METHOD AND APPARATUS FOR UREA CONDITIONING AND INJECTION CONTROL IN A SELECTIVE CATALYTIC REDUCTION SYSTEM
An apparatus for conditioning an aqueous urea solution for injection in an engine exhaust treatment system, includes a urea solution conditioning tank having an inlet to receive an unconditioned urea solution and an outlet to deliver conditioned urea solution to an injection system, a sensor generating a signal indicating a concentration of urea in the tank, a heater for heating the urea solution in the tank and, an evaporation device for lowering the vapor pressure in the tank to remove evaporated water vapor from the tank.
1 . An apparatus for conditioning an aqueous urea solution for injection in an engine exhaust treatment system, comprising:
a urea solution conditioning tank having an inlet to receive an unconditioned urea solution and an outlet, and,
a device for removing water from the urea solution.
2 . The apparatus of claim 1 , wherein the device for removing water from the urea solution comprises a device for lowering a vapor pressure in the tank.
3 . The apparatus of claim 2 , wherein the device for lowering the vapor pressure includes a venturi tube connected by an evaporation line to the conditioning tank.
4 . The apparatus of claim 2 , wherein the device for removing water from the urea solution comprises a heater for heating the urea solution in the tank.
5 . The apparatus of claim 4 , comprising a sensor generating a signal indicating a concentration of urea in the tank and a controller connected to receive the signal and further connected and configured to control the heater and the device for lowering the vapor pressure in the tank.
6 . The apparatus of claim 5 , wherein the controller is configured and connected to control a flow of unconditioned urea solution to the conditioning tank.
7 . The apparatus of claim 5 , wherein the controller is configured to control the heater to maintain the solution in the conditioning tank at a temperature sufficiently high to prevent precipitation of urea out of the higher concentrated solution.
8 . The apparatus of claim 1 , wherein the device for removing water from the urea solution comprises a heater for heating the urea solution in the tank.
9 . The apparatus of claim 8 , wherein the device for removing water from the urea solution comprises a device for lowering a vapor pressure in the tank.
10 . The apparatus of claim 9 , wherein the device for lowering the vapor pressure includes a venturi tube connected by an evaporation line to the conditioning tank.
11 . The apparatus of claim 9 , comprising a sensor generating a signal indicating a concentration of urea in the tank and a controller connected to receive the signal and further connected and configured to control the heater and the device for lowering the vapor pressure in the tank.
12 . The apparatus of claim 8 , wherein the controller is configured to control the heater to maintain the solution in the conditioning tank at a temperature sufficiently high to prevent precipitation of urea out of the higher concentrated solution.
13 . The apparatus of claim 1 , comprising a sensor generating a signal indicating a concentration of urea in the tank and a controller connected to receive the signal and further connected and configured to control the device for removing water from the urea solution.
14 . The apparatus of claim 13 , wherein the controller is configured and connected to control a flow of unconditioned urea solution to the conditioning tank.
15 . The apparatus of claim 1 , comprising a pressure relief valve mounted on the tank.
16 . The apparatus of claim 1 , comprising a line connected to the tank to deliver pressurized air from a source on the vehicle.
17 . A method of conditioning aqueous urea solution for injection in a selective catalytic reduction system for an internal combustion engine exhaust, comprising the steps of:
storing aqueous urea solution in a supply tank at an initial urea concentration;
pumping a quantity of the aqueous urea solution from the supply tank to a conditioning tank; and,
removing water from the aqueous urea solution in the conditioning tank to increase a concentration of urea in the aqueous urea solution to a target concentration.
18 . The method of claim 17 , wherein the step of removing water comprises lowering a pressure in the conditioning tank and conducting evaporated water from the conditioning tank.
19 . The method of claim 17 , comprising heating the aqueous urea solution in the conditioning tank to evaporate water from the aqueous urea solution.
20 . The method of claim 17 , comprising heating the aqueous urea solution in the conditioning tank to maintain a temperature sufficient to avoid precipitation of urea from the solution.
21 . The method of claim 17 , comprising sensing a level of solution in the conditioning tank and responsive to sensing a threshold level, pumping a predetermined quantity of aqueous urea into the conditioning tank.
22 . The method as claimed in claim 17 , wherein the target concentration of urea in the conditioned aqueous urea solution is greater than 32.5% urea.
23 . The method of claim 17 , wherein the target concentration of urea in the conditioned aqueous urea solution is about 76.9% urea.
24 . The method of claim 17 , comprising determining a concentration of urea in the aqueous urea in the conditioning tank, and, adding unconditioned urea solution to the conditioning tank if the target concentration is exceeded by a predetermined amount.