[Marmot]

I am both amused and saddened by your description of the contribution (or rather deteriment) of a turbocharger and aftercooler to an engine's efficiency. Amused because of the naivete, and saddened by this illustration of the level of technical literacy so prevalent aboard so many boats. Bon voyage, Cap.

[YachtForums]

Originally Posted by Capt J

Turbo's use HP in order to make more HP. It takes a certain amount of HP to spin them and most figures are about 40% of the additional power they create.

I think we have a little compressor confusion here?

[Capt J]

Originally Posted by Marmot

I am both amused and saddened by your description of the contribution (or rather deteriment) of a turbocharger and aftercooler to an engine's efficiency. Amused because of the naivete, and saddened by this illustration of the level of technical literacy so prevalent aboard so many boats. Bon voyage, Cap.

It does take a certain amount of airflow and power to turn the turbo, they do create additional power over and above that. Needless to say, I am not an engineer, nor am I an armchair engineer. I do however have a vast amount of real world experience with diesels and range, considering I do 15,000 NM's in deliveries each and every single year. And, I do know how to rebuild an engine, have built a few race engines, and have a working knowledge of how a diesel engine works. I am also quite versed as to how a turbo and aftercooler work as well as an intercooler. When a turbo (or anything) compresses air it creates heat, and it then passes through an aftercooler (usually cooled by seawater in a yacht application) and then helps to cool off the intake air. There are also many turbo diesels in yachts that do not have an aftercooler although that is not the case with the vast majority of newer diesels. It is still higher then ambient air that a natural diesel would take in, in a well ventilated engine room. Diesels with turbo's also go a LOT less hours between rebuilds then naturals. You're basically throwing fuel in there to cool off the air intake charge as well as slow down the combustion process and prevent detonation.

Needless to say, the published range figures are believable and probably accurate. I also have experience with 16v2000's as well as many other makes and models. In the experience I have, one one engine at 7.5knots we burned 5gph on the engine in gear and 1-2gph on the engine in neutral. At 9 knots, we burned 6-7gph at idle with both engines in gear. At 1200 rpm's (our best cruise speed) we did 22 knots at 28gph, at 1950 150gph at 35 knots, and wide open 43 knots and 220 gph. Almost all diesels under 1000rpm's burn very little because it takes very little HP to move the vessel, compared to getting on plane and keeping the boat on plane. You also fail to realize that load figures can be different at idle between one boat to the next and vary with propellor type, gear reduction, hull design and such. A yacht has a reduction and propellor so that it achieves 100% load at rated RPM in this case 2350. From idle to there depends on many variables such as propellor type, cup, pitch etc. etc.

Anyways here are some actual figures for you to chew on. I wasn't going to spend all day looking for more tests as the ones in other magazines don't show fuel burn below 1000 rpms for larger yachts and larger engines.

Here's a 48' searay that burns 1.3gph at idle and 5.5 knots, thats 4 mpg, yet at cruise burns 1.5 gpm.
http://www.motorboating.com/articleH...?ID=1000066679

Here's a 48 Fairlane similar scenario

http://www.motorboating.com/articleH...?ID=1000065239
A 41' Rampage
http://www.motorboating.com/articleH...?ID=1000063633

More reading:

Turbochargers allow an engine to burn more fuel and air by packing more into the existing cylinders. The typical boost provided by a turbocharger is 6 to 8 pounds per square inch (psi). Since normal atmospheric pressure is 14.7 psi at sea level, you can see that you are getting about 50 percent more air into the engine. Therefore, you would expect to get 50 percent more power. It's not perfectly efficient, so you might get a 30- to 40-percent improvement instead.

One cause of the inefficiency comes from the fact that the power to spin the turbine is not free. Having a turbine in the exhaust flow increases the restriction in the exhaust. This means that on the exhaust stroke, the engine has to push against a higher back-pressure. This subtracts a little bit of power from the cylinders that are firing at the same time.

http://auto.howstuffworks.com/turbo.htm

[K1W1]

Hi,

Before anyone has a fuel ( blood) starvation related seizure I want to know---

Has anyone actually determined how far this Broward that was the original subject of this thread actually managed to go on a tank of gas?

The turbine and compressor sides of a Exhaust Gas Driven Turbocharger will normally turn at all RPM.

[K1W1]

Hi,

CaptJ,-I missed the big post you did and feel that I have to comment upon some of the inaccuracies and confusing things posted there.

Originally Posted by Capt J

I am also quite versed as to how a turbo and aftercooler work as well as an intercooler. When a turbo (or anything) compresses air it creates heat, and it then passes through an aftercooler (usually cooled by seawater in a yacht application) and then helps to cool off the intake air.

What exactly cools the Intake Air?

Originally Posted by Capt J

Diesels with turbo's also go a LOT less hours between rebuilds then naturals.

Do you think that this might somehow be related to the amount of fuel being burnt in the hours those run versus the amount burnt in a NA Engine?

Originally Posted by Capt J

You're basically throwing fuel in there to cool off the air intake charge as well as slow down the combustion process and prevent detonation.

Where did you read this?

Originally Posted by Capt J

The typical boost provided by a turbocharger is 6 to 8 pounds per square inch (psi).

The article you referred to for this info is obviously used to dealing with small automotive GAS engines using figures like this.

20 Yrs ago I ran The Engine Room of boat that had a pair of MTU 16V396 TB 94 Engines rated at 3500 Hp each at 2100 Rpm and this one used to plane quite well. We used to have a boost pressure of 5 Bar at WOT, That is some 75 PSI.

Even the old and doddery CAT 3306 needs some 10 Psi to get it's 160 Ekw when used as a genset

[Capt J]

Originally Posted by K1W1

Hi,

Before anyone has a fuel ( blood) starvation related seizure I want to know---

Has anyone actually determined how far this Broward that was the original subject of this thread actually managed to go on a tank of gas?

The turbine and compressor sides of a Exhaust Gas Driven Turbocharger will normally turn at all RPM.

That is true, however the turbo won't spin fast enough to produce enough boost to create additional horsepower until 1300 rpm's or so on most engines.

[Capt J]

Do you think that this might somehow be related to the amount of fuel being burnt in the hours those run versus the amount burnt in a NA Engine?

Where did you read this?

The article you referred to for this info is obviously used to dealing with small automotive GAS engines using figures like this.

20 Yrs ago I ran The Engine Room of boat that had a pair of MTU 16V396 TB 94 Engines rated at 3500 Hp each at 2100 Rpm and this one used to plane quite well. We used to have a boost pressure of 5 Bar at WOT, That is some 75 PSI.

Even the old and doddery CAT 3306 needs some 10 Psi to get it's 160 Ekw when used as a genset

What exactly cools the Intake Air? The intake air is cooled off by an intercooler. The intake air coming out of the turbo is cooled by an aftercooler before it is ingested into the combustion chamber.

Do you think that this might somehow be related to the amount of fuel being burnt in the hours those run versus the amount burnt in a NA Engine?

I think fuel consumed has a good amount to do with how long an engine lasts but is not the entire factor. With a turbo, the more boost you cram into the engine, the more static compression, and the more stress you are putting on parts. Plus, if anything goes wrong on a turbo charged motor like an injector that doesn't open the less margin of error you have versus on a natural that's not producing as much compression and therefore heat in the cylinder. You cannot take most natural engines and put a large turbo on it and expect it to last a month. Many internal parts are made stronger to handle the turbo; connecting rods, pistons, valves, crankshafts, even the engine block. It is definately not linear, I have seen charter boats that always run low rpm's easy, and their engines definately don't last nearly as long as the boat with naturals next to them. They burn about the same amount of fuel per trip as the boats next to them because the one with naturals has to turn more rpm's to go the same speed. Also, in the older non-electronic controlled engines, the turbo engines have considerably larger injectors then the naturals and at low RPM's they don't meter the fuel as well and run as clean as a natural and in a pleasure yacht application a lot of time is spent running low rpm's. Also they don't stay or get up to proper operating temperature unless they're running higher rpm's creating more wear.

It came from airflow research's website which makes a good amount of turbo's that you do see in marine engine applications such as older detroit diesels. Yes it is explained in regards to gas engines. BUT, the concept is totally the same of how a turbo works and what it does for an engine. Yes the boost figures are different for gas engines and diesels and diesels generally run more boost (which doesn't necessarily equate to more HP, it is not linear). Boost is the amount of back pressure in the intake tract not airflow. If you increase the efficiency of the airflow in the intake tract of the engine, boost will actually go down (everything else equal) because more air can travel more efficiently into the motor. Also the more boost you create on an engine, the more heated the air intake charge becomes and you get to the point of where a bigger turbo does not create anymore HP then the smaller one.

[K1W1]

Originally Posted by Capt J

What exactly cools the Intake Air? The intake air is cooled off by an intercooler. The intake air coming out of the turbo is cooled by an aftercooler before it is ingested into the combustion chamber.

None of the modern high output high speed diesels I am familiar with use Intercoolers. They all do use Aftercoolers and not all of these are directly sea water cooled.

Originally Posted by Capt J

Do you think that this might somehow be related to the amount of fuel being burnt in the hours those run versus the amount burnt in a NA Engine?

I think fuel consumed has a good amount to do with how long an engine lasts but is not the entire factor. With a turbo, the more boost you cram into the engine, the more static compression, and the more stress you are putting on parts.

A Turbo ( when the Turbine is turning fast enough to drive the Compressor at a speed at which it can compress air )provides combustion air at a volume that makes the Inlet Tract pressurized to somewhere above the atmospheric pressure. It is extra air that is being forced into the Cylinders not boost. Boost refers to the increase in pressure that is generated by the
turbocharger in the intake manifold that exceeds normal atmospheric pressure.

Static Compression is the ratio between the volumetric contents of the whole cylinder with the piston at BDC and what's left when the piston is at TDC. This is a mathematical calculation and will not vary depending upon the turbo's performance.

The Dynamic Compression Ratio is what varies with the varying charge air volume and fuel load.

Originally Posted by Capt J

Plus, if anything goes wrong on a turbo charged motor like an injector that doesn't open the less margin of error you have versus on a natural that's not producing as much compression and therefore heat in the cylinder.

If you lose an Injector ( doesn't open)on a Turbo charged or Naturally Aspirated engine you lose an injector ( other than splitting the end of a DD 2 Stroke injector)you will normally also experience a misfire and suffer a reduction in power. There will not be some catastrophic failure for a simple unit failure like that. If you have a tip go from water in the fuel or similar your real danger is filling the Oil system with Fuel and having a crankcase explosion. This can happen to both Turbo and NA EAngines.

Originally Posted by Capt J

You cannot take most natural engines and put a large turbo on it and expect it to last a month. Many internal parts are made stronger to handle the turbo; connecting rods, pistons, valves, crankshafts, even the engine block.

I would tend to agree with this

Originally Posted by Capt J

It is definately not linear, I have seen charter boats that always run low rpm's easy, and their engines definately don't last nearly as long as the boat with naturals next to them. They burn about the same amount of fuel per trip as the boats next to them because the one with naturals has to turn more rpm's to go the same speed. Also, in the older non-electronic controlled engines, the turbo engines have considerably larger injectors then the naturals and at low RPM's they don't meter the fuel as well and run as clean as a natural and in a pleasure yacht application a lot of time is spent running low rpm's.

Fuel metering with mechanical unit injectors and mechanically controlled delivery valves have always been variable at best.

Originally Posted by Capt J

Also they don't stay or get up to proper operating temperature unless they're running higher rpm's creating more wear.

Running the engine cold will always cause premature wear to components.

Originally Posted by Capt J

It came from airflow research's website which makes a good amount of turbo's that you do see in marine engine applications such as older detroit diesels.

Would that be the same as Airesearch a division of Garrett?

Originally Posted by Capt J

Boost is the amount of back pressure in the intake tract not airflow.

Boost as I have explained above is, the increase in pressure that is generated by the turbocharger in the intake manifold that exceeds normal atmospheric pressure.

[Capt J]

What I was referring to with engines running cold is, in the US a lot of yachts will rarely see cruise RPM's..... You could let a DD 671TI-16v92TI as well as others CAT 3208t's, cummins 6bta's etc etc. , idle at the dock all day and it will never see past 140 degrees, you could let it warm up to 140 degrees, then take the vessel out all day and never see past 1,000 rpm's and 140 degrees water temp in the Intracoastal or trolling in the ocean, and the only way those engines will see proper operating temp is if run at cruise. Whereas the same natural engines would be run a little higher rpm-wise, as well as smaller injectors that are running a higher duty cycle (say 20%, versus 5% on the turbo motors (for example!) and they tend to meter fuel better the higher the duty cycle, and the naturals tend to run closer to operating temperature......180 degrees in most cases..... so in general yacht usage this is more of a reason the naturals will last much longer.......

[Marmot]

"...as well as smaller injectors that are running a higher duty cycle (say 20%, versus 5% on the turbo motors (for example!) and they tend to meter fuel better the higher the duty cycle,..."

Where on Earth are you getting this stuff?

[Capt J]

Originally Posted by Marmot

"...as well as smaller injectors that are running a higher duty cycle (say 20%, versus 5% on the turbo motors (for example!) and they tend to meter fuel better the higher the duty cycle,..."

Where on Earth are you getting this stuff?

Various Factory Certified CAT, MAN, and Detroit Diesel mechanics over 25 years of experience as well as over 300 engine startups on new vessels and 1000's seatrials with used vessels with factory trained engine surveyors. Where are you getting your stuff?

Let's use a hypothetical situation so you can get a real idea of what I am talking about. NOW, this is just an example. Let's say we have two different 1980 45' Hatteras SF's. Vessel #1 has 8v71 naturals with the factory N70 injectors (70 liters of fuel per hour), Vessel #2 has 8v71 TI's with the factory M110 injectors (110 liters of fuel per hour). Both vessels are going trolling for the day and want to do 7 knots.

Vessel #1- is at 1000-1200 RPM's due to running less pitch propellors and for example running a load factor of 25% to make 7 knots , considering a natural has a fairly linear RPM to power output ratio across the graph, the injector is probably running a 25% duty cycle. It is also running at 180 degrees because it is at a higher rpm and load factor then vessel #2. Cruise speed at 1950 rpm's would be 15 knots

Vessel #2 is running at 700 rpm's to maintain 7knots because it is running more propellor pitch because then vessel #1 because it makes 40% more torque and horsepower on the upper half of the RPM range. Vessel #2's injectors are probably running no more then 10% duty cycle because they are much larger, load factor is much less at 700rpm's, and the turbo is not spinning fast enough to greatly increase airflow and horsepower. Vessel #2's RPMvsPower Output ratio is not linear and greatly increases after 1400 rpms as the turbo boost starts increasing, so the injectors wouldn't start really running over 20% duty cycles until the rack sees a decent amount of boost/load usually around 1400rpm's on DD's. Engine temp would never exceed 150 degrees ALL day long, until rpm's have come up over 1,000 rpms. Cruise speed at 1950 rpm's would be 23 knots.

Can you now understand how this works? Both situations are pretty close to what you'd see in real life on a 45' Hatteras equipped with those engine combinations.

[K1W1]

Hi,

If you have the correct temperature thermostat there should be no way you can run your engine at 140 Deg F even if it is idling.

I second the previous posters question as to where some of the statements you are making concerning this facet of Marine Engineering really come from.


And by the way in the second line of your second paragraph of the post above--- There is NO such thing as a naturally aspirated 8V 71. They all have a Roots Blower

It has been more than 25 yrs since I had an 8V 71 apart but seem to recall that the Injector number was a capacity in millilitres not litres.

I certainly hope you know more about the duties and responsibilities of being a Captain than you do the engines that push you around for 15,000 N.M. a year.

What happens when you get to 15,001 miles?

[Capt J]

Originally Posted by K1W1

Hi,

If you have the correct temperature thermostat there should be no way you can run your engine at 140 Deg F even if it is idling.

I second the previous posters question as to where some of the statements you are making concerning this facet of Marine Engineering really come from.


And by the way in the second line of your second paragraph of the post above--- There is NO such thing as a naturally aspirated 8V 71. They all have a Roots Blower

I certainly hope you know more about the duties and responsibilities of being a Captain than you do the engines that push you around for 15,000 N.M. a year.

What happens when you get to 15,001 miles?

I know they ALL have a roots blower, but the blower is the same displacement as the engine it is on, so it does not produce any additional airflow. Any of the detroits that are not equipped with a Turbo, are referred to as "Naturals" by Detroit Diesel Corporation.

Post another topic "What water temp do your 2 stroke detroits run at, below 1000 rpms" and ask other captains whether any 2 stroke non-electronic detroit diesel reaches 180 degrees under 1000 rpms. Actually I will do it.

I have run tons of detroits (as well as other mechanical motors in yachts and electronic diesels) NONE of them do, this is with the proper 180 degree thermostats. They never reach operating temperature in a yacht under 1,000 rpms unless they have an ill-maintained cooling system (worn raw water impellor, clogged heat exchanger, etc.) where it would overheat at higher rpm's. Over the road trucks put a piece of vinyl over the grill in the front of the truck during the winter to block some of the airflow over the radiator to maintain operating temperatures.

Marmot and K1W1, have either of you operated ANY Detroit Diesel or other mechanical diesel in a yacht? Do you have any real world experience with these engines in operation in a yacht or sportfish?

[K1W1]

Originally Posted by Capt J

I know they ALL have a roots blower, but the blower is the same displacement as the engine it is on

So you think the Blower displaces 8 x 71= 568 cu in?

Originally Posted by Capt J

Marmot and K1W1, have either of you operated ANY Detroit Diesel or other mechanical diesel in a yacht? Do you have any real world experience with these engines in operation in a yacht or sportfish?

I would say the answer to this is yes.

[Marmot]

"... have either of you operated ANY Detroit Diesel or other mechanical diesel in a yacht? Do you have any real world experience with these engines in operation in a yacht or sportfish?"

Rather a substantial amount in both yacht and commercial applications from 2-71s up through the largest EMDs over a long period of time.

If you are finished trying to smokescreen the issue with a bunch of rubbish about duty cycles and airflow, would you like to make another attempt at explaining how your magic engine gets close to 50 percent efficiency at idle? This is especially interesting now given the volumes you have written about how badly these things run at low rpms.