Any Gearhead's?

[Gramp34]

US27inKS has it right.

In addition, turbo and non turbo diesels usually run with the same compression ratio. For instance, the Perkins M65 was 17.5:1; the M85T was the same engine turbocharged and was 17.5:1, and so on.

I think you'll find other than the manifolds and fuel pump calibration, they're the same engine.

You can turbocharge (or supercharge) a diesel without adding an aftercooler. By cooling the compressed intake air, you can stuff more oxygen into the cylinders, which can then burn more fuel and produce more power than with just the turbo.

Supercharging requires power off the crankshaft to compress the intake air. Turbocharging works off the heat in the exhaust, so it compresses the intake air for 'free'. (Supercharging doesn't have any turbo lag, which is why it's used on cars.)

The benefit of supercharging is to put more air into the engine, which allows you to use more fuel and produce more power. It doesn't improve the efficiency of the engine. In fact, the power to drive the prop will still be the same, but the engine will probably burn more fuel to go the same distance. After all, it's going to take engine power to run the supercharger, and the extra air pumped into the engine is just going to be pumped out the exhaust.

Tim

[Gramp34]

Originally Posted by sailingdog

Unfortunately, these features are generally not found on marine diesels used in sailboats, since they can't tolerate a small sailboat marine environment very well.

Oh, well electronic engine control units do show up on bigger recreational marine diesels, such as the Yanmar 6LY3 series, Cummins Mercruiser QSB series, Caterpillar C-7 propulsion series, Volvo Penta D6 series, and John Deere 6068 series.

Perhaps the "sailboat marine environment" is much worse than the powerboat marine environment?

[Capnblu]

You are correct Gramps, unless you then apply the MAX-PROP to the equation, lowering the rpm's for the same thrust.

[Gramp34]

Originally Posted by Capnblu

You are correct Gramps, unless you then apply the MAX-PROP to the equation, lowering the rpm's for the same thrust.

Yes, you can do this, but it won't change much in the way of fuel use. Industrial diesels usually are most efficient near their rated speed. Here's the data for a Cat engine:



The bottom graph is the Brake Specific Fuel Consumption in pounds per horsepower-hour. For a given horsepower load, the engine burns more pounds of fuel when it's run slower.

Tim

[sailingdog]

Yes, the small sailboat marine environment is much worse IMHO...

Originally Posted by Gramp34

Oh, well electronic engine control units do show up on bigger recreational marine diesels, such as the Yanmar 6LY3 series, Cummins Mercruiser QSB series, Caterpillar C-7 propulsion series, Volvo Penta D6 series, and John Deere 6068 series.

Perhaps the "sailboat marine environment" is much worse than the powerboat marine environment?

[Omatako]

Originally Posted by Gramp34

I think you'll find other than the manifolds and fuel pump calibration, they're the same engine.

No I don't think so. Most charge-air engines have different fuelling profiles, cam timing, pump timing, combustion chamber shapes, and so the list goes on.

Originally Posted by Gramp34

You can turbocharge (or supercharge) a diesel without adding an aftercooler. By cooling the compressed intake air, you can stuff more oxygen into the cylinders, which can then burn more fuel and produce more power than with just the turbo.

An intercooler (between the turbo and the inlet manifold) is what you're talking about. Aftercoolers are actually quite rare.

Originally Posted by Gramp34

Supercharging requires power off the crankshaft to compress the intake air.

Correct

Originally Posted by Gramp34

Turbocharging works off the heat in the exhaust, so it compresses the intake air for 'free'.

Wrong. The air being blown out of the exhaust spins one end of a turbine, the other end of the turbine compresses the air into the manifold. It has nothing to do with heat. Heat is the biggest enemy of engine efficiency which is why there are things like pre-coolers, intercoolers and aftercoolers.

Originally Posted by Gramp34

The benefit of supercharging is to put more air into the engine, which allows you to use more fuel and produce more power. It doesn't improve the efficiency of the engine.

What?!?!? Double the horsepower from the same cubic capacity?? No improvement in efficiency??

Originally Posted by Gramp34

In fact, the power to drive the prop will still be the same, but the engine will probably burn more fuel to go the same distance. After all, it's going to take engine power to run the supercharger, and the extra air pumped into the engine is just going to be pumped out the exhaust.

Sorry fellows, that last piece leaves me speechless. No I can't leave it there. The energy used to turn a supercharger is a very small fraction of the power that results from the charging of the engine. To say that the result will be the same or less efficient, is nothing short of daft.

Gramp has obviously never heard of drag racing. Nufsed.

[goboatingnow]

The 4-108 is a good old heavy block, and I'm sure it would handle turbo or supercharging ( they more or less have the same effect). However it will need changes to the injector and injector pump settings. I suspect that the longetivity of teh engines would be effected. But It would work, just for how long. I suspect a bit of research you will find that that block has been turbocharged by somebody maybe even perkins. IT as been used all over the place.

[Gramp34]

Originally Posted by Omatako

An intercooler (between the turbo and the inlet manifold) is what you're talking about. Aftercoolers are actually quite rare.

Here's more of that Cat datasheet:



I guess nobody told Caterpillar (or Cummins or Detroit Diesel) that aftercoolers are quite rare.

Wrong. The air being blown out of the exhaust spins one end of a turbine, the other end of the turbine compresses the air into the manifold. It has nothing to do with heat. Heat is the biggest enemy of engine efficiency which is why there are things like pre-coolers, intercoolers and aftercoolers.

No. A turbocharger consists of a turbine and a compressor connected by a shaft. The intake air comes in contact with _only_ the compressor and doesn't get near the turbine. It's the compression of the intake air that causes it to be heated, not any contact with the exhaust. By cooling the heated intake air it becomes more dense, allowing more oxygen to be crammed into the fixed displacement of the cylinder, which allows more fuel to be burned.

The turbine section is powered by the heat energy in the exhaust, rather than taking energy from the crankshaft. (In fact, the Detroit Diesel DD15 uses an extra turbine stage in the exhaust geared to the engine to develop an extra 50 horsepower and improve fuel efficiency by 5%. This is a case where engine efficiency is improved through turbocompounding.)

Sorry fellows, that last piece leaves me speechless. No I can't leave it there. The energy used to turn a supercharger is a very small fraction of the power that results from the charging of the engine. To say that the result will be the same or less efficient, is nothing short of daft.

Gramp has obviously never heard of drag racing. Nufsed.

You're trolling here, right?

From Wikipedia: "A top fuel dragster can consume 6 U.S. gallons (23 L) of nitromethane for a quarter-mile (400 m) run in about 4.5 seconds, which comes out to 24 U.S. gallons per mile (5600 L per 100 km). "

That's 0.042 mpg. (About 200 times worse than a Hummer.) You call that efficient?

Efficiency is energy out divided by energy in. The OP's sailboat requires the same energy out, but if you're driving a supercharger that's going to put more load on the engine, it will cause the engine to burn more fuel. Energy in goes up, efficiency goes down.

More air in the cylinder means that more fuel could be injected and burned, and the engine could produce more power. If you're not putting an extra load on the engine, the injection pump won't inject extra fuel, and that extra air is just along for the ride. It gets pumped into the engine, and pumped out the exhaust, taking energy to do so, but providing no benefit.

The OP's idea is to supercharge to produce his necessary power at lower RPM and repitching his prop to absorb that power. It'll make a cool sound, but I don't see much in the way of saving fuel.

Tim

[goboatingnow]

Gramp34 efficiency however is only indirectly related to fuel consumpton, Lots of a fuels available energy is not converted in motive power. All forced air systems inproves engine efficiency, ie more motive power is gained from the fuel consumed. If you dont beleive look at the fuel consumption of a 100hp inline 6 clyinder and compare it to an equivalent modern lightweight 4 clyinder supercharged diesel ( say teh volvo KAD32p for example). The fact is that its not a simple energy in and out, its the conversion of calorific energy in the fuel to motive power thats whats been improved.

[US27inKS]

Originally Posted by Gramp34

A top fuel dragster can consume 6 U.S. gallons (23 L) of nitromethane for a quarter-mile (400 m) run in about 4.5 seconds, which comes out to 24 U.S. gallons per mile (5600 L per 100 km).


Tim

Sorry Tim, this quote is way off. It's more like 13 gallons.

There's really not much to argue about here. The OP wants to know about putting a supercharger or turbocharger on his sailboat. I think everyone here can agree that he won't get his money's worth in either fuel efficiency or resale value. I think we can also agree that a turbocharged sailboat will get to hull speed quicker than a non turbocharged boat, due to increased power available.