A system and method for providing continuous measurement and control of a combustion device by altering the fuel composition delivered thereto. The system includes devices for sensing combustion characteristics or other device characteristics, and controlling the performance of the combustion device based on the sensed information. Performance control occurs via addition of one or more additives to the fuel to adjust combustion characteristics. Via such sensing and performance control, consistent combustion device performance may be maintained, despite varying fuel characteristics. In one variation,—characteristics of the combustion device in operation, such as flame characteristics, are sensed and used to adjust fuel characteristics via iterative addition of one or more additives.