Patent Grant
7278387
The present disclosure relates generally to spark-ignited internal combustion initiation devices and methods, and relates more particularly to such a device having multiple spark patterns and an internal combustion engine using the same.
One method of operating internal combustion engines consists of supplying gaseous fuel into a combustion chamber, adding air to get a particular air to fuel ratio (AFR), and then igniting the mixture, typically with a spark from a sparkplug in a conventional manner known to those skilled in the art. If this ignition is done with a relatively low AFR, then the resulting combustion tends to occur very quickly, and at a very high temperature. This can result in the formation of nitrogen-oxygen compounds (NOx).
One method of reducing the formation of NOx is thus to use a higher AFR or otherwise lean mixture, which results in a slower burn at a lower temperature. However, spark ignition becomes more difficult as the amount of fuel per unit volume decreases. Additionally, small scale turbulence in the spark gap makes the formation of suitable ignition sparks difficult. The increasing use of recirculated exhaust gas to affect the relative “richness” or “leanness” of the overall mixture has created additional challenges to igniting mixtures in the cylinders as desired.
Several methods have been developed in response to the difficulties encountered in attempting to run gaseous engines via lean burn strategies, such as an AFR on the order of 68:1. One method is to use a prechamber and sparkplug. A typical prechamber and sparkplug configuration includes at least one orifice leading to the combustion chamber. A spark gap is positioned inside the prechamber, and attached to an electrical lead. Because of the small size and relative isolation of the prechamber, turbulence in the fuel and air mixture therein is significantly reduced, facilitating the formation of sparks and flame generation. A spark arcs across the spark gap and ignites a combustion reaction inside the prechamber. The prechamber combustion propagates and expels a jet(s) of burning gas through the orifice(s) into the combustion chamber of the engine, which serves to ignite the main fuel charge in the combustion chamber. More recent designs will have more than one orifice so the flame will propagate on multiple fronts simultaneously, resulting in more efficient ignition. The art teaches different models for such sparkplugs such as U.S. Pat. Nos. 5,947,076 and 4,987,868. There are also examples of designs which attempt to increase the efficiency of the prechamber such as U.S. Pat. No. 5,105,780.
At specific conditions the internal combustion initiation device is optimally efficient, but as the AFR varies with engine operating condition, the efficiency of the engine may be reduced. This can result in the fuel burning too quickly, which results in increased temperature and increased NOx output, or the fuel incompletely burning which results in unburned hydrocarbons in the exhaust. While the most advanced of these prechamber sparkplugs enable a broader range of AFR's for a given engine than formerly available designs, there remains room for improvement.
The present disclosure is directed to one or more of the problems or shortcomings set forth above.
In one aspect, this disclosure provides an internal combustion initiation device having a body that defines a prechamber and a plurality of outlet orifices. Further, there is a first spark gap at a first position inside the prechamber, and a second spark gap at a second position inside the prechamber. The first spark gap and the second spark gap are coupled to a first electrical circuit and a second electrical circuit, respectively.
In another aspect, this disclosure provides an internal combustion engine comprising a housing including at least one combustion chamber, and further including an internal combustion initiation device attached to the engine housing. The device includes a plurality of orifices that open from a prechamber and fluidly connect with the combustion chamber. Further, the device includes means for initiating at least two different spark patterns in the prechamber.
In yet another aspect, this disclosure provides a method of operating an internal combustion engine comprising the steps of supplying fuel to a combustion chamber of the engine. One of a plurality of different spark patterns is selected, and the fuel is ignited at least in part by activating the selected spark pattern inside of a prechamber fluidly connected with the combustion chamber.
Referring to
The first electrical circuit 22a enters a first prechamber 13a parallel to the centerline 24. At a first position 25a the first circuit 22a bends and extends perpendicular to the centerline 24 until it reaches a first radius from the centerline 26a. The first spark gap 20a is formed at the first radius 26a between the first electrical circuit 22a and the electrical ground 21. In a similar manner, the second spark gap 20b is part of the second electrical circuit 22b and the electrical ground 21 at a second position 25b and a second radius 26b from the centerline 24. First body portion 111a includes a plurality of orifices 12a fluidly connecting first pre-chamber 13a with a second pre-chamber 13b, defined by body portions 111a and 111b. Second body portion 111b will likewise include a plurality of outlet orifices 12b fluidly connecting second pre-chamber 13b to an exterior of device 110, for instance an engine combustion chamber.
It will be recognized by those skilled in the art that
One alternative embodiment that has not yet been discussed herein could include a first spark gap at a first radius from a given location on the centerline, and a second spark gap at a second radius from the same location on the centerline such that the first and second spark gap are arranged opposite each other at differing radii from the centerline. A further example could include a first spark gap at a first position along the centerline, and a second spark gap at a second position along the centerline such that the first and second spark gaps are linearly aligned with each other along the centerline.
Further, it will be recognized that although only
Referring to
One skilled in the art will appreciate that the above example is merely one embodiment of the present disclosure, and several variations are contemplated. The internal combustion initiation device 10 may include at least two electrical circuits 22a and 22b, and additional circuits such as 22c are herein contemplated. It will further be recognized that the “air” could include air from outside the internal combustion engine 30, or air plus exhaust gas, air plus water or some other mixture. Finally, any means for introducing a mixture of gaseous fuel and air or some other type of mixture such as a premixed gasoline and air charge, or a mixture containing water into the combustion chamber 32 are herein contemplated. Examples could include pre-mixing the gaseous fuel and the air to a desired AFR and then introducing the mixture into the combustion chamber 32 via a single supply means, or any other conventional method known to one skilled in the art. For instance, gaseous fuel and air, and possibly recirculated exhaust gas, could be delivered to the engine cylinders via separate passages.
This disclosure contemplates use of the internal combustion initiation device 10 in a variety of internal combustion engines 30 which typically combine an amount of combustible gaseous fuel, such as natural gas, with a relatively large amount of air to form a relatively lean fuel mixture. This disclosure also contemplates the use of exhaust gas recirculation to affect the AFR. By way of illustration only, it is contemplated that the AFR could be on the order of 68:1 under certain operating conditions, though one skilled in the art will recognize that many other ratios and mixtures could be considered a lean fuel mixture. Moreover, it is common in the art to refer to a mixture of air and recirculated exhaust gas as “air” in calculating an AFR. Thus, references herein to a particular AFR should be understood as encompassing the use of reactants and/or diluents other than merely fuel and air. One skilled in the art will also recognize that although this disclosure is designed with gaseous fuel in mind, the use of an atomized liquid fuel such as a petroleum distillate fuel would be appropriately encompassed within the spirit and scope of this disclosure.
It is further contemplated that the selected fuel mixture will depend upon the load conditions of the internal combustion engine as in the flow diagram of
A firing event will be called for, and the algorithm for implementing the process will start at step 40. The algorithm may be operable to first determine whether the engine 30 is operating at a high load condition in step 41a. If the internal combustion engine 30 is operating at a high load condition, the combustion chamber 32 may be filled with a fuel mixture having an appropriate AFR in step 42a. Under high load conditions, the absolute amount of fuel will be larger than for low load conditions, however, in many instances, the mixture will actually be relatively leaner than the mixture used for lower load conditions. The selected AFR may be high in step 42a, because either a greater increase in air for a given increase in fuel takes place (as compared to lower load conditions), or because a diluent is added, such as exhaust gas. In either case, the combustion mixture will typically be relatively diluted with respect to fuel. Accordingly, a relatively slow burn at a relatively low temperature may be used to reduce the amount of NOx produced by the engine 30. Because the engine is operating at a high load, initiation of combustion may be relatively easier for a lean mixture than at lower load conditions, as is familiar to those skilled in the art.
From step 42a, the electronic controller may then select a first spark pattern of device 10 in step 43a, followed by directing the second electrical circuit 22b to fire the second spark gap 20b in step 44a. This will cause a spark to initiate combustion in the prechamber 13 of the internal combustion initiation device body 11 at a second position 25b, relatively far from orifices 12. The combustion process will expel a relatively large amount of unburned fuel mixture from the prechamber 13 followed by burning fuel mixture, creating a relatively small flame front and resulting in a relatively slow combustion process inside the combustion chamber 32, in turn resulting in relatively low NOx production. From step 44a the process may return to step 40 and repeat.
If it is determined in step 41a that the engine is not operating at a high load condition, the algorithm will next determine whether the engine is operating in a low load condition in step 41b. If the engine 30 is operating in neither a high nor a low load condition, then the engine 30 is determined to be in a medium load condition. This disclosure also contemplates more or less than the described low, medium and high load ranges. In other words, a multiple spark pattern device according to the present disclosure might be designed having more than three spark gaps, corresponding to more than three load ranges. If there is a medium load on the internal combustion engine 30, then the combustion chamber 32 may be filled with an appropriate fuel mixture in step 42b. The fuel mixture may have a medium AFR and medium leanness, though the present disclosure is not thereby limited. The electronic controller 34 will select a second spark pattern in step 43b, and thenceforth direct the first electrical circuit 22a to fire the first spark gap 20a in step 44b. This will cause a spark to initiate combustion in the prechamber 13 of the internal combustion initiation device body 11 at a first position 25a close to the orifices 12. Burning fuel will enter the combustion chamber 32 from the prechamber 13 before the unburned gasses due to the position 25a close to the orifices 12, resulting in a relatively larger flame front as compared to high load operation. From step 44b, the process may repeat.
Operation of a system using device 110 of
Similar control is available with the embodiments of
It is contemplated that the exact AFR (or proportion of exhaust gas or other diluent in the combustion mixture), richness, leanness, etc. used for each load condition, and the selection of an electrical circuit 22a-c according to the specified load condition will vary depending upon the exact specifications and requirements of the internal combustion engine 30. These variations are implicitly included within the spirit and scope of this disclosure. Further, it will be recognized that the variation of the relative proportions of air, fuel, exhaust gas, etc. in the combustion mixture, as well as spark gap selection could depend upon factors known to those skilled in the art other than load condition of the internal combustion engine 30, such as the placement of the orifices 12 in the internal combustion initiation device body 11.
The advantages of the presently described internal combustion initiation devices will be easily recognizable by one skilled in the art. Rather than having one operating condition where the internal combustion initiation device 10 is optimally efficient, the present disclosure provides a plurality of “optimal” operating conditions. By varying which of the spark gaps 20a-c or which spark gap combination creates a spark pattern that ignites a combustion reaction in the prechamber 13, the resulting plume shape and burn state of gas exiting through the orifices 12 can be altered. In this way, the combustion reaction inside the combustion chamber 32 can be maintained within a specific range where NOx production is reduced while the fuel mixture combusts more or less completely.
It will also be apparent to one skilled in the art that the number of possible spark patterns increases exponentially as the number of electrical circuits 22a-c increases. As described above, two electrical circuits 22a, 22b, each with a respective spark gap 20a, 20b have three different spark patterns. It will be recognized that three electrical circuits 22a-c, each with a respective spark gap 20a-c will have seven different spark patterns (20a, 20b, 20c, 20a+20b, 20a+20c, 20b+20c, 20a+20b+20c). It is contemplated that this number may be increased readily to create a wide range of efficient operating conditions for the internal combustion engine 30.
It will be recognized that another advantage of the internal combustion initiation device 10 herein disclosed is the ability to add an even greater amount of air 35a (or exhaust gas), based at least in part on the selected spark pattern, to the combustion chamber 32 and create an even leaner mixture which will have the benefit of reducing NOx production. In other words, the lean limit of an engine may be extended, as the initiation device can facilitate ignition of relatively leaner mixtures than might otherwise be practicable, and may further influence the burn rate of the combustion mixture to control NOx. It will be understood that by firing all of the spark gaps 20a-c simultaneously, a very large flame front can be produced from the orifices 12 in comparison to that which could be produced using conventional internal combustion initiation devices known in the art. The larger flame front can ignite a combustion reaction of a lean mixture that might not otherwise be combustible with a conventional internal combustion initiation device when balanced with a desire for fuel efficiency over a common operating range. In other words, a conventional internal combustion initiation device might be usable at a given AFR, but prohibitively inefficient at normal operating conditions. The internal combustion initiation device 10 herein disclosed will be efficient over a broad range of AFR's and range of exhaust gas diluent proportions given the ability to vary the spark pattern, and hence burned vs. unburned composition of the gases delivered to the combustion chamber of the engine.
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the intended spirit and scope of the present disclosure. Other aspects, objects, and advantages of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims.
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| Number | Date | Country | |
|---|---|---|---|
| 20070169737 A1 | Jul 2007 | US |
