# US 12,000,341 B1 · Method for starting an auxiliary power unit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,000,341 B1 - Document ID: US12000341B1 - Status: Granted - Kind: B1 - Application number: 18/097,340 - Filed: 2023-01-16 - Granted: 2024-06-04 - Earliest claimed: 2023-01-16 - Assignees: Pratt & Whitney Canada Corp. - Applicants: Pratt & Whitney Canada Corp. - Inventors: Louis Duranleau-Hendrickx - Web page: https://patentgrep.com/patent/US12000341B1 ## CPC - F02C 7/26: Starting; Ignition - F01D 19/00: Starting of machines or engines; Regulating, controlling, or safety means in connection therewith (warming-up before starting F01D25/10; turning or inching gear F01D25/34) - F02C 9/26: Control of fuel supply (F02C9/48 takes precedence; fuel valves F02C7/232) - F02C 9/28: Regulating systems responsive to plant or ambient parameters, e.g. temperature, pressure, rotor speed (F02C9/30 - F02C9/38, F02C9/44 take precedence) - F02C 9/56: with power transmission control - F05D 2220/323: for aircraft propulsion, e.g. jet engines - F05D 2220/50: for auxiliary power units (APU's) - F05D 2260/85: Starting - F02C: GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS (construction of turbines F01D; jet-propulsion plants F02K; construction of compressors or fans F04; generating combustion products of high pressure or high velocity F23R; using gas turbines in compression refrigeration plants F25B11/00) - F01D: NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES (machines or engines for liquids F03; non-positive displacement pumps F04D) - F05D: INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS ## Abstract Methods for starting an aircraft auxiliary power unit (APU) in different operating conditions are provided. A method includes performing a first start attempt on the APU when the APU is subjected to an operating condition and determining that the first start attempt was unsuccessful. The first start attempt includes delivering fuel to a combustion chamber of a combustion engine of the APU. After terminating the first start attempt, the method includes determining whether or not a change in the operating condition to which the APU is subjected is below a threshold. When the change in the operating condition is below the threshold, the method includes performing a second start attempt on the APU. The second start attempt includes delivering fuel to the combustion chamber of the combustion engine at a fuel flow rate greater than the fuel flow rate of the first start attempt. ## Claims ### Claim 1 A method for starting an aircraft auxiliary power unit (APU) including a combustion engine, the method comprising: performing a first start attempt on the APU when the APU is subjected to a first operating condition, the first start attempt including delivering fuel to a combustion chamber of the combustion engine at a first fuel flow rate; determining that the first start attempt was unsuccessful; terminating the first start attempt by ceasing to deliver the fuel to the combustion chamber of the combustion engine; determining that a difference between the first operating condition and a second operating condition to which the APU is subjected after terminating the first start attempt is below a threshold; and based on the determination that the difference is below the threshold, performing a second start attempt on the APU, the second start attempt including delivering the fuel to the combustion chamber of the combustion engine at a second fuel flow rate that is greater than the first fuel flow rate. ### Claim 2 (depends on 1) The method as defined in claim 1, wherein delivering the fuel to the combustion chamber during the first start attempt is controlled in an open-loop manner. ### Claim 3 (depends on 1) The method as defined in claim 1, wherein delivering the fuel to the combustion chamber during the second start attempt is controlled in an open-loop manner. ### Claim 4 (depends on 1) The method as defined in claim 1, wherein a first average fuel flow rate of the fuel delivered to the combustion chamber during the first start attempt is less than a second average fuel flow rate of the fuel delivered to the combustion chamber during the second start attempt. ### Claim 5 (depends on 1) The method as defined in claim 1, wherein a first initial plateau in the first fuel flow rate of the fuel delivered to the combustion chamber during the first start attempt is lower than a second initial plateau in the second fuel flow rate of the fuel delivered to the combustion chamber during the second start attempt. ### Claim 6 (depends on 1) The method as defined in claim 1, wherein a first cumulative amount of the fuel delivered to the combustion chamber during the first start attempt is less than a second cumulative amount of the fuel delivered to the combustion chamber during the second start attempt. ### Claim 7 (depends on 1) The method as defined in claim 1, wherein determining that the difference between the first operating condition and the second operating condition is below the threshold comprises determining that a time duration since terminating the first start attempt is less than a threshold time. ### Claim 8 (depends on 7) The method as defined in claim 7, wherein the threshold time is less than or equal to 30 seconds. ### Claim 9 (depends on 1) The method as defined in claim 1, wherein at least one of the first operating condition or the second operating condition includes an altitude of an aircraft including the APU. ### Claim 10 (depends on 1) The method as defined in claim 1, wherein at least one of the first operating condition or the second operating condition includes a temperature of an ambient environment external to an aircraft including the APU. ### Claim 11 (depends on 1) The method as defined in claim 1, wherein at least one of the first operating condition or the second operating condition includes a speed of an aircraft including the APU. ### Claim 12 (depends on 1) The method as defined in claim 1, comprising: determining that the second start attempt was unsuccessful; terminating the second start attempt by ceasing to deliver the fuel to the combustion chamber; and performing a third start attempt on the APU, the third start attempt including delivering the fuel to the combustion chamber at a third fuel flow rate greater than the second fuel flow rate. ### Claim 13 (depends on 12) The method as defined in claim 12, wherein performing the third start attempt is based in part on determining that a time duration since terminating the second start attempt is less than a threshold time. ### Claim 14 (depends on 1) The method as defined in claim 1, determining at least one of the first fuel flow rate or the second fuel flow rate using a machine learned model trained using historical data associated with APU start attempts. ### Claim 15 (depends on 14) The method as defined in claim 14, comprising training the model using a controller of the APU, the historical data including a prior start attempt of the APU. ### Claim 16 A method for starting an aircraft auxiliary power unit (APU) including a gas turbine engine, the method comprising: performing a first start attempt on the APU when the APU is subjected to a first operating condition, the first start attempt including delivering a first cumulative fuel amount to a combustor of the gas turbine engine during the first start attempt; determining that the first start attempt was unsuccessful; terminating the first start attempt by ceasing to deliver the fuel to the combustor of the gas turbine engine; and when the first operating condition has not substantially changed from a second operating condition to which the APU is subjected after terminating the first start attempt, performing a second start attempt on the APU, the second start attempt including delivering a second cumulative fuel amount to the combustor of the gas turbine engine during the second start attempt, the second cumulative fuel amount being greater than first cumulative fuel amount. ### Claim 17 (depends on 16) The method as defined in claim 16, comprising: determining that the second start attempt was unsuccessful; and performing a third start attempt on the APU. ### Claim 18 (depends on 16) The method as defined in claim 16, comprising determining that the first operating condition has not substantially changed from the second operating condition by evaluating a time duration since terminating the first start attempt. ### Claim 19 An aircraft auxiliary power unit (APU) comprising: a gas turbine engine configured to provide energy exclusively for non-propulsive functions of an aircraft; and a controller operatively connected to the gas turbine engine and configured to: initiate a first start attempt on the gas turbine engine when the APU is subjected to a first operating condition, the first start attempt including delivering fuel to a combustor of the gas turbine engine at a first fuel flow rate; determine that the first start attempt was unsuccessful; terminate the first start attempt by ceasing to deliver the fuel to the combustor of the gas turbine engine; determine that a difference between the first operating condition and a second operating condition to which the APU is subjected after terminating the first start attempt is below a threshold; and when the difference is below the threshold, initiate a second start attempt on the APU, the second start attempt including delivering the fuel to the combustor of the gas turbine engine at a second fuel flow rate greater than the first fuel flow rate. ### Claim 20 (depends on 19) The APU as defined in claim 19, wherein the controller includes a model trained using machine learning and historical data relating operating conditions and fuel flow rates to APU start attempts.