Internal-combustion engines – Two-cycle – Whirl through piston-controlled ports
Patent
1996-05-06
1998-10-13
McMahon, Marguerite
Internal-combustion engines
Two-cycle
Whirl through piston-controlled ports
123 65VD, 123 65BA, F02B 2500
Patent
active
058196935
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/FR94/01348, filed Nov. 18, 1994.
FIELD OF THE INVENTION
The invention applies to a process to improve the operating of an internal combustion engine (heat engine) which is supercharged, mainly with a turbocharger, and scavenged with air.
More specifically, the invention relates to diesel engines in which the cylinders are scavenged with air; however, the invention also applies to petrol engines (or even gas) with direct fuel (or gas) injection into the cylinder.
BACKGROUND OF THE INVENTION
FR-A-2 448 032 relates to supercharged four-stroke diesel engines with approximately constant pressure in the exhaust manifold. In this document the utilisation of the natural evolution of the relationship between the supercharging air pressure and the back-pressure in the exhaust of the cylinder relies on the instantaneous manifold pressure curves being as constant as possible, particularly in the exhaust manifold, that is, curves whose pressure fluctuations remain small in comparison to the average pressure. In this case care is taken to ensure that the maximum instantaneous pressure in the exhaust manifold does not exceed the boost pressure so that during the valve overlap period, the scavenging of the cylinder is not disturbed, except at very low loads when a slight backflow scavenging may be admissible. This type of exhaust manifold with constant pressure, which is well known in high-output industrial engines (where many cylinders are connected to a single manifold supplying the turbine inlet of the turbocharger) has two embodiments: the cylinder bore or greater, restricting the flow of the pulse by converting its pressure energy into velocity and thus permitting the use of a manifold with a smaller cross-sectional area in which the instantaneous pressure fluctuations are weak enough not to impair the scavenging of the different cylinders connected to a same manifold.
However, an embodiment has been envisaged (see Page 11, lines 28-32) for the characteristics set out in FR-A-2 448 032 in the case of an engine with an "impulse" or "pulse converter" system in which pressure variations or "pulses" occur in the exhaust manifold. This embodiment has been proposed for cases in which the time intervals between the pulses are sufficiently long. In other words, in the embodiment envisaged for an engine with pulses in its exhaust manifold, it is necessary to utilise the intervals between the pulses in order to avoid the perturbations created by the pressure variations corresponding to the pulses.
Conversely, the present invention, which follows a totally different approach from that of FR-A-2 448 032, aims to exploit the presence of pulses, i.e. of appreciable pressure variations in the exhaust manifold. It also aims to utilise these pulses to induce self-supercharging using a post-charging effect, which is advantageous especially at low engine speeds, without, however, producing an undesired effect at higher engine speeds, particularly that of post-charging with exhaust gas.
It is known that turbocharging, which is efficient at all engine speeds, is all the more difficult in an engine with a wide speed range and low power output, for example a car engine. In fact, the turbochargers in such engines have a low efficiency because they are small in size.
For such engines (cars or similar sized engines) in order to lessen the drawback of a lack of supercharging air at low engine speeds, two techniques have been developed: at the turbine inlet that opens above a certain boost pressure threshold so that this pressure does not exceed a given threshold; this technique permits the use of turbines with a very small flow area, resulting in a higher boost pressure at low engine speeds at the cost of increased exhaust back-pressure at high engine speeds; well allows a higher boost pressure at low engine speeds without increasing the exhaust back-pressure to such a large extent as in the first one.
SUMMARY OF THE INVENTION
One of the main aims of the invention is to
REFERENCES:
patent: 4809649 (1989-03-01), Brinkman
patent: 4986224 (1991-01-01), Zuffi
patent: 5063886 (1991-11-01), Kanamaru et al.
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