Swirl flow precombustion chamber

A combustion system of an internal combustion engine includes a main combustion chamber and a swirl flow precombustion chamber connected by a communicating passage. The communicating passage is connected tangentially to the precombustion chamber so as to induce a consistent, repeatable swirling flow pattern of gasses in the precombustion chamber during the compression stroke of the engine cycle. The swirl pattern thoroughly mixes the air, unburned fuel and burned fuel in the precombustion chamber. An igniter such as a spark plug is disposed in the precombustion chamber in a region having a low gas velocity during swirling to allow a small flame kernel to grow every engine cycle and consistently ignite the swirling gas, thereby improving engine efficiency, toxic emissions spark plug life, and allowing the igniter to run at a cooler temperature.

BACKGROUND 
1. Field of the Invention 
The present invention relates to a precombustion chamber in an internal 
combustion engine, and more particularly to a precombustion chamber in an 
internal combustion engine which ignites pilot quantities of an air/fuel 
mixture in order to ignite larger amounts of an air/fuel mixture within 
the main combustion chamber. 
2. Description of the Related Art 
Internal combustion engines with large reciprocating cylinders are commonly 
used in the oil and gas industry as prime movers for pipelines. These 
engines are also used in general industry to generate electric power. As 
with most internal combustion engines, a spark plug is employed to ignite 
the air/fuel mixture periodically in the engine cycle. However, as the 
size of the combustion chamber formed by the piston cylinder increases in 
diameter, the effectiveness of spark plugs to induce combustion is 
diminished. This is due in part because the arc generated by the spark 
plug is very localized. The situation is exacerbated when the air/fuel 
ratio is made lean in an effort to reduce emissions and increase fuel 
efficiency. In a large combustion chamber, for example, it may take an 
undesirable period of time for the combustion process to propagate 
throughout the combustion chamber. 
To solve such ignition problems in large combustion chambers, precombustion 
chambers have been developed which can be connected to the main combustion 
chamber by a suitable passage. Precombustion chambers in natural gas, 
spark ignited, stratified charge engines can be used to initiate 
combustion in the lean air/fuel ratio main chamber. In this type of 
combustion system, small amounts of fuel are injected into the 
precombustion chamber. A spark plug or other means of ignition is 
energized, forming a flame kernel which ignites the rich charge in the 
precombustion chamber. The hot, burning combustion products from the 
precombustion chamber flow through the orifice into the main combustion 
chamber thereby igniting an air/fuel mixture previously injected into the 
main combustion chamber. Usually, if the precombustion chamber combustion 
is satisfactory (i.e., on time and complete) the main chamber combustion 
will be satisfactory. As the burning air and fuel and combustion products 
from the precombustion chamber occupy a much larger volume than the spark 
plug arc, the combustion process within the main combustion chamber is 
completed much more rapidly, resulting in greater engine efficiency. 
However, in prior art engines having precombustion chambers, combustion of 
the precombustion charge has not been successful because the air/fuel 
mixture is admitted into the precombustion chamber from the main 
combustion chamber as a high velocity stream. High velocity flows, 
although turbulent, fail to mix the burned fuel, unburned fuel, and air 
sufficiently to ensure consistent precombustion chamber combustion near 
the spark plug gap. Poor mixing of the burned fuel, unburned fuel and air 
can cause inconsistent combustion because there is not always a 
combustible mixture at the spark plug gap. Consequently, inconsistent 
precombustion chamber combustion causes the main chamber combustion to 
occur either too early, too late, too slowly, or not at all, resulting in 
lower engine efficiency and higher toxic exhaust emissions. 
Inconsistencies in precombustion chamber combustion and in the hot gasses 
generated are particularly problematic when natural gas is used as the 
fuel with a lean air/fuel mixture, resulting in inconsistent main 
combustion chamber firing. The natural variability of the constituents in 
natural gas can introduce inconsistencies in burning, as different 
constituents burn hotter or colder in the engine. Further, a lean air/fuel 
ratio can increase the likelihood of inconsistencies in burning because 
there is a smaller margin of fuel in the combustion chamber in excess of 
that amount necessary for proper combustion. Particularly if the fuel is 
not mixed sufficiently, there can be regions of gas near the spark plug 
gap at the time of combustion that do not contain sufficient fuel for 
consistent burning. 
A partial solution to some of the aforementioned problems is described in 
U.S. Pat. No. 4,594,976 to Gonzalez which discloses a hybrid internal 
combustion reciprocating engine including a prechamber connected to the 
main combustion chamber by means of a passage or orifice located in such a 
manner as to induce a swirling airflow within the prechamber during the 
compression stroke. The Gonzalez invention, however, suffers from a 
problem similar to other precombustion chamber engines in which high 
velocity gas is injected into the precombustion chamber. That is, the 
combustion process is disrupted when the spark plug gap is located in a 
high gas velocity region of the precombustion chamber. A high gas velocity 
at the spark plug gap inhibits rapid propagation of the combustion process 
throughout the precombustion chamber. 
Typically, the combustion inside precombustion chambers is difficult to 
initiate and maintain consistently because the gas flow within the 
precombustion chamber is so fast and unorganized that the flame kernel 
(the small burning air and fuel mixture just after the spark plug first 
ignites it) is often forced against a cold wall in the chamber which 
either extinguishes this small flame kernel completely, resulting in a 
complete misfire, or causes a long delay before the kernel grows enough to 
light off the rest of the unburned precombustion chamber charge. 
By contrast, good consistent ignition occurs when the mixture at the spark 
plug gap is low in velocity and at a stoichiometric air-fuel ratio, where 
complete burning of the fuel occurs. These conditions allow the flame 
kernel to grow to sufficient size and strength to ignite the rest of the 
unburned charge. 
Prior art engines have also failed to include means for dispersing the 
ignited gas over a broad area in the main combustion chamber. Instead, the 
ignited gas from the precombustion chamber has been supplied to the main 
combustion chamber through a single small opening. Consequently, the 
period of propagation of the combustion process throughout the main 
combustion chamber has been unacceptably long in duration, especially in 
large main combustion chambers, resulting in inefficient and inconsistent 
firing. 
There is, therefore, a need in the art for an internal combustion engine 
with a precombustion chamber which burns pilot fuel and air consistently, 
evenly and efficiently and which prevents overheating of the spark plug 
unit. Further, there is a need in the art for an engine with a 
precombustion chamber that provides a consistently well-mixed, low 
velocity air/fuel mixture at the spark plug gap, and which broadly 
distributes the ignited gas throughout the main combustion chamber. 
SUMMARY 
Accordingly, it is an object of the present invention to provide a 
combustion system including a main combustion chamber and a precombustion 
chamber which promotes stable and consistent combustion, thereby improving 
engine efficiency, reducing toxic exhaust emissions, and reducing fuel 
consumption. 
According to an exemplary embodiment of the invention, a combustion system 
including a main combustion chamber and a precombustion chamber is 
provided in which the precombustion chamber organizes the gas flow from 
the main combustion chamber into a swirling motion (very similar to 
stirring a cup of coffee) to thoroughly mix the air, fuel and burned fuel 
into a homogeneous mixture. The organization of the flow into a swirling 
motion allows the gas velocity profile in the precombustion chamber to be 
consistent and predictable so that a repeatable flow pattern and a 
consistent air/fuel ratio can be provided inside the precombustion chamber 
for every engine cycle. Further, the predictable flow pattern allows the 
spark plug to be located in a region within the precombustion chamber 
having a consistently quiescent, low gas velocity. Placing the plug in a 
low velocity region allows a small flame kernel to grow every engine cycle 
to sufficient size to ignite the rest of the high velocity, swirling 
unburned charge, resulting in consistent dependable flame kernel inception 
and even burning within the precombustion chamber. 
A further object of the invention is to provide a precombustion chamber 
which allows the spark plug to operate at cooler temperatures, thereby 
increasing the life of the spark plug unit and increasing the overall 
reliability of the engine. 
It is a further object of the invention to provide a precombustion chamber 
assembly that is easily replaceable. 
It is a further object of the invention to provide a nozzle for dispersing 
a volume of ignited gas from the precombustion chamber over a large volume 
of the main combustion chamber. 
Advantages of the present invention include improved spark plug life, 
reduced fuel consumption and reduced toxic exhaust emissions.

DETAILED DESCRIPTION 
FIG. 1 shows an exemplary embodiment of a combustion system according to 
the present invention including a main combustion chamber 10, a swirl flow 
precombustion chamber 20, and a communicating passage 30. During the 
intake stroke of an internal combustion engine cycle, a pre-mixed air/fuel 
mixture is drawn into the main combustion chamber 10 through at least one 
intake valve 5. Also during the intake stroke, fuel is admitted into the 
precombustion chamber 20 through a precombustion chamber valve 40. 
Subsequently, in the compression stroke, a portion of the air/fuel mixture 
as well as residual burned fuel from the previous engine cycle are 
directed from the main combustion chamber 10 to the precombustion chamber 
20 through the connecting passage 30. The passage 30 enters the 
precombustion chamber 20 tangentially to induce swirling of the gasses in 
the precombustion chamber 20. The swirling gasses in the precombustion 
chamber 20 thoroughly mix the air, burned fuel, and unburned fuel from the 
main combustion chamber with the precombustion chamber fuel previously 
admitted through the precombustion chamber valve 40, and the mixture can 
then be ignited by igniter 50 at an appropriate time during the engine 
cycle. The ignited mixture then expands rapidly and is forced through the 
passage 30 into the main combustion chamber 10 where it ignites the 
air/fuel mixture in the main combustion chamber 10. The system allows 
even, consistent, and predictable ignition of an air/fuel mixture in the 
main combustion chamber 10. 
FIG. 2 shows an exemplary embodiment of the communicating passage 30 
disposed between the swirl flow precombustion chamber 20 and the main 
combustion chamber 10. The wall of the precombustion chamber 20 preferably 
is curved in at least one portion 21 thereof to encourage swirling of the 
mixture of fuel, air, and burned fuel from the main combustion chamber 10 
as the mixture enters the precombustion chamber 20. The communicating 
passage 30 opens into the precombustion chamber 20 along the curved 
portion 21 of the wall of the precombustion chamber 20 to direct the 
mixture to flow into the precombustion chamber 20 tangentially as 
indicated by the flow lines 24. This arrangement of the passage 30 causes 
the flow pattern in the precombustion chamber 20 to swirl preferably about 
a horizontal axis 35 as shown in FIGS. 1 and 2. The organized swirling 
motion is preferably achieved by a passage 30 having a length/diameter 
ratio greater than 2. 
As swirling is induced during the compression stroke of the engine cycle, a 
fuel such as natural gas, which has been introduced by the fuel valve 40 
into the precombustion chamber 20 during the intake stroke, is mixed with 
the swirling gasses. The swirl flow precombustion chamber 20 thoroughly 
mixes the burned fuel, unburned fuel and air from the main combustion 
chamber with the precombustion chamber fuel into a homogeneous mixture 
which can be used to consistently and evenly ignite a lean air/fuel 
mixture in a large main combustion chamber 10, for example. This process 
overcomes the problem in prior engines of poor mixing of the burned fuel, 
unburned fuel and air, which has caused inconsistent combustion because 
there has not always been a combustible mixture at the spark plug gap 
during ignition. 
The fuel valve 40, which introduces the fuel into the precombustion chamber 
during the intake stroke, can be a pressure-activated valve such as a 
check valve, which opens and closes according the pressure difference 
between the precombustion chamber and the fuel header. According to a 
preferred embodiment of the invention, the fuel valve 40 can be a 
mechanically-actuated valve, such as a poppet valve. The poppet valve may 
be actuated by an intake camshaft, for example. A mechanically-activated 
precombustion chamber valve 40 offers the advantage of reliability and can 
overcome leaking and sticking problems encountered in the prior art. 
FIG. 3 shows an exemplary embodiment of the precombustion chamber 20 
including an igniter 50, such as a spark plug or a glow plug, disposed in 
the precombustion chamber 20 for igniting the swirling air/fuel mixture. 
Flow lines 24 indicate the direction of flow of the gasses in the 
precombustion chamber during swirling. The configuration of two combustion 
chambers and a communicating passage therebetween allows a consistent flow 
pattern to be established during every engine cycle. Further, because the 
flow pattern is consistent and repeatable, the precombustion chamber 20 is 
preferably designed with the spark plug 50 in a region having a low gas 
velocity. 
Specifically, as the gasses enter the precombustion chamber 20 from the 
main combustion chamber 10 via the passage 30, a swirling effect is 
created in the precombustion chamber 20. As in any vortical flow pattern, 
the mixture is calmest, i.e., less turbulent at the center or axis of 
rotation 35 of the flow. 
Taking advantage of this phenomenon, a recess 45 is created in a wall of 
the precombustion chamber 20 in alignment with the axis of rotation 35 of 
the vortical flow pattern. The spark plug 50 is located such that the 
spark plug gap 48 is within the recess 45 so that the spark plug gap 48 
contacts the calmest section of the vortical flow. 
A low velocity of the flow near the spark plug gap 48 is desirable for 
developing a good flame kernel and allows for consistent and rapid 
ignition of the air/fuel mixture because the combustion process is able to 
propagate much more rapidly throughout the precombustion chamber when the 
gas surrounding the spark plug has a low velocity. 
A low velocity of the flow near the spark plug gap during ignition also 
allows the spark plug to operate at cooler temperatures because the spark 
plug is not immersed in hot gasses during and after ignition, as would be 
the case in a high-velocity region. 
Locating the spark plug 50 in a low velocity region also overcomes a 
problem in prior art engines in which the flame kernel is forced against a 
cold wall in the precombustion chamber. The present invention eliminates 
this problem by positioning the spark plug 50 such that the flow lines do 
not extend from the spark plug 50 directly to the precombustion chamber 
wall. 
Good consistent ignition is also promoted when the air/fuel ratio at the 
spark plug gap 48 is such that all the air and fuel are converted to 
combustion products. This is known as the stoichiometric air-fuel ratio. 
These conditions allow the flame kernel to grow to sufficient size and 
strength to ignite all of the unburned charge within the precombustion 
chamber. 
As the air/fuel mixture in the precombustion chamber 20 is ignited, the 
pressure in the precombustion chamber 20 increases, directing the ignited 
mixture out of the precombustion chamber 20, through the communicating 
passage 30 and into the main combustion chamber 10 to ignite the air/fuel 
mixture in the main combustion chamber 10. As shown in FIGS. 2 and 4, the 
communicating passage 30 can include a nozzle 55 including a plurality of 
nozzle openings 60 to direct ignited gas in different directions and into 
different regions of the main combustion chamber 10 and to disperse 
ignited gas into the main combustion chamber 10 over a broad area. 
Dispersion of the ignited gas by the nozzle facilitates ignition of the 
mixture and allows the air/fuel mixture in the main combustion chamber 10 
to be ignited more rapidly than would a single nozzle opening. Thus, the 
ignited charge from the precombustion chamber can ignite the air/fuel 
mixture in the entire main combustion chamber consistently, evenly and 
repeatedly, even when natural gas is used in a relatively large main 
combustion chamber 10. 
According to a further embodiment of the invention, the precombustion 
chamber 20 and the nozzle unit 55 can be included in a precombustion 
chamber assembly 70, as shown in FIG. 1, which is removably attached to 
the engine. The precombustion chamber assembly can be attached by any 
suitable means, for example a clamp. FIG. 1 shows a clamp 65 which can 
secure a flange 75 of the precombustion chamber assembly 70 to the 
cylinder head 85 with a bolt 80. The clamp 65 can be easily removed, 
allowing the precombustion chamber assembly 70, which includes the 
precombustion chamber 20 and the nozzle 55, to be easily replaced. Once 
the clamp 65 is removed, a slide hammer tool can be used to remove the 
precombustion chamber assembly 70 from the cylinder head 85. 
Filed concurrently herewith are two U.S. patent applications by the same 
inventor, and which are entitled "Natural Gas Molecular Weight Sensor" and 
"Natural Gas Engine Control System". The subject matter of the present 
application may be used in conjunction with the subject matter of either 
or both of the concurrently filed applications. Accordingly, the subject 
matter of the two concurrently filed applications is incorporated herein 
by reference. 
The above-described exemplary embodiments are intended to be illustrative 
in all respects, rather than restrictive, of the present invention. Thus 
the present invention is capable of many variations in detailed 
implementation that can be derived from the description contained herein 
by a person skilled in the art. All such variations and modifications are 
to be considered within the scope and spirit of the present invention as 
defined by the following claims.