Diesel pundits have consistently argued that a good oil-burner can match, and in some cases outdo, a comparable hybrid powertrain when it comes to fuel-economy. Carmakers on the other hand, possibly motivated by the green image presented by hybrid vehicles, have been spending billions of dollars on developing new hybrid and plug-in hybrid technologies.

Mazda is one of the few major carmakers bucking this trend, announcing today that it plans to develop a new diesel engine that will be cheaper and about as fuel-efficient as some hybrid cars by 2011.

Mazda has already set itself a target of increasing its fleet average fuel-economy by 30% by 2015, and to achieve this the carmaker will not only launch the new diesel but also new turbocharged petrol engines, ultra-efficient automatic and dual-clutch transmissions, and lighter vehicles.

Most of the technologies are still being developed, but Mazda has already announced that a 2.0L version of its next-generation diesel will offer the fuel-economy of a 660cc petrol engine or similarly sized mild hybrid system.

Speaking with Reuters, Mazda R&D chief Seita Kanai explained that hybrids, while popular, are usually more expensive than simple diesel models. He added that a diesel engine tends to be more reliable and cheaper to repair than petrol-electric hybrid powertrain.

Kanai was keen to point out, however, that Mazda hasn’t completely given up on hybrid and electric vehicles, and that it would start to launch such models beyond 2015.