Claims:We Claim:
1. A piston (100) for an engine cylinder, comprising:
at least one crown (102); characterized in that
at least a cavity (103) located in said crown 102, and
an impeller 104 located in said cavity, said impeller 104 adapted to rotate during reciprocating motion of said piston 100.

2. The piston 100 of claim 1, wherein said impeller 104 is integrated with said piston crown 102.

3. The piston 100 of claim 1, wherein said impeller 104 is attached to said crown 102 of said piston 100.

4. The piston 100 of claim 3, wherein said impeller 104 is attached to said crown 102 via a bearing (106).

5. The piston 100 of claim 3, wherein said impeller 104 is attached to said piston crown 102 via a snap ring.

6. An impeller for use with a piston 100, said impeller adapted to be attached to the crown 102 of a piston 100.

7. The impeller of claim 6, wherein rotation of said impeller during reciprocating motion of said piston 100 generates swirl motion within an engine cylinder.
, Description:Field of the invention
[0001] This invention relates to the field piston used in internal combustion engine.

Background of the invention
[0002] Internal combustion (IC) engines are well known in the art. IC engines are of two types, that is, spark ignition engines using gasoline as a fuel, and compression ignition (CI) engine using diesel as a fuel. In the case of latter that is the CI engine, the combustion process happens through compressing the fuel first, and then injecting the compressed fuel into an engine cylinder. The compressed fuel mixes with hot compressed air the charge ignites to form a combustible mixture. The combustible mixture is in the form of a swirl within the engine cylinder. During movement of the piston, the swirl motion is converted to tumble. In order to ensure complete combustion and for keeping meeting the stringent emission norms, it is desirable to maintain swirl motion in the combustion chamber.
[0003] Prior art patent application US6170454 discloses a piston for use with an internal combustion engine is disclosed in one embodiment of the present invention as including a crown having an exhaust valve area, an intake valve area, and means for moving exhaust toward the exhaust valve area. The exhaust moving means includes means for homogenizing the air/fuel mixture. The homogenizing means may also include means for creating eddies within the air/fuel mixture. In addition, the piston may include means for concentrating the air/fuel mixture toward the area of ignition. In one presently preferred embodiment, the structure used to accomplish the invention includes a raised portion formed on the crown of the piston. The raised portion increases in height from the center of the crown toward the perimeter of the crown. Moreover, the raised portion also has an arcuate shape declining in height along the arcuate shape. The presently preferred raised portion includes a plurality of dimples formed therein for creating eddies within the air/fuel mixture.

Brief description of the accompanying drawing
[0004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:
[0005] FIG. 1 illustrates a piston for an engine cylinder.

Detailed description of the embodiments
[0006] FIG. 1 illustrates a piston 100 for an engine cylinder. The piston 100 comprises at least a crown 102, a cavity 103 is located in the crown 102 and an impeller 104 located in the cavity 103.The impeller 104 is adapted to rotate during reciprocating motion of the piston 100 for generating a swirl motion of air-fuel mixture in the engine cylinder. The impeller 104 is integrated with the piston crown 102. Alternately, the impeller 104 may be attached to the crown 102 of the piston 100 via a bearing or a snap ring.
[0007] The constructional features of the piston 100 will be disclosed in further detail. The piston 100 is located within the engine cylinder and comprises a crown 102. The piston 100 is driven by engine crankshaft. The rotation of the crankshaft causes the piston 100 to reciprocate within the engine cylinder. The crown 102 of the piston 100 is exposed to the combustible charge of fuel and air. The crown 102 comprises a cavity 103 in which an impeller 104 is located. Grooves may be provided on the impeller 104 blade to improve energy transfer to the blade. The impeller 104 is held in place by a bolt. The impeller 104 may be made from mild steel and leads to higher swirl and better mixing thereby reducing particulate matter emissions and improving fuel consumption. This gives a better leverage to tweak the timing of intake and exhaust stroke to reduce Nox emissions. The non-threaded portion of the bolt gives the bearing area required to press fit the needle bearing onto it. The needle bearing in turn, is press fit into the counter bore area in the piston 100. The impeller 104 is fastened to the both by the threaded portion of the bolt at the end. The inner race of the bearing rotates and the outer race is stationary.
[0008] The working of the piston 100 used in the engine cylinder of an internal combustion engine will be explained in further detail. As the piston 100 moves downwards during suction stroke, fresh air is sucked into the cylinder through the helical port with a designed (cylinder head) swirl ratio. This rotates the impeller 104 blade along the direction of swirl, thereby maintaining this rotational direction. As the piston 100 moves upwards during compression stroke, this motion is kept intact. This will enable better fuel-air mixing when the diesel is sprayed near the end of compression stroke. As the combustion gases expand, they add energy to the rotating impeller 104, thereby increasing its velocity which in turn helps the combustion to continue. The impeller 104 rotates due to the air swirl velocity which in turn keeps the swirl intact during the compression stroke thereby enhancing fuel and air mixing. The number of blades on the impeller 104 can be made equal to the number of holes in the injector, so that adjacent sprays do not interact with each other, initially. The impeller 104 keeps rotating throughout the cycle. The impeller helps to purge out exhaust gases at the end of exhaust stroke. Direction of rotation of the impeller can be fixed based on the requirement, by proper blade angle selection. During expansion stroke, combustion gases at high pressure and temperature strike the blades and owing to the pressure equalization phenomenon between top and bottom edges of the blade, the blades rotates. The annular grooves additional provide a passage to guide the flow. This is achieved since the impeller 104 induces a forced vortex flow within the high pressure combustion gases (fuel and air mixture). As the piston 100 moves upwards during the exhaust stroke, this rotating impeller 104 tries to push out the exhaust gases through the exhaust valve, since the direction of flow is the same. As the impeller 104 blade rotates due to the air swirl when fresh air enters through the intake port and in turn the air swirl is held intact by this rotating fan. The rotation of the impeller 104 continues throughout the four strokes of the engine, but at different velocities, which depend on the momentum transfer to the impeller 104. In the absence of a rotating member, the swirl gets to near zero during the compression stroke since there is essentially nothing that maintains this vorticity in air against the opposing piston 100 travelling upwards. This in turn imparts more turbulence to the already turbulent air thereby improving the air availability to the sprayed diesel. This leads to better fuel consumption and HC, CO & PM emissions. Hence the reciprocating motion of the piston 100 together with the rotary motion of the impeller 104 helps in maintaining the swirl generated due to mixing of air and fuel. This leads to the better combustion of air-fuel mixture leading to a reduction in NOx.
[0009] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention in terms of design of inlet connector used and the type of inlet connector used. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.