A system comprising: an air manifold ; a fuel manifold ; a plurality of fuel injectors , each connected in fluid communication to receive fuel from the fuel manifold, wherein at least one fuel injector in the plurality of fuel injectors includes: a heat exchanger portion wherein an air channel and a fuel channel are in thermal communication with one another for heat exchange between fuel and air passing through the heat exchanger portion, wherein the fuel channel passes from a fuel channel inlet , through the heat exchanger portion to a nozzle outlet , and wherein the air channel passes from the heat exchanger portion, to an air channel outlet , wherein the respective inlet of the fuel channel is connected to the fuel manifold for fluid communication of fuel from the fuel manifold to the nozzle outlet for combustion, and wherein the respective outlet of the air channel is connected to the air manifold for fluid communication of air from the heat exchanger portion into the air manifold; an air valve operatively connected to an outlet of the air manifold for controlling release of air from the air manifold; and a controller operatively connected to the air valve, wherein the controller includes machine readable instructions configured to control the air valve to regulate flow of air through the air valve based on fuel temperatures in the fuel channel, the system characterized by further comprising an auxiliary source of conditioned, compressed air selectively in fluid communication with the air manifold, wherein the machine readable instructions are configured to prevent air flow out of the air manifold and instead flow air from the auxiliary source into the air manifold in a fuel cooling mode. an air manifold ; a fuel manifold ; a plurality of fuel injectors , each connected in fluid communication to receive fuel from the fuel manifold, wherein at least one fuel injector in the plurality of fuel injectors includes: a heat exchanger portion wherein an air channel and a fuel channel are in thermal communication with one another for heat exchange between fuel and air passing through the heat exchanger portion, wherein the fuel channel passes from a fuel channel inlet , through the heat exchanger portion to a nozzle outlet , and wherein the air channel passes from the heat exchanger portion, to an air channel outlet , wherein the respective inlet of the fuel channel is connected to the fuel manifold for fluid communication of fuel from the fuel manifold to the nozzle outlet for combustion, and wherein the respective outlet of the air channel is connected to the air manifold for fluid communication of air from the heat exchanger portion into the air manifold; wherein the fuel channel passes from a fuel channel inlet , through the heat exchanger portion to a nozzle outlet , and wherein the air channel passes from the heat exchanger portion, to an air channel outlet , wherein the respective inlet of the fuel channel is connected to the fuel manifold for fluid communication of fuel from the fuel manifold to the nozzle outlet for combustion, and wherein the respective outlet of the air channel is connected to the air manifold for fluid communication of air from the heat exchanger portion into the air manifold; an air valve operatively connected to an outlet of the air manifold for controlling release of air from the air manifold; and a controller operatively connected to the air valve, wherein the controller includes machine readable instructions configured to control the air valve to regulate flow of air through the air valve based on fuel temperatures in the fuel channel, the system characterized by further comprising an auxiliary source of conditioned, compressed air selectively in fluid communication with the air manifold, wherein the machine readable instructions are configured to prevent air flow out of the air manifold and instead flow air from the auxiliary source into the air manifold in a fuel cooling mode. <EOS>