16-03-2012, 01:58 PM
six-stroke diesel engine
B830_SIX_STROKE_ENGINE_BY_A.DOC (Size: 423 KB / Downloads: 181)
ABSTRACT
In this report, a new six-stroke diesel engine is proposed and the thermodynamic performances of this engine are numerically and experimentally analyzed. Since the six-stroke diesel engine introduced here has two combustion processes in one cycle, it offers new methods of combustion control which can't be attained in an ordinary four-stroke diesel engine. In the analysis, we use a simple single zone thermodynamic model with considering the Wiebe's function for heat release rate and the Foschini’s equation for heat transfer coefficient. As a results, it was confirmed when the heat release of 1st combustion stroke and 2nd combustion stroke were equivalent, the maximum in-cylinder gas temperature was the lowest, and further it was lower than that of the four stroke diesel engine.
INTRODUCTION
Diesel engines have wide range of utilization for automobiles, locomotives & marines and co-generation systems. However, large problem is still related to undesirable emission.
To improve exhaust emissions from DI diesel engines, a new concept of Six Stroke Engine has been proposed. This engine has a second com¬pression and combustion processes before exhaust pro¬cess.
As the fuel in one cycle was divided into two combus¬tion processes and the EGR effect appeared in the sec¬ond combustion process, the decreased maximum cylinder temperature reduced NO concentration in the exhaust gas It was further confirmed that soot formed in the first combustion process was oxidized in the second combustion process .Therefore, a six¬ stroke DI diesel engine has significant possibilities to improve combustion process because of its more control¬lable factors relative to a conventional four-stroke engine.
INTAKE / SUCTION STROKE:
To start with the piston is at or very near to the T.D.C., the inlet valve is open and the exhaust valve is closed. A rotation is given to the crank by the energy from a flywheel or by a starter motor when the engine is just being started. As the piston moves from top to bottom dead centre the rarefaction is formed inside the cylinder i.e. the pressure in the cylinder is reduced to a value below atmospheric pressure. The pressure difference causes the fresh air to rush in and fill the space vacated by the piston. The admission of air continues until the inlet valve closes at B.D.C.
FIRST COMPRESSION STROKE:
Both the valves are closed and the piston moves from bottom to top dead centre. The air is compressed up to compression ratio that depends upon type of engine. For diesel engines the compression ratio is 12-18 and pressure and temperature towards the end of compression are 35-40 kgf/cm2 and 600-700 0C
FIRST COMBUSTION STROKE:
This stroke includes combustion of first fuel (most probably diesel) and expansion of product of combustion. The combustion of the charge commences when the piston approaches T.D.C.
Here the fuel in the form of fine spray is injected in the combustion space. The atomization of the fuel is accomplished by air supplied. The air entering the cylinder with fuel is so regulated that the pressure theoretically remains constant during burning process.