Method and system for exhaust heat recovery

Patent metadata

Field	Value
Publication number	US-10330033-B2
Application number	US-201615367038-A
Country	US
Kind code	B2
Filing date	Dec 1, 2016
Priority date	Dec 1, 2016
Publication date	Jun 25, 2019
Grant date	Jun 25, 2019

Abstract

Methods and systems are provided for exhaust gas heat recovery using a bottoming cycle comprising an exhaust heat exchanger. In one example, a method may include maintaining a target thermal energy input to the heat exchanger by opportunistically flowing exhaust through the heat exchanger after storing a portion of thermal energy from the exhaust in a thermal storage device or prior to flowing exhaust through the heat exchanger, heating the exhaust by drawing thermal energy from the thermal storage device.

First claim

The invention claimed is:

1. A method for an engine, comprising:
in response to an exhaust thermal energy being higher than a first threshold, flowing exhaust through a heat exchanger to maintain a target thermal energy input to the heat exchanger after storing a portion of the thermal energy at a thermal energy storage device upstream of the heat exchanger; and
in response to the exhaust thermal energy being lower than a second threshold, flowing exhaust through the heat exchanger to maintain the target thermal energy input to the heat exchanger after drawing thermal energy from the thermal energy storage device, the first threshold being higher than the second threshold.

2. The method of claim 1 , wherein the exhaust thermal energy is determined as a function of exhaust temperature and exhaust flow-rate.

3. The method of claim 1 , wherein the heat exchanger is included in a bottoming cycle, the cycle further comprising an expander, a condenser, a pump, and a battery coupled to the expander, and wherein flowing exhaust through the heat exchanger includes transferring heat from the exhaust to a working fluid of the bottoming cycle at the heat exchanger.

4. The method of claim 3 , wherein each of the first and the second threshold are based on a parameter of the bottoming cycle, the parameter including a pressure drop across the expander, a nature of the working fluid, and a temperature of the working fluid.

5. The method of claim 1 , further comprising, when exhaust thermal energy is between the first threshold and the second threshold, flowing exhaust to the heat exchanger via a bypass passage, while bypassing the thermal storage device.

6. The method of claim 1 , wherein, when exhaust thermal energy is higher than the first threshold, flowing exhaust through the heat exchanger includes flowing a first portion of exhaust directly to the heat exchanger, bypassing the thermal storage device, and concurrently flowing a second portion of exhaust to the heat exchanger via the thermal storage device, wherein the portion of thermal energy stored in the thermal storage device is derived from the second portion of exhaust.

7. The method of claim 1 , further comprising, when exhaust thermal energy is lower than the second threshold:
during a first condition, recirculating a portion of exhaust from downstream of the heat exchanger to upstream of the thermal storage device, mixing the recirculated exhaust with exhaust generated by the engine to form a combined exhaust flow, heating the combined exhaust flow by drawing thermal energy from the thermal storage device, and then flowing the combined exhaust flow through the heat exchanger; and
during a second condition, drawing in ambient air via a blower coupled to a vent line, routing the ambient air to upstream of the thermal storage device, mixing the ambient air with exhaust generated by the engine to form the combined exhaust flow, heating the combined exhaust flow by drawing thermal energy from the thermal storage device, and then flowing the combined exhaust flow through the heat exchanger.

8. The method of claim 7 , wherein the thermal storage device includes a phase change material, wherein storing thermal energy includes transitioning the phase change material from a solid phase to a liquid phase, and wherein discharging thermal energy includes transitioning the phase change material from the liquid phase to the solid phase.

9. The method of claim 7 , wherein the first condition includes a lower than second threshold thermal energy due to a lower than threshold exhaust temperature and a higher than threshold exhaust flow-rate, and the second condition includes a lower than second threshold thermal energy due to a higher than threshold exhaust temperature and a lower than threshold exhaust flow-rate.

10. The method of claim 7 , wherein the portion of exhaust recirculated from downstream of the heat exchanger to upstream of the thermal storage device is based on a difference between the exhaust thermal energy and the second threshold, the portion increased with an increase in the difference between the exhaust thermal energy and the second threshold, the portion of exhaust increased by increasing an opening of a recirculation valve coupled to a recirculation passage.

11. The method of claim 10 , wherein an amount of ambient air drawn in via the blower is based on the difference between the exhaust thermal energy and the second threshold, the amount increased as the difference between the exhaust thermal energy and the second threshold increases, the amount of ambient air drawn increased by increasing one or more of an opening of a vent valve and an output of the blower.

12. The method of claim 1 , further comprising, during an engine cold-start, independent of the exhaust thermal energy, flowing exhaust directly to the heat exchanger, bypassing the thermal storage device.

13. An engine method comprising:
during a first condition, storing thermal energy from at least a portion of exhaust at a thermal energy storage device, and then flowing exhaust through a heat exchanger; and
during a second condition, recirculating a portion of exhaust from downstream of the heat exchanger to upstream of the thermal storage device, drawing thermal energy into the exhaust from the thermal storage device before flowing the exhaust through the heat exchanger;
wherein, during each of the first and second conditions, a thermal input from the exhaust into the heat exchanger is maintained.

14. The method of claim 13 , further comprising, during a third condition, increasing exhaust flow-rate through the heat exchanger by drawing ambient air into the exhaust, upstream of the thermal storage device, mixing the ambient air with the exhaust, and then flowing an air-exhaust mixture through the heat exchanger, wherein the thermal input is also maintained in the third condition.

15. The method of claim 14 , wherein the first condition includes a higher than first threshold exhaust thermal energy, the second condition includes a lower than second threshold exhaust thermal energy and a lower than threshold exhaust temperature, and the third condition includes a lower than second threshold exhaust thermal energy and a lower than threshold exhaust flow-rate, wherein the exhaust thermal energy is based on each of an exhaust temperature and an exhaust flow-rate, the exhaust thermal energy increasing with an increase in at least one of the exhaust temperature and the exhaust flow-rate, and wherein maintaining the thermal input includes maintaining the exhaust thermal energy within the first and second threshold exhaust thermal energies, wherein the first threshold is higher than the second threshold.

16. The method of claim 13 , further comprising, during a fourth condition, when the exhaust thermal energy is between the first and second thresholds, flowing exhaust to the heat exchanger while bypassing the thermal storage device.

17. The method of claim 13 , wherein, during exhaust flow through the heat exchanger, thermal energy is transferred to an organic fluid circulating through the heat exchanger, electrical energy is generated from the thermal energy via a bottoming cycle including the heat exchanger, and the electrical energy is stored in a battery coupled to an expander of the bottoming cycle.

18. An engine system coupled to a vehicle, comprising:
an engine intake manifold;
an engine exhaust system including an exhaust temperature sensor and an exhaust pressure sensor coupled to a main exhaust passage, a bypass passage coupled to the maintain exhaust p

Assignees

• Ford Global Tech Llc

Inventors

• Hussain Quazi Ehtesham

Classifications

• F01N5/02 Primary

  the devices using heat · CPC title

• F02D41/064

  at cold start (F02D41/067 takes precedence) · CPC title

• F01N2240/02

  a heat exchanger · CPC title

• F02D41/1448

  the characteristics being an exhaust gas pressure · CPC title

• F02D41/1446

  the characteristics being exhaust temperatures · CPC title