The present disclosure is directed to fuel injectors that provide efficient injection, ignition, and combustion of various types of fuels. One example of such an injector can include a sensor that detects one or more conditions in the combustion chamber. The injector can also include an acoustical force generator or modifier that is responsive to the sensor and can be configured to (a) induce vibrations in the fuel in the injector body and/or in the combustion chamber, (b) induce vibrations in air in the combustion chamber, (c) induce vibrations in a valve driver or other injector component to actuate a flow valve, and/or (d) control patterning of fuel injected into the combustion chamber.