Internal-combustion engines – Precombustion and main combustion chambers in series – Two-cycle
Patent
1987-07-31
1989-08-08
Argenbright, Tony M.
Internal-combustion engines
Precombustion and main combustion chambers in series
Two-cycle
123 65VD, 123286, F02B 2518
Patent
active
048542806
DESCRIPTION:
BRIEF SUMMARY
The present invention generally relates to a two-stroke internal combustion engine having at least one cylinder containing a reciprocating piston, in particular but not exclusively of the diesel type, and it more particularly concerns a valve device exclusively incorporated in the cylinder head which permits the replacement of the burnt gases by fresh air required for the combustion.
The invention also relates to a cylinder head for internal combustion engines which is provided with said device and to the various applications and utilizations resulting from its use.
The replacement of the burnt gases by the charge of fresh air presents a particular problem in two-stroke internal combustion engines, since there is only a short period of time (corresponding to an angle of rotation of about 120.degree. to 140.degree. of the crankshaft) for achieving it, whereas, in four-stroke engines, the lapse of time available for this purpose is substantially longer and may correspond to an angle of rotation of about 400.degree. of the crankshaft.
In two-stroke engines having modern valves, one tries to improve the scavenging:
(a) by increasing the permeability of the work chamber or cylinder when the intake and exhaust valves are simultaneously open;
(b) by decreasing the short-circuit between the intake and the exhaust by means of the orientation of the current of particles of fresh air entering the cylinder, in a direction which prevents them from passing directly from the intake to the exhaust,
(c) by reducing as far as possible the mixture, in the cylinder, between the fresh air and the burnt gases coming from the preceding cycle or cycles.
In U.S. Pat. No. 2,061,157 (Hurum), it has already been proposed to dispose, in the cylinder head of a two-stroke internal combustion engine, one or two intake valves which open onto a prechamber of flat shape and whose axis or axes are orthogonal to the axis of the cylinder, and an exhaust valve whose axis is parallel to that of the cylinder and offset relative to the last-mentioned axis. The prechamber communicates with the cylinder through an orifice of restricted section so as to cause the mixture of air and fuel to enter the cylinder in the form of a compact jet and the stem of the or each intake valve extends through the space defined in the cylinder head by the geometrical extension of the wall of the cylinder, which gives rise to a throttled and dissymmetrical flow of the mixture into the cylinder. Experience has shown that said compact jet was not very effective from the scavenging point of view: indeed, if the criterion (b) is respected, owing to the introduction at high velocity of particles of air in the cylinder toward the piston, on the other hand, the criterion (c) is not respected: the introduction of particles of air at high velocity in the cylinder is effected, owing to the disposition of the intake valve, in the very midst of the gas mass--particularly at the moment when the intake valve is at the beginning of the opening--and creates an intense mixture of the fresh air and burnt gases. Further, this disposition leaves dead regions which are not scavenged, which still further reduces the scavenging effectiveness. Owing to the presence of the orifice of restricted section, the permeability of the cylinder head to the flow (criterion a) is very poor. Lastly, the flat shape of the prechamber results in a bad mixture between the fresh air and the fuel which is injected thereinto. This analysis of U.S. Pat. No. 2,061,157 is confirmed in the third paragraph of U.S. Pat. No. 4,616,605 (Kline) which was only published on Oct. 14, 1986.
In U.S. Pat. No. 2,222,134 (Augustine) there is described a two-stroke internal combustion engine having an intake and an exhaust valve whose axes are parallel to that of the cylinder and whose opening movements are in opposite directions The seat of the intake valve opens upwardly onto the prechamber which opens downwardly onto the cylinder through an orifice in the shape of a crescent disposed tangentially to the cylinder. The geometry
REFERENCES:
patent: 1626387 (1927-04-01), Burtnett
patent: 2061157 (1936-11-01), Hurum
patent: 2222134 (1940-11-01), Augustine
patent: 2685869 (1954-08-01), Fenney et al.
patent: 4616605 (1986-10-01), Kline
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