An automotive powerplant using an organic Rankine-cycle engine has been designed, built, and tested in a preprototype configuration. A description of the system and results from expander, combustor, and preprototype system testing is presented. Emission results show that the system could meet the 1976 emission standards specified by Congress in the 1970 Clean Air Act. Performance and fuel consumption predictions are presented for a prototype system based on both experimental and analytical results obtained to date.EMPHASIS ON REDUCING automotive exhaust emissions in the last few years has led to research on many alternative powerplants to replace the internal combustion engine. An inherently clean engine due to separation of the power cycle from the combustion process, the Rankine-cycle vapor engine has received attention as potentially a more desirable longterm solution to the emissions problem. Programs conducted recently by different investigators (1, 2, 3, 4, 5, 6 and 7)* have shown that Rankine-cycle engines can produce emissions below the standards of the Clean Air Act passed by Congress in 1970 and intended to be in effect for the 1976 model year. The low emissions obtainable from the Rankine cycle have also been demonstrated in steam buses (8).Moreover, the Rankine-cycle engine offers the potential for high reliability, low maintenance requirements, moderate cost, good driveability, and good fuel economy. Because of the strong potential of the Rankine-cycle vapor engine, the Division of Advanced Automotive Power Systems Development of the Environmental Protection Agency is sponsoring development at Thermo Electron Corp. of a Rankine-cycle vapor engine utilizing an organic-based working fluid and reciprocating expander, for low emission automotive propulsion. The Ford Motor Co. is also contributing both financially and technically to the development effort.