Optimum speed power turbine to recover the exhaust energy of compression ignition diesel and gas engines

The efficiency of internal combustion engines may be improved recovering the fuel energy loss in the exhaust gases or the coolant that is the predominant portion of the fuel energy, being the amount of fuel energy transformed in mechanical energy usually less than 50% in the top efficiency operating points and well below that figure in the other operating points of the load and speed map. This paper consider the opportunity to recover part of the exhaust energy with a power turbine that is operational only when convenient and it is run at optimum speed thanks to a by-pass and a continuously variable transmission link to the crankshaft. The power turbine operates at optimum speed only when producing more power than the power loss for back pressure while permitting temperatures to the downstream after treatment system high enough. Simulations for a 12.8 liters straight 6-cylinder Diesel engine with turbocharger and intercooler show improvements in both the fuel conversion efficiency at medium-to-high speeds and medium-to-high loads