Fans of the internal combustion engine can breathe easy for the next couple of decades, say researchers at DRI-WEFA and Arthur D. Little.

Their recently released “Future Powertrain Technologies” study concludes that the internal combustion engine will be alive and well by the year 2020.

Other findings, based on three realistic but varied market scenarios, predict that a strong environmental movement could kill the diesel, especially in Europe.

A diesel-averse scenario does not portend a bright future for fuel cells, however. Because of a still-abundant — and cheap — supply of crude oil, fuel cells will make up less than 1% of vehicle powerplants a couple of decades hence.

They do predict, however, a sharp rise in the number of hybrid vehicles and a concomitant rise in the use of 42-volt vehicle electrical systems. They predict a 30% usage rate for 42 volts by 2010 and 100% use by 2020.

Hybrids similar to the current Honda Insight or Toyota Prius by 2020 will make up anywhere from 9% to 11% of vehicle sales. With a serious environmental mandate, however, those hybrid numbers could climb as high as 57% by then.