Car techies have been clamoring for a diesel hybrid, assumedly to match an efficient fuel-burning construct with an electric drive system to make a giant synergy sandwich. Here in Frankfurt, Mercedes is showing a few hybrid prototypes that may hearken what's to come. A few of those combine its low-C02 Bluetec diesel system with its parallel hybrid system, while one — the ML 450 — combines electric with gas using the two-mode torque-split module developed with GM and BMW. The diesel hybrids include the flagships S 300, debuting this year, and the S 400, revealed at the 2005 Frankfurt show. Word is the S 400 will hit the streets in 2009. Of course, the main event is the C 300 Bluetec Hybrid saloon — a version of the new C-Class wagon fitted with a diesel-electric powerplant. With 224 horsepower and 413 lb-ft of torque, the C 300 prototype can get from zero to 62 mph in 7.2 seconds, while meeting Euro 6 emissions standards. Mercedes says we can expect a market launch sometime after 2010.