Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
2000-06-08
2001-11-20
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C123S308000, C123S430000, C123S090150
Reexamination Certificate
active
06318348
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a four-stroke reciprocating piston internal combustion engine in which a portion of the exhaust gas is selectively recirculated and added to the cylinder along with fuel and air to create a stratified exhaust gas/air-fuel mixture within the combustion chambers.
2. Description of the Related Art
It is well known that many spark-ignition four-stroke reciprocating piston internal combustion engine designs have a lower efficiency at low/partial load. The loss of efficiency is caused by a number of factors including: losses due to the throttling of the intake mixture, slow combustion due to lower density of the throttled mixture, and excessive heat loss to the combustion chamber walls. In addition to low efficiency at low/partial load, some engines emit unacceptable levels of nitrogen oxides (NOx) and hydrocarbons (HC) during partial-load operation.
Engine designs that use exhaust gas recirculation (EGR) have been developed as one solution to the efficiency and emission problems associated with low/partial load operation. It has been well documented that the use of exhaust gas recirculation in engines provides some reduction in throttling losses and significant reductions in engine NOx emissions because the peak combustion temperature is reduced. It is also known that exhaust gas recirculation can be used with stoichiometric air-fuel mixtures to allow the use of conventional three-way catalysts for effective exhaust emission control.
A number of engine configurations that implement exhaust gas recirculation are known in the art. For example, in U.S. Pat. No. 4,870,941 there is disclosed a basic type of an engine EGR system wherein the engine exhaust manifold is placed in fluid communication with the intake manifold by way of an EGR passage. In this configuration, exhaust gas is recirculated or fed back to the intake manifold through the EGR passage and an EGR valve. Another type of engine EGR system is disclosed in U.S. Pat. No. 5,404,844 wherein a first portion of the exhaust gas in an upper portion of the cylinder is expelled into an exhaust port and a second portion of the exhaust gas from a lower portion of the cylinder is expelled into an intake port for subsequent reintroduction into the cylinder from the intake port during the intake stroke. Yet another type of engine EGR system is disclosed in U.S. Pat. No. 5,005,552 wherein exhaust gas is recirculated into the cylinder by opening the exhaust valve during the intake stroke thereby drawing a backflow of exhaust gas into the cylinder.
Engines that use charge stratification have been developed as another solution to the efficiency and emission problems associated with low/partial load operation. In a typical stratified charge spark ignition engine, the air/fuel mixture is deliberately delivered to the cylinder in a non-homogeneous fashion to produce a small kernel of a relatively rich mixture at the spark plug while the remainder of the air/fuel mixture is relatively lean. As the rich mixture ignites, it in turn ignites the lean mixture in the combustion chamber. In such engines, therefore, the air/fuel mixture can be burned completely even if the air/fuel mixture, as a whole, is lean. Accordingly, fuel economy is improved and regulated gaseous emissions, such as carbon monoxide and NOx, that are contained in the exhaust of the engine can be reduced. However, engines using charge stratification methods typically require special expensive lean NOx trap catalysts for emission control, and therefore have not achieved widespread use.
The charge stratification may take place in different ways within the combustion chamber. The common forms of stratification are axial stratification in which the fuel is concentrated at the top of the combustion chamber and radial stratification in which the fuel is concentrated near the central axis of the combustion chamber. Other forms of stratification are created by causing the intake charge to tumble, that is to say rotate about an axis perpendicular to the cylinder axis. Such motion is not to be confused with swirl in which gases rotate about the axis of the cylinder, the latter normally resulting in radial stratification. When tumble is promoted in the intake charge, stratification can occur in one of two ways. In one way, if the composition of the gases varies across the width of the combustion chamber, a sandwich-like structure with vertical layers is created that is referred to as vertical stratification, the vertical direction being taken as the axis of reciprocation of the piston. In the other form of stratification produced by tumble, which is termed envelope stratification, the tumble produces a horizontal cylinder of one composition enveloped in a second outer layer having a different composition, the two layers tumbling in unison at right angles to the cylinder axis.
In order to produce radial stratification, the gases entering the combustion chamber can be provided as two streams of different composition that are aimed tangentially into the combustion chamber. U.S. Pat. No. 5,765,525 discloses an engine that produces radial stratification by directing one stream to swirl near the cylinder wall while the other stream is directed towards the center of the cylinder.
Envelope stratification can be produced by splitting the intake gases into two streams of different composition with the separation between them extending at right angles to the stem of the intake valve. U.S. Pat. No. 5,915,354 discloses an engine that produces envelope stratification using this method. The lower of the two streams is directed towards the center of the combustion chamber while the upper stream is directed towards the roof of the combustion chamber, the two streams then tumbling together at right angles to the cylinder axis.
Stratified exhaust gas recirculation (EGR) has been developed as yet another solution to the efficiency and emission problems associated with low/partial load operation. U.S. Pat. Nos. 4,393,853, 5,870,993, 5,894,826 and 5,918,577 all represent various forms of stratified exhaust gas recirculation (EGR).
In U.S. Pat. No. 4,393,853, there is disclosed an engine which implements stratified exhaust gas recirculation (EGR) methods. In the engine configuration described in this patent, a swirling fuel-air mixture is introduced through an intake valve into the center of the cylinder near the spark plug, and exhaust gas is directed from another cylinder or the exhaust gas manifold through a tangential port located in the middle of the cylinder wall. This engine configuration creates radial stratification wherein exhaust gas swirls adjacent the cylinder wall and the fuel-air mixture swirls in the center of the cylinder.
U.S. Pat. No. 5,870,993 discloses an engine configuration wherein exhaust gas is recirculated into the cylinder by opening the exhaust valve during the intake stroke thereby drawing a backflow of exhaust gas into the cylinder. A chamfer on the exhaust valve opening creates a swirling flow of recirculated exhaust gas that rotates about an axis parallel to the direction of motion of the reciprocating piston. A fuel-air mixture is also introduced into the cylinder in a manner that creates a tumble flow in the center region of the cylinder. The swirling exhaust gas flow and the tumbling fuel-air flow create stratification in the combustion chamber.
In U.S. Pat. No. 5,894,826, there is disclosed an engine with a first inlet port for introducing air tangentially into the cylinder to produce a generally circular motion in a peripheral region of the cylinder and a second inlet port to introduce air and recirculated exhaust gas, which is provided to the second inlet by way of an EGR passageway, toward the center of the cylinder.
U.S. Pat. No. 5,918,577 discloses another stratified EGR engine wherein exhaust gas is recirculated into the cylinder by opening the exhaust valve during the intake stroke thereby drawing a backflow of exhaust gas into the cylinder. A helical exhaust port creates a swirling flow of re
Kajander John E.
Shelton Larry
Visteon Global Technologies Inc.
Wolfe Willis R.
LandOfFree
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