# US 2021/0277835 A1 · Staged combustion > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0277835 A1 - Document ID: US20210277835A1 - Status: Published application - Kind: A1 - Application number: 17/189,650 - Filed: 2021-03-02 - Published: 2021-09-09 - Earliest claimed: 2020-03-04 - Assignees: ROLLS-ROYCE plc - Applicants: ROLLS-ROYCE plc - Inventors: Christopher P. MADDEN; Peter SWANN - Web page: https://patentgrep.com/patent/US20210277835A1 ## CPC - F02C 7/228: Dividing fuel between various burners - 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 3/30: Adding water, steam or other fluids {for influencing combustion, e.g. to obtain cleaner exhaust gases (F02C7/141, F02C7/30, F01D21/00, F01K21/04, F23D11/10 take precedence)} - F23R 3/346: {for staged combustion} - F02C 9/263: {by means of fuel metering valves} - F02C 9/40: specially adapted to the use of a special fuel or a plurality of fuels - F05D 2270/08: to produce clean exhaust gases - F05D 2270/081: with as little smoke as possible - F05D 2270/331: Mechanical loads - F05D 2270/804: Optical devices - Y02T 50/60: Efficient propulsion technologies, e.g. for aircraft - 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) - F23R: GENERATING COMBUSTION PRODUCTS OF HIGH PRESSURE OR HIGH VELOCITY, e.g. GAS-TURBINE COMBUSTION CHAMBERS (fluidised bed combustion apparatus specially adapted for operation at superatmospheric pressures F23C10/16) - F05D: INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS - Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION ## Abstract A gas turbine engine for an aircraft. The gas turbine comprises a staged combustion system having pilot injectors and main injectors, a fuel metering system configured to control fuel flow to the pilot injectors and the main injectors, and a fuel system controller. The controller is configured to identify an atmospheric condition, determine a ratio of pilot fuel flow rate for the pilot injectors to main fuel flow rate for the main injectors in response to the atmospheric condition, and inject fuel by the pilot injectors and the main injectors in accordance with said ratio to control an index of soot emissions caused by combustion of fuel therein. ## Claims ### Claim 1 A method of operating a staged combustion system in an aircraft gas turbine engine, comprising: providing pilot injectors for rich combustion and main injectors for lean combustion in said staged combustion system; identifying an atmospheric condition; determining a ratio of pilot fuel flow rate for the pilot injectors to main fuel flow rate for the main injectors in response to the atmospheric condition; injecting fuel by the pilot injectors and the main injectors in accordance with said ratio to control an index of soot emissions caused by combustion of fuel therein. ### Claim 2 (depends on 1) The method of claim 1, in which the index of soot emissions is the quantity of soot particles discharged from the combustor per unit mass of fuel injected by both the pilot injectors and the main injectors. ### Claim 3 (depends on 1) The method of claim 1, in which the atmospheric condition is an atmospheric condition causative of a condensation trail. ### Claim 4 (depends on 1) The method of claim 1, further comprising detecting the atmospheric condition using a measurement device, which optionally comprises one or more of: a humidity sensor configured to sense an atmospheric humidity; an optical sensor configured to sense the formation, or not, of a condensation trail. ### Claim 5 (depends on 1) The method of claim 1, further comprising inferring the atmospheric condition, optionally using location data in combination with one or more of: satellite imagery; weather forecasts. ### Claim 6 (depends on 1) The method of claim 1, wherein the determining step comprises: identifying a condition to the effect that an optical depth of a condensation trail produced by the engine should be reduced; evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that varies soot production to reduce ice particle formation. ### Claim 7 (depends on 6) The method of claim 6, wherein the evaluating step comprises: obtaining a measurement of an ambient temperature from a temperature sensor; in response to the ambient temperature being greater than a transition temperature, evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that decreases the index of soot emissions; in response to the ambient temperature being less than or equal to the transition temperature and a current index of soot emissions being less than a transition value, evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that increases the index of soot emissions; in response to the ambient temperature being less than or equal to the transition temperature and the current index of soot emissions being greater than a transition value, evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that decreases the index of soot emissions. ### Claim 8 (depends on 1) The method of claim 1, wherein the determining step comprises: identifying a condition to the effect that an optical depth of a condensation trail produced by the engine should be increased; evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that varies soot production to increase ice particle formation. ### Claim 9 (depends on 8) The method of claim 8, wherein the evaluating step comprises: obtaining a measurement of an ambient temperature from a temperature sensor; in response to the ambient temperature being greater than a transition temperature, evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that increases the index of soot emissions; in response to the ambient temperature being less than or equal to the transition temperature and a current index of soot emissions being greater than a transition value, evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that increases the index of soot emissions; in response to the ambient temperature being less than or equal to the transition temperature and the current index of soot emissions being less than or equal to a transition value, evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that decreases the index of soot production. ### Claim 10 (depends on 1) The method of claim 1, in which the determining step comprises: identifying a condition to the effect that an optical depth of a condensation trail produced by the engine should be reduced or increased on the basis of a time-integrated effect of a persistent condensation contrail over its lifespan given a current atmospheric condition and a predicted future atmospheric condition. ### Claim 11 A gas turbine engine for an aircraft, comprising: a staged combustion system having pilot injectors and main injectors; a fuel metering system configured to control fuel flow to the pilot injectors and the main injectors; a fuel system controller configured to: identify an atmospheric condition; determine a ratio of pilot fuel flow rate for the pilot injectors to main fuel flow rate for the main injectors in response to the atmospheric condition; and inject fuel by the pilot injectors and the main injectors in accordance with said ratio to control an index of soot emissions caused by combustion of fuel therein. ### Claim 12 (depends on 11) The gas turbine engine of claim 11, in which the index of soot emissions is the quantity of soot particles discharged from the combustor per unit mass of fuel injected by both the pilot injectors and the main injectors. ### Claim 13 (depends on 11) The gas turbine engine of claim 11, in which the atmospheric condition is an atmospheric condition causative of a condensation trail, optionally a persistent condensation trail. ### Claim 14 (depends on 11) The gas turbine engine of claim 11, further comprising a measurement device configured to detect the atmospheric condition, the measurement device optionally comprising one or more of: a hygrometer configured to sense an atmospheric humidity; an optical sensor configured to sense the formation, or not, of a condensation trail. ### Claim 15 (depends on 11) The gas turbine engine of claim 11, in which the fuel system controller is configured to infer the atmospheric condition from one or more of: satellite imagery; weather forecasts. ### Claim 16 (depends on 11) The gas turbine engine of claim 11, in which the fuel system controller is configured to determine the ratio of pilot fuel flow rate to main fuel flow rate by: identifying a condition to the effect that an optical depth of a condensation trail produced by the engine should be reduced; evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that varies soot production to reduce ice particle formation. ### Claim 17 (depends on 16) The gas turbine engine of claim 16, in which the fuel system controller is configured to evaluate the ratio of pilot fuel flow rate to main fuel flow rate by: obtaining a measurement of an ambient temperature from a temperature sensor; in response to the ambient temperature being greater than or equal to a transition temperature, evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that decreases the index of soot emissions; in response to the ambient temperature being less than or equal to the transition temperature and a current index of soot emissions being less than a transition value, evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that increases the index of soot emissions; in response to the ambient temperature being less than or equal to the transition temperature and the current index of soot emissions being to greater than a transition value, evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that decreases soot production. ### Claim 18 (depends on 11) The gas turbine engine of claim 11, in which the fuel system controller is configured to determine the ratio of pilot fuel flow rate to main fuel flow rate by: identifying a condition to the effect that an optical depth of a condensation trail produced by the engine should be increased; evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that varies soot production to increase ice particle formation. ### Claim 19 (depends on 18) The gas turbine engine of claim 18, in which the fuel system controller is configured to evaluate the ratio of pilot fuel flow rate to main fuel flow rate by: obtaining a measurement of an ambient temperature from a temperature sensor; in response to the ambient temperature being greater than a transition temperature, evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that increases the index of soot emissions; in response to the ambient temperature being less than or equal to the transition temperature and a current index of soot emissions being greater than a transition value, evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that increases the index of soot emissions; in response to the ambient temperature being less than or equal to the transition temperature and the current index of soot emissions being less than or equal to a transition value, evaluating a ratio of pilot fuel flow rate to main pilot fuel flow rate that decreases the index of soot production. ### Claim 20 (depends on 16) The gas turbine engine of claim 16, in which the fuel system controller is configured to determine the ratio of pilot fuel flow rate to main fuel flow rate by: identifying a condition to the effect that an optical depth of a condensation trail produced by the engine should be reduced or increased on the basis of the time-integrated effect of a persistent condensation contrail over its lifespan given a current atmospheric condition and a predicted future atmospheric condition.