A car that can go 80 miles on a gallon would seem like an ideal solution to oil prices topping $50 a barrel.
In fact, the technology already exists in the form of so-called diesel hybrid vehicles, which yoke a conventional diesel engine to an electric motor and battery to store unused energy for clean and quiet driving at lower speeds.
But automakers say such cars are unlikely to move out of the research lab any time soon, even as fuel efficiency becomes a must for more and more customers appalled by prices at the pump.
The main problem is that diesel hybrid cars cost too much to produce -- thousands of dollars more than gas-electric hybrids.
“Diesel hybrid is one possible propulsion system that we are researching and testing, but no one can say whether this is the path to the future,” said Edith Meissner, a spokeswoman for German-American carmaker DaimlerChrysler. “It is certainly the most efficient method among the conventional powertrains ... but also the most expensive.”
Toyota, Honda also see high costs
Standard diesel engines burn less fuel than gasoline engines. Hybrid technology makes them even more frugal by letting cars run on stored electricity captured during braking and coasting.
But this lands a double whammy on costs. A diesel engine typically costs around 10 percent more than its gasoline-driven cousin of similar power, even without the cost of adding an electric motor, batteries and the electronics to run them.
Toyota, for one, questions whether it is viable, practical or sensible to sell diesel hybrid passenger vehicles in the foreseeable future.
“Before adding a hybrid system to a diesel engine, we still think there’s room for improvement in the diesel-only and gasoline-only engines in terms of fuel efficiency,” a Toyota spokesman said.
Honda Motor, another force in hybrids, also played up the costs and played down the prospects of launching serial production of a diesel hybrid car.
MIT study favors diesel hybrids
General Motors, Ford and DaimlerChrysler all came up with fuel-sipping diesel hybrids in the 1990s under the U.S. government-backed Partnership for a New Generation of Vehicles, but never marketed them.
Still, some researchers think diesel hybrids could hold their own even against highly touted hydrogen fuel cells -- widely seen as a candidate for powering a big portion of future cars, but which would need a huge energy infrastructure overhaul.
A study by the Massachusetts Institute of Technology’s Laboratory for Energy and the Environment found that even with aggressive research, fuel-cell cars won’t beat diesel hybrids on total energy use or greenhouse gas emissions by 2020.
It concluded that intense research on a diesel-engine hybrid could produce by 2020 a vehicle that is twice as efficient and half as polluting as gasoline cars.
Peugot Citroen, VW more optimistic
Moreover, some carmakers are more optimistic than others.
“It is more difficult to hybridize diesel, but we are going to show that it is possible,” Jean-Martin Folz, chief executive of Europe’s number-two carmaker PSA Peugeot Citroen, recently told an industry conference in Frankfurt.
A spokesman said PSA was working with two British firms to develop a diesel hybrid version of the Citroen Berlingo car, but had not yet decided whether to make it commercially.
And Volkswagen will enter an experimental diesel hybrid car at the Michelin Challenge Bibendum in Shanghai in mid-October, a contest for alternative powertrain vehicles.
“The technology is there and has been well known for years. The problem with hybrid is the battery technology,” a VW spokesman said, noting that it's not known if battery packs would last as long as diesel engines, which have longer lives than their gasoline counterparts.