Abstract:
An apparatus to deliver a fuel into a chamber is provided. In one embodiment, the apparatus includes a fuel inlet and a substantially circular fuel distribution canal communicating with the fuel inlet. A biasing element is coupled to the substantially circular fuel distribution canal, with the biasing element having a plurality of slots arranged to non-uniformly dispense the fuel into the chamber. Another embodiment includes a flange positioned in the substantially circular fuel canal, with the flange structured to perturb a fuel passing into the chamber. This Abstract is provided for the sole purpose of complying with the Abstract requirement rules that allow a reader to quickly ascertain the subject matter of the disclosure contained herein. This Abstract is submitted with the explicit understanding that it will not be used to interpret or to limit the scope or the meaning of the claims.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to internal combustion engines. More particularly, the invention concerns a method and apparatus to mix air and fuel in an internal combustion engine. 
   BACKGROUND OF THE INVENTION 
   Spark ignition engines that employ single or multipoint fuel metering concepts rely upon a throttle body to proportion the air flow rate in response to the operators commanded power level. Simply put, the more air flow allowed into the engine, the higher the power output. For most engines, the operator commands power via the foot pedal which either directly moves the throttle plate through an intermediate cable, or indirectly with a drive-by-wire throttle. In either case, the fuel management system adds the correct amount of fuel as required by the commanded airflow to achieve a desired air-to-fuel ratio (AFR). 
   As an engine is driven though different speeds and loads, the fuel management system calculates and delivers the ideal amount of fuel in proportion to the airflow to both maximize performance and minimize emissions. Of course, control of the air-fuel ratio is an important part of engine performance and emissions minimization. However, there are several common problems exhibited by internal combustion engines that tend to disturb the AFR. 
   In an ideal situation, the same ratio of air and fuel are introduced into each cylinder and in a mixed form, or in other words, in the form of a homogeneous charge. This results in a power balanced engine with excellent emission characteristics. In the real world, air flow balance from cylinder to cylinder is achieved only with significant intake system development. Intake system development is extensive for automotive engines utilizing multipoint injection, but intake systems on medium and heavy duty engines are generally neglected. This is especially true for diesel engines because diesel engines operate with excess air in the combustion chamber, so small variations in the air flow from cylinder to cylinder are not critical to achieving good emissions. However, when a diesel engine is converted to a gaseous fuel, the intake system becomes more important. 
   On the fuel side of the equation, carburetors have provided limited performance and can meet older emission standards, however it should be noted that no carbureted engines are currently sold in the United States, as they simply will not pass current emission standards. Next is the single-point metering concept, where typically two fuel injectors are mounted in a throttle body and perform basically like an electronic carburetor. Again, this type of a system has difficulty meeting current emissions levels. The current state of the art is the multipoint injection system where one injector is used per cylinder. When coupled with an engine with an intake system that has been air flow balanced, the system is capable of meeting the most stringent emissions standards. 
   Unfortunately, the multipoint system which has worked so well for gasoline engines is not a good solution for a diesel engine converted to natural gas. Therefore, there remains a need to overcome one or more of the limitations in the above-described, existing art. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view of the fuel mixer coupled to a throttle body; 
       FIG. 2  is an end view of the fuel mixer of  FIG. 1 , as viewed from the intake manifold side of the fuel mixer; 
       FIG. 3  is a sectional view of the fuel mixer taken along cutting plane  3 - 3  of  FIG. 2 ; 
       FIG. 4  is a plan view of the biasing element illustrated in  FIG. 2 ; and 
       FIG. 5  is a plan view of a section of another embodiment of the biasing element illustrated in  FIGS. 2 and 4 , showing alternative embodiment fuel slots. 
   

   It will be recognized that some or all of the Figures are schematic representations for purposes of illustration and do not necessarily depict the actual relative sizes or locations of the elements shown. The Figures are provided for the purpose of illustrating one or more embodiments of the invention with the explicit understanding that they will not be used to limit the scope or the meaning of the claims. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following paragraphs, the fuel mixer will be described in detail by way of example with reference to the attached drawings. While the fuel mixer is capable of embodiment in many different forms, there is shown in the drawings and will herein be described in detail specific embodiments, with the understanding that the present disclosure is to be considered as an example of the principles of the fuel mixer and not intended to limit the invention to the specific embodiments shown and described. That is, throughout this description, the embodiments and examples shown should be considered as exemplars, rather than as limitations on the fuel mixer. As used herein, the “fuel mixer” to any one of the embodiments of the invention described herein, and any equivalents. Furthermore, reference to various feature(s) of the “fuel mixer” throughout this document does not mean that all claimed embodiments or methods must include the referenced feature(s). 
   Specific embodiments of the fuel mixer  5 , illustrated in  FIGS. 1-5  will now be further described by the following, non-limiting examples which will serve to illustrate various features. The examples are intended merely to facilitate an understanding of ways in which the fuel mixer  5  may be practiced and to further enable those of skill in the art to practice the invention. Accordingly, the examples should not be construed as limiting the scope of the fuel mixer  5 . 
   The fuel mixer  5  described herein is a device which allows the addition, or injection of natural gas, hydrogen, propane, acetylene or another fuel, which may be in a gaseous state, into a stream or sample of air that is ultimately combusted in an internal combustion engine (IC Engine). The fuel mixer  5  mixes the air and gas such that low, or ideal emission levels are attainable. One feature of the fuel mixer  5  is that the mixing occurs downstream of the throttle plate  15 . This positioning results in a very simple installation, or retrofit of an existing gaseous metering system, and provides very good results at a low cost. 
   One feature of the fuel mixer  5  is that it enables the conversion of diesel engines, that usually combust diesel fuel, to instead combust natural gas fuel, at a cost that is significantly lower than previously possible. In addition, due to the enhanced mixing or blending of the air and natural gas fuel, and engine containing the fuel mixer  5  generates good emission levels. Furthermore, the fuel mixer  5  provides a more robust and simple design that minimizes any mechanical problems. Finally, different embodiments of the fuel mixer  5  having different radii, slot or nozzle configurations, sizes, and/or arrangements is adaptable to almost any engine, with a few different embodiments covering a wide range of different engine models, or types. This minimizes production cost, and also reduces the number of inventoried parts. 
   Referring now to  FIG. 1 , the air intake system for an internal combustion engine includes a throttle body  10  that includes a throttle plate  15  that rotates about a throttle pin or shaft  20 . As is well known to those skilled in the art of internal combustion engines, a throttle body  10  comprises a housing (usually having a substantially circular cross-section) containing a valve, or throttle plate  15  to regulate air flowing from an air intake  30  through a chamber or air channel  55  into the intake manifold  25  and then into each cylinder&#39;s combustion chamber (not shown). The throttle body  10  is usually located between the air intake  30  and the intake manifold  25 , and the air channel  55  may be considered to comprise part of, all of, or a portion of, the path from the air intake  30  to the combustion chamber  35  that is taken by the air (and fuel, once it is introduced into the air channel). 
   Air that is either at ambient pressure, or pressurized above ambient by a supercharger or turbocharger, and which may or may not have passed through an air filter enters the throttle body  10  and the amount, or mass of air allowed to pass through the throttle body  10  is regulated by the throttle plate  15  which is controlled by the operator, usually by a cable or electronically. The throttle plate  15  rotates about the shaft  20 , and a larger mass or flow of air tends to pass around one side of the throttle plate  15  than the other, as shown by the larger and smaller arrows in  FIG. 1 , respectively. Generally, this is due to the momentum effects of the air and the biasing effect of the throttle plate  15 . Additionally, no air flow passes around the throttle body  10  where the shaft  20  mounts to the throttle body  10 . Clearly, airflow through the air channel  55  is uneven, or irregular. 
   Due to the uneven flow of air through the throttle body  10  downstream of the throttle plate  15 , conventional fuel-air mixers do not work well downstream of the throttle body  10 . “Downstream” is defined as a location in the air channel  55  that is between the throttle plate  15  and the combustion chamber  35 , and “upstream” is defined as a location in the air channel  55  that is between the air intake  30  and the throttle plate  15 , as shown in  FIG. 1 . Conventional mixers typically provide a fuel flow that is axial-symmetric (i.e. fuel or gas is introduced equally around the perimeter of the throttle body  10 ). Thus, the gas or fuel entering the air stream is uniform around the perimeter of the throttle body  10 , but due to the throttle plate  15 , and shaft  20 , the air flow downstream of the throttle plate  15  is not uniform. The result is that areas within the throttle body  10  and areas within the remaining downstream intake system (such as the tubing connecting the throttle body  10  to the intake manifold, and the intake manifold itself) are rich (contain extra fuel) while others are lean (not enough fuel). 
   This stratified, or unequal charge of air and fuel is a result of the throttle plate  15  angle as well as the shaft  20 . The amount of stratification, or unevenness of the air-fuel mixture changes with throttle plate  15  angle, or “openness”, with a substantially closed throttle plate  15  corresponding to the highest level of stratification while a substantially “wide-open” throttle plate  15  results in the best available mixture, and least stratification, of air and fuel.  FIG. 1  illustrates the throttle plate  15  in a substantially “closed” position (blocking a majority of the interior passage of the throttle body  10 ) while an open position has the throttle plate  15  substantially parallel to the direction of air flow (maximizing air flow through the throttle body  10 ). Therefore, an ideal method for introducing fuel downstream of the throttle plate  15  generally requires an adjustment, or fine-tuning of the location(s) of fuel introduction in response to the uneven air flow caused by the throttle plate  15  and shaft  20 . However, conventional methods do not account for this disruption in air flow, and simply introduce the fuel in a uniform fashion. 
   However, engine designers have built multipoint fuel injection systems to provide uniform gas flow directly to each engine&#39;s cylinder. As pointed out above, while this works with engines designed for multipoint gasoline injection, it does not work for most medium or heavy-duty engines because the air flow to each cylinder in not uniform. These problems have plagued the natural gas engine industry and resulted in poor air-to-fuel ratio (“AFR”) control. AFR that differs from cylinder to cylinder can cause premature engine failure, detonation, poor performance and inconsistent emission levels and are responsible for the myth that engines fueled by natural gas are unreliable and produce high emissions that increase air pollution. 
   In addition, once the gas and air are mixed, it is an explosive mixture ready to be ignited. Backfires do occur. The severity of the backfire is determined by the total volume of air and fuel contained within the intake system. Multipoint injected systems have the least combustible mixture in the intake system because the injector is only injecting while the engine is drawing the mixture into the cylinder. This is not the case for carbureted and single-point injection systems. Here there is a volume of air and fuel ready to be ignited and the total volume of the air-fuel mixture is greater for systems that introduce the fuel upstream of the throttle body  10 . 
   Moreover, regarding pollutant emission levels, generally, the farther the fuel introduction device is away from the air intake valve in each of the engine&#39;s cylinders, the slower the engine responds to inputs that require changes to the ideal air-to-fuel ratio (“AFR”). For example, every movement of the gas or throttle pedal by the operator causes a commensurate change in the position of the throttle plate  15 , and hence air flow, requiring a change in the amount of fuel, but a system with a large volume is slow to respond to throttle changes. Put differently, the actual AFR lags the ideal AFR. The magnitude of this response lag directly correlates to higher pollutant emission levels. Thus, the ideal situation is to have the fuel introduction device, or metering system as close to each cylinder&#39;s intake valve as possible. 
   Also, gaseous fuels (such as natural gas or hydrogen), as compared to a liquid fuel such as gasoline or diesel, when introduced into an air stream were initially thought to mix readily with the air to achieve a homogeneous mixture. However, this is not the case, and after much research and development a single point metering, or fuel introduction approach is now usually employed in an attempt to provide adequate mixing. 
   However, among the several shortcomings of conventional devices that provide axially symmetric flow of natural gas or other gaseous fuels into the air stream, all of them are installed upstream of the throttle body  10 . The rationale is that additional mixing of the air and fuel occurs as it passes the throttle plate  15 . These conventional devices installed downstream of the throttle body  10  do not provide adequate mixing over the engine&#39;s entire operating range. For example, many systems for turbocharged engines introduce the fuel just before the turbocharger&#39;s compressor to provide additional mixing, but backfires are a significant problem with these engines. 
   The fuel mixer  5  described herein provides a solution to all of the above-described problems. The fuel mixer  5  allows the gas, or fuel to be mixed with the air downstream of the throttle plate  15 . By introducing fuel downstream of the throttle plate  15 , the fuel system has better response than any conventional system that introduces fuel upstream of the throttle plate  15  and the volume of mixed fuel and air is minimized, thereby reducing the risk of backfires. In addition, the fuel mixer  5  introduces fuel non-symmetrically to account for the non-uniform flow of air downstream of the throttle plate  15 . 
   As shown in  FIG. 1 , the fuel mixer  5  is located downstream of the throttle plate  15 , and may either be attached to the end of the throttle body  10 , or preferably, is attached to the intake manifold  25 , by fasteners or other suitable means. Gaseous fuel, such as natural gas or hydrogen, or another type fuel enters through port  50 , as shown in  FIGS. 1 and 2 . A fuel canal  60  that is substantially circular, or annular distributes fuel completely around the perimeter of the air channel  55 . 
   Fuel is then introduced into the air channel  55  through a plurality of slots  7  that are located in biasing element  9 , both of which are illustrated in  FIGS. 2-4 . The fuel, or metering slots  7  cut in the biasing element  9  only allow fuel to enter the air chamber  55  at specific pre-determined points. In this way, the fuel system designer is free to bias, or “tune” the fuel flow around the internal periphery of the air channel  55  to offset the air flow bias resulting from the throttle plate  15 , shaft  20  and other factors, as described above. That is, other embodiments of the biasing element may change the location of the metering slots  7  to tune the location of fuel introduction for each different throttle body  10 . Put differently, one feature of the biasing element  9  is that it is “tuned” for each different application, thereby enabling each different engine to have an ideal air-to-fuel ratio. 
   As shown in  FIGS. 2 and 4 , the biasing element  9  comprises a generally disk-like, or ring-like shape with several gas metering slots  7  placed in specific locations around the biasing element  9 . In one embodiment, the biasing element  9  may also include a positioning tab  40 , shown in  FIGS. 2-4  that locates the orientation of the gas metering slots  7  for the ideal “tuned” introduction of fuel as described above. In one embodiment, the fuel mixer  5  includes an area sized to receive the positioning tab  40 , as shown in  FIG. 3 , where the positioning tab  40  fits into an appropriately sized area in the fuel mixer  5 . 
   The biasing element  9  may also function as a gasket to seal the interface between the fuel mixer  5  and the throttle body  10 . In one embodiment, the biasing element  9  may be made of a compressed aramid/Buna-N sheet gasket material, but any suitable gasket material, such as brass, aluminum, copper, other alloys, paper, rubber, silicone, polymers, plastics, polyesters, neoprenes, Ethylene Propylene Diamine Monomers (EPDMs) or other suitable materials may be employed. 
   As shown in  FIG. 4 , in one embodiment the biasing element  9  may have an outer radius of 45 millimeters (mm) with an inner radius of 32 mm, with each slot  7  having a length of 8 mm, and a width of 1.7 mm. In the illustrated embodiment, the slots  7  are located in groups, with each slot 12 degrees apart, separated by gaps of 36 degrees and 24 degrees (as measured using 360 degrees to describe the circumference of the biasing element  9 ). This non-symmetric arrangement of slots  7  tunes the introduction of fuel as it accounts for the location of the throttle plate shaft  20 , as well as the rotational direction of the throttle plate  15 . For example, as shown in  FIG. 1 , when the throttle plate  15  is in the position shown, most of the air passing through the air channel  55  is biased toward the “downstream pointing” end of the throttle plate  15 , as shown by the large arrow. Thus, most of the slots  7  are arranged on that side of the air channel  55 , as shown by the grouping of slots  7  in  FIG. 4  (located from 10 o&#39;clock to 2 o&#39;clock, with the width dimension of 1.7 mm as the 12 o&#39;clock position). No slots  7  are located from 8 to the 10 o&#39;clock position, nor are any slots  7  located from the 2 to 4 o&#39;clock position, which is where the throttle plate shaft  20  attaches to the throttle body  10 . Also, a smaller number of slots  7  are located in the 4 to 8 o&#39;clock location, as this corresponds to the “upstream pointing” end of the throttle plate  15 . It will be appreciated that other embodiments of the biasing element  9  may have different physical dimensions to fit different throttle bodies and the locations and dimensions of the slots may also vary. 
   In one embodiment, each slot  7  may be 1.2 millimeters (mm) wide, 1.2 mm high, and 8 mm long. However, it will be appreciated that the dimensions of the slot  7  may vary with each application. For example, for a chamber, or air channel  55  having a 3 or 4 inch diameter, the above-listed dimensions for the slot  7  are effective, but for a chamber, or air channel  55  having a 6 or 8 inch diameter, the above-listed dimensions for the slot  7  may be changed. An embodiment for this diameter air channel  55  may size the slots  7  to create a flow of fuel that reaches 0.7 or 0.8 Mach speed to inject the fuel into the interior of the air channel  55 . In this embodiment, the trip, or flange  45  may be removed to allow the fuel to be laminarly injected into the air channel  55 . However, the energy imparted to the fuel by the high-speed configuration of the slots  7  causes the fuel to mix with the air in the air channel  55 . Alternatively, the flange  45  may be removed only in sections, thereby causing the fuel to be laminarly injected into the air channel  55  is some areas, and turbulently injected into the air channel  55  in other areas. 
   For example, as shown in  FIG. 5 , the slots  7  may also have different shapes to enhance the “nozzle” effect. That is, one feature of the biasing element  9  is that the slots  7 , shown in  FIGS. 2 and 4 , act as nozzles to eject the fuel deep into the air channel  55 , resulting in superior mixing of the fuel and air. Generally, the fuel is introduced into the air channel  55  at a pressure that is 5 pounds-per-square-inch (psi) above the pressure in the air channel  55 . When the pressure of the fuel is twice that of the air pressure in the air channel  55 , flow through the slots  7  can approach sonic speeds (i.e, Mach speeds), which results in violent, and effective mixing. 
   Referring now to  FIG. 5 , the shape of slots  7  may differ from that shown in  FIGS. 2 and 4  that illustrate the slots  7  having straight sides, in a substantially rectangular shape. Specifically, the slot  7  may diverge  7   a , converge  7   b , or converge and then diverge  7   c . These, and other shapes may be used to accelerate the gas to sonic (converging) or supersonic (converging-diverging) velocities to further enhance mixing with the air. Other shapes may also be employed, depending on the need to either penetrate fuel deep into the air channel  55 , or to introduce fuel at other locations, or distances into the air channel  55 . For example, angled slot  7   d  is used to create a “swirl” effect that causes the fuel to rotate as it enters the air channel  55 . Swirl is important to mixing and combustion for engines that employ gaseous fuels. The use of slots  7  allows the fuel system designer to convert the pressure of the compressed natural gas (CNG) or hydrogen, into mixing energy and/or swirl energy as the fuel passes into the air channel  55  from the fuel canal  60 . 
   Returning now to  FIGS. 2 and 3 , another feature of the fuel mixer  5  is illustrated. As the fuel passes through the port  50 , around the fuel canal  60  and into slots  7  in biasing element  9 , it is “tripped” by projection, or flange  45  before it enters the air channel  55 . The flange  45  creates a laminar to turbulent flow trip point. In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity. Flow that is not turbulent is called laminar flow. Generally, the gas flow is mostly laminar as it approaches the flange  45 , but upon contact with the flange  45 , the gas flow is “tripped” causing it to tumble, swirl, and otherwise chaotically flow into the air chamber  55 . This irregular movement of the fuel greatly improves mixing with the air. In the embodiment illustrated in  FIG. 2 , the flange  45  comprises a continuous ring substantially located at the inner diameter of the fuel mixer  5 , adjacent to the perimeter of the air channel  55 . However, in other embodiments, the flange  45  may have gaps, allowing some fuel to enter the air channel  55  in a laminar fashion. 
   Also, the dimension (height and/or width) of the flange  45  may vary, depending on the amount of desired mixing. For example, in one embodiment, the flange  45  may extend from the fuel canal  60  a sufficient amount to reduce the cross-sectional area of the fuel canal  60  by 10% to 12%. Other embodiments may increase or decrease this percent reduction in cross-sectional area. 
   Once the fuel is introduced into the air channel  55  it mixes with the air and enters the intake manifold  25  and then each cylinder&#39;s combustion chamber  35 . Thus as described above, the fuel mixer  5  and biasing element  9  have several features that combine to generate vigorous mixing of the air and fuel in the air chamber  55 , thereby enabling each different engine to have an ideal air-to-fuel ratio in every cylinder. These features are especially important on large engines that use large diameter throttle bodies, where adequate mixing of air and fuel is particularly difficult. 
   Thus, it is seen that an apparatus and method of introducing and mixing gaseous fuel and air for an internal combustion engine is provided. One skilled in the art will appreciate that the present invention can be practiced by other than the above-described embodiments, which are presented in this description for purposes of illustration and not of limitation. The specification and drawings are not intended to limit the exclusionary scope of this patent document. It is noted that various equivalents for the particular embodiments discussed in this description may practice the invention as well. That is, while the present invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those of ordinary skill in the art in light of the foregoing description. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations as fall within the scope of the appended claims. The fact that a product, process or method exhibits differences from one or more of the above-described exemplary embodiments does not mean that the product or process is outside the scope (literal scope and/or other legally-recognized scope) of the following claims.