Search Results

The homogeneous charge compression ignition (HCCI) is one of the alternative to reduce significantly engine emissions for the future regulations. The combustion process in HCCI engines does not involve flame propagation or flame diffusion as in conventional internal combustion engines. Many studies have confirmed that during this mode the combustion process is mainly controlled by chemical kinetics. However, a coupled CFD and detailed chemistry simulation requires substantial memory and CPU time which may be very difficult with current computer capabilities. Thus a reduced mechanism is required to simulate the engine cycle during this operating mode to achieve more accurate analysis. In this study reduced chemistry was used with an engine CFD code combustion (Star-CD/Kinetics) to study combustion process in homogeneous charge compression ignition (HCCI) engines.

To provide fuel/air ratio quantitative measurements in an S.I engines, a transparent cylinder engine is investigated with the Fuel-Air Ratio Laser Induced Fluorescence (FARLIF) technique. In a homogeneous mixture, the two dimensional distribution for the fuel/air ratio is calibrated and measured during the compression stroke for different equivalence ratios. After spark ignition, the combustion zone and the flame front are visualized by laser sheet LIF. The direct-injection stratified-charge, new concept for gasoline engines is investigated with FARLIF. In the direct injection gasoline engine where the fuel is directly injected into a cylinder and the flow is highly turbulent, two injection timings are used: -early injection (i.e. during the intake stroke) to promote a homogeneous distribution; -late injection during the compression stroke, to generate a ultra-lean stratified charge.

Tumble flow pattern, during the intake and compression strokes, is investigated on a four-valve, four stroke transparent single-cylinder research engine. Two-dimensional in-cylinder velocity distributions are measured with cross-correlation Particle Image Velocimetry (PIV) on planes both parallel and perpendicular to the piston. The velocity fields are obtained at several crank angles. The single-cylinder engine has a transparent quartz liner and an extended piston with a quartz top. PIV investigation in the different planes allows the tumble flow pattern to be deduced from the two-dimensional ensemble-averaged flow pattern. The tumble motion is similar to a 2D roll motion with a rotation axis deformed on the two extremities towards the piston head. With such a pattern, the two-dimensional velocity fields in horizontal sections exhibit two vortices in the upper part of the cylinder.

An experimental investigation is carried out on the effect of Swirl and Tumble on turbulence and combustion characteristics in four-valve spark ignition engines. This study is conducted on an optically accessed single cylinder research engine. The in-cylinder motion is varied by means of flow-control baffle located between the intake manifold and the cylinder head. Several baffle sizes and shapes have been designed to induce various in-cylinder flow fields. The equivalent angular speed of the tumble and swirl vortices, occurring inside the cylinder, are determined from Laser Doppler Velocimetry. Comparisons with measurements from a conventional steady flow rig which measures air motion speed with a paddle wheel anemometer are presented and show a good correlation between the two measurement techniques.