Reducing no.sub.x emissions from an engine by temperature-controlled urea injection for selective catalytic reduction

• US 6,063,350 A
• Filed: 10/13/1998
• Issued: 05/16/2000
• Est. Priority Date: 04/02/1997
• Status: Expired due to Term

• Current Assignee: Clean Diesel Technologies, Inc.
• Original Assignee: Clean Diesel Technologies, Inc.
• Inventors: Tarabulski, Theodore J., Valentine, James M., Knapper, Curtis J., Peter-Hoblyn, Jeremy D.
• Primary Examiner(s): DUNN, THOMAS G
• Application Number:
  US09/170,476
• Time in Patent Office: 581 Days
• Field of Search: 423/212, 423/235, 423/239.1
• US Class Current: 423/239.1
• CPC Class Codes: B01D 2251/2067 Urea
• CPC Class Codes: B01D 53/90 Injecting reactants
• CPC Class Codes: B01D 53/9431 Processes characterised by a specific device
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• CPC Class Codes: F01N 11/00 Monitoring or diagnostic devices for exhaust-gas treatment apparatus , e.g. for catalytic activity safety, indicating or supervising devices for internal combustion engines F02B77/08; testing of machines G01M13/00
• CPC Class Codes: F01N 2550/05 Systems for adding substances into exhaust
• CPC Class Codes: F01N 2560/06 the means being a temperature sensor
• CPC Class Codes: F01N 2570/14 Nitrogen oxides
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 2610/03 the substance being hydrocarbons, e.g. engine fuel
• CPC Class Codes: F01N 2610/10 the substance being heated, e.g. by heating tank or supply line of the added substance
• CPC Class Codes: F01N 2610/14 Arrangements for the supply of substances, e.g. conduits
• CPC Class Codes: F01N 2610/1406 Storage means for substances, e.g. tanks or reservoirs
• CPC Class Codes: F01N 2610/146 Control thereof, e.g. control of injectors or injection valves
• CPC Class Codes: F01N 2610/1473 Overflow or return means for the substances, e.g. conduits or valves for the return path
• CPC Class Codes: F01N 2610/148 Arrangement of sensors
• CPC Class Codes: F01N 2900/0411 using a feed-forward control
• CPC Class Codes: F01N 2900/08 said parameters being related to the engine
• CPC Class Codes: F01N 2900/1811 Temperature
• CPC Class Codes: F01N 2900/1814 Tank level
• CPC Class Codes: F01N 3/2066 : Selective catalytic reduction [SCR]
• CPC Class Codes: F01N 3/208 : Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
• CPC Class Codes: Y02A 50/20 : Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02T 10/12 : Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 : Engine management systems

Abstract

A safe, reliable SCR system for reducing NO_x emissions from a lean-burn internal combustion engine utilizes urea in aqueous solution. A modular assembly is provided for mounting inside a urea reagent tank enables controlled feeding an aqueous urea solution to an injector. The assembly includes a reagent quality sensor, a reagent temperature sensor, a reagent level sensor and a pump.

Claims

1. A method for reducing the emissions of NO_x in an exhaust gas from a lean-burn engine, comprising:

monitoring the quality, temperature and level of urea solution in a storage vessel;

generating sensor signals representative of the quality, temperature and level of urea in the storage vessel;

comparing the sensor signals to reference values;

generating control signals representative of the results of the comparison;

responsive to the control signals, controlling the flow of urea solution to the exhaust gas; and

passing the exhaust gas through an SCR reactor.

2. A method according to claim 1, wherein other parameters, including pressure in the vessel and/or feed lines are also monitored and employed to facilitate control.

3. A method according to claim 1, wherein at least one of the control parameters is processed by a dedicated signal processor.

4. A method according to claim 1, wherein at least one of the control parameters is processed by a main engine control unit and comparisons made there are to a comprehensive engine parameter map.

5. A method according to claim 1, wherein a heater is provided within the storage vessel for temperature maintenance of the urea solution upon receiving control signals.

6. A method according to claim 1, wherein a return line is provided from the injector back to the storage vessel to maintain the temperature of the urea solution within predetermined limits.

7. A method according to claim 1, wherein a control signal is generated responsive to an excessively low temperature for the urea in the storage vessel starts a heater to maintain the temperature of the solution within a desired range.

8. A method according to claim 7, wherein the availability of battery power to run the heater is monitored and if it determined that insufficient battery power is available, injectors and feed lines will be drained to avoid freezing.

9. A method according to claim 8, wherein a warning to the operator is provided and control engine operation is controlled to maintain low NO_x levels without the use of reagent by exhaust gas recirculation, engine timing or derating to produce less power.

10. A method according to claim 1, wherein the quality of the urea solution is monitored and if it fails testing on one or more criteria, the injectors and feed lines will be drained to prevent operation with a defective solution.

11. A method according to claim 10, wherein responsive to a control signal representative of a defective solution, a warning is provided to the operator and engine operation is controlled to maintain low NO_x levels without the use of reagent, by exhaust gas recirculation, engine timing or derating to produce less power.