CLIAMS:We claim:
1. A diesel oxidation catalyst (10) in an exhaust gas after treatment device , said diesel oxidation catalyst (10) comprising :
at least two sections (12,14) adapted to oxidize a plurality of diesel particles;
said at least two sections (12, 14) is connected upstream of a diesel particulate filter;
one said section (12) will have lower cells per square inch and an another said section (14) will have higher cells per square inch.
2. An exhaust gas after treatment device (20) in a vehicle, said exhaust gas after treatment device (20) comprising :
an inlet (24) adapted to allow an exhaust gas; a diesel particulate filter (22) adapted to oxidize a plurality of diesel particles present in said exhaust gas;
said exhaust gas after treatment device (20) characterized in:
a diesel oxidation catalyst (10) comprising atleast two sections (12,14), one said section (12) will have lower cells per square inch and an another said section (14) will have higher cells per square inch.
3. An exhaust gas after treatment system (30) comprising :
an exhaust passage (34) adapted to allow an exhaust gas flow from an engine cylinder (32); and
a exhaust gas after treatment device (20) comprising a diesel particulate filter (22);
said exhaust gas treatment system (30) characterized in:
said exhaust gas after treatment device (20) comprising a diesel oxidation catalyst (10), said diesel oxidation catalyst (10) comprising atleast two sections (12, 14) adapted to oxidize a plurality of diesel particles present in said exhaust gas.
4. The exhaust gas after treatment system claimed in claim (3), said temperature to oxidize said plurality of diesel particles can be achieved by post injecting a fuel in said engine cylinder (32).
,TagSPECI:Field of the invention
[001] This invention relates to a diesel oxidation catalyst in an exhaust gas after treatment device.
Background of the invention
[002] Exhaust gases discharged from diesel engines are one of the major source for air pollution. The main pollutants from diesel engines include fine soot particulates, hydrocarbons, carbon monoxide, soluble organic solvents, and nitrogen oxides. Soot removal in diesel engine exhaust is achieved most effectively through the use of a filter called Diesel Particulate Filter. Continuously Regenerated Traps (Diesel particulate filters) works on the principle of retaining soot particles within a ceramic or silicon carbide filter which collects the soot particles within porous walls of the honeycomb structure of the filter. The accumulation of this soot within the surface of the filter increases the back pressure of the filter, which then requires the filter to be regenerated. When the temperature reaches above around 400°C, the component of oxygen in exhaust gas stream reacts with the soot creating an exothermic reaction which increases the temperature inside the filter to over 600°C and the soot is oxidized at a very high rate and burnt away forming Carbon dioxide. The temperature of the exhaust gas is very critical for the regeneration process. In most widely used applications with single section of diesel oxidation catalyst with optimum cells per square inch, diesel soot particulates tend to accumulate on its frontal area due to less exhaust temperatures of around 150°C – 350°C.
[003] A DE Patent application 20102007021468 discloses a procedure for the production of filters for removing soot particulates from exhaust gas of an internal combustion engine. The particles have a maximum extension of 200 nm and a ratio of maximum to minimum expansion of 1-20. The particles exist in the form of chopstick, leaf, pane or its combination and are adhered with one another.

Brief description of the accompanying drawings
[004] An exemplifying embodiment of the invention is disclosed in detail in the description and illustrated in the accompanying drawings:
[005] Figure 1 illustrates a block diagram of a diesel oxidation catalyst diesel oxidation catalyst according to one embodiment of the invention;
[006] Figure 2 illustrates a block diagram of a exhaust gas after treatment device according to one embodiment of the invention; and
[007] Figure 3 illustrates a block diagram of an exhaust gas after treatment system according to one embodiment of the invention.
Detailed description of the invention:
[008] Figure 1 illustrates a block diagram of a diesel oxidation catalyst 10 for a diesel particulate filter according to one embodiment of the invention. The diesel oxidation catalyst 10 comprises at least two sections (12, 14) adapted to oxidize a plurality of diesel particles. The atleast two sections (12, 14) are connected upstream of an exhaust gas after treatment device (not shown). One section 12 will have lower cells per square inch and an another section 14 will have higher cells per square inch.

[009] Figure 2 illustrates a exhaust gas after treatment device 20 according to one embodiment of the invention. The exhaust gas after treatment device 20 including 20 comprises an inlet 24 adapted to allow an exhaust gas. A diesel particulate filter 22 adapted to filter a plurality of diesel particles present in the exhaust gas. The exhaust gas after treatment device 20 comprises a diesel oxidation catalyst 10 comprising atleast two sections (12, 14), one section 12 will have lower cells per square inch and an another section 14 will have higher cells per square inch.

[0010] Figure 3 illustrates an exhaust gas treatment system 30 in a vehicle according to one embodiment of the invention. The exhaust gas treatment system 30 comprises an exhaust passage 34 adapted to allow an exhaust gas flow from an engine cylinder 32. The exhaust gas treatment system 30 comprises an exhaust gas after treatment device 20. The exhaust gas after treatment device 20 comprises a diesel oxidation catalyst 10 comprising atleast two sections (12, 14) adapted to oxidize a plurality of diesel particles present in the exhaust gas.

[0011] The plurality of diesel particles comprises a plurality of diesel soot particles and a plurality of diesel fuel particles. The first section 12 of the diesel oxidation catalyst 10 will have a low probability of forming of the soot due to lower cells per square inch area. Due to lesser cells per square inch of the first section 12 which offer low surface area against the inflowing exhaust gas. There is a very low probability of forming diesel soot particle in front of the first section 12 and due to higher cells per square inch of the second section 14, probability of majority of diesel soot particles getting accumulated will be more. The diesel oxidation catalyst 10 oxidizes the plurality of diesel soot particles resulting from combustion of diesel fuel in the engine cylinder 34 to prevent their release into the atmosphere. During a normal working condition of the vehicle, the diesel particulate filter 22 in the exhaust gas after treatment device 20 filters the plurality of a diesel soot particles present in the exhaust gas and the filtered plurality of diesel soot particles will be accumulated in the diesel particulate filter 22. The plurality of diesel soot particles passes through the diesel oxidation catalyst 10 and gets oxidized within the diesel oxidation catalyst 10 during a regeneration process. Due to the flow of the plurality of diesel soot particles through the cells of the diesel oxidation catalyst 10, the cells will be blocked progressively forming a soot. The collected plurality of diesel soot particles would eventually cause a high exhaust gas pressure drop in the diesel particulate filter 20, which would negatively affect the operation of the engine 32. The temperature at the frontage of the diesel oxidation catalyst 10 will vary in between 200-350 degrees. Due to lower operating exhaust temperatures produced from the engine cylinder 32, the plurality of diesel soot particles tends to accumulate progressively at the frontage of diesel oxidation catalyst 10 blocking the path for the exhaust gas to flow through the diesel oxidation catalyst 10 and also to decreases a hydrocarbon conversion efficiency of diesel oxidation catalyst 10 resulting in a hydrocarbon slip.
[0012] The method of working of the exhaust gas after treatment device 20 in the exhaust gas after treatment system 30 according to one embodiment of the invention, the plurality of diesel soot particles present in the exhaust gas flows through the exhaust passage 34 and will be accumulated in the diesel oxidation catalyst 10. The diesel particulate filter 22 which is connected upstream of the diesel oxidation catalyst 10 filters the plurality of diesel soot particles and avoids the plurality of diesel soot particles emitting into the atmosphere. Due to the accumulation of the plurality of diesel soot particles at the cells of the diesel oxidation catalyst 10, the exhaust gas after treatment device 20 will be clogged .In order to avoid the clogging of the exhaust gas after treatment device 20, the plurality of diesel soot particles is oxidized in the diesel oxidation catalyst 10. The first section 12 of diesel oxidation catalyst 10 which has lower cells per square inch allows a large amount of diesel soot particles generated in engine cylinder 32 to pass through the diesel oxidation catalyst 10 and not getting accumulated at the diesel oxidation catalyst section 12 frontal area, thus by avoiding the diesel soot particles from blocking the cells of the first section 12 of diesel oxidation catalyst 10. The temperature at the first section 12 will not be sufficient to oxidize the diesel particles. The second section 14 which has higher cells per square inch has higher surface area exposed against the inflowing exhaust gases, oxidizes the diesel particles that are entering into the diesel particulate filter 22. Since, frontal area and cells of the first section 12 of diesel oxidation catalyst 10 will not allow having soot accumulated cells of the first section 12 helps in oxidizing the diesel fuel particles present in the exhaust gas. For oxidation of diesel soot particles which is accumulated at second section 14 due to the higher cells per square inch and in diesel particulate filter 22 the temperature is increased the temperature to more than 550°C in the diesel oxidation catalyst 10. After the main injection of the fuel in the engine cylinder 32, the exhaust gas flows into the diesel oxidation catalyst 10 and the diesel particulate filter 22 filters the plurality of diesel soot particles present in the exhaust gas. The diesel fuel is post injected into the engine cylinder 32. A post injection of the diesel fuel is the injection occurring near to the end of a power stroke after the main injection. The post injected fuel produces higher combustion temperatures in the diesel oxidation catalyst 10 thereby increasing the temperature of the exhaust that passes into the diesel particulate filter 22. Due to the post injection of the diesel fuel, the diesel fuel particles gets oxidized in diesel oxidation catalyst 10 and increases the temperature of the diesel oxidization catalyst 10. The post injection of diesel fuel will occur when there is no normal combustion in the engine cylinder 32. The post injection will be done after 145degrees of top dead center. The post injected fuel creates a post combustion before a normal combustion occurrence. Due to the increase in the temperature, diesel soot particles accumulated is oxidized for a predefined time period. The temperature of the exhaust passing the diesel oxidation catalyst 10 will reach approximately 600 °C. A regeneration process will be initiated for the predefined time period by an oxidization sensor (not shown) when the accumulated diesel soot particles reaches a threshold level. The diesel fuel is injected again into the engine cylinder 22 to have the post combustion. The plurality of diesel particles present in the exhaust gas will pass through the first section 12 and due to the higher temperature at the second section 14, the plurality of diesel particles are oxidized. The plurality of diesel particles is oxidized by an exothermal process. The exothermal process is a chemical reaction that releases energy in the form of a heat. The organic compounds present in the fuel react with an oxidizing element to have combustion in the engine cylinder 22. Due to this reaction, the heat is developed and the temperature of the exhaust gas passing the diesel oxidation catalyst 10 increases. The increased temperature in the diesel oxidation catalyst 10 oxidizes the plurality of diesel particles.
[0013] With the diesel oxidation catalyst 10 present in the diesel particulate filter 22 disclosed above, a greater than 85 percentage of reductions can be achieved in the emissions. With the combustion of the collected plurality of diesel particles and reducing to ash during regeneration process, effectively unblocks the pores of the diesel oxidation catalyst 10 and decreases exhaust backpressure.
[0014] It must be understood that the examples and embodiments of the components explained in the detailed description are only illustrative and do not limit the scope of the invention. The scope of this invention is only limited by the scope of the claims.