Diesel hp rating not always what's advertised!

Discussion in 'Diesel Engines' started by Chuck Bates, Feb 4, 2005.

  1. I did mean legal beef-- as, I agree with you. :)
     
  2. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 110, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    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
     
  3. 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.
     
  4. fredrosse
    Joined: Jan 2005
    Posts: 399
    Likes: 55, Points: 38, Legacy Rep: 56
    Location: Philadelphia PA

    fredrosse USACE Steam

    Fuel Cooler - Diesel Output

    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.
     
  5. Karl2
    Joined: Feb 2005
    Posts: 67
    Likes: 1, Points: 0, Legacy Rep: 34
    Location: Right Coast

    Karl2 Junior Member

    Fuel Temp - Diesel Output

    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
     
  6. PowerTech
    Joined: Feb 2005
    Posts: 183
    Likes: 0, Points: 0, Legacy Rep: 4
    Location: FL,Keys

    PowerTech Senior Member

    ha ha ha vapor lock

    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
     
    Last edited: Mar 1, 2005
  7. gonzo
    Joined: Aug 2002
    Posts: 15,242
    Likes: 948, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    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.
     
  8. PowerTech
    Joined: Feb 2005
    Posts: 183
    Likes: 0, Points: 0, Legacy Rep: 4
    Location: FL,Keys

    PowerTech Senior Member

    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.
     
  9. Karl2
    Joined: Feb 2005
    Posts: 67
    Likes: 1, Points: 0, Legacy Rep: 34
    Location: Right Coast

    Karl2 Junior Member

    Fuel - Air and Diesels

    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
     
  10. PowerTech
    Joined: Feb 2005
    Posts: 183
    Likes: 0, Points: 0, Legacy Rep: 4
    Location: FL,Keys

    PowerTech Senior Member

    Preaching to the quier.I smell gas from some of the other post's.
     
  11. woodboat
    Joined: Nov 2003
    Posts: 312
    Likes: 1, Points: 0, Legacy Rep: 14
    Location: Baltimore MD, USA

    woodboat Senior Member

    A blurb from dana
    http://www.dana.com/Automotive_Syst...Products/Fuel Coolers/fuelcooleroverview.aspx
     
  12. gonzo
    Joined: Aug 2002
    Posts: 15,242
    Likes: 948, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    I think you are talking of obsolete systems. The thread is about current models.
     
  13. Karl2
    Joined: Feb 2005
    Posts: 67
    Likes: 1, Points: 0, Legacy Rep: 34
    Location: Right Coast

    Karl2 Junior Member

    "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
     
  14. Alexph
    Joined: Feb 2005
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Dorset, U.K.

    Alexph Junior Member

    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
     

  15. globaldude
    Joined: Jan 2005
    Posts: 110
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Whangarei New Zealand

    globaldude court jester

    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 .
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.