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Diesel and stop-start systems

Discussion in 'Gen 2 Prius Main Forum' started by bredekamp, Mar 13, 2009.

  1. bredekamp

    bredekamp Member

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    A friend and I enjoy chatting about technology. Cars and car engines often enter the conversation. We were talking about diesel engines and he mentioned that even large diesel engines use almost no fuel when they're idling. Is this true?

    If so, why bother adding an engine stop-start system to a diesel vehicle if idling isn't going to waste fuel? Perhaps diesel emissions are more harmful from an idling engine?

    BMW isn't offering the 1 series 120d with stop-start here. They say it needs "low sulphur" fuel, but gas stations here do sell diesel with 50ppm of sulphur. Do they need even less?
     
  2. jayman

    jayman Senior Member

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    No, it is not.

    I'm not sure why a person would even idle a diesel engine in SA, unless to keep the air conditioner running. Here, with winter temps of -40 C, some like to keep their diesel engine running as without a powerful coolant heater, it's almost impossible to start a diesel engine at those temps

    Diesel engines suffer from incomplete combustion at a "dead" idle. The residual fuel washes oil from the cylinder walls, and contaminates the engine oil. This results in much increased engine wear.

    To avoid incomplete combustion resulting from a "dead" idle of say 500 RPM, most large diesel engines offer an "idle up" switch. The Idle Up feature raises engine RPM to 1,000-1,400 RPM

    Especially when fuel prices peaked, the sales of aftermarket diesel-fired engine heaters, and even APU's, soared. With diesel prices lower now, folks are buying the engine heaters and APU's to reduce wear on their motors

    For example, this diesel fired coolant heater

    Proheat? X45 Truck Heater

    Uses a fraction of the fuel that running the engine at idle does. More sophisticated approaches use a small 1 or 2 cylinder diesel motor to run a generator

    This is the Teleflex APU solution

    Teleflex Power Systems - Idle Reduction & Power Management Solutions

    North America Truck, Trailer, and Rail

    An advantage of the Teleflex APU is that it can also run a separate A/C system in summer, so you don't have to idle the engine to keep the cab cool

    Rail locomotives are also being adapted to use APU's

    Teleflex Power Systems - Rail Solutions

    I realize truck drivers aren't the brightest bunch, but a lot of them still believe idling a diesel motor is somehow "good" for it. At one time, you could even buy a system that would automatically start the motor, to run it from time to time, or based on outside temp

    Almost every big truck now has an idle kill system. After so many minutes, typically 5-10 mins, the motor automatically shuts down
     
  3. jayman

    jayman Senior Member

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    The emissions controls are now integrated with the powertrain and engine management system. Probably the SCR would plug up and die run on 50 ppm, ideally it should be under 12 ppm
     
  4. bredekamp

    bredekamp Member

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    Thank you.
     
  5. JSH

    JSH Senior Member

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    Diesel engines use less fuel than gasoline engines when idling. The reason is the diesel don't keep a near constant air-fuel mixture like gasoline engines do.
    • Diesels don't have a throttle plate and do not regulate the amount of air that goes into an engine. Instead the amount of diesel fuel is regulated in accordance to how much power is needed. Diesel engines can idle with air-fuel ratios as low as 50:1
    • On the other hand gasoline engines have an ideal air-fuel ratio of 14.7:1. This can range from about 12:1 to 17:1 but outside of this range a gasoline engine will not run.

    However, this does not mean that modern diesel engines should be idled. It still wastes fuel even if it is not as much as idling a gasoline engine. That is why BMW has the idle stop feature on many of their engines both diesel and gasoline.

    At one time there where good reasons to idle a diesel engine but modern technology has made this unnecessary.

    Old diesel engines used indirect mechanical injection and were very difficult to start when the engine was cold. In cold ambient temperatures it was almost impossible to start a diesel engine without a electric engine block heater. This is because a diesel ignites fuel by compression and does not have a spark plug. Drivers simply idled their engines anytime they were away from there maintenance shop to avoid being stranded with a cold engine that would not start.

    Modern diesel engines have electronic fuel injection that inject fuel directly into the combustion chamber as very small droplets. They also have effective glow plugs that preheat the combustion chamber. These two things combine to make modern diesel engines almost as easy to start in cold weather as gasoline engines. I have a 2003 VW diesel and I've had no problem starting it in temperatures as cold as -20C. I simple turn on the engine, watch the light on the dash that tells me the glow plugs are heating up the combustion chamber. When that light goes out, I turn the key and the engine starts. This process only takes about 30 seconds.

    The other reason that truckers would idle their engines is to maintain power and heat when they sleep. As Jayman pointed out, now you can get small generators that will supply heat and power to a truck without idling the main engine. This small generator is much more fuel efficient that idling the main engine.
     
  6. jayman

    jayman Senior Member

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    To clarify a few things I pointed out:

    A "dead" idle with a diesel engine - or any engine for that matter - is bad for it. Incomplete combustion = increased blowby = increased wear

    When you use the "idle up" switch on a large diesel engine, to run it at 1,000-1,400 RPM, that uses a hell of a lot more fuel than a "dead" idle.

    Even modern diesel engines are difficult to start in temps of -30 C and colder. Ford claims their new PowerStroke will start "unassisted" at -30 C. A neighbor of mine, about 3 km from my hobby farm, has a 2008 F-450. He tried their claim with me watching, as he wanted to really know if the motor was capable of this:

    Took a lot of cranking, several tries, and it ran like s***. He finally shut it down, and plugged it in to warm up. After being plugged in 10 hours, it started and ran just fine

    Another point with diesel engines, is the diesel fuel itself. Even fuel that is blended for cold weather use may still gel up at -30 C and colder. Once the fuel gels up, you're in deep s***. There are additives you can use, but they only help if you remember to use them *before* the trouble starts

    If you anticipate routine operation at -40 C and colder, a large diesel engine can be outfitted with heated fuel tanks, heated fuel lines, and a heated fuel filter
     
  7. bredekamp

    bredekamp Member

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    Check these sweet trucks used at the South Pole. They have standard 3.0 D-4D engines, but were modified by Arctic Trucks for operation at -30C.

    Story at:

    Wheels24
     

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  8. jayman

    jayman Senior Member

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    Good article, I noticed they absolutely put in a coolant heater

    At one time, the diesel fuel used at the South Pole research sites, and at radar sites in the Canadian Arctic, Thule, and Alaska, was called DFA "Diesel Fuel Arctic"

    DFA was specially formulated to not gel up even at -50 C. However, the formulation and additives used in DFA would be incompatible with modern Common Rail fuel injection systems. You wouldn't get too much life out of the Common Rail system

    Equipment used in Arctic environments doesn't roll up highway km's like road transport in North America or Australia. So the lower lifespan isn't much of an issue

    The replacement for DFA is JP-8. JP-8 is used in diesel powered trucks, aircraft, generators, etc, of the US Military. It is widely used in the Canadian Arctic, and exclusively used at the Amundsen-Scott base at the South Pole

    Like DFA, JP-8 will reduce the life of Common Rail fuel systems

    Thule lays in supplies during summer season

    http://www.msc.navy.mil/sealift/2007/September/pacergoose.htm

    http://www.lockheedmartin.com/data/assets/4094.pdf

    JP-8: Facts, Discussion Forum, and Encyclopedia Article

    :: NASA Quest > Archives ::
     
  9. bredekamp

    bredekamp Member

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    I saw a documentary about THULE AIR BASE on Discovery.
     
  10. jayman

    jayman Senior Member

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    I was stationed there for about 1.5 years when we were doing the radar upgrades to the newer phased array solid state hardware. The old radar had mechanical waveguide tuning, it was called an "organ tuner" due to looking like a giant church organ.

    The equipment that was kept outside - the *majority* of the equipment had to be, there are only so many heated garages and hangers you can build - had a wide array of electric heaters that were kept plugged in most of the year

    Eg: the diesel equipment like front end loaders had heaters in the fuel tanks, hydraulic sumps, axles, transmission oil sumps, engine oil sumps in addition to the coolant heaters. The gasoline equipment had heaters in the axles, transmission sumps, engine oil sumps, and coolant heaters

    All the lubes are synthetic. Engines ran a special military spec motor oil - MIL-L-46167 - which is a synthetic 0W-20

    The logistics of running a place like Thule are pretty daunting. The bitter cold makes everything that much more difficult