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Numerical investigation into the effect of direct fuel injection on thermal stratification in HCCI engine

Gęca M., Hunicz J., Jaworski P.

Combustion Engines

2017

R. 56, nr 2

137--140

Despite the fact that HCCI engines are distinguished by mixture homogeneity, some degree of stratification always appears inside a combustion chamber. It is especially applied to residual effect engines utilizing negative valve overlap. Mixture stratification is a result of the imperfect mixing of fresh air with trapped residuals. Direct fuel injection introduces stratification as well, due to fuel vaporization. As a consequence, the temperature within the combustion chamber is uneven. Thermal stratification affects auto-ignition timing and combustion evolution in a high extent. The purpose of this study was to evaluate a degree of thermal stratification in HCCI engine utilizing negative valve overlap. Investigations were performed using three-dimensional CFD model of the combustion system, made by using AVL FIRE software. Simulations were realized for various timings of fuel injection into the cylinder. It was found that fuel injection timing had a significant effect on the thermal stratification and resulting auto-ignition timing.

Thermodynamic simulation comparison of AVL BOOST and Ricardo WAVE for HCCI and SI engines optimization

Alqahtani A., Shokrollahihassanbarough F., Wyszynski M. L.

Combustion Engines

2015

R. 54, nr 2

68--72

The aim of this paper is to compare two simulation software platforms, AVL BOOSTTM and Ricardo WAVETM as used to simulate HCCI and SI GDI engines with the intention of maximising the engine’s efficiency and minimising the emissions. This paper compares these platforms in an experimentally validated model to analyse a spark ignition and a Homogeneous Compression Ignition Charge (HCCI) single cylinder 4 valve gasoline engines with multiple configurations and running parameters in order to find the most optimal set-up for the engine, with the prospect of allowing an optimum engine to be built and tested in real world conditions without the need for multiple expensive prototypes and long delays.

Effects of spark assist on HCCI combustion

Hunicz J., Gęca M., Kordos P., Medina A.

Combustion Engines

2015

R. 54, nr 2

73--77

HCCI (homogeneous charge compression ignition) combustion is initiated by compression temperature and is independent of spark discharge. However, spark discharge can be applied under certain conditions to achieve hybrid combustion, where combustion by flame propagation is followed by auto-ignition of the unburned mixture. Spark assist can be applied to improve combustion stability at low loads or to reduce pressure rise rates under high load regime. In the current study variable spark ignition timing was applied for stoichiometric HCCI combustion, achieved using negative valve overlap technique. Under investigated conditions increase of nitrogen oxides emissions, due to flame propagation, was not observed. To provide more insight into combustion evolution, double Wiebe function was fitted to experimental heat release rates. It was found that only less than 10% of mixture was burned by flame propagation, even for very advanced spark discharge.