Newbie pitch

[jamesqf]

Originally Posted by theunchosen

It's more simple to swap out the trans for an EM, but then you still have to spin an axle thats 4-5 feet long and several inches in diameter.

Huh? What sort of car do you plan on converting? Two half-shafts an inch or so in diameter and a couple of feet long on anything I've owned recently. Even in old rear-wheel drive, solid axle setups the shaft that actually spins isn't all that thick.

Of course you have the CVJ/DOJ on each end, but you would need something similar if you were going to attach an electric motor to the wheel via a shaft. I think what I'm trying to say is that you've already got a well-engineered & tested transmission-to-wheel connection, so why re-invent it when the gains seem likely to be marginal? You can (I think) buy suitable motors & adaptors pretty much off-the-shelf, so why not do that, and invest your time & money in getting the Stirling engine part to work.

[diesel_john]

If we could just change hydrocarbons into electrons directly.

[Christ]

Wouldn't that be awesome... but we can't... so ideas like this are the next best things... I'm throwing my personal support toward the OP for the idea, now lets see some sort of implementation?

[theunchosen]

And thats where the problem comes in(Christ), I have a neighbor who managed to build a functioning stirling engine that is pretty fantastic(considering its home-made from scratch) but its not anywhere near being able to produce 25 hp off my exhaust. Although it is light(less than 10lbs). So it may be possible to stack them in series. Although. . .not on my car. The Del Sol if anyone else owns one has a very cramped engine bay and adding a cubic foot box somewhere. . . Of course I could rip out the cooling fans(since my car never gets hot enough to use them(un-FE she has a wide open grille that is not stock and I've done a few things to improve air flow to keep the fans off)). Would have to shield the engine thermally to trap as much heat against the stirlings as possible while venting cold air to the cold side without heat soaking from the radiator(or freezing the hotside or the engine)

Ok James I'll stand corrected on the axles for sure. Sorry. You wouldn't neccessarily still have to use the CV's. . .Power doesn't necessarily HAVE to flow through them. . .

Wheel-Emotor-pivots-chassis. motion does not have to pass through a joint(making the joint cheaper and the drive more efficient). I'm not sure what this would do to the engine itself but if it were light enough it wouldn't drastically change the unsprung car weight. . .(I think assuming we are popping things off that are also unsprung?).

[Christ]

There actually isn't too much about the unsprung sections of a car that would be changed doing the emotor per wheel thing... there is a company out there that makes kits for Minis already.

IIRC, they have kits that have the same HP as the ICE engine does PER WHEEL, thus making your Mini a 600HP monster with no lagtime waiting for torque to build up or a turbo to spool.

Nicest thing I've ever found about E-Motors is that their torque rating is at 0 RPM. They don't need to be spun up to have torque, since they aren't fuel based. The electrical current can be just as strong at 1rpm as it is at 1200 rpm.

It'd be great to have torque on demand.

Linky: Electric Mini: 0-60 in 4 Seconds: It Has Motors In Its Wheels : TreeHugger

[theunchosen]

Yeah I hadn't actually considered the better torque stability, but that would also be a plus.

I got to thinking and it may be the best idea(key operator = may) to insulate the exhaust pipes. With asbestos. . .or since its the 21st century how about mylar and some pink fuzzy coated in flame retardent spray and maybe a very thin aluminum shield(also doubles to bring the underside of the car to lowest drag possible(and then I can wax it. . .)). But if that were done I could route the pipes into part of the trunk(where the spare goes) and put a stirling there. would just have to mount it inline and pipe air from outside in the same gap and then out the same gap(through separate pipes same hole).

Obviously its more beneficial for the engines to be mounted up front for increased traction(FWD) and the heat would not dissipate, but thats asking to get alot of room out of my engine bay only removing a trans and both cooling fans.

I will definitely be going to visit my family over thanksgiving and my neighbor with the engine to check and see exactly what kind of HP and weight. . .

[Christ]

I don't know about most other cars, but I know on my Honda, I can actually grab the muffler for a short period of time before it feels like it's burning... which means it's not that hot, compared to other sections of the pipe.

Believe it or not, one of the greatest areas of potential heat loss due to convection is the catalytic convertor... hence the reason there's a heat shield on it... it's always in close quarters to flammable materials.

If I still had my Delta 88, I could show you what happens when the cat is too close to the body and overheats. The floor of the car actually caught on fire... burned most of the driver's side carpet and underlayment, but I put it out before it seriously damaged anything. The car was idling in my driveway when it happened, running richer than ever.

Rich mixtures heat up the cat... lean mixtures cause parts of the engine to overheat... I won't go into detail on that.

Anyway, have you ever considered driving a sterling with the pressure from the exhaust, rather the heat? Or even using both... recapturing even more energy. Don't forget, part of the waste of the engine is in the pressure exhausted. (It takes energy to create the pressure, therefore exhausting the pressure without using it is a waste of energy.)

[theunchosen]

I had considered harnessing the expansion that causes the pressure, but at the same time I am hesitant to consider it. I'll get to it in a second.

The most opportune place is the hottest place for a stirling to run and thats right out the block, but I probably at best would only be able to get one small unit at that location right now. Insulating everything would be advantageous if you wanted to take advantage of trunk space and put them there for ease of access and mounting.My muffler usually takes a bit of time to get hot but once it does it's scorching. I burned myself rather badly just leaning into my trunk before I realized my leg was touching the muffler. . . it protrudes slightly.

To the pressure/expansion/turbulence. . . I considered it but I'm not certain it actually saves you energy. It would be like running a turbo or supercharger. You can gain more power but it comes at the cost of the engine having to fight the backpressure. In the case of the turbo you typically lose fuel economy(efficiency typically means power/weight and thats always a gain in the case of more air and fuel in the engine). The reason economy usually goes down is because the engine, standard ecu, will inject more fuel to match the greater airflow. Usually this exacerbates the normal inefficiencies, rubbing two pieces of metal together wears them down and rubbing them faster usually has an inceased effect kind of thing.

All that said I tend to lean away from the turbo and towards heat recovery because the kinetic energy of the air from the exhaust is not immense, but creating back-pressure is a huge problem for the engine. The Stirling would cause the air to become more dense and slow down but not enough to cause a measurable backpressure.

Another point of consideration would be creating ramscoops for the stirling cold-sides. the colder the air, or the more cold air, you can get the faster, or more heat you can convert to motion. Effectively the stirling could become much more efficient at highway speeds since it follows carnot ideals rather closely((700-430)/750 or (700-343)/700 degrees input-output/input in kelvins).

[Christ]

Turbo chargers don't add that much backpressure to the exhaust stream.. Granted, it's measurable, but after installing a turbo, you can almost run a resonated straight pipe to exhaust the engine, therefore you lose the backpressure of a muffler, and it's not harshly loud in the lower ranges.

Anyway, good enough reasoning, but I was thinking something more like venting SOME of the pressure from the exhaust, like where air-pumps used to pipe into cat convertors... take that pipe, and use it's exhaust pressure to drive the sterling, instead of blocking the entire exhaust flow.

One could add several of those pipes to use the pressure instead of heat, and they could be mounted just about anywhere, since you'd be connecting them with pipes.

They'd be decreasingly efficient the longer those pipes were, and the further from the point of exhaust, but it might present another option to reclaim some energy.

[jamesqf]

I'm more than a little puzzled here. You're talking about adding a Stirling engine to the exhaust of a conventional IC engine, but having that drive a generator which (with batteries) drives the wheel motors (or other electric propulsion). Aren't you getting more than a bit Rube Goldbergish? Why not cut out the IC, and have the Stirling drive a generator which extends the range of your plug-in hybrid?

The battery wouldn't even have to be that large, say enough for 5-10 minutes of driving while the SE comes on-line, so you save on weight & cost.