Abstract: The present invention provides a method and system to control emissions in an engine by controlling spray plume characteristics, such as length and angle. Specifically, a system implementing the present invention includes an fuel injector, an engine cylinder and an electronic control module (ECM). The ECM determines spray plume parameters, including time from start of injection, nozzle hole diameter, pressure differential between the cylinder and fuel in the fuel injector nozzle, and gas temperature and density in the cylinder. Upon determining the spray plume parameters, the ECM calculates the spray plume characteristics and compares them to the optimal spray plume characteristics. The ECM then proceeds to adjust fuel injection characteristics, such as injection on time, rail pressure, and injection timing relative to piston position, to optimize the spray plume.