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Old 06-03-2008, 09:33 AM   #1
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building a fuel miser bus.

Well, perhaps miser is the wrong word. How about slightly less glutonous bus.

From my year or so lurking around this place, I have gathered that pretty much anything in the double digit mpg range is considered good. Well, sorry, but in a world of 5 dollar a gallon diesel, that just ain't good enough. I doubt 20 mpg could ever be realized without some real crazy weight reduction/streamlining, but, I would think you might get into the upper teens.

Obviously, this wouldn't happen in a 40 foot DT466/allison fully loaded (hot tub) kinda rig, but, I would think that a 30ish footer 5.9 cummins (or maybe it's little brother 4 banger) 5/6 speed stick and ridiculously high rear end gears, with a bit of aero moding and weight reduction, ought to get you close.

Skoolies are incredibly overbuilt, so I would guess that you could loose a fair bit of weight and still be sturdier than a stick and staple P.O.S. RV. You could also save weight by using a composting toilet and limiting your potable water carrying capacity.

BTW, who is the fuel mileage champ among you bus owners? Anybody over 15 mpg?
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Old 06-03-2008, 10:55 AM   #2
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Re: building a fuel miser bus.

I think that 6BT guys and the 8.2 Detroit guys are the mileage winners. I do like the idea of using a 4BT instead, but those things are SO expensive because everyone buys up the used ones to stuff in their trucks or offroad rigs.
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Old 06-04-2008, 08:57 AM   #3
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Re: building a fuel miser bus.

hybrid drive is used in trains because it's the only way to put that much torque to drive wheels. It is not done for efficiency reasons.

A hybrid drive bus might make sense in a city bus or one that drives lots of hills, but, otherwise it wouldn't.

BTW, I'm guessing you'd need a hell of a lot more than 20 Kwatts. A 5 hp motor can make 3 Kwatts. So, I am guesing that a 20 K genie must need around 30-40 hp. Imagine your bus with a 40 hp motor.
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Old 06-04-2008, 11:04 AM   #4
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Re: building a fuel miser bus.

This thing can get near 30 with the 3 cylinder mercedes benz diesel. i have a buddy that has one in a motorhome configuration and he loves it.....except for that new car payment.

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Old 06-04-2008, 12:51 PM   #5
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Re: building a fuel miser bus.

Ah Jason ya beat me to it... I was going to mention that at RV shows I see these sprinter vans advertised as getting 20mpg. They are a bit "cozy" though...
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Old 06-04-2008, 08:59 PM   #6
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Re: building a fuel miser bus.

I am aware of the sprinter and it's RV conversion. But, it ain't a skoolie and you sure as hell ain't gonna find one at a gov. auction for 800 bucks.

I think we will be seeing quite a few of the euro RVs here in the next few years. Who the hell can afford to drive a large gas or diesel RV today? Some of these rigs are looking at damn close to a dollar a mile just for fuel.
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Old 06-05-2008, 05:04 PM   #7
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Re: building a fuel miser bus.

They're testing hybrid Buses and garbage trucks, maybe in about 15 years or so these will trickle down the the skoolie market, but by that time the batteries would most likely need replacement. May not ever benefit us, but cool none the less.

Hybrid garbage trucks and buses make a lot of sense with all the stopping and taking off they do throughout the day, there's a lot of energy being wasted in a traditional bus.



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Old 06-05-2008, 09:13 PM   #8
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Re: building a fuel miser bus.

Battery technology is so far behind the game. Batteries, even the various high end lithium types, are grossly inefficient in terms of space, cost, and output. I think that if hybrids really want to stand a chance of success they need to be based off of a capacitive discharge system instead. Capacitors have a much higher cycle life than batteries, to the degree of tens of thousands more cycles. They also are potentially far less expensive to produce while being much lighter and smaller than batteries with a similar storage capacity.

I think that a bus of the future could potentially be powered by a true diesel-electric hybrid system. A relatively small diesel engine (say a 4BT for a 40 foot city transit bus) could operate at its peak brake specific horsepower charging the bank of capacitors at all times. Meainwhile, traction motors at the wheels would provide the actual motion using the stored energy in the capacitors to provide overcome all the forces acting against acceleration. At cruise speed I think it would be an essentially zero loss system with the energy provided by the diesel engine being sufficient to power the wheel motors without charging or discharging the capacitor bank. Deceleration would allow for regenerative braking to charge the batteries. While decelerating or sitting idle (say to pick up passengers) the diesel would be charging the capacitors.

It's all theory, but I think with some proper engineering it could be made to work rather well. It's not mind shattering to realize that industrial motors that operate under an essentially constant load and a constant RPM are extremely fuel efficient for the amount of work they do and long lasting. A margin of safety would need to be built in of course, but with the intelligence of today's computers I think the power generation of the diesel could be set in much the same way as modern cars use short and long term fuel trim settings. As such a bus would always be operating most efficiently, be it stop and go in hill country or flat country cruising.

Just theory, mind you...
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Old 06-06-2008, 08:54 AM   #9
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Re: building a fuel miser bus.

I think that a hybrid drive system as you mention would work well if you had some means to directly link the diesel to the drive wheels at cruise speed. This would cut out the losses associated with generating electricity to drive a motor.
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Old 06-06-2008, 02:39 PM   #10
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Re: building a fuel miser bus.

hybrid stuff is fine for the future, but for skoolie owners right now, i think that a good rear end gear set, a 6 speed manual and the cummins 5.9 as well as reduced weight are gonna be about as good as you can get.

i would imagine that lowering the suspension on the bus closer to the ground, and even doing the opposite of everyone else and lowering the roof should both decrease wind resistance and thus improve fuel economy. If you were really creative you could have a very low ceiling in transit, and have a "pop-up" when you park.
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