srimes said:
The MPG guys do something called a "coast down test," which should give you a good idea about the resistance. I haven't worked with it so I don't know how specific it will be at a given speed.
Another test which could be the most accurate, but harder to perform, would be some version of a tow test, where a seperate vehicle provides the motive force for the jeep, say by pulling, and that load is measured with a spring scale. You can then measure the lb-thrust needed at any speed and grade and calculate the needed horspower. You'll just need a rope long enough to not throw off the drag too much, or do an offset pull, or a push, or something. And it probably would not be legal on public roads.
I can see that working - given the vehicles mass and some soft of half-way reliable estimate of rolling resistance (which according to what I've read changes very little as speed increases), take it up to speed and then shift into neutral and plot the change in speed over time.
For the rolling resistance, just get on a flat road and tow it up to a steady 5MPH where the wind resistance is minimal and note the strain on a force-meter/tension gauge of some kind. This could work.
Now that I think about it, I guess I could even do 10MPH and 20MPH towing tests - the change in necessary force to pull the vehicle would be almost 100% due to increased wind resistance. That would alow me to fairly accurately calculate the drag coefficient (CxA or CdA). I think I could then use that with some formulas I found on Wikipedia to verify or augment the coast-down data/results.
You are right about the legalities - but at 5-20MPH I there are plenty of long, flat (it's Florida) straight residential roads around here that see no traffic at 6:00 or 7:00 am on a Sunday morning and the cops don't care what you do off the main roads
srimes said:
The 4.0 is a heavy pig, but it think you are being very optimistic. A diesel genset that puts out 30 hp is not going to be light. Most probably weigh more than the 4.0 and transmission, and new will cost more than the jeep is currently worth. To do it cheaply will require a great deal or creating your own with a used engine.
Optomistic - perhaps. maybe not - just depends on how much power it takes. And it wouldn't be fun if I just buy all the parts right from the factory. I plan to play around a good bit. Ideally I could find a used 3 cylinder turbo charged diesel that I can use with bio and/or flex mixtures
srimes said:
Why did you decide on a series-hybrid system?
Drive-line simplicity
srimes said:
Do you need to be able to drive at highway speeds indefinetly? If so you may be better served by a parallel system, like what is used in production hybrids today. If you don't need full-time highway capibilities then a series system with a smaller genset may be a better idea. If you size it for continuous opperation in the 30 to 45 mph range you can use a much smaller engine, which can change while you're stopped.
When I hit the highway I may have to go as far as 100 miles before getting off into stop & go traffic. I'm going to size the diesel/generator set such that even at highway speeds, there will be a little juice left over after powering the motor to do a little charging of the batteries. I will build/program the controller such that the motor turns on at the predetermined level of battery discharge, or if it senses the batteries cannot put out the power I need given my throttle position. When the diesel does kick in, it runs full bore at it's most efficient speed until the batteries reach a certain level of charge, and/or my foot loses some lead.
On my return trip, as I near home, I will manually turn down the charging thresholds - there's no sense in getting home with fully charged battery sets.
BTW, from the research I've done, I intend to put a bank of supercapacitors between the motor and its power supply. They act as an "accumulator" (for those of you familiar with hydraulic systems), smoothing out voltage and amerage fluctations from the batteries or generator, and acting as a short-term reserve of power to allow for time necessary to spin up the diesel/generator set.
srimes said:
If you do a lot of highway driving you may just want to swap in a diesel and check out biofuels.
I think a smaller diesel that is run only at a full-bore constant throttle/rpm will end up being SIGNIFICANTLY more efficient than any I.C.E. running any kind of fuel when mechanically connected to the driveline - but we'll find out one way or the other.
:cheers:
