Hi Aspire,
In your first message above you did not quote me. Instead you just imputed to me positions that I have not taken. I then wonder whether it's worth responding? I mean, if you're gonna put words in my mouth that I never wrote, what's the point in discussing anything with you at all? You might as well just talk to yourself, merely inventing positions that I never took, and arguing with yourself against those invented positions.
I did
not say that expedition vehicles on land should be designed like big catamarans. I never said anything of the sort. And it does not take a genius to realize that an expedition vehicle should not and cannot accommodate everything that a
Gunboat can accommodate. And yet you seem to think that I have been suggesting that
Gunboat-sized systems should be able to fit into a 6x6 expedition motorhome?
Even if I were not a transportation designer, I would never think anything so foolish. In fact,
most people would never think anything so foolish. And certainly not regular participants on ExPo.
So it would be nice if you were to extend to other forum participants, including myself, some
“benefit of the doubt”. It's usually good policy on a forum like this to assume that other participants are reasonably rational, and that they are probably just as intelligent as oneself. Perhaps even more intelligent. And if you were to begin with that assumption, you might be less quick to impute foolish positions to other participants, positions that they never took.
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1. Fuel Tank: 1500 Liters
As regards the amount of fuel carried specifically, I've made it clear earlier in the thread that a 6x6 motorhome of this sort would carry 1500 liters of diesel, just like the Doleoni MAN-KAT.
Egn's “
Blue Thunder” carries 1300 liters of diesel.
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2. The Question of Thermal Efficiency
As for your other point, new-car gasoline engines are usually about 25 % thermally efficient, and diesels can be 30 – 49 % efficient. Diesel semi tractor-trailer trucks are about 35 % thermally efficient. Only when ICE engines get
really big, do they achieve much better thermal efficiencies, nearing 50 %. See
https://en.wikipedia.org/wiki/Engine_efficiency and
http://www.researchgate.net/post/Wh...he_commercially_available_automobile_engines2 .
This is one of the reasons why Capstone turbines have proven so attractive in power generation. Because when you combine their 30 % thermal efficiency generating electricity, with CHP – “
combined heat and power” – their overall efficiency radically improves. Microturbines used in power generation that employ CHP to recover heat energy from the exhaust, can typically achieve efficiencies topping 60 %. Capstone even claims 75 or 80 % efficiency for some applications. Which is better than anything that smaller, diesel-fueled ICE power generators can achieve -- see
http://www.capstoneturbine.com/prodsol/solutions/chp.asp ,
http://www.microturbine.com/_docs/WCEMC04.pdf , and
http://www.epa.gov/chp/documents/microturbine_tech.pdf .
Which is why Capstone microturbines have become so popular for small-to-medium-sized power generation.
For what it's worth, this is precisely why I asked the question about CHP energy recovery, to heat the motorhome and provide hot water. Because with that included, it's possible that
overall, a pair of C30 microturbines (a pair for redundancy) might be much more thermally efficient than the standard combination of internal combustion diesel + separate diesel heaters. A Capstone C30 microturbine might not be the most thermally efficient solution for a small car. But for a motorhome that needs substantial camper heating in any case, it just might be.
Now I do not know if this is true. Those reading this who are engineers would be in a much better position to judge.
And yet even without CHP, the owner of the “
Lethantia” seemed to think that his new Capstone C-30 turbine was a vast improvement over the diesel-electric generators that it replaced. The owner of the “
Lethantia” did not care about “flat floor” design. Rather, he cared about low maintenance, and environmentally friendly exhaust, for instance. Watch the video again, and see if his reasoning makes sense to you:
[video=youtube;vLTinWDhZNk]https://www.youtube.com/watch?v=vLTinWDhZNk [/video]
Of course, he also claims that his Capstone microturbine is much less noisy than the diesel generators that it replaced, a claim that you would probably deny.....:coffeedrink:
Now earlier in the thread you suggested that 30 % efficiency is a "terrible waste":
One last thing:
Heat is wasted energy if your aim is to produce electricity. If Capstone's turbine makes 70% of the fuel used into heat, that means that only 30% of it becomes electricity. If you don't need the heat, that is a terrible waste…..
But as suggested by the websites just quoted above, about the thermal efficiency of automobiles, 30 % thermal efficiency is
not terribly bad. Most gasoline internal combustion engines in cars are
less efficient than 30 %.
Even still, I should thank you for getting me to think in a focused way about thermal efficiency. It would be very interesting to know:
(a) the thermal efficiency of the more popular, large, turbo-charged diesel-electric generators available for motorhomes, for instance, Cummins, Kohler, Fischer-Panda, etc.
(b) the thermal efficiency of the best possible ICE range-extender currently on the market: an ICE range-extender that has an electrical power output equivalent to a Capstone C30, or a Capstone C65.
I don't know the numbers on these, but they are clearly important. If anyone reading this actually knows the numbers, or can point me towards useful websites where I might find the numbers, please post!
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3. The Question of Size, Design Flexibility, and Center of Balance
As for size, a Capstone C30 microturbine (the smallest kind) has been successfully placed inside a not-very-large sports car (the CMT-380), and a Ford Crossover. The C30 has also been successfully placed inside larger vehicles like garbage trucks and buses. And the Capstone C65 microturbine – which is quite a bit bigger than a C30 – has been successfully placed inside a semi tractor-trailer truck, the Peterbilt/Walmart concept truck.
Now perhaps when we add up the weight of microturbines + lithium-ion batteries + electric motors + anything else associated with a serial hybrid system, maybe the total hybrid package comes out weighing much the same as a big MAN diesel + equally heavy transmission. Or maybe it does not. Maybe it really will weigh less. I honestly do not know, and as you suggest, the devil is in the details. However, I doubt that the combined weight would be more.
But suppose the weight of the total hybrid package were the same. Even then, as
egn has remarked earlier in the thread, the advantage of hybrid technology is that you can “spread” the components around, instead of having so much weight concentrated in one place, as with a traditional big diesel motor + transmission:
Weight distribution is a very important issue for offroad vehicle. It should be equal on all axles with a tendency to have a bit more weight in the back to get best traction. Empty trucks have most of there weight in front. As an off-road vehicle should be as light as possible, especially if you build an 6x6, the truck will be still be heavy at front. This may be compensated by distributing the axles differently. Two steerable axles in front and one in back would be a solution.
The engine/transmission for such an vehicle will be large and heavy. Therefore it is critical where everything is placed. Most of the time engine and transmission build on large block, but it is also possible to separate engine and transmission like it is done with the MAN KAT1 8x8. This had to be done here because there was just no place because of the second steering axle......
All this problems around engine placement and weight distribution brings me back to the idea of using a totally different propulsion system.
Shouldn't an advanced vehicle concept not only look at the interior and exterior design, but also at the propulsion system?
The trend goes towards hybrid and electric vehicles, not only because this is more fuel efficient and has lower emissions. It has also large advantages regarding power and torque, which is very important off-road. With an hybrid driveline it is possible to distribute all the components of engine/transmission all over the vehicle and most smaller components can be placed without much additional space.
In other words, even though
egn is an very successful engineer by profession, and very practically-minded,
egn was able to recognize that hybrid technology provides more “design freedom”. And "design freedom" not only matters to
egn; it also matters to me, as a designer.
Design freedom may not matter to
you,
Aspire. But it does matter to
me. And more to the point, design freedom matters, very much, in this particular thread. More below.
Hybrid technology also allows one to play with the center of balance, which is very important in an expedition motorhome.
egn stated in one of his posts that he spent lots of time trying to get
Blue Thunder's center of balance right, and that going hybrid would have made achieving an optimal center of balance much easier.
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CONTINUED IN NEXT POST
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