404 /MUM /05
ABSTRACT:

A piston for

a diesel engine is disclosed. The piston defines a cylindrical

circumferential surface. The piston comprises an eccentric re-entrant cavity on one face of the piston, a plurality of grooves on the circumferential surface, the grooves adapted to accommodate a piston ring and a relieved
skirt.

FORM-2

THE PATENTS ACT, 1970
(39 of 1970)
&


THE PATENTS RULES, 2003
COMPLETE
Specification
(See section 10 and rule 13)
AN IMPROVED PISTON FOR A DIESEL ENGINE AND A
DIESEL ENGINE COMPRISING THE SAME HAVING
IMPROVED EMISSION CHARACTERISTICS
KIRLOSKAR OIL ENGINES LTD.
an Indian Company
of Laxmanrao Kirloskar Road, Khadki, Pune 411003,
Maharashtra, India.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
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Field of invention
This invention relates to an improved piston for a diesel engine and a diesel engine comprising the same having improved emission characteristics.
Definitions:
As used in this specification the following words are generally intended to have a meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
'Grooves' mean a plurality of indentations on the cylindrical face of the piston for the purpose of accommodating piston rings.
'Omega' means a geometrical shape in the form of the Greek alphabet omega.
'Piston' means a cylindrical, hollow aluminum or iron part, closed on top and open at the bottom, fitting closely within an engine cylinder or sleeve and capable of being driven alternately up and down in a cylinder.
'Piston Head means the top piston surface against which the combustion gases exert pressure. The piston head may be flat, concave, convex or of irregular shape.
'Re-entrant' means going out and coming back in.
'Relieved' means curved not straight, slightly arcuate having a radius.
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‘Skirt’: A part of a piston located between a first ring groove above the pin hole, and the bottom (open end) of a piston. The skirt forms a bearing area in contact with the cylinder wall.

'Top Dead Centre': In piston engine, the position of the piston head nearest to the cylinder head and farthest from the crankshaft is known as Top Dead Centre' (TDC).
'Bottom Dead Centre': In piston engine, the position of the piston head nearest to the crankshaft and farthest from the cylinder head is known as 'Bottom Dead Centre' (BDC).
Introduction

In a diesel engine that works on a 4-stroke cycle, air is drawn inside the cylinder due to the motion of the piston, from one end to the other, in the cylinder. These ends are termed as 'top dead center (TDC)' and 'bottom dead center (BDC)". Air comes in through a passage in the cylinder head, generally called as "inlet port" that has a valve at one of its opening at the cylinder end. This valve is opened at a particular moment during the cycle and air is admitted into the cylinder head, this is called the 'suction stroke' out of the 4-stroke cycle. Further this air is compressed in the next stroke called as 'compression stroke' due to the motion of the piston from BDC to TDC. The air gets compressed upto such an extent that temperature of air rises resulting in spontaneous igniting of the fine droplets of diesel sprayed at the end of the compression stroke. These fine droplets are mixed intimately with the air in the cylinder. Ignition causes violent explosion,
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which expands the air and fuel gases resulting in motion of the piston from TDC to BDC, which is called the 'expansion/power stroke' The burnt gases are then expelled out of the cylinder during the next stroke, called 'exhaust stroke' during which the piston moves from BDC to TDC. For expelling the burnt gases, there is another passage in the cylinder head called as the ', ‘exhaust port’, which also has a valve similar to the inlet valve and opens at a particular moment during the above cycle. The reciprocating motion of the piston during repetitive and sequential suction, compression, expansion and exhaust strokes (called as 4-stroke cycle) causes rotation of a crankshaft due to its connection to the piston by a 'connecting rod'.
In diesel engines the inlet and exhaust ports act as pathway for admitting fresh air and removing exhaust gases respectively. The design of these ports has a large effect on the economy and performance of the engine. Two dimensionless numbers namely 'swirl number and 'flow coefficient' play a dominant role in engine design, thermodynamic performance and exhaust emissions. Swirl number relates to the rotation of the fluid in the cylinder and the flow coefficient is a measure of the pressure loss introduced by the port/valve combination.
Swirl number is defined as the ratio of the anemometer speed measured by the stationary flow test and fictitious engine speeds obtained by equating the mean axial flow velocity to mean piston speed. The swirl number represents airflow patterns. Swirl number is optimized based on the engine size. The swirl improves air and fuel mixing which results in efficient combustion in turn resulting into reduction in exhaust emissions like smoke and particulate matter.
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Flow co-efficient is the ratio of actual flow rate at a certain pressure drop through a known cross-section to the theoretical mass flow rate at equal pressure drop through a reference cross-section. Flow coefficient improves breathing of the engine and hence improves air to fuel ratio, which reduces emissions like NOx, HC and CO.
Emission of various types of gases is an important consideration for the purpose of engine design. It is a mandatory requirement that engine should meet the national and international emission requirements. Hence it is necessary that engine components be designed in a manner such that the emission is below the prescribed limit.
Prior Art:
Figures 1, 1A1 and 1B illustrates a sectional side view, top plan view and side view of the conventional prior art piston component for a diesel engine. The cavity (10), (12), (14) in the piston is an open cavity, which is concentric in nature having a typical volume 50.4 cc. The top piston ring (16) has a rectangular cross section and the skirt diameter is not relieved.
The piston cavity forms a combustion chamber bowl, and the position of combustion cavity on the piston top is governed by the position of air entry through the inlet port and the fuel sprays from the injector. The injector fuel sprays must enter the combustion cavity on the piston and stay inside the bowl for its proper mixing with air in order to achieve complete combustion of fuel and thereby reducing the fuel consumption and pollution in engine

exhaust emissions. But due to the top edge/ridge of the piston cavity being straight and the cavity being concentric, the fuel sprays from the injector are not completely entering the piston cavity and staying therein, thereby air fuel mixing is not proper and hence complete combustion is not achieved resulting into higher pollutants in emissions from the engines which being more than prescribed limits are not acceptable.
Also the top piston ring being of rectangular cross-section does not withstand high working temperature and sticks with the piston causing building-up of combustion residues, resulting into lower efficiency of the engine with higher pollutants in the emissions from the engine.

Further the skirt of the piston being convex, area of contact between piston and the inner wall of the liner is more, giving higher friction, resulting into lower efficiency of the engine. Gudgeon pin of the piston is also quite longer which increases the piston pin mass.

The piston is having drilled holes for oil drain into the crank case/sump but it is noticed that there is a risk of feeding more oil to the piston, through these holes than draining surplus oil. Due to the construction of prior art pistons a limitation of the prior art Diesel Engines is that the emissions from the engines are not acceptable besides the fuel consumption is high with low efficiency.
The main object of this invention is to obviate the above said draw backs and limitations of the existing pistons of the Diesel Engine and to provide an improved piston for the Diesel Engine in which the piston cavity consists of

inward curved edge and made off set, piston skirt is provided with depression and the top piston ring is having trapezoidal cross section, in order to achieve reduced pollutants in engine exhaust emissions to comply with the acceptance norms for emission control.
Another object of this invention is to provide an improved piston for the Diesel engine in which the length and mass of the piston gudgeon pin is reduced and the piston production becomes simpler.
A further object of this invention is to provide an improved piston in which friction between the piston skirt and inner wall of the liner is reduced giving higher engine efficiency.
A further object of this invention is to provide an improved piston in which oil consumption is controlled by providing better drain passage for surplus oil return into the crankcase.
A further object of this invention is to provide an improved piston in which

sticking of the top piston ring with the piston is avoided to minimize the

building-up of combustion residues.
A further object of this invention is to provide an improved piston with top ring having! trapezoidal cross section to with stand higher working temperature.
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Accordingly this invention provides.
an improved piston for diesel engine comprising of a cylindrical hollow body closed at one end and open at the other end, the closed end called as piston head being provided with a piston cavity, forming combustion chamber bowl, with its top edge/ridge curved inward called re-entrant cavity for imparting orderly and controlled movement of air and fuel, a plurality of grooves provided on the cylindrical hollow body near its closed end, for accommodating therein a number of piston rings, a skirt for guiding the

piston in the

cylinder bore or liner and a gudgeon piston pin for connecting

the piston with the connecting rod.
Typically, the said re-entrant cavity is substantially omega 'w' shaped.
Typically, the said re-entrant cavity is 'off set' with the centerline of the
piston.

Typically, the said skirt is provide with depression called as 'relieved skirt' for reducing friction and for providing a good drain passage for surplus oil return into the crank case/sump.

Typically, the said Gudgeon piston pin is of reduced length and mass.
Typically, the top piston ring accommodated in top groove is of trapezoidal cross section called as 'keystone ring' for avoiding ring sticking to piston,
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minimizing building-up of combustion residues and to withstand high working temperature.
Typically, the volume of re-entrant cavity is 40.8 cc.
Typically, the improved piston for diesel engine substantially as herein described and illustrated in Figures 2, 2A and 2B of the accompanying drawings.
An diesel engine incorporated with an improved piston as claimed in any of the above claims 1 to 8, having improved emission charactersties.
Brief description of the accompanying drawings:
The invention will be described in detail with reference to a preferred embodiments Reference to this embodiment does not limit the scope of the invention.
In the accompanying drawings:
Figure 1 illustrates a sectional side view of the conventional prior art piston
component for a diesel engine;
Figure 1A illustrates the top plan view of the piston component of figure 1;
Figure 1B illustrates the side view of the piston component of figure 1;
i
Figure 2 illustrates a sectional side view of the piston component in accordance with this invention;
Figure 2A illustrates the top plan view of the piston component of figure 2;
i
and
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Figure 2B illustrates a side view of the piston component of figure 2.
Figure 3 illustrates a tabulated emission report of a water-cooled engine for
an engine incorporating a piston component known in the prior art;
Figure 4 illustrates a tabulated emission report of a water-cooled engine for
an engine incorporating a piston component in accordance with this
invention;
Figure 5 illustrates a tabulated emission report of an air-cooled engine for an
i
engine incorporating a piston component known in the prior art; and Figure 6 illustrates a tabulated emission report of an air-cooled engine for an engine incorporating a piston component in accordance with this invention.
Detailed description of the accompanying drawings:
The invention will now be explained with reference to Figures 2 to 6 of the accompanying drawings.
The invention will now be described with reference to figures 2, 2A and 2B, wherein an improved piston for diesel engine according to an embodiment of this invention, comprises a cylindrical hollow body closed at top and open at bottom. The closed end of the piston, known as piston head is provided with a re-entrant cavity (18) which is of Omega 'w' shape, that is the top edge/ridge is curved inward, which helps fuel sprays stay inside for its proper mixing with air to achieve complete combustion and reduced particulate emissions. The cavity (18) is 'offset' as indicated by reference line (20) in Figs. 2 and 2A. The re-entrant off set cavity facilitates injector fuel sprays entry into the cavity for proper air fuel mixing and combustion.
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The volume of the re-entrant cavity (18) is reduced to 40.8 cc from a volume of 50.4 cc of the prior art piston cavity.
A plurality of grooves are provided on the cylindrical surface of the piston towards its closed end for accommodating a number of piston rings. Generally the piston rings are of rectangular cross section, which sticks to piston, creating building up of combustion residues and does not withstand high working temperature.
According to this invention the top piston ring (22) is made of trapezoidal cross-section, which is called keystone ring. It avoids ring sticking to piston, minimizes building-up of combustion residues and also withstands high working temperature.
The cylindrical portion of the piston below the grooves for piston rings which is called skirt is provided with a depression (24) which is termed as 'relieved skirt'. The relieved skirt (24) reduces the area of contact between inner wall of the liner and the piston, which reduces friction during piston movements. Further the relieved skirt provides a good drain passage for surplus oil return into the crank case/sump to control the oil consumption.

The relieved skirt also results into reduced piston pin length and mass and

simpler production of piston.
The re-entrant cavity (18) of the piston imparts orderly and controlled movement of air and fuel. The re-entrant cavity (18) of the piston provides continuous supply of fresh air mixture to each burning droplet and products of combustion are swept away, hence reducing the suffocation of products of combustion to negligible inside the cylinder.
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Due to omega shaped cavity (18), rotating movement is set and air contained in the cavity is fed (i.e. in two depressions) into the gases coming out of the swirl chamber. This helps for complete combustion. The air in the shallow depression is embraced by the fuel and is utilized. This increases load carrying capacity of the engine by 10%.
For the purpose of testing a test rig was set up to determine the smoke and exhaust emissions for different types of water cooled and air cooled engines as known in the prior art and in accordance with this invention. Similar engines were selected as known in the prior art and in accordance with this invention with respect to bore x stroke values. Three representative engines of each type having an inlet port of length 145mm were selected in the trials, all engines were set up at a uniform speed of 1500 rpm, the following parameter namely specific fuel consumption (SFC), exhaust temperature, lub oil pressure and temperature, smoke and exhaust emissions were noted for all the engines except that the volume of smoke generated was not checked for engine of the prior art. The results were tabulated and are shown in figures 3 to 6 of the accompanying drawings. The specific fuel consumption for all bore x stroke values was found to be consistently lower in engines in accordance with the present invention as compared to engines known in the prior art.
The smoke generated in the exhaust emissions measured in BOSCH was

significantly compared to

lower in engines in accordance with the present invention as engines known in the prior art.

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Similarly values of NOx, HC, CO and particulate matter in the exhaust emissions was found to be consistently and significantly lower in engines in accordance with this invention as compared to engines known in the prior art. These test results therefore confirm the adoption of the features of the present invention, which on one hand improves the fuel consumption and also concomitantly improves the quality of the emissions including smoke, HC, CO, NOx and particulate matter.
A diesel engine used for gensets, incorporating a piston component in accordance with this invention was tested, the data tabulated below was obtained as a result of the tests. The improvements achieved in the emission levels are as below:

While considerable emphasis has been placed herein on the structures and
Structural interrelationships between the component parts of the preferred embodiments, it will be appreciated that many embodiments can be made
and that many changes can be made in the preferred embodiments without
departing from the principles of the invention. These and other changes in
the preferred embodiment as well as other embodiments of the invention will
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be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.
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We Claim:
1. An improved piston for diesel engine comprising of a cylindrical

hollow body closed at one end and open at the other end, the closed end called as piston head being provided with a piston cavity, forming
combustion chamber bowl, with its top edge/ridge curved inward called re-entrant cavity for imparting orderly and controlled movement of air and fuel, a plurality of grooves provided on the cylindrical hollow body near its closed end, for accommodating therein a number of piston rings, a skirt for guiding the piston in the cylinder bore or liner and a gudgeon piston pin for connecting the piston with the connecting rod.
2. The improved piston according to claim 1, in which said re-entrant

cavity is substantially omega 'w' shaped.

3. The improved piston according to claim 1, in which the said re-entrant cavity is 'offset' with the centerline of the piston.
4. The improved piston according to claim 1, in which the said skirt is provide with depression called as 'relieved skirt' for reducing friction and for providing a good drain passage for surplus oil return into the crank case/sump.
5. The improved piston, according to claim 1, in which said Gudgeon piston pin is of reduced length and mass.
6. The improved piston, according to claim 1, in with the top piston ring accommodated in top groove is of trapezoidal cross section called as 'keystone ring' for avoiding ring sticking to piston, minimizing
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building-up of combustion residues and to withstand high working temperature.
7. The improved piston, according to claim 1, in which the volume of reentrant cavity is 40.8 cc.
8. The improved piston for diesel engine substantially as herein described and illustrated in Figures 2, 2 A and 2B of the accompanying drawings.
9. The diesel engine incorporated with an improved piston as claimed in any of the above claims 1 to 8, having improved emission charactersties.

Dated this 27th day of March, 2006.

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