DESC:TECHNICAL FIELD
The present invention relates to controlling the engine exhaust gas temperature suitable for improving the Selective Catalytic Reduction (SCR) catalysts efficiency. More particularly, the present invention relates to improving the NOx conversion efficiency by controlling the exhaust gas temperature after the turbocharger ie, NOx conversion efficiency will be improved without affecting the engine performance.
BACKGROUND
Due to growing environmental issues related to clean air policy all over the world, the leading diesel engine manufacturers are manufacturing the engines to meet stringent emission regulation. In order to control the engine emission pollutants like NOx (Oxides of Nitrogen), PM (Particulate Matter), CO (Carbon Monoxide), un-burnt HC (Hydro Carbon) etc, adaptation of EGR (Exhaust Gas Recirculation), after treatment systems like SCR, DOC (Diesel Oxidation Catalyst), DPF (Diesel Particulate Filter) etc., are become inevitable in diesel engine emission reduction.
Emission Norms notified by Govt. of India for the Construction Equipment Vehicles (CEV) is shown below.
Pollutants\Emission Level
BS-III (CEV) (g/kWh)
BS-IV (CEV) (g/kWh)
% reduction
Nox
4.0
0.4
90 (approx.)
HC
0.19
CO
3.5
3.5
0
PM
0.2
0.025
87.5
Table: 1 Emission reduction % from BS-III (CEV) to BS-IV (CEV)
As illustrated in the above table, the reduction of engine emission within the cylinder become more stringent from BS-III to BS-IV ie approximately 90% of NOx reduction and 87.5% of PM reduction. Hence, there is a strong desire to extract maximum
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conversion efficiency from the exhaust gas after treatment systems like SCR, DOC, DPF etc., with less operating cost.
1. DOC is utilized to reduce HC, CO and to oxidize NO to NO2.
2. DPF is utilized to trap particulate matter (PM) from the engine and it will oxidize those particulate matter when the temperature is about 550°C ie. Passive Regeneration. Also SCR catalyst needs to be protected from the high temperature.
3. SCR is utilized to reduce NOx (Oxides of Nitrogen) emission by injecting AUS32 (Aqueous Urea Solution) in the exhaust pipe before the SCR catalyst. AUS32 will undergo thermal decomposition and hydrolysis process and convert into NH3 molecules. This NH3 will react with NOX in the SCR catalyst and reduce into N2 and H2O molecules and the reactions are shown below,
NH-CO-NH2 (aq) + H2O (gas) ? 2NH3 (gas) + CO2 (gas)..........equ.1
4NH3 + 4NO + O2 ? 4N2 + 6H2O.............................................equ.2
2NO + 2NO2+ 4NH3 ? 4N2 + 6H2O..........................................equ.3
The above equations depend on temperature of the exhaust gas, because catalyst material will thermal deactivate above certain temperature, for ex: Vanadium based catalyst will undergo thermal deactivation and loss in NOx conversion above 550°C. During the engine test trial with vanadium catalyst, it is observed that, the NOx conversion efficiency is depends on the exhaust gas temperature.
Graph: 1 NOx conversion
0.9
0.92
0.94
0.96
0.98
1
250
300
350
400
450
500
550
%
Catalyst In temp (deg C)
NOx conversion
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Graph: 2 Urea Consumption
The above Graph:2 indicates the percentage of Urea consumption with respect to fuel consumption Vs Catalyst inlet temperature.
Note: The above two chart data is taken from in-house test result of BEML make 15.24L capacity diesel engine with Vanadium based SCR catalyst.
From Graph:1 & 2, it is found that Vanadium based catalyst will have maximum conversion efficiency at the exhaust gas temperature between 300°C to 450°C with optimum Urea consumption. If the temperature is maintained at this desired level, the NOx conversion efficiency will be maximum with the optimum Urea consumption.
However in the diesel engine, the exhaust gas temperature will be more than 450°C in the maximum load region and during DPF (Diesel Particulate Filter) regeneration. At this condition, achieving the NOx level as per the regulated norms is very difficult and the consumption of urea will also be high.
"Hence the engine exhaust gas shall be maintained between 300°C to 450°C by the coolant with controlled flow when the temperature is crossing the desired level and the flow of coolant is controlled by electronic valve which will be operated in the closed loop system".
The engines as existing in the prior art are not capable of maintaining the desired level of exhaust gas temperature after turbocharger for achieving the required emission levels as is required by the regulated norms.
0
2
4
6
8
250
300
350
400
450
500
550
%
Catalyst In temp (deg C)
Urea consumption
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OBJECTIVE
The primary objective of the present invention is to achieve better NOx conversion efficiency of SCR catalyst to reduce oxides of nitrogen.
Yet another objective of the present invention is to reduce the consumption of urea for the process of Selective Catalytic Reduction (SCR).
Yet another objective of the present invention is to avoid the damage or thermal cracking of the SCR catalyst by higher exhaust gas temperature and improve the life of the catalyst.
The instant invention achieves the objective by reducing the exhaust gas temperature after turbocharger to the desired level by using engine coolant in a closed loop system without affecting the engine performance.
SUMMARY
According to the present invention, the temperature of the engine exhaust gas is controlled as suitable for the Selective Catalytic Reduction (SCR) catalysts in order to achieve better conversion efficiency for NOx reduction and to safeguard the SCR catalyst during Diesel Particulate Filter (DPF) regeneration. The exhaust gas temperature is controlled by passing the engine coolant over the exhaust gas pipe before the entry into the SCR catalyst. The flow of the coolant is controlled by an electronic control valve. Since the exhaust gas temperature is controlled after the turbocharger the engine performance will not have any implication.
According to a preferred embodiment of the invention, the said engine is provided with exhaust gas conditioner that comprises of an exhaust pipe with the provision for engine coolant.
According to another preferred embodiment of the present invention, the flow of the engine coolant to the exhaust gas conditioner is controlled by an electronic control valve.
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According to yet another preferred embodiment of the present invention, the said engine is provided with an Electronic Control Unit (ECU) that operates the valve as per the temperature signal-closed loop.
BRIEF DESCRIPTION OF THE DRAWINGS
The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings.
Fig. 1 illustrates the overview of the proposed system layout on the engine
Component Description:
? Heat Exchanger: Exhaust pipe with provision for coolant flow.
? Electronically Controlled valve: Coolant flow control to the exhaust gas cooler.
? Temperature Sensor: to measure the temperature before the catalyst.
? ECU: Electronic Control Unit to control the water flow valve based on the temperature input.
Present invention relays to controlling of engine exhaust gas temperature to achieve higher NOx conversion efficiency from SCR catalyst in which the temperature of the engine exhaust gas is controlled as suitable for the Selective Catalytic Reduction (SCR) catalysts in order to achieve better conversion efficiency for NOx reduction and to safeguard the SCR catalyst during Diesel Particulate Filter (DPF) regeneration wherein the exhaust gas temperature is controlled by passing the engine coolant over the exhaust gas pipe (6) before the entry into the SCR catalyst and the flow of the coolant is controlled by an electronic control valve (2).
According to a preferred embodiment of the invention the said engine is provided with exhaust gas conditioner that comprises of an exhaust pipe with the provision for engine coolant.
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According to a preferred embodiment of the invention the flow of the engine coolant to the exhaust gas conditioner is controlled by an electronic control valve (2).
According to yet another preferred embodiment of the present invention, the said engine is provided with an Electronic Control Unit (ECU) (4) that operates the valve as per the temperature signal-closed loop.
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-discussed embodiments may be used in combination with each other. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description.
The benefits and advantages which may be provided by the present invention have been described above with regard to specific embodiments. These benefits and advantages, and any elements or limitations that may cause them to occur or to become more pronounced are not to be construed as critical, required, or essential features of any or all of the embodiments.
While the present invention has been described with reference to particular embodiments, it should be understood that the embodiments are illustrative and that the scope of the invention is not limited to these embodiments. Many variations, modifications, additions and improvements to the embodiments described above are possible. It is contemplated that these variations, modifications, additions and improvements fall within the scope of the invention. ,CLAIMS:
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WE CLAIM:
1. Controlling of engine exhaust gas temperature to achieve higher NOx conversion efficiency from SCR catalyst wherein the system is comprising of heat exchanger (1) having exhaust pipe with provision for coolant flow, electronically controlled valve (2) for coolant flow control to the exhaust gas cooler, temperature Sensor (3) to measure the temperature before the catalyst (5), electronic control unit (4) to control the water flow valve based on the temperature input.
2. Controlling of engine exhaust gas temperature to achieve higher NOx conversion efficiency from SCR catalyst as claimed in claim 1 in which the temperature of the engine exhaust gas is controlled as suitable for the Selective Catalytic Reduction (SCR) catalysts in order to achieve better conversion efficiency for NOx reduction and to safeguard the SCR catalyst during diesel particulate filter (DPF) regeneration wherein the exhaust gas temperature is controlled by passing the engine coolant over the exhaust gas pipe (6) before the entry into the SCR catalyst and the flow of the coolant is controlled by an electronic control valve (2).
3. Controlling of engine exhaust gas temperature to achieve higher NOx conversion efficiency from SCR catalyst as claimed in claim 2 wherein the said engine is provided with exhaust gas conditioner that comprises of an exhaust pipe with the provision for engine coolant.
4. Controlling of engine exhaust gas temperature to achieve higher NOx conversion efficiency from SCR catalyst as claimed in claim 3 wherein the flow of the engine coolant to the exhaust gas conditioner is controlled by an electronic control valve (2).
5. Controlling of engine exhaust gas temperature to achieve higher NOx conversion efficiency from SCR catalyst as claimed in any of the preceding claim wherein said engine is provided with an Electronic Control Unit (ECU) (4) that operates the valve as per the temperature signal-closed loop.
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6. Controlling of engine exhaust gas temperature to achieve higher NOx conversion efficiency from SCR catalyst as claimed in any of the preceding claim wherein said engine performance will not be disturbed/affected since the exhaust gas temperature is controlled after the turbocharger.