rate were chosen for further investigations by scale-resolving simulations. Three different meshes (coarse, medium and fine) and two turbulence models (Sigma and Detached Eddy Simulation-Shear Stress Transport (DES-SST)) are applied to consider their effect on the numerical results. An ad-hoc post-processing methodology based on the ensemble-averaged velocity field is presented capturing the jet centerline’s mean velocity and velocity fluctuations as well as its orientation, curvature and penetration depth. The simulation results are compared to each other as well as to measurements by PIV.
Highlights
During the last few decades, regulations in terms of emission and fuel consumption have become very strict for Internal Combustion (IC) engines
For the smallest valve lift (3 mm), flow-field measurements using Particle Image Velocimetry (PIV) show that the orientation of the intake jet significantly depends on the air flow rate, attaching to the pent roof for low flow rates
The engine head was mounted on an optical table, a constant airflow was supplied to the intake at a fixed valve lift, and the resulting flow below one of the intake valves was imaged by PIV
Summary
During the last few decades, regulations in terms of emission and fuel consumption have become very strict for Internal Combustion (IC) engines. Modern spark-ignited IC engines are based on direct injection, downsizing and supercharging These technologies require a significant in-cylinder charge motion (usually described as “tumble”), which is generated during the intake stroke. In several studies it was shown that the momentum introduced by the intake jet is the main contributor to the large-scale tumble [3,4,5]. Due to this strong dependency on the intake jet, the intake port is optimized intensively during the engine design process to obtain a distinctive tumble motion throughout the intake and compression stroke. Curvature and shape are determined based on an ad-hoc postprocessing methodology
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