The present disclosure is directed to integrated injector/igniters providing efficient injection, ignition, and complete combustion of various types of fuels. One example of such an injectors/igniter can include a body having a base portion opposite a nozzle portion. The base portion receives the fuel into the body and the nozzle portion can be positioned adjacent to the combustion chamber. The injector further includes a valve carried by the nozzle portion that is movable between a closed position and an open position to inject the fuel into the combustion chamber. An actuator is coupled the valve and extends longitudinally through the body towards the base portion, and a driver is carried by the body and is movable between a first position and a second position. Thermochemical regeneration of waste heat produced by combustion and associated combustion events is captured and invested in endothermic reactions to improve efficiency of the combustion event. Hydrogen characterized fuel may be used as a heat sink.