The idea of combining a diesel engine with a gas-electric hybrid powertrain has been on the drawing boards for many years. The Clinton Administration’s fuel efficiency research programs program of the 1990s produced a trio of 80-mpg diesel-hybrids. None went into production. Peugeot has been showing a diesel-hybrid concept for years. GM unveiled a 60-mpg diesel-hybrid Opel Astra concept about five years ago. Volkswagen, BMW and Mercedes were all talking about diesel hybrids in early 2008. And buzz about a 70-mpg VW Diesel-Hybrid Golf spread across the blogosphere, also in 2008, with rumors that Volkswagen would deliver one “as early as 2009.”
Here we are in 2010, and it’s diesel-hybrid-déjà vu all over again. It’s not a surprising development, considering that the combined fuel efficiency of a diesel engine and a hybrid system could send mpg into a new strata. The problem all along has been cost. Most analysts believe that diesel hybrids will double the incremental cost of an advanced fuel-efficient car—but not the benefit. Hybrids and diesels—used alone rather than in tandem—have remained niche technologies largely because of price tags beyond the reach of a real mainstream market. Combining the systems would send costs even higher.
Nonetheless, the vision persists. Daimler chairman Dieter Zetsche has confirmed suggestions from last summer that Mercedes will launch the 2012 Mercedes-Benz E300 Hybrid using a 2.2-liter four-cylinder diesel engine with twin turbochargers, in late 2011 (probably only for the European market). The lithium ion battery and electric motor in the E300 would be similar to those used in the $89,000 Mercedes-Benz S400 Hybrid, which went on sale late last year. Add a diesel engine to that vehicle and expect a price tag close to $100,000.
According to Autocar, a UK-based auto website, engineers at GM Europe are also “studying the feasibility of integrating the company’s existing hybrid components—motor-generators, batteries and control electronics—with diesel engines.” The report suggest that a diesel-hybrid version of Opel Astra could make sense—a claim that is eerily similar to one appearing five years ago when Wired magazine claimed that diesel hybrids were “on the fast track.”
The GM engineers are even reported to be considering a diesel version of the plug-in hybrid Chevy Volt. The prospect of a diesel plug-in hybrid—even better if running on biodiesel—could mean operating a car almost entirely on electricity, and using biofuel to extend its range. That would be the holy grail of long range and zero petroleum. Unfortunately, the cost of a large lithium ion battery pack, electric motors and a diesel engine is likely to keep this idea in research labs for many years. Green car fans shouldn’t get their hopes up again.