Exhaust system and method of operating the same

1 . A system comprising:

an exhaust discharge line configured to receive exhaust gases from an engine;

a first junction disposed at a first location along the exhaust discharge line;

a second junction disposed at a second location along the exhaust discharge line downstream of the first location and fluidically coupled to a tailpipe;

an after-treatment system disposed between the first junction and the second junction, the after-treatment system configured to reduce pollutants comprising Nitrogen Oxides (NOx) in the exhaust gases from the engine using a catalytic converter;

an exhaust recirculation line fluidically coupled to the first junction and the second junction of the exhaust discharge line,

a pressurized exhaust storage tank disposed along the exhaust recirculation line;

a first control valve disposed in the exhaust discharge line downstream of the second junction;

a second control valve disposed in the exhaust recirculation line between the second junction and the pressurized exhaust storage tank;

a third control valve disposed in the exhaust recirculation line between the pressurized exhaust storage tank and the first junction;

wherein each of the first control valve, the second control valve, and the third control valve comprise butterfly valves having an aperture of configurable diameter occupying a state inclusively between open and closed; and

an electronic control unit (ECU) comprising a memory and at least one processor, where the ECU is communicatively coupled to the after-treatment system, the first control valve, the second control valve, and the third control valve, and the processor is configured to execute commands stored on the memory comprising:

executing a filling phase by at least partially closing the first control valve, opening the second control valve, and closing the third control valve to accumulate a portion of the exhaust gases in the pressurized exhaust storage tank, thereby increasing a tank pressure of the pressurized exhaust storage tank, and increasing a system pressure of the after-treatment system and pressure heating the catalytic converter,

determining, with a pressure sensor, whether the tank pressure exceeds a predetermined pressure threshold,

ending the filling phase by at least partially closing the second control valve and at least partially opening the first control valve, while maintaining the tank pressure, in response to the determination that the tank pressure exceeds the predetermined pressure threshold,

measuring a temperature of the catalytic converter,

determining a maximum predicted conversion capacity of the after-treatment system based, at least in part, on the temperature of the catalytic converter,

determining whether the temperature of the catalytic converter exceeds a light-off temperature of the catalytic converter, and

opening the third control valve to release the portion of exhaust gases in response to the determination that the temperature of the catalytic converter exceeds the light-off temperature,

wherein the third control valve is opened to an aperture that provides a flow rate across a predetermined unit of time less than or equal to the maximum predicted conversion capacity of the after-treatment system.

2 . The system of claim 1 , wherein opening the third control valve, the processor executes a recirculation phase by:

partially opening the third control valve in response to the determination that the temperature of the catalytic converter is less than the light-off temperature; and

circulating the portion of exhaust gases stored in the pressurized storage tank through the exhaust recirculation line and through the after-treatment system;

wherein circulating the portion of exhaust gases further pressure-heats the catalytic converter due to a gas pressure of the portion of exhaust gases.

3 . The system of claim 1 , wherein the maximum predicted conversion capacity is determined using a computational model of the after-treatment system, wherein the computational model of the after-treatment system is defined by a set of after-treatment parameters comprising a size of the catalytic converter.

4 . The system of claim 1 , wherein the predetermined unit of time is an average amount of time required for exhaust gases to traverse the after-treatment system.

5 . The system of claim 3 , wherein the set of after-treatment parameters further comprises an expected chemical composition of the exhaust gases.

6 . The system of claim 1 , wherein the after-treatment system comprises:

an oxidation catalyst configured to oxidize carbon monoxide (CO) in the exhaust gases;

a particulate filter configured to remove soot from the exhaust gases; and

a selective catalytic reduction (SCR) catalyst configured to convert the NOx in the exhaust gases in Nitrogen (N) and water (H 2 O).

7 . The system of claim 1 , wherein the engine is a component of a light-duty vehicle and has a volume within 20% of 2 L, inclusively.

8 . The system of claim 7 , wherein the pressurized exhaust storage tank has a volume within 20% of 37.5 L, inclusively, and the predetermined pressure threshold is 2 bar.

9 . The system of claim 1 , wherein the processor is further configured to:

obtain an engine temperature from an engine temperature sensor;

compare the engine temperature to an engine temperature threshold; and

execute the commands in response to the engine temperature being lower than the engine temperature threshold.

10 . The system of claim 9 , wherein the processor is further configured to execute the commands in response to the engine temperature being greater than the engine temperature threshold.

11 . A method comprising:

executing a filling phase by:

receiving exhaust gas from an engine at a first junction disposed at a first location of an exhaust discharge line,

transporting the exhaust gas through an after-treatment system disposed downstream of the first junction and to a second junction, wherein the second junction is disposed at a second location of the exhaust discharge line downstream of the after-treatment system,

at least partially closing a first control valve disposed downstream of the second junction to direct the exhaust gas away from a tailpipe and towards an exhaust recirculation line fluidically coupled to the first junction and the second junction of the exhaust discharge line, wherein the exhaust recirculation line comprises a pressurized exhaust storage tank,

opening a second control valve disposed between the second junction and the pressurized exhaust storage tank,

closing a third control valve disposed between the pressurized exhaust storage tank and the first junction,

wherein each of the first control valve, the second control valve, and the third control valve comprise butterfly valves having an aperture of configurable diameter occupying a state inclusively between open and closed,

accumulating a portion of exhaust gases in the pressurized exhaust storage tank thereby increasing a tank pressure of the pressurized exhaust storage tank, increasing a system pressure of the after-treatment system, and pressure heating a catalytic converter, and

determining, with a pressure sensor, whether the tank pressure exceeds a predetermined pressure threshold,

ending the filling phase by:

at least partially closing the second control valve and at least partially opening the first control valve, while maintaining the tank pressure, in response to the determination that the tank pressure exceeds the predetermined pressure threshold;

obtaining a temperature of the catalytic converter using an after-treatment system temperature sensor,

determining a maximum predicted conversion capacity of the after-treatment system based, at least in part, on the temperature of the catalytic converter,

determining whether the temperature of the catalytic converter exceeds a light-off temperature of the catalytic converter, and

opening the third control valve to release the portion of exhaust gases in response to the determination that the temperature of the catalytic converter exceeds the light-off temperature,

wherein the third control valve is opened to an aperture that provides a flow rate across a predetermined unit of time less than or equal to the maximum predicted conversion capacity of the after-treatment system.

12 . The method of claim 11 , further comprising executing a recirculation phase by:

partially opening the third control valve in response to the determination that the temperature of the catalytic converter is less than the light-off temperature; and

circulating the portion of exhaust gases stored in the pressurized storage tank through the exhaust recirculation line and through the after-treatment system;

wherein circulating the portion of exhaust gases further pressure-heats the catalytic converter due to a gas pressure of the portion of exhaust gases.

13 . The method of claim 11 , wherein the maximum predicted conversion capacity is determined using a computational model of the after-treatment system, wherein the computational model of the after-treatment system is defined by a set of after-treatment parameters comprising a size of the catalytic converter.

14 . The method of claim 13 , wherein the set of after-treatment parameters further comprises an expected chemical composition of the exhaust gas.

15 . The method of claim 11 , wherein the after-treatment system comprises:

an oxidation catalyst configured to oxidize carbon monoxide (CO) in the exhaust gases;

a particulate filter configured to remove soot from the exhaust gases; and

a selective catalytic reduction (SCR) catalyst configured to convert NOx in the exhaust gases into Nitrogen and water.

16 . The method of claim 11 , wherein the engine is a component of a light-duty vehicle and has a volume within 20% of 2 L, inclusively.

17 . The method of claim 16 , wherein the pressurized exhaust storage tank has a volume within 20% of 37.5 L, inclusively and the predetermined pressure threshold is 2 bar.

18 . The method of claim 13 , wherein the first control valve, the second control valve, and the third control valve are opened and closed according to commands from an electronic control unit (ECU) comprising a processor and a memory, wherein the commands are stored on the memory.

19 . The method of claim 11 , further comprising:

obtaining an engine temperature from an engine temperature sensor;

comparing the engine temperature an engine temperature threshold; and

adjusting the states of the first control valve, the second control valve, and the third control valve in response to the engine temperature being lower than the engine temperature threshold.

20 . The method of claim 19 , wherein the states of the first control valve, the second control valve, and the third control valve are adjusted in response to the engine temperature being greater than the engine temperature threshold.