Diesel hp rating not always what's advertised!

[Chuck Bates]

An interesting thread on how some Marine Diesel manufacturers alter the conditions to make their hp figures inflated:

www.boatdiesel.com
then: forums
then under Volvo Penta: Volvo General
then: Volvo IPS and something entirely different

Buyer Beware!! :eek:

[Richard Petersen]

Looks like another person has found out that diesel PR people rate their engine by a combination of hours and horsepower. 1 minute at 1,000 hp or 250 hp at 2,500 hours. Same engine can do both.--------------I see nothing wrong with it, as they are giving YOU the option of blowing the engine.

[gonzo]

The HP is correctly advertized at 25C, that is the standard. They may offer performance at other temperatures also. It is up to the buyer to educate himself and read the specifications.

[ABoatGuy]

Also make sure what HP you are looking at (metric, or BHP). Almost all use metric now because the numbers are a little higher. Most companys do base there ratings on some standard (DIN 6271 / ISO 3046) and most state on there brochures what the conditions are. Pay attention and you should be OK.

[Karl2]

25C is not the standard. It is an option that some manufacters, obviously, is taking advantage of. This enables them to post 2-3% higher hp numbers.
25C is an unrealistic fuel temp and will never occur in a boat while running unless an efficient fuel cooler is used.
Compare to a car manufacturer advertising fuel consumption going downhill only.

Karl2

[gonzo]

A car going downhill? Lets not exagerate. Any standard is arbitrary. As long as they publish it, the data is significant.

[Karl2]

Significant...Hmmmm. If you publish data derived under conditions that the consumer will never experience and then leave it to the consumer to read the fine print and figure this out I'm not sure I agree that there is any value to the data. I mentioned 25C fuel temp - Unrealistic but doable if you employ fuel cooler(s) - The manufacturers using 25C does not supply a fuel cooler with their engines.

Worse is the specific gravity of the fuel - .84 (give or take some on the second decimal) is what most manufacturers use. .86 is used by one manufacturer, which nets another 3% gain in publishable hp. .86 fuel is not available to the general public.

Karl2

[Richard Petersen]

I had to check, GM owns SAAB, FORD owns VOLVO.OK. The new rating system is being done by the same PR group that told us BAD tires made Ford suv's roll over like broken eggs. :eek:

[Chuck Bates]

Richard,
I think you're missing the point. Check out the website described in my initial thread then check out boatdiesel.com and see what Karl is trying to say. It is Yanmar that's fudging the hp figures, not Volvo.

P.S. Volvo AB sold Volvo car to Ford 6-7 years ago. Ford has NOTHING to do with Volvo Penta.

[gonzo]

Karl2: please do your homework before making claims. Name one large diesel engine without factory installed fuel cooler.

[FAST FRED]

Detroit Diesel 2-71, 3-71,4-71 6-71 8V71 12V71, 16V71 for a start.

FAST FRED

[Karl2]

In the the 10 - 800 hp bracket: CAT, Cummins, Volvo, Yanmar, Perkins, Scania to start with. Some of these manufacturers have fuel coolers on some models. For example: Common rail engines (Volvo D4/D6, Cummins QSB/QSC)
may require fuel coolers by the nature of the system - Not to preserve output but to prevent injectors from seizing.

My point was that the manufacturer(s) that are advertising output @ 25C does not supply a fuel cooler with the engine package.

I'm expressing an opinion: I do not belive that the engine buying public can keep this straight nor do I belive that it is fair to expect that the public should be able to do so. Is it your opinion that this is OK and the buyer needs to figure this out with the help of the fine print ?

If am looking for a diesel engine in the 300 - 325 hp range I would probarbly be looking at The Yanmar 6LPA-STP, Volvo D6-310 and Cummins 330B (Just three examples - there may be several others that belong on the list). Marketing has "established" that the Yanmar is 315 hp, the Volvo 310 hp and the Cummins 330 hp. I'm submitting that 99 out of 100 educated buyers would quote those hp figures if asked.
What is the "real" hp if you employ the same rating conditions for the three ?

Karl

[woodboat]

This is an interesting post from the thread:
I was involved in a recent discussion with another fellow that has the exact same year and model boat as I do. Mine is powered with twin 200 HP Volvo's and his with twin 220 HP Cummins (you may have seen the posts below). I like my Volvo's but to be honest, I would likely have gone with Cummins if I could have... (so I'm not pro or against any brand per se). Our boats appear comparable in weight (without actually measuring) yet his boats performance is off by about 4 knots at both cruise and WOT (about 20%) despite having more rated power ... I'm wondering if this might in part be explained by the same phenominon?
http://boatdiesel.com/BDR/Forums/Thread.cfm?CFApp=6&Thread_ID=17911&SearchKey=&mc=34

[Richard Petersen]

I think Karl2 has a legal beef, if I am reading him right. The test is with a fuel cooler not normally as standard equipment on most Diesel engines. He would be able to say the same with gas Mercruisers. They are not normally standard, but are a option.

[Karl2]

I don't belive there is a legal issue here nor do I belive there is merit(s) for a legal case - The conditions for the ratings are disclosed in the fine print.

I see it more as a ethical issue.

Karl

[Richard Petersen]

I did mean legal beef-- as, I agree with you. :)

[FAST FRED]

Although its hard to get , a FUEL MAP , at the style of service rating needed can be had from some Mfg.

First decide if you need cont. 24/7 power or if one of the "higher power" short limited service life is what you need.

A fuel map will look like a set of clouds drawn one on top of the next.

The smalest area is the lowest fuel consumption in the power and rpm areas covered by the "cloud".

Next larger area will be less efficent fuel burn , but usually a larger RPM choice and loading choice.

The fuel consumption is given for each "Cloud".

This is the ONLY way to know how low an engine can be operated with out harm from underloading , usefull mostly for the long range cruising folks, and commercial vessel operators.

FAST FRED

[Richard Petersen]

Those extreme conditions are taken care of by a transmission with 2 or more gears in foward. Cars do it all the time to squeeze speed, acceleration and economy out of 1 engine. And they do not lug or foul the engine. As we stretch the boating envelope, we must steal proven designs from other types of transportation.

[fredrosse]

For Diesel and gas turbine engines, output power capability is a function of the inlet air temperature, not the fuel temperature. Supplying the engine with the coolest intake air available will make for the highest output, because the intake air density is greater at low temperatures. This allows more air (and fuel) for higher output. Drawing intake air from a warm engine compartment is costly in terms of engine output and fuel efficiency.

Engine manufacturers like to rate their engines with the lowest reasonable intake air temperature, gas turbines are rated at 15C (59F), but there are many different rating standards. Anyone who has had a Diesel automobile knows how much better performance is with cold weather conditions. Gasoline (spark ignition) engines are less sensitive to intake air temperature than Diesel engines.

Fuel coolers may be employed to reduce or eliminate vapor lock conditions of the fuel system, this has almost nothing to do with output power or engine fuel efficiency.

[Karl2]

Fred,

Not sure about gas turbines but as far as diesel engines go – Power is related to fuel temperature.

a) In all, high speed, diesels (a couple of exceptions that I’ll get to later) the fuel injection event relies on some sort of mechanical pump action. This pump action is, by design, locked to a specific fuel volume per stroke for each governor setting. As fuel temp goes up the viscosity changes. This viscosity change results in higher internal losses in this mechanical pump device. Higher losses = less fuel injected = less power.
b) A given volume of fuel contains a specific amount of energy. 10 mm3 @ 25C° contains y btu. If we increase the temperature 10C° this volume will expand, lets say, 1% to 10.1 mm3 and it will still contain the same y btu. We will still only inject 10 mm3 thus the btu content for the 10 mm3 @ 35C° will be lower. Lower btu per injection event = less power.

This is true for all systems using a mechanical pump device. Different designs react different to this but a good rule of thumb is a power loss of 1% per 10C° of increased fuel temp. At some point you will, of course, get into other problems besides power loss due to high fuel temp.

The exceptions are modern electronically controlled systems:
Unit injectors: These systems are still affected by the internal losses under a) but if the injector is electronically controlled the on-time can be manipulated and to some degree compensate for the increased fuel temp.

Common Rail Systems: These systems can be designed to be virtually unaffected by fuel temp. The system does not rely on a mechanical pump action for each injection event. A reservoir (fuel rail) is pre-charged with fuel at high pressure and the injector (connected to this reservoir) is opened electronically.
The issue under a) is eliminated and b) can be compensated for by a fuel temp sensor and manipulating injector on-time.

Karl

[PowerTech]

intake air temp is darn inportant for horse power.but so is feul temp with a small tank i have seen a 100 rpm lost on the ride home untill a feul cooler was aded.Hot air sucks to.low oxegen you guy are both rite

[gonzo]

Karl2: Diesels have an oversupply of fuel at the injectors. That's why there is a return line. In a modern diesel the injector will send the amount of fuel needed for the mass of air.

[PowerTech]

I have always thought that the over supply of feul to the injectors be it unit,electronic,or mechanical was to only cool the injector.And that it was one of the injection pumps jobs to get the rite amount of feul into the cylinder via the injector whose sole purpose is to atomize the feul on a mechanical injection system.And that the injection pump or mecanical unitinjector only controls injection volumes relitive to intake air volumes if it is turbo carged and then only if equiped with a aniroid valve for regular injectors.Or other smoke limmiting type device found on mechanical unit injectors.And that the mechanical systems have no way of adjusting for changing inlet air tempatures at all.They can only adjust for volume of air="boost presure". Mecanical injection with coputer controled electronic governors and computer controled HPCR can adjust to perform corectly under extream air and feul temps but they to have there limmits and will derate them selfs until they are happy again.

[Karl2]

Gonzo, Carlwun

Yes, in a pure mechanical system (mechanical pump, mechanical injectors) there is a surplus of fuel delivered to the injectors. This has nothing to do with air-fuel ratio but rather the nature of the system: The pump element delivers a fixed qty of fuel to the injector. This qty is set by the diameter and allowed stroke of the pump element (Allowed stroke is set by the operators throttle lever position and the governor setting). Since the injector is opened by fuel pressure you need to maintain this pressure over a period of time to inject the desired qty. To maintain this pressure (and an open injector) you need to deliver more fuel to the injector that what is actually injected. The surplus is returned to the tank via the return line. And BTW – This surplus is also used as a cooling media for the injector itself.
A mechanical system as the one described is a dumb system. It has no clue how much air is supplied – I know of no diesel engine (below 1500 hp – not familiar with the larger stuff) that employs a mass flow sensor on the air supply side.

The solenoid valve (aneroid valve) present on many of these mechanical systems fills no function at full power. They do give the system a sense of the air supply during the acceleration phase. This valve assembly, typically, is mounted on the fuel pump itself and is via a mechanical linkage connected to the fuel rack. The linkage is connected to a diaphragm that in turn is connected to the intake manifold. With no boost pressure the linkage limits the fuel racks travel and as boost pressure comes up more rack travel is allowed. This is a “smoke limiter” that controls fuel rate during the acceleration phase. The device is, typically, fully open and fuel qty is completely controlled by the conventional governor by the time you reach 60-65% of rated speed.
More modern systems (unit injectors, common rail) work differently but there is no direct link between air and fuel in order to make power. Boost and airtemp is monitored by the system and feed to the fuel management system but more so for the purpose of controlling smoke.
Maybe there are engines out there that operates different as far as “aneroid valve”, monitoring airflow and adjusting fuel as a result, etc. etc. but I’m not aware of any.

A common misunderstanding, I believe, stems from our experience with gasoline motors. There you need a precise air/fuel ratio or trouble will ensue. The ideal air/fuel ratio (Stoichiometric) is in the range of 12 or 14:1 (With new technologies this has been creeping up in the last decade or so). You go too lean and pistons will melt (and other unpleasant issues), you go too rich and you loose power. In a diesel you have no butterfly valve on the intake to manipulate air volume – From the intake valve to the atmosphere there is a wide-open hole (after cooler, turbo and air cleaner in the way but nothing to “control” air volume). So.. A diesel engine runs, over its rpm/load band a spectrum of air/fuel ratios and they all work fine. If you manipulate the air only and run a diesel “rich” you will make power and plenty of smoke, run it lean and you will still make power and minimal smoke. There are, of course, borders for this too and if you cross them it will start to affect output. My point is that these borders are way broader than compared to a gasoline burner.
And…Don’t read this as if air supply has no impact on output – That is certainly not the case. Turbo chargers are there to increase air volume so more fuel can be injected and more ponies generated.

Karl

[PowerTech]

Preaching to the quier.I smell gas from some of the other post's.

[woodboat]

A blurb from dana
Recent reductions in emissions from High Speed diesel engines have created a new need to cool the diesel fuel. The extremely high injection pressure provide many benefits, but one side effect is a large increase in the fuel temperature when the fuel is depressurized and sent back to the tank via the return line. This can create extremely hot return fuel that exceeds the limitations of the fuel tank (often plastic) and the fuel injection equipment.

In response to this challenge our engineers have developed a variety of fuel cooling designs to meet all market needs. In doing so, we have become the market leader in the area of diesel fuel coolers.

Many of these coolers are designed for mounting underbody and cooling by ambient air, but engine mounted and coolant cooled solutions are possible as well. Please follow the links below for more information on our current production fuel coolers and inquire for more information as new developments are continually underway.


http://www.dana.com/Automotive_Systems/Products/Thermal%20Products/Fuel%20Coolers/fuelcooleroverview.aspx

[gonzo]

I think you are talking of obsolete systems. The thread is about current models.

[Karl2]

"Old" Technology - Yes. Obsolete ? Not really (Although I agree with you - They should be obsolete). Point from previous post still applies, to varied extent, to "modern" systems

Completely mechanical systems are still in use by many manufacturers. EPA II will, I'm sure, eliminate some of them but they will still be with us for years to come.

Karl

[Alexph]

i worked for perkins sabre and the hp they can get is reachable but not with an alternator water pump etc a complete no load engine will pull the hp but not under load or anything liike that

[globaldude]

Hi guys, I'm not sure if everyone on this thread gets a notice to say there's a new posting here, but I hope so, as most of you are "up" on HP, I'm wondering if you can explain to me the relationship of torque !?.
I've just brought an old [ albeit very low hrs] lister 4cyl 40 hp diesel engine.
It weighs in @ 1.5 ton & with a 3 to 1 box, was to have spun a 4 bladed 36" prop !!!.
Try that with a 40hp yanmar !!
It has a max rpm of 1200 & I'm thinking to lose the 3 to 1 reduction behind the box & have a direct drive through a 24" x ?? prop [ that's all I have room to swing ]
All thoughts / comments welcome .

[fredrosse]

The fundamental relationship between Torque and Horsepower is as follows:

HP (USA STANDARD) = Torque (Ft-LBf) x RPM x ( 2 x 3.14159 / 33,000 )

Where :
HP = USA STANDARD = James Watt Standard = 33,000 Ft-LBf / min
Torque = (Ft-LBf)
RPM = Revolutions per minute

Rearranging for conveinence:

HP (USA STANDARD) = Torque (Ft-LBf) x RPM / 5252

Torque (Ft-LBf) = 5252 x HP (USA STANDARD) / RPM

Reduction gears change the RPM output, and the output torque, horsepower remains essentially constant, except for some small loss (nominally 1 to 3%) across each gear reduction.

If you can give further details as to the boat displacement, hull type, waterline length, and desired speed, the proper propeller diameter and pitch can be selected. Depending on the availability to mount the ideal prop, some compromise is ususlly met, adjusting prop size and pitch to fit the constraints of the hull.

[gonzo]

40 HP is 40 HP regardless of brand. The RPMs at which the power is rated will indicate what the torque is. However, with a higher revving engine and a higher ratio reduction, it is possible to turn the same wheel. There is no difference.

[FAST FRED]

"We will still only inject 10 mm3 thus the btu content for the 10 mm3 @ 35C° will be lower. Lower btu per injection event = less power."

Even the lowly mechanical govenor on a Detriot 2 stroke will compensate for thin hot fuel.

The rack simply calls for MORE FUEL to keep the rpm the same , weather the load changes or the fuel does.

They were no dummies in 1936!

FAST FRED

[Karl2]

Fred,

Yes - And all mechanical engines with a governor will do the same. BUT only at partial load. At full load (and this is where your power loss due to fuel temp is noticable) the mechanical governor can do nothing to compensate.

Karl2

[Thunderhead19]

40 HP is 40 HP regardless of brand. The RPMs at which the power is rated will indicate what the torque is. However, with a higher revving engine and a higher ratio reduction, it is possible to turn the same wheel. There is no difference.

The standard for measuring engine horsepower output is "Brake" horsepower (which, as Gonzo describes is measured by torque at RPM acting on a water brake). I have, however, seen horespower published in terms of "shaft" horsepower, and in another way that I can't quite recall (Similar to Drawbar horsepower).

I have had diesel engines Dyno tested, and actually have never seen one fail to meet the publilshed values. I have heard of them though.

One interesting point is that some manufacturers will sell the same engine as a commercial engine and as a recreational engine. The commercial engine has a lower reccommended continuous operating RPM and therefore a lower Max Horsepower rating. (But it's the same engine)