Methods and apparatuses for laser ignited engines

Details Methods and apparatuses for laser ignited engines Methods and apparatuses for laser ignited engines

2002-05-24

2004-09-28

Mohanty, Bibhu (Department: 3747)

Internal-combustion engines

Igniters

Reexamination Certificate

active

06796278

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of internal combustion engines. More particularly, it concerns methods and apparatuses for using laser ignition to adaptively adjust the position of one or more ignition locations within a combustion chamber during operation of an engine. It also concerns methods and apparatuses for providing multiple ignition locations during a single cycle of engine operation.
2. Description of Related Art
In a usual ignition apparatus for an internal combustion engine, a high voltage is applied to an ignition plug that is fixed on the wall surface of a combustion chamber in order to ignite an air-fuel mixture by spark discharge. In an ignition apparatus of this kind, however, several problems arise. For instance, since the ignition plug is exposed directly to the combustion chamber, carbon attaches to the ignition plug to render the discharge of the ignition plug difficult. Furthermore, due to a heat loss of the electrodes of the ignition plug, a torch or nucleus of flame generated by the discharge is cooled, and vanishes before reaching a flame. Since the ignition occurs on or very near the wall surface of the combustion chamber, the air-fuel mixture is more difficult to ignite than it would be at the center part of the chamber. Even if it is ignited, it takes a considerable time before the flame spreads over the whole space of the combustion chamber. Further, because the ignition occurs on or very near the wall surface, poor mixing often results due to the difficulties associated with burning fuel from the wall surface.
The problems mentioned above are present not only in conventional carburetor-type engines and port injection engines, but also in newer-generation, direct-injection engines, which have come about, in part, due to ever decreasing NO
x
emissions standards that require leaner air/fuel ratios. Shown in
FIG. 1
is a port injection engine
2
. Included in this engine are an inlet port
12
, inlet valve
4
, exhaust port
14
, exhaust valve
6
, fuel injector
10
, spark plug
8
, combustion chamber
17
, and piston
16
. Air enters the combustion chamber
17
from the inlet port
12
via the inlet valve
4
(with exhaust valve
6
closed). This air is pre-mixed with fuel from fuel injector
10
prior to entering the combustion chamber
17
(i.e., the mixture is “port-injected”). The fuel-air mixture is compressed with piston
16
and then ignited by spark plug
8
, forcing the piston
16
downwards in what is called a power-stroke. Exhaust gases may then exit the engine through exhaust port
14
via exhaust valve
6
(with inlet valve
4
closed).
Glancing at
FIG. 1
, it is apparent that the geometry of the system mandates that the fuel gas mixture be directed toward walls of the combustion chamber
17
. Thus, ignition via the confined spark plug
8
must overcome the corresponding quenching and poor mixing discussed above.
Shown in
FIG. 2
is a direct injection engine
20
, which suffers from the same problems discussed above. In fact, the quenching and poor mixing suffered by the port injection engine
2
may be exacerbated in the direct engines due to the need to have a fuel rich mixture near the spark plug and the resulting very tight physical clearances within the combustion chamber. Engine
20
includes an inlet port
12
, inlet valve
4
, exhaust port
14
, exhaust valve
6
, fuel injector
10
, spark plug
8
, combustion chamber
17
, and piston
16
. Air enters the combustion chamber
17
from the inlet port
12
via the inlet valve
4
(with exhaust valve
6
closed). The fuel is mixed with this air “directly” within the combustion chamber
17
(with valves
4
and
6
closed). The gas-fuel mixture is compressed with piston
16
and then ignited by the spark plug
8
, forcing the piston
16
downwards in the power-stroke. Exhaust gases may then exit the engine through exhaust port
14
via the exhaust vale
6
(with inlet valve
4
closed).
It is apparent that, in
FIG. 2
, the fuel injector
10
and spark plug
8
may be even more physically constrained than in FIG.
1
. Due to the illustrated geometry, the fuel must be directed toward the spark plug and the walls of the combustion chamber
17
. Correspondingly, ignition via the confined spark plug
8
must overcome quenching and poor mixing conditions associated with the cold boundary layer of the walls of combustion chamber
17
.
Several attempts have been made to address these and other numerous, well-known problems in the art of internal combustion engines. One of the most common attempts involves controlling the fuel and air flow within an engine. For instance, to address mixing problems, others have used intake air motion to provide tumble or swirl. Shown in
FIG. 3
, which illustrates a direct injection engine
30
, is a piston
16
having a shaped top
19
. Top
19
, during operation of the engine, creates a fluid flow pattern (both air and fuel) within combustion chamber
17
that generally resembles the curved arrow illustrated in FIG.
3
. In particular, fuel and air “tumble” within combustion chamber
17
, easing, at least to a degree, some of the deleterious effects of quenching and poor mixing.
Other shaped piston tops and arrangements of different components can lead to different fluid flow patterns, as is known in the art. For example, U.S. Pat. No. 5,058,548, which is hereby incorporated by reference in its entirety, involves an arc-shaped offset cavity in the roof of a combustion chamber and an injector for injecting fuel in the form of a cone. Other examples include effecting the following flows: swirling, swishing, and reverse tumbling, to name a few.
Although such methods have exhibited at least a degree of success, room for improvement remains because these methods are still hampered by the fixed, confined location of ignition. Moreover, quenching and poor mixing problems, although reduced, can still remain troublesome. Further, controlling the fuel injection and the in-cylinder air motion in these aerodynamically dominated systems may be very complex because the air motion and injection processes must change significantly as the engine load changes. At light load, for instance, the fuel is injected late in the compression stroke, into the vicinity of the spark plug, which is located very close to the combustion chamber wall. This is accomplished by a combination of fuel jet modifications, surface interactions, and controlled air motion. Conversely, at high load, the fuel is injected very early during the compression stroke, and efforts must be made to completely mix the fuel and air to homogeneous stoichiometric conditions prior to ignition. Such complexities detract from certain advantages these methods may provide.
Another attempted solution to problems discussed herein involves laser ignition rather than ignition by a spark plug. The following representative patents that disclose this, or related, approaches are: U.S. Pat. Nos. 6,053,140; 5,769,621; 5,756,924; 4,852,529; 4,434,753; and 4,416,226, all of which are hereby incorporated by reference in their entirety.
U.S. Pat. No. 6,053,140 discusses an internal combustion engine with externally supplied ignition, where a compressed air-fuel mixture is ignited, at least partially, with the use of at least one laser beam. The laser beam can be introduced into a combustion chamber via at least one optical waveguide and is focused onto an ignition location. The optical waveguide is positioned in a sealing element bounding the combustion chamber, and the sealing element is located in a cutting plane through the combustion chamber and preferably is constituted by a cylinder head gasket.
U.S. Pat. No. 5,769,621 discusses a method of fuel/oxidizer ignition comprising: (a) application of laser light to a material surface which is absorptive to the laser radiation; (b) heating of the material surface with the laser light to produce a high temperature ablation plume which emanates from the heated surface as an intensely hot cloud of vaporized su

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