On graduation in 1943, Longwell joined Exxon, then Standard Oil of New Jersey or Esso, in the Process Research Division in Bayway, New Jersey. In 1945 he was assigned to work on government-supported research on high-output combustion. The mission was to design a propulsion system, on the Bumblebee project directed by John Hopkins, which ultimately led to the development of the long-range Talos naval surface-to-air missile. He would later take satisfaction in the successful use of the Talos missile in the Vietnam War. His research on high-output combustion—in application to gas turbines, rockets, and ramjets—led to the invention, with Malcolm Weiss, of the well-stirred reactor, which is now widely used by the combustion community for studying high-temperature kinetics. The well-stirred reactor uses sonic feed-jets to induce recirculation in the reactor to minimize mass transfer limitations. It is of great value in determining the maximum throughput achievable by a combustor without flame blowout.
“Jack showed an unusual ability and delight in taking a piece of science and showing where it could be applied, along with a singular ability to analyze all dimensions of a problem.” These attributes led to his being assigned a series of management positions of increasing responsibilities, including setting up the predecessor of the Government Research Laboratory, serving as the first head of the Exploratory Division of the Process Research Division, heading up the Chemical Research Division in 1960, serving as director of the Central Basic Research Laboratory in 1965, and becoming manager of corporate research in 1968. His breadth of experience and his penetrating technical insight were recognized in his appointment as senior scientific advisor, the company’s highest technical rank. Jack’s responsibilities went beyond combustion to include development of a wide range of technologies for fuel conversion and utilization, as well as helping younger researchers convert their ideas into products and processes.
Jack retired from Exxon to join the MIT faculty in 1976, where he pursued his interests in combustion, pollution abatement, and the health effects of combustion-generated pollutants.