Internal-combustion engines – Four-cycle – Having subcharger associated with the cylinder
Reexamination Certificate
2002-01-23
2004-05-18
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Four-cycle
Having subcharger associated with the cylinder
C123S347000
Reexamination Certificate
active
06736106
ABSTRACT:
FIELD OF THE INVENTION
This disclosure concerns an invention relating generally to combustion methodologies for internal combustion engines, and more specifically to combustion methodologies resulting in decreased pollutant emissions.
BACKGROUND OF THE INVENTION
For better understanding of the invention described in this document, it is initially useful to review basic principles of internal combustion engine structure and operation.
FIG. 1
depicts a cylinder in a simple idealized internal combustion engine
100
, including a combustion chamber
102
defined between a piston
104
and a cylinder head
106
. The cylinder head
106
includes a fuel injector
108
and a pair of combustion chamber valves, an intake valve
110
for intake of air from an intake manifold
112
, and an exhaust valve
114
for exhaust of combustion products to an exhaust manifold
116
and exhaust system. As is well known, the engine
100
operates by engaging in a combustion cycle, wherein fuel is burned in the combustion chamber
102
to expand the gases (primarily air) therein and drive the piston
104
. The piston
104
in turn drives a crank
118
associated with the piston
104
, with the crank
118
in turn driving the crankshaft (not shown) which provides power output for a vehicle drive train or to other structures for transmitting mechanical power. The classical four-stroke combustion cycle for both SI (spark ignition or gasoline) engines and CI (compression ignition or diesel) engines involves the following steps:
(1) An intake stroke, wherein the intake valve
110
is opened while piston
104
retreats from cylinder head
106
to draw air into the combustion chamber
102
from the intake manifold
112
.
(2) A compression stroke, wherein the piston
104
approaches cylinder head
106
with the combustion chamber valves
110
and
114
closed (at least during the latter portion of the stroke).
(3) A power or expansion stroke, wherein fuel injected into the combustion chamber
102
is ignited and the expanding gases within the combustion chamber
102
push the piston
104
outwardly (as during the intake stroke). Again, the combustion chamber valves
110
and
114
usually remain closed (at least during the early portion of the stroke).
(4) An exhaust stroke, wherein the combustion products within the combustion chamber
102
are expelled to the exhaust manifold
116
by advancing the piston
104
towards the cylinder head
106
with the exhaust valve
114
open.
Each stroke occurs over 180 degrees of crankshaft rotation, with the entire cycle thereby occurring over 720 degrees (two full crankshaft revolutions). The combustion chamber valves
110
and
114
are usually opened and closed at the desired times by valve actuators such as cams or other structures, which are in turn driven by the crankshaft (not shown). Since such arrangements couple the timing and extent of valve opening and closing to the positioning of the crankshaft, and since it may be desirable to have a greater degree of control over valve actuation to achieve desired combustion chamber conditions, there has been a recent trend towards the use of variable valve timing technologies. These technologies wholly or partially decouple the timing and/or extent of valve actuation from the crankshaft position, and allow the valves
110
and
114
to be opened and/or closed when desired (and may also allow the degree of opening to be varied as desired). Examples of variable valve actuation (VVA) schemes may be found, for example, in U.S. Pat. Nos. 4,777,915; 4,829,947; and 5,515,818.
The foregoing combustion cycle steps/strokes differ between classical SI and CI engines in that SI engines tend to inject fuel during the intake stroke, whereas CI engines tend to inject fuel late in the compression stroke or early in the power stroke, close to “top dead center” (TDC), the piston
104
's point of closest approach to the cylinder head
106
. Additionally, in SI engines, ignition of the fuel/air mixture occurs by introduction of a spark (with no spark plug being illustrated in FIG.
1
). In contrast, classical CI engines rely on the compression stroke to increase the heat and pressure in the combustion chamber
102
to such a degree that ignition results. There are also various types of “hybrid” engines which operate using a combination of SI and CI principles, or example, engines which run primarily on CI principles but which use a spark or “glow plug” to assist with ignition. (Also note that the engine of
FIG. 1
is described as a “simple idealized” one since real-world engines may have a wide variety of combustion chamber configurations other than those shown at
102
in
FIG. 1
, and may have varying numbers, locations, and configurations of combustion chamber valves
110
and
114
and/or injectors
108
.)
In the field of engine development and manufacture, two concerns of critical importance are engine efficiency (e.g., power output per fuel consumption) and engine emissions. Diesel engines tend to operate more efficiently than SI engines, but they unfortunately also tend to have much greater pollutant emissions than SI engines. Common pollutants arising from the use of internal combustion engines are nitrogen oxides (commonly denoted NO
x
) and particulates (also known simply as “soot”). NO
x
is generally associated with high-temperature engine conditions, and may be reduced by use of measures such as exhaust gas recirculation (EGR), wherein the engine intake air is diluted with relatively inert exhaust gas (generally after cooling the exhaust gas). This reduces the oxygen in the combustion chamber and obtains a reduction in maximum combustion temperature, thereby deterring NO
x
formation. Particulates (soot) include a variety of matter such as elemental carbon, heavy hydrocarbons, hydrated sulfuric acid, and other large molecules, and are generally associated with incomplete combustion. Particulates can be reduced by increasing combustion and/or exhaust temperatures, or by providing more oxygen to promote oxidation of the soot particles. Unfortunately, measures which reduce NO
x
tend to increase particulate emissions, and measures which reduce particulates tend to increase NO
x
emissions, resulting in what is often termed the “soot-NO
x
tradeoff”.
At the time of this writing, the diesel engine industry is facing stringent emissions legislation in the United States, and is struggling to find methods to meet government-imposed NO
x
and soot targets for the years 2002-2004 and even more strict standards to be phased in starting in 2007. One measure under consideration is use of exhaust after-treatment (e.g., particulate traps) for soot emissions control in both heavy-duty truck and automotive diesel engines. However, in order to meet mandated durability standards (e.g., 50,000 to 100,000 miles), the soot trap must be periodically regenerated (the trapped soot must be periodically re-burned). This requires considerable expense and complexity, since typically additional fuel must be mixed and ignited in the exhaust stream in order to oxidize the accumulated particulate deposits.
Apart from studies directed to after-treatment, there has also been intense interest in the more fundamental issue of how to reduce NO
x
and particulates generation from the combustion process and thereby obtain cleaner “engine out” emissions (i.e., emissions directly exiting the engine, prior to exhaust after-treatment or similar measures). Studies in this area relate to shaping combustion chambers, timing the fuel injection, tailoring the injection rate during injection so as to meet desired emissions standards, or modifying the mode of injection (e.g, modifying the injection spray pattern). One field of study relates to premixing methodologies, wherein the object is to attain more complete mixing of fuel and air in order to simultaneously reduce soot and NO
x
emissions. In diesel engines, the object of premixing methodologies is to move away from the diffusion burning mechanism which drives diesel combustion, and instead attempt to attain premi
Jhavar Rahul
Reitz Rolf Deneys
Rutland Christopher J.
Benton Jason
DeWitt Ross & Stevens S.C.
Fieschko, Esq. Craig A.
Wisconsin Alumni Research Foundation
Yuen Henry C.
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