Primus has worked as a reciprocating engine technologist and researcher in the areas of heat transfer, fluid mechanics, combustion, emissions and thermodynamics for over 30 years. He worked for Cummins during the first 25 years of his career. As executive director of Cummins Technical Systems, he was responsible for the worldwide coordination of technical tools, methods and training. In 2002, he left Cummins to become chief technologist–advanced cycles at the General Electric Global Research Center. Primus became a Society of Automotive Engineers Fellow in 2001. He has been a member of the governing board of the Central States Section of the Combustion Institute and a licensed professional engineer in Indiana. He has a bachelor’s degree in mathematics and a master’s degree in mechanical engineering from Rose-Hulman Institute of Technology.