Rankine cycle waste heat recovery system and method with improved egr temperature control

Abstract

A waste heat recovery (WHR) system and method for regulating exhaust gas recirculation (EGR) cooling is described. More particularly, a Rankine cycle WHR system and method is described, including an arrangement to improve the precision of EGR cooling for engine efficiency improvement and thermal management.

What is claimed is: 
     
         1 . An internal combustion engine, comprising:
 an exhaust gas recirculation (EGR) system containing an EGR gas; and   a waste heat recovery (WHR) system adapted to provide cooling to the EGR gas, the WHR system including a WHR circuit, an EGR temperature control circuit connected to the WHR circuit and positioned to receive working fluid from the WHR circuit downstream of the fluid containment portion and to return the working fluid to the WHR circuit upstream of the fluid containment portion, and a thermal control unit (TCU) positioned along the EGR temperature control circuit to cool the EGR gas.   
     
     
         2 . The internal combustion engine of  claim 1 , wherein the TCU is configured to controllably adjust a temperature of the EGR gas independent of a WHR function of the WHR system. 
     
     
         3 . The internal combustion engine of  claim 1 , further comprising an expansion valve positioned along the EGR temperature control circuit upstream of the TCU, the expansion valve operable to cause a pressure drop in the working fluid sufficient to cause the working fluid to change phase from a liquid to a gas. 
     
     
         4 . The internal combustion engine of  claim 3 , wherein the expansion valve is operable to:
 selectively decrease the flow rate of the working fluid so as to increase the pressure of the working fluid in the TCU, thereby increasing the phase change temperature of the working fluid to provide less cooling to the EGR gas; and   selectively increase the flow rate of the working fluid so as to decrease the pressure of the working fluid in the TCU, thereby decreasing the phase change temperature of the working fluid to provide more cooling to the EGR gas.   
     
     
         5 . The internal combustion engine of  claim 1 , further comprising a compressor positioned along the EGR temperature control circuit downstream of the TCU, the compressor operable to control a flow rate of the working fluid through the TCU so as to adjust the temperature of the EGR gas flowing through the TCU. 
     
     
         6 . The internal combustion engine of  claim 5 , wherein the compressor is operable to:
 selectively decrease the flow rate of the working fluid so as to increase the pressure of the working fluid in the TCU, thereby increasing the phase change temperature of the working fluid to provide less cooling to the EGR gas; and   selectively increase the flow rate of the working fluid so as to decrease the pressure of the working fluid in the TCU, thereby decreasing the phase change temperature of the working fluid to provide more cooling to the EGR gas.   
     
     
         7 . An internal combustion engine, comprising:
 an exhaust gas recirculation (EGR) system containing an EGR gas;   a waste heat recovery (WHR) system adapted to provide cooling to the EGR gas, the WHR system including a WHR circuit, an EGR temperature control circuit connected to the WHR circuit and positioned to receive working fluid from the WHR circuit downstream of the fluid containment portion and to return the working fluid to the WHR circuit upstream of the fluid containment portion, a thermal control unit (TCU) positioned along the EGR temperature control circuit to cool the EGR gas, an expansion valve positioned along the EGR temperature control circuit upstream of the TCU, and a compressor positioned along the EGR temperature control circuit downstream of the TCU; and   a control module operatively coupled to each of the EGR system and the WHR system, the control module configured to receive a temperature measurement signal from a temperature sensor positioned along the EGR system downstream of the TCU, and to control operation of at least one of the EGR system and the WHR system so as to controllably adjust a temperature of the EGR gas.   
     
     
         8 . The internal combustion engine of  claim 7 , wherein the control module is further configured to adjust a flow rate of the EGR gas through the TCU by adjusting a position of an EGR valve positioned along an EGR circuit of the EGR system upstream of the TCU so as to controllably adjust the temperature of the EGR gas. 
     
     
         9 . The internal combustion engine of  claim 7 , wherein the control module is further configured to adjust a flow rate of the working fluid through the TCU by adjusting a speed of the compressor so as to controllably adjust the temperature of the EGR gas. 
     
     
         10 . The internal combustion engine of  claim 7 , wherein the control module is further configured to adjust a pressure of the working fluid in the TCU by adjusting a speed of the compressor so as to controllably adjust the temperature of the EGR gas. 
     
     
         11 . The internal combustion engine of  claim 10 , wherein, when a position of the expansion valve is fixed,
 increasing the speed of the compressor operates to decrease the pressure of the working fluid in the TCU, thereby decreasing a phase change temperature of the working fluid and increasing cooling of the EGR gas, and   decreasing the speed of the compressor operates to increase the pressure of the working fluid in the TCU, thereby increasing a phase change temperature of the working fluid and decreasing cooling of the EGR gas.   
     
     
         12 . The internal combustion engine of  claim 7 , wherein the control module is further configured to adjust a pressure of the working fluid in the TCU by adjusting a position of the expansion valve so as to controllably adjust the temperature of the EGR gas. 
     
     
         13 . The internal combustion engine of  claim 12 , wherein, when a speed of the compressor is fixed,
 adjusting the position of the expansion valve to decrease a flow rate of the working fluid through the expansion valve operates to increase the pressure of the working fluid in the TCU, thereby increasing a phase change temperature of the working fluid and decreasing cooling of the EGR gas, and   adjusting the position of the expansion valve to increase a flow rate of the working fluid through the expansion valve operates to decrease the pressure of the working fluid in the TCU, thereby decreasing a phase change temperature of the working fluid and increasing cooling of the EGR gas.   
     
     
         14 . The internal combustion engine of  claim 7 , wherein the control module is configured to adjust a pressure of the working fluid in the TCU by adjusting each of a speed of the compressor and a position of the expansion valve so as to controllably adjust the temperature of the EGR gas. 
     
     
         15 . The internal combustion engine of  claim 7 , wherein the control module is configured to:
 receive a NO x  measurement signal from a NO x  sensor positioned along an exhaust system operably coupled to the internal combustion engine; and   adjust the temperature of the EGR gas based on the received NO x  measurement signal.   
     
     
         16 . The internal combustion engine of  claim 15 , wherein the control system is configured to increase the flow of the working fluid through the TCU if the NO x  measurement signal indicates an increase in the NO x  level.