Patent Publication Number: US-2011067671-A1

Title: Non-soot emitting fuel combustion chamber

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims a priority to and claims the benefit of U.S. Provisional Application No. 61/275,813. U.S. Provisional Application No. 61/275,813 is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Soot is emitted from the combustion of fuel with carbon content, such as gasoline or diesel. Diesel, in particular, has rich carbon content that leads to soot emission during combustion. In contrast, the combustion of alcohol fuel and ammonia does not emit soot because carbon is not present in these types of non-soot producing fuel. When fuel does not have carbon, the only available carbon element is from the CO 2  molecule in the air, and there is no soot emission because of the oxygen content in the molecule. 
     The Meurer combustion system provides a narrowed focused fuel spray that impinges and is entrained on the combustion chamber wall of a piston bowl. Therefore, the piston bowl is wet with fuel that rotates in the same sense (direction) as the air swirl within the piston bowl. As the piston approaches top dead center (TDC), the air swirl moves from the cylinder into the piston bowl and increases in rotation velocity. The air swirl will skim off the fuel from the chamber wall, in a layer by layer manner. The skimmed fuel is then introduced for combustion. Since the Meurer combustion system uses diesel, high soot emission occurs from combustion. While the Meurer combustion system is multi-fuel type suitable and has a low pressure gradient, soot emission is a problem with this combustion system. 
     The human sense of smell can detect very low concentrations of aldehydes which are partly-burned hydrocarbons. An after-treatment stage is typically implemented in current combustion systems in order to reduce or eliminate the aldehydes emitted from combustion. As a result, the after-treatment stage prevents the human sense of smell from detecting the unpleasant scent of aldehydes. Therefore, current combustion systems typically require the use of this additional after-treatment stage in order to eliminate the aldehydes that are emitted during combustion. 
     One current combustion system that uses fuel impingement on the combustion chamber wall and that uses ethanol is commercially available from Scania AB. However, this current combustion system is only limited to piston engines with a normal cylinder head and the single piston per cylinder arrangement. 
     Therefore, improvements in the current technology would be desirable in order to overcome current constraints or deficiencies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. 
         FIG. 1A  is a top view of a non-soot emitting fuel combustion chamber, in accordance with an embodiment of the invention. 
         FIG. 1B  is a top view of a non-soot emitting fuel combustion chamber, in accordance with another embodiment of the invention. 
         FIG. 2A  is a partial side elevational view of an ignition source pocket in a non-soot emitting fuel combustion chamber, in accordance with an embodiment of the invention. 
         FIG. 2B  is a partial side elevational view of an ignition source pocket in a non-soot emitting fuel combustion chamber, in accordance with another embodiment of the invention. 
         FIG. 3  is a perspective view of a non-soot emitting fuel combustion chamber, in accordance with an embodiment of the invention. 
         FIG. 4  is an axial cross-sectional view of a piston bowl as implemented with a cylinder in a horizontal layout, in accordance with an embodiment of the invention. 
         FIG. 5  is an additional perspective view of a piston bowl, in accordance with an embodiment of the invention. 
         FIG. 6  is an additional isometric view of a piston bowl, in accordance with an embodiment of the invention. 
         FIG. 7  is an additional perspective view of a piston bowl, in accordance with an embodiment of the invention. 
         FIG. 8  is a cross-sectional view of an opposed piston arrangement that can be used in an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the description herein, numerous specific details are provided, such as examples of components and/or methods, to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that an embodiment of the invention can be practiced without one or more of the specific details, or with other apparatus, systems, methods, components, materials, parts, and/or the like. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of embodiments of the invention. 
       FIG. 1  is a top cross-sectional view of an apparatus  100  in accordance with an embodiment of the invention. A piston bowl  105  forms a combustion chamber  107 , in accordance with an embodiment of the invention. An embodiment of the invention is suitable for use with opposed-piston engines and also suitable for use with piston engines with the single piston per cylinder arrangement. The piston bowl  105  is injected with non-soot emitting fuel such as, for example, alcohol fuel (e.g., ethanol, methanol, ISO buthanol, D.M.E. or other alcohol fuel types) or ammonia (NH 3 ). Alcohol fuel has a higher octane number than gasoline or diesel. Both alcohol fuel and ammonia do not produce soot because these types of fuel do not contain carbon. Another advantage of using alcohol fuel is that due to the properties of various types of alcohol, a high compression ratio and high boost pressure can be used without causing engine knock. 
     The piston bowl  105  includes a fuel injector pocket (injector recess)  110  and an ignition source pocket (ignition source recess)  115  on a squish area  117 . The details of the pockets  110  and  115  are discussed below. A fuel injector  120  injects a fuel plume (fuel spray)  130  through the injector pocket  110  and the ignition source  130  would provide ignition to the vaporized fuel. The fuel injector  120  can be, for example, a GDI (gasoline) injector and provides pressure in the range of, for example, approximately 100 bar to approximate 300 bar. However, the fuel injector  120  can also be of the type that provides a higher amount of pressure that is greater than 300 bar. For example, the fuel injector  120  can provide a pressure amount of approximately 1000 bar which is the capability of typical diesel injectors. As will be discussed below and shown in subsequent drawings, the injector  120  is mounted through the cylinder wall (cylinder liner) of a cylinder with the piston bowl  105 . 
     The ignition source  130  supplies a catalyst for igniting the vaporized fuel. The ignition source  130  is, for example, a spark plug that provides sparks for fuel ignition, a laser source that provides a laser signal for fuel ignition, an electrical source type that provides an electrical signal or voltage/current for fuel ignition, or other suitable types of ignition sources that are currently available or that may be developed as technology improves. As a non-limiting example, the ignition source  130  is a multi-spark ignition system or provides one spark per crank angle. The thread of the ignition source  130  can be, for example, 10×1.5. 
     Additionally, in an embodiment of the invention, the piston bowl  105  preferably has its center  145  in the same axis as the center of the cylinder. The center  145  is within the center portion  146  of the piston bowl  105 . However, in other embodiments of the invention, the piston bowl center  145  is not required to be in the same axis as the center of the cylinder and can be located at an offset position from the axis of the cylinder center. 
     The fuel injector  120  injects the non-soot emitting fuel (e.g., alcohol or ammonia) onto the chamber wall  147  (piston wall  147 ) as a focused fuel plume  130  with a narrow plume angle A 1 . As an example, the angle A 1  is approximately 5 degrees or less. The plume  130  has an impulse that creates momentum for fuel rotation along the wall  147 . A higher injection pressure from the injection source  120  for the fuel plume  130  will result in an increase impulse that will cause the fuel to rotate along the wall  147  at an increased duration as long as the liquid state of the fuel is not vaporized. 
     The piston wall  147  forms the boundary of the piston bowl  105 . Preferably, the injector  120  is positioned (or is aimed) so that the plume  130  will come into contact with the wall  147  in a tangential manner  140  or in a substantially tangential manner  140  in order to maintain the momentum of the fuel plume  130  along the wall  147  and reduce the reflection (splashing off) of the fuel plume  130  from the wall  147 . Therefore, the plume  130  will at least substantially follow the curvature of the wall  147 . If the fuel plume  130  comes into contact against the wall  147  in at least a substantially tangential manner  140 , the momentum (rotation) of the liquid fuel  130 A along the wall  147  is substantially conserved because the liquid fuel  130 A will be entrained and will rotate along the curvature of the wall  147 , and the reflection of the liquid fuel  130 A from the wall  147  toward the bowl  136  is minimized. It is desirable to minimize any reflected (splashed) liquid fuel from the wall  147  because any reflected liquid fuel will lose its momentum of its rotation along the wall  147 . It is desirable that the liquid fuel  130 A maintains its momentum of rotation along the wall  147  until the liquid fuel  130 A is drawn into the pocket  115  as vaporized fuel  130 B prior to combustion. 
     The aim of the injector  120  is typically not directed toward the center  145  of the bowl  105 , so that the plume  130  can hit the wall  147  in a substantially tangential manner  140 . In one embodiment of the invention, the injector  120  is inclined toward the axis of the cylinder that contains the piston  105 . In another embodiment of the invention, the injector  120  is not inclined toward the axis of the cylinder. 
     The air swirl  150  within the bowl  105  is in the same rotation direction (sense of rotation) as the rotation direction of the liquid fuel  130 A that is travelling along the curvature of the wall  147 . Therefore, the air swirl  150  aids the travel and rotation movement of the liquid fuel  130 A along the curvature of the wall  147 . On the other hand, if there is sufficient pressure (energy) that is provided by the injector  120  to the plume  130 , then the liquid fuel  130 A will not have to significantly rely on the air swirl  150  for travel and entrainment along the curvature of wall  147 . 
     The squish area  117  of the bowl  105  will accelerate and increase the velocity of the air swirl  150  (and the air charge portion in the swirl) around the combustion chamber  107 . The air swirl  150  will accelerate because the diameter of the combustion chamber  107  decreases from the piston crown  154  of the bowl  105  to the lower portions of the bowl  105 . The swirl number is the ratio of the angular speed (i.e., rotation rate or omega) of the air charge portion and the angular speed of the crankshaft. The swirl number is typically, for example, at a value of approximately 1 or more. 
     As also shown in  FIG. 1A , on most portions of the circumference of the piston bowl  105 , the distance from the center  145  to the wall  147  is the first radius r. For example, as shown in  FIG. 1 , the distance from the center  145  to each of the wall portions  160 ,  162 ,  164 ,  168 , and  174  is the radius r. 
     The wall portion  162  of the wall  147  has the radius distance r from the center  145 . Moving along the wall  147  in a counter-clockwise direction in  FIG. 1A , the wall portion  170  is shown as being on a first side  171  of the ignition source pocket  115  along the wall  147 . The distance from center  145  to the wall portion  170  is the radius r 1 , where r 1 &lt;r. Therefore, the radius of the bowl  105  (i.e., distance r from center  145  to the wall  147 ) will vary and have different values. 
     The wall portion  172  is on a second side  173  of the ignition source pocket  115  along the wall  147 . The second side  173  is on an opposed side of the pocket  115  from the first side  171 . The distance from center  145  to the wall portion  172  is the radius r 2 , where r 2 &gt;r. Therefore, the first wall portion  170  and the second wall portion  172  are not on a same circumference path but are offset by a first offset distance, OF 1  as shown in equation (1). 
         OF 1 =r 2 −r 1  (1)
 
     Since the first wall portion  170  and the second wall portion  172  are not on a same circumference path but are offset by the first offset distance, OF 1 =r 2 −r 1 , fuel  130 A that is entrained on and is travelling along the wall portion  171  will be lifted (pulled) in a direction towards the center  145 . Therefore, the wall portion  170  effectively functions as a ramp for the liquid fuel  130 A in order to prevent the liquid fuel  130 A from falling (moving) into the ignition source pocket  115  and to prevent the liquid fuel  130 A from hitting the wall (edge)  116  of the pocket  115 . The liquid fuel  130 A will jump over the pocket  115  and land on the wall portion  172  and continue its rotation and tangential movement along the wall  147 . Since the wall portion  172  has the radius r 2 , where r 2 &gt;r, the offset distance OF 1  (where OF 1 =r 2 −r 1 ) permits the liquid fuel  130 A to have an additional distance of r 2 −r 1  for landing on the wall portion  172  after the fuel  130 A has jumped over the pocket  115 . 
     As also shown in  FIG. 1A , the distance from center  145  to the wall portion  164  and to the wall portion  168  are each at the radius r. 
     Moving along the wall  147  in a counter-clockwise direction in  FIG. 1A , the wall portion  174  is shown as being on a first side  175  of the injector pocket  110  along the wall  147 . The distance from center  145  to the position  174  is the radius r 3 . In an embodiment of the invention, the radius r 3  is less than r (r 3 &lt;r). However, in other embodiments of the invention, the radius r 3  can also be equal to r (r 3 =r). 
     The wall portion  175  is on a second side  176  of the injector pocket  110  along the wall  147 . The second side  176  is on an opposed side of the pocket  110  from the first side  175 . The distance from the center  145  to the wall portion  175  is the radius r. Therefore, in an embodiment of the invention where r 3 &lt;r, the first wall portion  175  and the second wall portion  176  are not on a same circumference path but are offset by a second offset distance, OF 2  as shown in equation (2). 
         OF 2 =r−r 3.  (2)
 
     If r 3 &lt;r, then liquid fuel  130 A travelling at wall portion  174  will be lifted toward center  145 , will be able to jump over the pocket  110 , will then land on the wall portion  175 , and then continue its rotation and tangential movement along the wall. 
     In an embodiment of the invention, the curvature of the wall side  171  (adjacent to ignition source pocket  115 ) is increased in order to have a ramp configuration. The ramp configuration also helps to lift up the liquid fuel  130 A away from the pocket  115  and substantially prevent the movement (or splashing) of the liquid fuel  130 A into the pocket  115 . However, in another embodiment of the invention, this ramp-like shape is omitted and only the configuration r 2 &gt;r 1  is used to lift the liquid fuel  130 A away from the pocket  115 . 
     The pocket  115  is shaped and has dimensions that will draw the vaporized fuel  130 B from the liquid fuel  130 A that is rotating along the wall  147 . As the liquid fuel phase  130 A jumps over the pocket  115 , the vaporized fuel phase  130 B will move within the pocket  115 . The liquid fuel phase  130 A and the vaporized fuel phase  130 B will have opposite senses of rotation. Therefore, the sense of rotation of the charge motion of the vaporized fuel and air in the pocket  115  will be opposite to the sense of rotation of the liquid fuel  130 A along the piston bowl wall  147 . For example, if the liquid fuel phase  130 A is rotating counter-clockwise along wall  147 , then the vaporized fuel phase  130 B will rotate clockwise within the pocket  115 , and vice versa. The flow within the pocket  115  will be the vaporized fuel phase  130 B and some air mixture in the vaporized fuel phase  130 B. The dimension of the ignition pocket  115  is sufficiently narrow so that the backflow due to the vaporized fuel  130 B and entrained air in the vaporized fuel  130 B will not disturb the flow of the liquid fuel  130 A along the wall  147 . The ignition source  130  provides ignition catalyst  180  (e.g., spark) that ignites the vaporized fuel  1308  for starting combustion. 
     Since the liquid fuel phase  130 A will not impinge within the pocket  115  and will not come into contact with the ignition source tip  131 , the liquid fuel will not short-circuit the insulator of a spark source that may be implemented as an ignition source  130 . As a result, the ignition source  130  will be able to function properly by providing the ignition catalyst  180  (e.g., spark) to ignite the vaporized fuel phase  130 B. 
     In an embodiment of the invention, one wall of the pocket  115  can be shaped as an undercut  182 A. This undercut  305 A provides a cover to shield the ignition source tip  131  from splashes of liquid fuel  130 A that is entrained along the wall  147 . The opposed edge  116  of the pocket  115  is typically straight in configuration. 
     The undercut  182 A covers (or partially covers) the tip  131  so that a center axis line  183  of the tip  131  will intersect a curved portion  184 A of the undercut  182 A. Therefore, the curved portion  184 A provides the tip  131  as a cover or shield of any liquid fuel  130 A. 
     The following parameters may be used as example dimensions in the piston bowl  105  and are, therefore, not intended to limit the embodiments of the invention. 
     The injector pocket  110  is preferably narrow in dimension in order to reduce the air volume that may be entrained from the piston bowl wall  147  toward the inside of the pocket  110  and to not sufficiently deteriorate the compression ratio. 
       FIG. 1B  is a top view of a piston bowl  105 A in accordance with another embodiment of the invention. The piston bowl  105 A has an ignition source pocket  115 A which does not have the undercut  182 A of  FIG. 1A . Instead, the pocket  115 A will have a straight or substantially straight side  182 B without an undercut. 
       FIGS. 2A and 2B  are partial side elevational views of piston bowls in accordance with various embodiments of the invention. The piston bowl  105  of  FIG. 2A  has the ignition source pocket  115  with the undercut  182 A on a pocket wall  205 A. In contrast, the piston bowl  105 B of  FIG. 2B  has the ignition source pocket  115 A with the non-undercut shape  182 B on a pocket wall  205 B. 
     The configuration of the piston bowls  105 / 105 A can be achieved by use of conventional casting techniques, numerical control (NC) machining, or/and other standard manufacturing techniques for the manufacture of pistons. Additionally, the materials used for the piston bowl  105  can be any suitable material used for standard pistons such as, for example, metals, irons, alloys, or combinations of metals, irons, alloys, and/or other suitable materials. 
     In an embodiment of the invention as shown in  FIG. 1A , the center portion  146  of the piston bowl  105  is substantially flat. However, in another embodiment of the invention as shown in  FIG. 3 , the center portion  146  of the piston bowl  105  can have a bulge  305  in order to increase the compression ratio ε. 
     The formula for peak compression pressure is shown in equation (1) 
         P   cp   =P   0 *ε Y   (1)
 
     where, P 0  is the boost pressure, cis the compression ratio, and Y is the polytropic exponent. The boost pressure P 0  can be achieved by use of, for example, a conventional turbo-charge stage or conventional super-charge stage. The polytropic exponent Y is typically approximately 1.4 for air and is normally in the 1.36 to 1.38 range. The compression ratio can have a value of, for example, 14/1 or other suitable high compression ratio value. The boost pressure can be in the range of, for example, approximately 2.5 bar to approximately 3.0 bar. Based on the above equation (1), the peak compression pressure can be in the range of, for example, approximately 100 bar to 144 bar. In order for the fuel injection to overcome the back pressure in the combustion chamber  107 , the pressure of the fuel plume  130  must be greater than P cp . In other words, the pressure of the fuel plume  130  is typically required to be at least approximately 100 bar. 
     It is difficult to produce a pressure of 1000 bar with ethanol because the lubrication capability of ethanol is very poor and a high pressure mechanical pump has a high amount of friction and very little or no lubrication. On the other hand, it is less difficult and more economical for a GDI injector to produce a pressure amount in the range of about 200 to 300 bar. Note that a diesel injector is also much larger in size and more expensive than a GDI injector. For example, a typical diesel injector is approximately three times larger and approximately five times more expensive than a typical GDI injector. Therefore, one advantage that is provided by an embodiment of the invention is that a very high pressure is not required for an injector  120  to be used with the piston bowl  105 . As a result, the smaller sized and relatively less expensive GDI injector type can be used advantageously in an embodiment of the invention. 
       FIG. 4  is an axial cross-sectional view of the piston bowl  105  as implemented with a cylinder  405  in a horizontal layout, in accordance with an embodiment of the invention. For a cylinder  405  in a horizontal layout, the ignition source  130  and injector  120  are positioned in an upper portion  410  with respect to a bore of the cylinder  405 . The upper portion  410  is a position above the horizontal reference line  415  as shown in  FIG. 4 . The upward direction is shown by reference arrow  417 . Since the ignition source  130  (shown as a non-limiting example of a spark plug in  FIG. 4 ) and the injector  120  are positioned in the upper portion  410 , it follows that the injection pocket  110  ( FIG. 1 ) and ignition source pocket  115  ( FIG. 1 ) are also located in the upper portion  410 . As a result, any liquid fuel  130 A that loses its momentum of rotation around the chamber wall  147  will not fall into the pockets  110  and  115 . 
       FIG. 4  also shows the squish area  117  at the piston crown. The threads  422  of the example spark plug are inserted through the cylinder liner  425  which is of a suitable thickness. Therefore,  FIG. 4  shows an example of a portion of the injector source  130  as being mounted through the cylinder  405 . A portion of the injector  120  is also mounted through the cylinder  405 . 
     A recess in the squish area  117  may be required in one implementation, so that when the piston moves by the ignition source  130 , the piston will not contact the tip of the ignition source  130 . A multi-spark ignition source may be required to insure reliable ignition, if an opposing squish flow from that squish area recess would press the vaporized fuel and air away from the ignition source pocket  115 . A multi-spark ignition source would also provide a reliable ignition start in the cold start situation, in the event that vaporization deteriorates during cold start. 
     The injector  120  is outside of the cylinder liner  425  so that the piston  105  can travel along the cylinder  105 . The cylinder liner  425  will have open spaces to accommodate the injector  120  and the ignition source  130 . 
     The tip  421  of the piston bowl is at the outer edge of the squish area  117 . The squish area  117  is designed as an undercut so that the fuel does not come into contact or splash on the wall of the cylinder  405 . It is desirable that fuel contact or fuel impingement does not occur on the inner wall of the cylinder  405  for the following reasons. First, the impinging fuel would dilute the lubrication oil on the inner wall of the cylinder  405  and would also come into contact with the crank case. Second, the impinging fuel would be wasted because this fuel will not be able to participate in combustion. 
     In an embodiment of the invention, the piston bowl is preferably in the center of the cylinder  405 . However, in another embodiment, the piston bowl can be offset from the center of the cylinder  405 . 
       FIG. 5  is an additional perspective view of the piston bowl  105 , in accordance with an embodiment of the invention. In a horizontal cylinder layout, the injector  120  is, for example, approximately 35 degrees before top dead center (TDC) when the piston is, e.g., approximately 5 millimeters before TDC. 
       FIG. 6  is an additional isometric view of the piston bowl  105  in accordance with an embodiment of the invention. The piston  105  is viewed transparently through the cylinder  405 , for purposes of clarity. 
       FIG. 7  is an additional perspective view of the piston bowl  105 , in accordance with an embodiment of the invention. The tip of the injector  120  is shown in TDC. Preferably, the injector  120  is inclined at an injector incline angle A 2  with respect to a reference line  705 , so that the direction of the fuel plume (spray)  130  is inclined downward into the opening  736  of the piston bowl  105 . In other words, the injector  120  is inclined toward the axis of the cylinder. The angle A 2  can range from, for example, about 2 degrees to about 5 degrees. 
       FIG. 8  is a cross-sectional view of an opposed piston arrangement that can be used in an embodiment of the invention. This opposed piston arrangement is one non-limiting example that can implement an embodiment of the invention. As mentioned above, an embodiment of the invention can also be implemented in a single piston per cylinder arrangement. A squish area  802  is between the exhaust piston  802  and the intake piston  805 . The piston ring grooves  810  in the exhaust piston  804  are also shown in  FIG. 8  as an additional detail. The squish area  802  can be, for example 1 mm in TDC. The various inventive features of the piston bowl, as previously discussed above, can be included in the opposed pistons  804 / 805 . 
     Various advantages have been achieved with methanol turbo-charged direct injection diesel engines. First, cold start from −30 degrees was available. In contrast, cold start issues arise with standard ethanol engines. 
     Second, smoke and carbon deposit were avoided as compared to a port injected engine with M85 (methanol 85%). 
     Third, a lower NOx is achieved as compared to diesel. Because of the cooling effect and a very little amount of EGR for this combustion, the engine knock problem is minimized. 
     Fourth, approximately 30% higher low speed torque is achieved at an air-fuel ratio of about 1.1, with no smoke production. 
     Fifth, the fuel consumption is similar to baseline diesel. 
     Sixth, combustion is robust with use of the wall guide concept (i.e., fuel entrainment on the combustion chamber wall). A precise air to fuel ratio is not required and non-throttle operation is available. Additionally, a relatively wide range of injection timing tolerance and ignition timing tolerance is permitted. Therefore, the use of a multi-spark ignition might be potentially eliminated. 
     As a result, various advantages are achieved by use of alcohol fuel. 
     The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. 
     These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.