SESSION 8

INTERNAL COMBUSTION ENGINES

ABSTRACT

This paper presents the preliminary results of some of a few of its kind effort in large eddy simulation (LES) of engine flows to predict turbulent fluctuations, and the statistics of turbulence quantities inside IC engine cylinders. For this purpose, the wellknown engine simulation code KIVA is used with special precautions to keep the numerical accuracy at a. sufficiently higher level, as well as using relatively fine grid resolution. The capabilities of this code are tested against benchmark eases such as lid-driven cavity flow and swirling and non-swirling free jet flows. It is then applied to a typical engine geometry under motored conditions. In particular, turbulence generated during the intake stroke, and the instabilities induced by a typical piston-bowl assembly are investigated. The computed velocity fluctuations, correlation coefficients and energy spectra of turbulent fluctuations are compared to experimental results. The predictions seem to extend well into the inertial range of turbulence and depict a good qualitative agreement with measurements. The results also shed light into the mechanisms by which turbulence may be generated by the piston-bowl assembly.

ABSTRACT

An experimental investigation of the effect of thermal barrier coating on a turbocharged DI diesel engine performance was conducted. Tests were carried out over a range of engine speeds at low middle, and high loads conditions. Combustion chamber surfaces of the test engine were coated with ceramic materials. Cylinder head and valves was coated with a 0.35 mm thickness of CaZrO₃ over a 0.15mm thickness of NiCrAl bond coat. The material used on pistons was MgZrO₃. The coating process was done by using atmospheric plasma spray technique. The test data of the both cases were analyzed by using a computer program and the results were compared as diagrams.

ABSTRACT

A multidimensional turbulent, evaporating and reactive fuel spray model has been suggested. The model includes fluid flow conservation and turbulence equations, to simulate air flow pattern during compression and expansion strokes, coupled with the governing equations of a droplet having a diameter equal to the spray Sauter mean diameter, to define the spray axis, and the cross fuel distribution along the spray axis. Heat release is calculated from a verified single zone combustion model. The model estimates the instant evaporated fuel quantities and void fraction. Effect of droplet interaction and vaporization has been considered. Theoretical results show the effect of different operating conditions and design parameters on the spray behavior. A comparison of the predicted results with the available analytical and experimental data shows reasonable agreement. The model is able to predict the overall behaviour of the reacting fuel spray and could be expanded to include more sophisticated combustion models.

ABSTRACT

The influence of fuel composition on first stage of combustion and soot formation, in an IDI Diesel engine, was analyzed from measurements of spectral extinction and flame intensity using Tetradecane, N-heptane and Diesel fuel Monocomponent fuels with high paraffinic content, such as Tetradecane and N- heptane, free of aromatics, were compared with commercial Diesel fuel in order to evaluate the effect of aromatic compounds of Diesel fuel on soot formation. The soot formation process, its inception and the amount of the soot volume fraction are strongly dependent on the chemical and physical characteristics of fuels. Monocomponent fuels revealed the presence of species, formed from pyrolysis of fuel and characterized by UV absorption bands that seem to contribute to soot formation. An evaluation of the soot volumetric fraction was made at different times for all the fuels and at different A/F ratios. N-heptane is the fuel which gives rise to the lowest soot production. The total amount of soot formed during the combustion of Tetradecane resulted to be intermediate between N-heptane and Diesel fuel.