On Fri, 15 May 2009, RJ Kanary wrote:
I'm not all that sharp on pumping losses, volumetric efficiency and all that sort of thing............but since a Diesel engine is unthrottled, essentially becoming an air compressor when de fueled, doesn't that rob one of coasting efficiency?
Yes - there is considerable engine drag with any diesel when you leave it in gear without the accelerator pressed. That's why they refer to it as "engine braking". That's one of the very nice things about driving a manual tranny diesel up here in New ENgland - you can rely heavily on engine braking for slowing down when driving in the snow, limiting the use of your brakes, which are more likely to cause loss of traction. But, that is also why it is very nice to be able to shift the car into neutral when you just want to coast (such as down a slight incline).
Mike