Internal-combustion engines – Two-cycle – Whirl through piston-controlled ports
Patent
1993-12-16
1996-05-21
Okonsky, David A.
Internal-combustion engines
Two-cycle
Whirl through piston-controlled ports
123295, F02B 7502
Patent
active
055179541
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The subject of the invention is an induction method for a compression-ignition internal combustion engine, which comprises variable volume limited inside a cylinder by a piston and by a cylinder head; to make the said working chamber communicate respectively with a first cavity gathering the combustion gases formed in the working chamber and successively and/or simultaneously with a second cavity supplied with fresh air; and
In internal combustion engines of the type defined hereinabove, the fuel is injected under pressure into the combustion chamber when the piston is close to top dead centre (TDC), that is to say when the abovementioned variable volume is close to its minimum value. The adiabatic compression of the air trapped in the cylinder heats this air so that its temperature exceeds the self-ignition temperature of the injected fuel.
The finely atomised fuel is introduced into the combustion chamber in the form of droplets. By penetrating into the ambient medium, each droplet is vaporised and the fuel vapour diffuses in this medium creating a zone where spontaneous ignition conditions are reached, the ignition of the fuel then taking place here spontaneously. The time which elapses between the start of injection of the fuel and the beginning of combustion, during each cycle, is called the "ignition delay".
BACKGROUND OF THE INVENTION
This first phase of the combustion is very abrupt: the fuel vapour, premixed with hot air (under the pressure and temperature conditions required for self-ignition), ignites on mass. The reaction speed is very high and each partially vaporised droplet has very rapidly consumed all of the oxygen present in the air which is mixed with the vapour. In such a short time, since the mixture is not homogeneous, the unmixed air does not have time to sustain combustion, taking into account its distance from the centre (the droplet) of the combustion. The reaction therefore stops very rapidly, or at least slows down due to the rarefaction of the available oxygen. This mass combustion phase (uncontrolled combustion) is called the "pre-mix combustion".
The air and fuel movements which are preestablished or induced by the injection of the highly-pressurised fuel, or brought about by the expansion of the gases heated by the abrupt chemical reaction during this first phase of combustion allow the exothermic reaction to follow. The latter then develops in a controlled fashion, by virtue of the mass transfers, by diffusion, from the zones rich in fuel to the zones which are poor in fuel, that is to say towards the zones where the oxygen content is high. This phase of combustion by diffusion is called "progressive combustion". It is much slower and continues at the rate of mixing sustained by the relative movements of air and fuel in the working chamber.
Diagrams a, b, c and d of the appended FIG. 1 illustrate the phenomena which have just been described. These diagrams have, as common abscissa, the angle .alpha. of the crankshaft with respect to a defined angular position, the common ordinate axis Y corresponding to TDC of the piston. Diagram "a" shows the variation in pressure of the cylinder of the engine, in solid line (curve A) when there is combustion, and in broken line (curve B) when there is no combustion. Diagram "b" shows the variation in the position of the injection needle (curve C), which needle forms part of the abovementioned means for introducing pressurised fuel, and it shows up the ignition delay .tau. which is expressed in angular duration between the angular position of the crank shaft corresponding to the start of the introduction of fuel and that corresponding to the start of ignition, detected by the release of heat. In diagram "c", the instantaneous release of heat has been brought onto the ordinate axis, the first area D corresponding to the pre-mix combustion and the second area E corresponding to the progressive combustion. Finally, in diagram "d" the accumulative quantity of heat, in percentages of the total heat released during one
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