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Technical Paper

Numerical Investigation of Combustion in a Lean Burn Gasoline Engine

This research effort focuses on lean-burn combustion in gasoline internal combustion engines. Gasoline is largely known to be characterized by narrow flammability range, which makes the use of ultra-lean mixtures very challenging. In order to fully explore the gasoline lean burn potential, a promising strategy should combine advanced intake geometries, injection strategies, and ignition technologies. In this paper, a CFD methodology is developed in order to provide proper insight into lean-burn gasoline combustion. A baseline homogenous/lean case is analyzed and numerical results are validated against engine data. Two critical issues are addressed. First, a relatively large detailed mechanism is validated against the experimental data for extreme operating conditions (low pressure values, lean mixtures). The large cycle-to-cycle variation characterizing lean combustion is shown experimentally.
Journal Article

Mixture Formation in Direct Injection Hydrogen Engines: CFD and Optical Analysis of Single- and Multi-Hole Nozzles

This paper describes the validation of a CFD code for mixture preparation in a direct injection hydrogen-fueled engine. The cylinder geometry is typical of passenger-car sized spark-ignited engines, with a centrally located injector. A single-hole and a 13-hole nozzle are used at about 100 bar and 25 bar injection pressure. Numerical results from the commercial code Fluent (v6.3.35) are compared to measurements in an optically accessible engine. Quantitative planar laser-induced fluorescence provides phase-locked images of the fuel mole-fraction, while single-cycle visualization of the early jet penetration is achieved by a high-speed schlieren technique. The characteristics of the computational grids are discussed, especially for the near-nozzle region, where the jets are under-expanded. Simulation of injection from the single-hole nozzle yields good agreement between numerical and optical results in terms of jet penetration and overall evolution.
Technical Paper

Numerical and Optical Evolution of Gaseous Jets in Direct Injection Hydrogen Engines

This paper performs a parametric analysis of the influence of numerical grid resolution and turbulence model on jet penetration and mixture formation in a DI-H2 ICE. The cylinder geometry is typical of passenger-car sized spark-ignited engines, with a centrally located single-hole injector nozzle. The simulation includes the intake and exhaust port geometry, in order to account for the actual flow field within the cylinder when injection of hydrogen starts. A reduced geometry is then used to focus on the mixture formation process. The numerically predicted hydrogen mole-fraction fields are compared to experimental data from quantitative laser-based imaging in a corresponding optically accessible engine. In general, the results show that with proper mesh and turbulence settings, remarkable agreement between numerical and experimental data in terms of fuel jet evolution and mixture formation can be achieved.