Miller Cycle Application to the Scuderi Split Cycle Engine (by Downsizing the Compressor Cylinder) 2012-01-0419
The Scuderi engine is a split cycle design that divides the four strokes of a conventional combustion cycle over two paired cylinders, one intake/compression cylinder and one power/exhaust cylinder, connected by a crossover port. This configuration provides potential benefits to the combustion process, as well as presenting some challenges. A Miller cycle configuration of the engine is made possible by turbocharging with a downsized compressor cylinder and has been modeled in 1-dimensional cycle simulation software. Several positive interactions were found between the split cycle engine and Miller cycle operating principles, namely:
The reduced compression stroke facilitates actual displacement (and physical size) reduction of the split cycle engine, providing a more advantageous brake mean effective pressure (BMEP) characteristic compared to traditional reciprocating internal combustion engines (RICE) with Miller cycle operation.
Reduction of the compression cylinder displacement allows Miller cycle operation while still closing the intake valve at an optimum trapped mass condition. This results in more favorable pumping work than the Miller cycle applied to traditional RICE, due to the avoidance of closing the intake valve during a period of high piston velocity.
The extremely high turbulence and resulting fast combustion and late fuel addition provides a natural knock avoidance characteristic that allow the utilization of higher boost levels than are typically achievable with stoichiometric, spark-ignited engines.
Parametric variations are made across the operating range of the engine, investigating a range of potential Miller factors and boost levels. Analysis is performed to determine engine performance sensitivity to turbomachinery performance. At low load, a secondary level Miller cycle is applied through the use of early intake valve closure to provide near throttle-less load control. Simulation results indicate that high BMEP and good thermal efficiency are achievable in the main operating region. The resulting improvements in thermal efficiency and maximum BMEP provide the potential for significant fuel energy savings in an automotive application. BMEP provides benefits both through the effect of downsizing reducing the mass and size of the engine payload that must be transported, as well as by allowing the engine to operate at a higher operational BMEP and therefore higher efficiency during typical driving conditions.