Internal-combustion engines – Means to whirl fluid before – upon – or after entry into... – Having multiple oxidant inlet means
Patent
1997-09-15
1998-06-16
Nelli, Raymond A.
Internal-combustion engines
Means to whirl fluid before, upon, or after entry into...
Having multiple oxidant inlet means
123430, 123432, F02B 3100, F02B 1700, F02B 1500
Patent
active
057655251
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an intake system for an internal combustion engine of the type having two intake ports per cylinder.
BACKGROUND OF THE INVENTION
Engines with two intake valves per cylinder are known that have one of the intake ports delivering the charge tangentially near the outer circumference of the cylinder and into which fuel is injected. During low load operation, port deactivation is used to close off the other intake port so that high swirl is produced in the combustion chamber by the first port. The injection of the fuel into the swirl port achieves good mixing and produces a homogeneous charge of fuel and air even at low flow rates. At higher speed and load, both the intake ports are active and the fuel injection system could be arranged such that the fuel is also well mixed in the combustion chamber.
U.S. Pat. No. 5,094,210 describes an engine with two intake valves per cylinder, having separate intake manifolds leading to respective first and second set of intake ports. The manifolds are separately throttled and fuel is supplied to both sets of intake ports, in the case of the first ports by a central fuelling system located at the plenum of the first intake manifold and in the case of the second ports by fuel injection into the individual ports. The design of the intake ports in this patent is such that when the charge is drawn equally through both ports, it tumbles within the combustion chamber, whereas when it is drawn through only one port the charge swirls within the combustion chamber. By varying the flows separately between the two sets of intake ports, a mixture of tumble and swirl is achieved.
The term swirl is used herein in its normally accepted sense to describe the charge motion when a vortex is created in the cylinder with its axis parallel to the cylinder axis. Tumble, on the other hand, describes the motion in which the charge rotates about an axis perpendicular to the cylinder axis and parallel to the plane containing the axes of the two intake valves.
The above system is suitable primarily for homogeneous charge but it is also possible to achieve some degree of charge stratification by fuelling the set of ports differently or by introducing exhaust gas recirculation (EGR) gases into one set of ports. Published data of an engine incorporating the above system (SAE 940449) shows the average lean air-fuel ratio (AFR) limit is in the region of 22:1 and the EGR limit is in the region of 22%. Such data is typical of most homogeneous lean burn engines and is a fair indication that only a small degree of charge stratification is achieved. It is not possible to exaggerate the degree of charge stratification further in this system and to operate at even higher average AFR or higher average EGR because mixing that occurs in the combustion chamber makes it difficult to keep different parts of the charge separate from each other.
Another known system has two intake valves per cylinder in which EGR is introduced through the second intake port while air and fuel mixture is introduced through the first intake port. The two intake ports are symmetrically designed for producing strong tumble and the system is aimed at creating charge stratification across the width of the cylinder with the different charge contents remaining directly under the respective intake ports thus substantially dividing the total charge into two half cylindrical charge volumes.
This system is not suitable, however, for stable ignition with a spark plug located at the center of the cylinder, as the spark occurs at the boundary between the two stratified charge volumes. Moreover, varying the flows separately between the two intake ports produces a skewed tumble motion which causes increased mixing and the stratification is quickly destroyed.
In all the above systems, during high load operation, although both intake ports are open and fully utilised to give maximum volumetric efficiency, care must be take to introduce fuel equally to both intake ports otherwise undesirable strati
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Ford Global Technologies Inc.
Nelli Raymond A.
Wilkinson Donald A.
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