Internal-combustion engines – Precombustion and main combustion chambers in series – Plural precombustion chambers
Reexamination Certificate
2001-10-10
2004-03-23
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Precombustion and main combustion chambers in series
Plural precombustion chambers
C123S193500, C123S193600, C123S279000, C123S281000, C123S663000, C123S664000, C123S671000
Reexamination Certificate
active
06708666
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Embodiments of the invention generally relate to an apparatus and method of use in an internal combustion engine. More particularly, embodiments of the invention relate to a combustion chamber design that physically segregates the chamber into multiple smaller chambers during combustion in a combustion engine.
2. Description of the Related Art
Conventional combustion, reciprocating engines are widely used as automotive engines. These engines are designed to work on a predetermined mixture of air and fuel, which is ignited by an ignition plug, such as a spark plug or a glow plug, in a combustion chamber.
FIG. 1
is a cross-sectional view of a conventional power cylinder assembly
50
. The power cylinder assembly
50
includes a cylinder
110
, a piston
100
, a cylinder head
117
, valves
140
and
150
, an ignition plug
160
, and manifolds
145
and
155
. A combustion chamber
115
is defined by an inner wall
111
of the cylinder
110
, the crown or top surface
107
of the piston
100
, along with the cylinder head
117
. The piston
100
, which is slideably disposed in the cylinder
110
, and the inner wall
111
of the cylinder
110
are generally cylindrical in shape. The piston
100
includes several compression seals
120
(commonly referred to as piston rings) disposed within annular grooves
122
on an outer surface
124
of the piston
100
to keep the fuel/air mixture (hereinafter “mixture”) within combustion chamber
115
. Additionally, the piston
100
includes an aperture
105
for connecting the piston to a connecting rod (not shown), whereby the piston may be moved in a reciprocating fashion (e.g., axially within the cylinder
110
). The movement of the piston
100
is translated to the rod, which provides power to an engine crank shaft (not shown). The intake manifold
145
delivers the mixture to the combustion chamber
115
and the intake valve
140
regulates the amount of mixture that enters the chamber. The ignition plug
160
ignites the mixture in the combustion chamber
115
and produces a combustion flame. The exhaust valve
150
and the exhaust manifold
155
exhaust the burned mixture and any remaining mixture from the chamber
115
.
Typically, an engine cycle starts with an intake stroke, wherein the mixture is delivered into the combustion chamber
115
. During the intake stroke, the piston
100
descends to bottom dead center or the lowest point that the piston may travel in the cylinder
110
. At this point, the intake valve
140
opens and supplies the combustion chamber
115
with the appropriate amount of mixture through the intake manifold
145
. During the intake stroke, the exhaust valve
150
remains closed. As the mixture enters the combustion chamber
115
, a swirl, which mixes the air and fuel, is created by the positioning of the intake valve
140
at a certain angle in the cylinder head
117
. Further, the swirl may be utilized to create turbulence for combustion enhancement. After the piston
100
reaches bottom dead center, the intake valve
140
is closed and ends the intake stroke. The compression stroke begins when the piston
100
ascends in the cylinder
110
. The compression stroke compresses the mixture for better combustion. In the compression stroke, the piston
100
ascends in the cylinder
110
and causes the mixture to squish or move radially inward, causing a squish flow. The squish flow helps to promote faster combustion by enhancing flame propagation. Before the piston
100
reaches top dead center, or the highest point that the piston can travel in the cylinder, an ignition plug
160
is fired to ignite the mixture. In diesel engines, no ignition plug is present, but instead, ignition can occur when the compression pressure and temperature in the chamber is sufficient to support ignition. The pressure and temperature in the combustion chamber
115
are increased by the burning mixture and the pressure forces the piston
100
to descend during the expansion stroke, which moves the connecting rod to power the engine. The expansion stroke provides power to the engine. The piston
100
reaches bottom dead center and ends the expansion stroke. The exhaust stroke, which removes the combusted mixture from the chamber
115
, begins when the piston
100
ascends in the cylinder
110
. As the piston
100
ascends, the exhaust valve
150
opens to remove the combustion by-products and any remaining mixture through the exhaust manifold
155
. The cycle is then repeated.
The efficiency of the combustion chamber to combust the mixture determines the amount of pollutants such as oxides of nitrogen or NO
x
that are released into the atmosphere. To achieve higher efficiency using hydrocarbon fuels, leaner fuel to air ratios have been utilized. For equivalent power output, a leaner fuel to air ratio must be accompanied by a higher over-all airflow to the engine. The leaner fuel to air ratio leads to high thermal efficiencies, when the airflow has been compensated, and to higher peak temperatures. At higher peak temperatures, combustion efficiency improves at the expense of increased production of NO
x
. It is known that above 1300-1500° K. (Kelvin), NO
x
production increases greatly; hence it is desirable to control the peak temperature below this range. Additionally, faster flame propagation speed increases engine thermal efficiency, but can cause knock (commonly referred to as auto ignition). Knock occurs when the chemical kinetic reactions within the unburned mixture spontaneously ignite during the engine cycle. Typically, knock is initiated by compression of the unburned mixture during the combustion portion of the engine cycle. After the spark ignition process, the unburned mixture is subjected to compression by the combined effects of piston's motion and flame propagation. If the flame produced by the ignition plug fails to consume the entire unburned mixture before compression-induced chemical reactions cause spontaneous ignition within the unburned mixture, knock will occur. Hence, control of the propagation of the flame has a direct impact on the propensity for a given engine to knock. Knock decreases combustion efficiency because the energy created during auto ignition is uncontrolled and can lead to catastrophic engine failure.
In a conventional combustion chamber, the squish region, where squish flow is created, may be up to 70% of the crown's surface and is a continuous region. Because the squish region is one, large continuous area, there is more area for a flame to lose energy into the piston and quench due to wall heat transfer losses. Additionally, the flame tends to extinguish by the time it reaches the outer portion of the squish region, thereby leaving some mixture unburned leading to combustion inefficiency.
In engines, a brake mean effective pressure (BMEP) is generated within the combustion chamber as a resultant pressure force produced from the controlled burning of the mixture. High BMEP is associated with high power output and high engine efficiency. In conventional high BMEP applications, the ignition plug is fired at a relatively high pressure and temperature. However, firing at higher pressure decreases the life of the ignition plug. In order for the ignition plug to last longer, it should be fired at a lower pressure than the pressure required in conventional engine designs used in high BMEP applications. However, if the ignition plug is fired at a lower pressure or earlier ignition timing (advanced ignition timing), the productions of knock and NO
x
emissions increase.
Various attempts have been made to improve combustion chambers for use with lean mixtures to reduce concentrations of NO
x
and knock. U.S. Pat. No. 5,224,449 discloses using a toroidal chamber on the crown of the piston, whereby a mixture is ignited in the main chamber then reaches the toroidal chamber and ignites the fuel in the toroidal chamber. The pressure in the toroidal chamber increases, whereby a combustion jet gas is shot into the main chamber causing a turbu
Argenbright Tony M.
Baker & Hostetler LLP
Southwest Research Institute
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