Systems and methods for directing cooling flow into the surge plenum of an exhaust eductor cooling system

Abstract

A method and apparatus is provided for cooling the external surface of an aircraft APU eductor assembly. A processor is configured to open a surge valve by a predetermined amount when the surge valve is closed and the temperature of the exhaust gas exceeds a predetermined temperature in order to cool the surge plenum surfaces.

What is claimed is: 
     
         1 . A method for cooling the external surface of an aircraft APU inductor assembly surge plenum, comprising diverting customer airflow to the surge plenum when there is otherwise no surge flow. 
     
     
         2 . The method of  claim 1  wherein the step of diverting comprises opening a surge valve by a predetermined amount. 
     
     
         3 . The method of  claim 2  wherein the step of opening comprises opening the surge valve at least ten percent. 
     
     
         4 . The method of  claim 3  wherein the step of opening comprises opening the surge valve no more than fifteen percent. 
     
     
         5 . The method of  claim 2  wherein the step of opening comprises opening the surge valve if the temperature of APU exhaust is at least 1,000° F. 
     
     
         6 . The method of  claim 2  further comprising opening the surge valve if an APU inlet door is open no more than thirty degrees. 
     
     
         7 . The method of  claim 2  further comprising determining if the aircraft is on the ground. 
     
     
         8 . The method of  claim 2  further comprising first determining if the surge valve is closed. 
     
     
         9 . The method of  claim 2  wherein the step of opening comprises opening the surge valve between ten and fifteen percent. 
     
     
         10 . An eductor system for use in conjunction with an aircraft APU, the system comprising:
 a surge plenum;   a surge duct coupled to the surge plenum for providing excess airflow not required by the aircraft to the surge plenum; and   a processor coupled to the surge duct and configured to divert airflow to the surge plenum when there is otherwise no excess customer airflow, the diverted air for cooling the surge plenum.   
     
     
         11 . The system of  claim 10  further comprising a surge valve coupled to the surge duct, and wherein the processor is configured to open the surge valve between ten and fifteen percent to divert air to the surge plenum. 
     
     
         12 . The system of  claim 11  further comprising an exhaust gas temperature sensor and wherein the processor is configured to open the surge valve when the APU exhaust gas exceeds a predetermined temperature. 
     
     
         13 . The system according to  claim 12  wherein the predetermined temperature is 1,000° F. 
     
     
         14 . The system of  claim 13  further comprising an APU inlet door and wherein the processor is configured to open the surge valve when the inlet door is open no more than thirty degrees. 
     
     
         15 . The system of  claim 14  further comprising an altitude sensor coupled to the processor and wherein the processor opens the surge valve when the aircraft is on the ground. 
     
     
         16 . The system according to  claim 10  wherein the surge valve is opened between then and fifteen percent. 
     
     
         17 . A method for cooling the external surface of an aircraft APU eductor assembly surge plenum, comprising diverting customer airflow to the surge plenum by opening a surge valve between ten and fifteen degrees when the APU exhaust gas temperature exceeds 1,000° F. 
     
     
         18 . The method of  claim 17  wherein the step of diverting comprises first determining if the aircraft is on the ground. 
     
     
         19 . The method of  claim 17  wherein the step of diverting comprises first determining if the surge valve is closed. 
     
     
         20 . The method of  claim 17  wherein the step of diverting comprises first determining if the APU inlet door is open no more than thirty degrees.