Rankine cycle system

Abstract

A Rankine cycle system includes an evaporator for heating water with thermal energy of exhaust gas of an engine so as to generate steam; a displacement type expander for converting the thermal energy of the steam generated by the evaporator into mechanical energy; a temperature controller for manipulating the amount of water supplied to the evaporator so that the temperature of the steam supplied from the evaporator to the expander coincides with a target temperature; and a pressure controller for manipulating the rotational speed of the expander by changing a load of the expander so that the pressure of the steam supplied from the evaporator to the expander coincides with a target pressure. The temperature controller and the pressure controller control the amount of water supplied to the evaporator and/or the rotational speed of the expander according to at least an internal density of the evaporator.

1 . A Rankine cycle system comprising: 
 an evaporator for heating a liquid-phase working medium with thermal energy of exhaust gas of an engine so as to generate a gas-phase working medium;    a displacement type expander for converting the thermal energy of the gas-phase working medium generated by the evaporator into mechanical energy;    temperature control means for manipulating the amount of liquid-phase working medium supplied to the evaporator so that the temperature of the gas-phase working medium supplied from the evaporator to the expander coincides with a target temperature; and    pressure control means for manipulating the rotational speed of the expander by changing a load of the expander so that the pressure of the gas-phase working medium supplied from the evaporator to the expander coincides with a target pressure,    wherein the temperature control means and the pressure control means controls the amount of liquid-phase working medium supplied to the evaporator and/or the rotational speed of the expander according to at least an internal density of the evaporator.    
   
   
       2 . The Rankine cycle system according to  claim 1  wherein, when the engine is started, the temperature control means and the pressure control means control the amount of liquid-phase working medium supplied to the evaporator and/or the rotational speed of the expander according to at least the internal density of the evaporator.  
   
   
       3 . The Rankine cycle system according to  claim 2 , wherein the temperature control means increases the amount of liquid-phase working medium supplied when the internal density of the evaporator is lower than a set value, and decreases the amount of liquid-phase working medium supplied or makes it zero when the internal density of the evaporator is higher than the set value.  
   
   
       4 . The Rankine cycle system according to  claim 2 , wherein the pressure control means controls the rotational speed of the expander so that the expander stops or rotates at a very low rotational speed that is close to stopping when the internal density of the evaporator is lower than a set value, and controls the rotational speed of the expander so that the expander is rotated in advance when the internal density of the evaporator is higher than the set value.  
   
   
       5 . The Rankine cycle system according to  claim 3 , wherein the pressure control means controls the rotational speed of the expander so that the expander stops or rotates at a very low rotational speed that is close to stopping when the internal density of the evaporator is lower than a set value, and controls the rotational speed of the expander so that the expander is rotated in advance when the internal density of the evaporator is higher than the set value.  
   
   
       6 . The Rankine cycle system according to  claim 1 , wherein the internal density of the evaporator is based on a flow rate Qin of water supplied and a flow rate out Qout according to the following formula:  
       ρ=∫ {Q in( t )− Q out( t )} dt/V.    
   
   
       7 . The Rankine cycle system according to  claim 1 , wherein the pressure control means includes a feedforward rotational speed calculation means, feedback rotational speed calculation means, rotational speed control changeover means and feedback term calculation means for manipulating the rotational speed of the expander.  
   
   
       8 . The Rankine cycle system according to  claim 7 , wherein the feedforward rotational speed calculation means calculates a feedforward rotational speed based on a target pressure of steam supplied to the expander, a commanded water supply amount and a steam temperature at an entrance of the expander.  
   
   
       9 . The Rankine cycle system according to  claim 7 , wherein the feedback rotational speed calculation means calculates a feedback rotational speed by multiplying a deviation of steam pressure at an entrance of the expander from the target pressure for steam at the entrance of the expander by a predetermined gain.  
   
   
       10 . The Rankine cycle system according to  claim 1 , wherein the rotational speed changeover means controls an entrance steam pressure of the expander by changing, based on an ON/OFF signal of an ignition switch, a positive torque or a negative torque generated by a motor/generator.  
   
   
       11 . A Rankine cycle system comprising: 
 an evaporator for heating a liquid-phase working medium with thermal energy of exhaust gas of an engine so as to generate a gas-phase working medium;    a displacement type expander for converting the thermal energy of the gas-phase working medium generated by the evaporator into mechanical energy;    a temperature controller to manipulate the amount of liquid-phase working medium supplied to the evaporator so that the temperature of the gas-phase working medium supplied from the evaporator to the expander coincides with a target temperature; and    a pressure controller to manipulate the rotational speed of the expander by changing a load of the expander so that the pressure of the gas-phase working medium supplied from the evaporator to the expander coincides with a target pressure,    wherein the temperature controller and the pressure controller control the amount of liquid-phase working medium supplied to the evaporator and/or the rotational speed of the expander according to at least an internal density of the evaporator.    
   
   
       12 . The Rankine cycle system according to  claim 11  wherein, when the engine is started, the temperature controller and the pressure controller control the amount of liquid-phase working medium supplied to the evaporator and/or the rotational speed of the expander according to at least the internal density of the evaporator.  
   
   
       13 . The Rankine cycle system according to  claim 12 , wherein the temperature controller increases the amount of liquid-phase working medium supplied when the internal density of the evaporator is lower than a set value, and decreases the amount of liquid-phase working medium supplied or makes it zero when the internal density of the evaporator is higher than the set value.  
   
   
       14 . The Rankine cycle system according to  claim 12 , wherein the pressure controller controls the rotational speed of the expander so that the expander stops or rotates at a very low rotational speed that is close to stopping when the internal density of the evaporator is lower than a set value, and controls the rotational speed of the expander so that the expander is rotated in advance when the internal density of the evaporator is higher than the set value.  
   
   
       15 . The Rankine cycle system according to  claim 13 , wherein the pressure controller controls the rotational speed of the expander so that the expander stops or rotates at a very low rotational speed that is close to stopping when the internal density of the evaporator is lower than a set value, and controls the rotational speed of the expander so that the expander is rotated in advance when the internal density of the evaporator is higher than the set value.  
   
   
       16 . The Rankine cycle system according to  claim 11 , wherein the internal density of the evaporator is based on a flow rate Qin of water supplied and a flow rate out Qout according to the following formula:  
       ρ∫ {Q in( t )− Q out( t )} dt/V.    
   
   
       17 . The Rankine cycle system according to  claim 11 , wherein the pressure controller includes a feedforward rotational speed calculation means, feedback rotational speed calculation means, rotational speed control changeover means and feedback term calculation means for manipulating the rotational speed of the expander.  
   
   
       18 . The Rankine cycle system according to  claim 17 , wherein the feedforward rotational speed calculation means calculates a feedforward rotational speed based on a target pressure of steam supplied to the expander, a commanded water supply amount and a steam temperature at an entrance of the expander.  
   
   
       19 . The Rankine cycle system according to  claim 17 , wherein the feedback rotational speed calculation means calculates a feedback rotational speed by multiplying a deviation of steam pressure at an entrance of the expander from the. target pressure for steam at the entrance of the expander by a predetermined gain.  
   
   
       20 . The Rankine cycle system according to  claim 1   1 , wherein the rotational speed changeover means controls an entrance steam pressure of the expander by changing, based on an ON/OFF signal of an ignition switch, a positive torque or a negative torque generated by a motor/generator.