Why not supercharge a diesel?
Discussion
Some Gump said:
Imo dervs don't need more low down, and most are engineered for effiency - i'd guess that expaiins the choice of turbo.
would be my guess too. If there was a market for diesels with a throttle response turbo's couldn't provide, then maybe... until then, it's an efficiency loss with little upside - possibly none if the gearbox limits how much torque is sensible. I believe some two-stroke marine diesels are turbo and supercharged however.Waugh-terfall said:
That's 8 years old, technology may have moved on 
simoid said:
Waugh-terfall said:
That's 8 years old, technology may have moved on Diesels use compression ignition, not sparks, as you know.
(Guess) At low rpm, diesels are already using the limits of detonation without extra intake pressure.
At higher engine speeds, as intake volumes increase, the extra pressure from a turbo does not overcompress the combustion.
(/Guess)
(Guess) At low rpm, diesels are already using the limits of detonation without extra intake pressure.
At higher engine speeds, as intake volumes increase, the extra pressure from a turbo does not overcompress the combustion.
(/Guess)
MissChief said:
Didn't Mazda supercharge a diesel once?
They certainly did, I drove their 626 'Comprex' diesel and it was ok but not especially quick with its 76bhp (approx). It had a very prominent supercharger whine and linear power delivery but I can never remember and particular benefits of that particular engine and the fuel economy wasn't particularly great either. Quite a rare car even when they were released though.1point7bar said:
(Guess) At low rpm, diesels are already using the limits of detonation without extra intake pressure.
At higher engine speeds, as intake volumes increase, the extra pressure from a turbo does not overcompress the combustion.
(/Guess)
Detonation isn't really the same issue in a diesel engine as it is in a petrol engine since there is no fuel in the cylinder until it is actually required. You could have a high boost at low speed, since the only difference between high and low engine speed is the number of cycles that happen in a given time. Boost at high revs is in principle the same as boost at low revs.At higher engine speeds, as intake volumes increase, the extra pressure from a turbo does not overcompress the combustion.
(/Guess)
Diesels can run with extremely high pressures, as long as the block and bottom end are strong enough to cope with it. The JCB Dieselmax world record car ran with about 90psi of boost.
tank slapper said:
Detonation isn't really the same issue in a diesel engine as it is in a petrol engine since there is no fuel in the cylinder until it is actually required. You could have a high boost at low speed, since the only difference between high and low engine speed is the number of cycles that happen in a given time..
Manifold flow?Big end bearing durability must be a consideration.
There would definitely be practical considerations that would have to be accounted for, but nothing that would be impossible. I imagine that it isn't done because there is little point - engines usually operate through gearboxes to give an output speed that is suitable for the task they are performing. There will be an optimal speed for efficiency so the minimal additional power (product of torque and engine revs: low revs = low power) doesn't make it worthwhile. Why make life difficult, when you can just use a conventional system and adjust the gearing to suit?
diesels already generate alot of their torque at lower revs anyway, thats why there's no need for a diesel. petrols tend to generate it at higer revs, thats why it's more useful for those.
surely having a twin-turbo configuration would be better then a supercharger? Might not be super instant/snappy power delivery from the get go, but it doesnt really sacrifice MPG unless you're flooring it.
surely having a twin-turbo configuration would be better then a supercharger? Might not be super instant/snappy power delivery from the get go, but it doesnt really sacrifice MPG unless you're flooring it.
Monty Zoomer said:
Detroit Diesel used to make supercharged diesel engines but they were two-strokes and they stopped making them and changed over to turbocharged ones.
All 2 stroke diesels have forced induction(specifically scavenge blowing); latterly the DD diesels were available with turbos as well offering greatly increased power, over here we had the Commer TS3, Foden FD series, Napier Deltic and the Leyland K60 and L60. Everyone stopped making 2 stroke diesels because they cost more to build than 4 stroke, which is a pity as they make a cool noise and potentially offer better power density.Gassing Station | General Gassing | Top of Page | What's New | My Stuff