Diesel engine "compressor", what is it?

[Simi 60]

Originally Posted by blueazimuth

Volvo engines -
love 'em or hate 'em

Love em when you buy them
A week later.....

[Dockhead]

Originally Posted by 01kiwijohn

Poor translation? Kompressor is German for Turbocharger. Usually gives more power, and better fuel consumption for a given engine model/size. One of the only cases of (well almost) "free lunch".

"Kompressor" , actually, is German for "compressor". But when referring to cars, it commonly means a mechanical supercharger. What we refer to as a "turbo" is more precisely a "turbo-supercharger", because the compressor is driven by an exhaust turbine, rather than mechanically. In both cases, the intake air is compressed to get a greater mass of air into the combustion chambers ("supercharging" the combustion chambers) . The turbo-supercharger is more efficient, because the energy needed to compress the intake air is mostly free, unlike the case with the mechanically driven supercharger.

[NewMoon]

How about some input from someone who actually owns a Volvo Penta diesel with Kompressor? It's a belt driven supercharger, not a turbo.

My 26-footer's 1998 electronically controlled 260hp KAD44P (one generation earlier than the D4 and D6) has both. It's a heavy (11,000 lb fully loaded) moderately deep-v planing-hull cruiser that takes a pretty good push to get up onto plane. There's only so much room in the engine compartment, so a diesel that's a good alternative to a big-block gas engine for this boat has to be pretty compact. VP's solution was to add the supercharger, which runs at mid-rpm's, roughly 1800-2300, on an engine with a WOT RPM of 3900.



The turbo doesn't kick in much until higher RPM, so it's not so much help getting the boat up onto plane. The supercharger makes the difference - the boat pops up onto plane quickly, then the turbo takes over and the supercharger turns off. On plane, we cruise at 16-18 knots and 3100-3300 RPM.

As far as longevity: in a hard-working application like this, setting the boat up properly is key. It's essential that props are the right pitch so that with a full load the engine can reach recommended WOT RPM. Unfortunately many owners don't take care to get this right, have props that are fine before the boat gets loaded up with fuel, cruising gear, fishing gear and people, but not with a full load. Their engines tend to be severely overstressed at full load, with way too high exhaust gas temps. Stern drives are way overstressed to, with high failure rates. Boats that are really too heavy for the size of the engine, so that the engine gets run on the ragged edge of too high a cruising RPM, overstress their engines too.

Get the right engine for the boat and the way it will be used, set it up properly, and run it reasonably, and such an engine can last. We've put 6,502 hours on ours in 17 summers, and it's still fine. After replacement of the original sterndrive under warranty (out of spec parts), the new leg has run some 5,700 hours with only periodic maintenance.

D4 and D6 are considerably more robust than our KAD44, but have the same sort of need to be set up, maintained, and run correctly. Some stories I've read of troubles with them seem to involve boats too heavy for the engine choice, overpropping, or both.

[nic26]

Originally Posted by Dockhead

"Kompressor" , actually, is German for "compressor". But when referring to cars, it commonly means a mechanical supercharger. What we refer to as a "turbo" is more precisely a "turbo-supercharger", because the compressor is driven by an exhaust turbine, rather than mechanically. In both cases, the intake air is compressed to get a greater mass of air into the combustion chambers ("supercharging" the combustion chambers) . The turbo-supercharger is more efficient, because the energy needed to compress the intake air is mostly free, unlike the case with the mechanically driven supercharger.

You mixed it up here: "compressor is driven by an exhaust turbine" is quite a bit beside reality. A compressor is a device that compresses air (duh) and in cars mechanically driven by a belt (i,e, VW) or gears. It has absolutely nothing to do with exhaust gas or anything in that area. You can also have a compressor to fill your dinghy if you like.

A turbo charger is a device with 2 turbine wheels, where 1 sits in the exhaust stream and is driven by that and the other 1 sits in the intake of the engine and pumps more fresh air into the combustion chambers leading in the end to more power for a given combustion chamber size.

[jimbunyard]

Originally Posted by nic26

You mixed it up here: "compressor is driven by an exhaust turbine" is quite a bit beside reality. A compressor is a device that compresses air (duh) and in cars mechanically driven by a belt (i,e, VW) or gears. It has absolutely nothing to do with exhaust gas or anything in that area. You can also have a compressor to fill your dinghy if you like.

A turbo charger is a device with 2 turbine wheels, where 1 sits in the exhaust stream and is driven by that and the other 1 sits in the intake of the engine and pumps more fresh air into the combustion chambers leading in the end to more power for a given combustion chamber size.

Further, turbos are centrifugal pumps, with the corresponding loss of efficiency (of operation, not of overall engine efficiency) and narrow operating range, whilst, generally speaking, kompressors, superchargers, blowers, whatever one wants to call them, are positive displacement pumps which deliver a specific volume per rotation, which is why they are most often driven by cogged belts or gears. The Volvos, belt driven, have an electric clutch that disengages the supercharger drive when the engine reaches a certain RPM, whence the turbo provides the boost to reach rated power...while Detroits, which are 2 stroke engines, require that the blower operate continuously to provide proper intake air calibrated to RPM and then 'scavenge' exhaust gases after combustion, so their blowers are gear driven with no 'clutching mechanism'.

[zeehag]

think about engine driven refrigeration. yes it still exists....needs engine driven compressor.
that item missing from my engine has been my reasonbable excuse for no refrigerator.

[newhaul]

Originally Posted by zeehag

think about engine driven refrigeration. yes it still exists....needs engine driven compressor.
that item missing from my engine has been my reasonbable excuse for no refrigerator.

zee that was solved with 12v refrigeration compressors.

[David M]

I don't see why one would be concerned about turbo lag on a boat.

I always bring the throttles up slowly on my turbo Diesel first so that nobody loses their balance and so that the oil pressure can also come up with the increase in RPM. Backing off the throttle slowly is also beneficial in that it gives the turbo time to slow down and cool before the oil pressure drops as the RPM's decrease. A hot turbo can burn the oil on the shaft in which the turbo spins. The oil helps to cool the turbo some.

Sure, I can see with a car not wanting any turbo lag if one likes jackrabbit starts and quick shifts with a manual transmission.

With a supercharger-blower-kompressor (whatever one chooses to call the same thing) adding a belt or two adds one more thing that has the possibility of breaking.

Naturally aspirated is the simplest way to go and adds a small element of reliability but you will not get the same horsepower out of the same displacement and weight of the same or similar engine.

[a64pilot]

Turbo lag isn’t the issue, the issue is that the turbo won’t begin to make significant boost until X RPM, and you can’t get to X RPM until after you get onto plane, but need the extra HP to get there.
Classic example of being behind the power curve.
A supercharger gives you power now, boost is there, always.
I’m surprised at the complexity of a compound engine though, especially if the Supercharger actually disconnects.
The advantage of a Turbo is it’s more efficient, it uses “free” energy from the exhaust, where a Supercharger steals crankshaft power and therefore is less efficient, however the decrease in efficiency isn’t all that much and isn’t worth the complexity of a compound engine in my opinion.
I have never seen a blower that is disconnected, I didn’t think that was possible, they are positive displacement pumps, if it doesn’t spin, air doesn’t go through it, so there must be an alternate air path too?
Unless it’s a centrifugal blower?

[newhaul]

A turbo a supercharger and a blower are all different critters that do the same job in different ways and efficiencies.

[David M]

Originally Posted by a64pilot

Turbo lag isn’t the issue, the issue is that the turbo won’t begin to make significant boost until X RPM, and you can’t get to X RPM until after you get onto plane, but need the extra HP to get there.
Classic example of being behind the power curve.
A supercharger gives you power now, boost is there, always.
I’m surprised at the complexity of a compound engine though, especially if the Supercharger actually disconnects.
The advantage of a Turbo is it’s more efficient, it uses “free” energy from the exhaust, where a Supercharger steals crankshaft power and therefore is less efficient, however the decrease in efficiency isn’t all that much and isn’t worth the complexity of a compound engine in my opinion.
I have never seen a blower that is disconnected, I didn’t think that was possible, they are positive displacement pumps, if it doesn’t spin, air doesn’t go through it, so there must be an alternate air path too?
Unless it’s a centrifugal blower?

I have operated a LOT of different turbocharged marine Diesels and the torque when throttling up is pretty linear between when the turbo has not kicked in and near full engine RPM. There has never been an issue with this in my experience.

Turbos are more efficient in that they are taking heat energy in the exhaust gas, converting that to mechanical energy in the turbo and then that energy is being used to compress the inlet air. They work much the same as a jet engine except that there is no burn stage and obviously they do not produce thrust.

[Dockhead]

Originally Posted by nic26

You mixed it up here: "compressor is driven by an exhaust turbine" is quite a bit beside reality. A compressor is a device that compresses air (duh) and in cars mechanically driven by a belt (i,e, VW) or gears. It has absolutely nothing to do with exhaust gas or anything in that area. You can also have a compressor to fill your dinghy if you like.

A turbo charger is a device with 2 turbine wheels, where 1 sits in the exhaust stream and is driven by that and the other 1 sits in the intake of the engine and pumps more fresh air into the combustion chambers leading in the end to more power for a given combustion chamber size.

Nothing mixed up -- what I said was exactly correct. Turbochargers also have compressors, and they do exactly the same function as a mechanical supercharger's compressor -- compressing the intake charge.




The compressor section of a turbocharger is not indeed a turbine. It is a centrifugal compressor:

https://en.wikipedia.org/wiki/Centrifugal_compressor

A centrifugal compressor LOOKS like a turbine, and works much the same way, just in reverse, but it's not a turbine -- a turbine extracts mechanical energy from a moving stream of fluid, and a compressor does the opposite -- taking mechanical energy and imparting that energy to the fluid stream.

So a turbocharger does not indeed consist of two turbines; it consists of one turbine and one centrifugal compressor.

https://en.wikipedia.org/wiki/Turbine

Even jet engines have compressors:

[David M]

True Dockhead...that is the correct terminology.

They all compress air, just in different ways.

[David M]

Originally Posted by jsc7

I am looking at deciding between a Volvo D4-300 and D6-370 and one difference is apparently that the D4 has "compressor" but the D6 does not.

What is a diesel compressor and the advantages/disadvantages?

Before considering purchasing a Volvo, check the prices on more commonly replaced parts like exhaust risers, fuel injectors, starters and water pumps. That might change your mind about buying a Volvo.

[NewMoon]

Originally Posted by a64pilot

I have never seen a blower that is disconnected, I didn’t think that was possible, they are positive displacement pumps, if it doesn’t spin, air doesn’t go through it, so there must be an alternate air path too?
Unless it’s a centrifugal blower?

On our 26-footer's VP KAD44P, the Kompressor (supercharger) is belt driven, via an electric clutch that engages and disengages under electronic engine controls. The air it pumps is ducted into the intake air passage only when it is on, via a sort of one-way flapper valve.

It's turned on when the engine is first started, to add air and thus reduce smoking at cold startup. When the engine has warmed up a bit, the supercharger is turned off. After that, the supercharger is engaged only under a fair amount of throttle in mid RPMs (about 1800-2300), which in our planing hull is only while the boat is pushing up onto plane.

The electronics know RPM, temperature at various points, air pressure, throttle position, and more. They adjust fuel amount and turn the supercharger on and off to optimize operation. Result is cleaner burning, less smoke, better fuel efficiency, and significantly more torque in mid RPM's.

We've seen the advantage of the supercharger when once we lost the supercharger belt, and being heavily loaded could not get up onto plane without it. If we had room and weight carrying ability for a bigger engine, we might not need it - the 44 is only 3.6 liters. If the 26-footer were not a planing boat, we certainly wouldn't need it.