The theory of extra-expansion engines

A single cylinder, spark ignition, four stroke engine operating on the extra-expansion thermodynamic cycle was evaluated. Improved brake specific fuel consumption was the ultimate goal. The extra-expansion cycle was achieved using a four-bar linkage to vary mechanical compression ratio from 9:1 to 16:1 while the engine was running. A secondary rotary valve was used to control intake flow without throttling associated with a conventional butterfly valve. This research complements previous work and is the first published research testing an extra-expansion engine with dynamically variable intake timing and compression ratio.; Theoretical analysis of the ideal Otto and extra-expansion cycles shows thermal efficiency and indicated work is significantly increased by increasing mechanical compression ratio. Analysis also shows pumping work is reduced a maximum of over 75% by using rotary valve control. The theory of rotary valve design was also developed.; A complete data acquisition and analysis system was developed to monitor 16 sensors encompassing brake performance, indicated performance and ambient conditions. Analysis output includes average cylinder, intake and exhaust pressure cycles for each test as a function of crank angle. Cylinder pressure-volume diagrams are also generated for the average, minimum and maximum peak pressure and work cycles. A series of tests were performed with the rotary and butterfly valve controls to quantify the performance improvements associated with the variable compression ratio and rotary valve control. Brake specific fuel consumption was reduced over the entire operating range from the 9:1 compression ratio, butterfly control baseline. Reductions ranged from 8% at higher loads to over 50% at low loads. Pumping losses were reduced from 25% to over 85% by the rotary valve control. Driving cycle simulations show fuel economy utilizing this type of engine could be as much as 40% higher than a conventional engine with 9:1 compression ratio.; In summary, actual test results show the extra-expansion engine cycle reduces brake specific fuel consumption as predicted by the theoretical analysis and can significantly improve the fuel economy of vehicles with conventional drivetrain configurations. The engine cycle and technology can also be implemented in hybrid vehicle applications and used with alternative fuels.