In early April, at the SAE 2011 High Efficiency IC Engines Symposium in Detroit, MI, Toyota's Koichi Nakata declared that the Japanese automaker is exploring ways to further reduce the fuel consumption of its upcoming hybrid models. According to Nakata, Toyota aims to develop a gasoline engine that operates at more than 45 percent thermal efficiency for use in future hybrid vehicles.
To put that number into perspective, the engine in the first- and second-generation Toyota Prius had a thermal efficiency of approximately 37 percent and the 1.8-liter mill in the third-gen Prius boasts a thermal efficiency of 38 percent.
Toyota is focusing on two concepts to reach its thermal efficiency goal. Concept 1 is a cooled EGR stoichiometric spark-ignited direct-injection engine that features a long stroke design. The long-stroke setup, according to Toyota, reduces heat loss, increases piston speed and creates more chamber turbulence, which improves combustion. Concept 2 is a turbocharged, lean-burning engine that incorporates the same basic design of Concept 1.
So far, Nakata claims that the engine development team has achieved a 42.4 percent thermal efficiency with Concept 1 and 43.7 percent thermal efficiency using the turbocharged, lean-burning Concept 2 design. Does this mean that a turbo'd Prius may be coming soon?