computeralex

Hey RC Tech!

Sorry to ask a potentially stupid question but:
we all know about an overheating engine, but what is the danger of cooling a nitro engine (beyond the obvious glow plug failure)? how cool can you go before, assuming the glow plug is actively powered, you either witness a large drop in power output or another sort of failure that makes running the engine extremely inefficient?


The reason I ask this question is because I plan to use peltier junctions and an additional heat sink/cutout to allow for a leaner engine and to use waste heat to recharge a battery(and yes I understand that a peltier junction requires cooling on one side + heat on another to maintain a temp gradient and generate a current).

Lastly, approximately what percent of the nitro fuel's potential energy is actually converted to KE and heat through the engine (individually). There are ways of finding this out, but nothing beats a racer's experience/knowledge. Is there a place to find detailed specs on popular engines, such as approximate fuel consumption at stock tune/temp over time/efficiency in terms of actual data?

Thanks for the help, Alex

P.S. I really hate being on of "those guys" with overambitious projects and high expectations, so I'll come clean and say I don't expect this thing to race, I'm doing it more for the novelty of energy recovery via thermoelectric generation. hence the post on r/c tech. And who doesn't like not replacing those damn receiver packs?!

dreaux

iTrader: (5)

very strange. I was thinking about this today at work. About the potential energy of nitro and how to make it the most efficient. I was thinking more along the lines of something other then nitro methane. Maybe propane? acetylene? nitroglycerin's? how bout liquid oxygen and hydrogen i mean something really explosive, so you don't have to use as much.

I even thought of a way to make a pneumatic powered motor

draggin87

iTrader: (33)

LOX and petrolium do not mix!

computeralex

Well, no trouble getting air into the chamber if your already using liquid oxygen!
and on the nitroglycerin front.... hey, it's still 'nitro'

in the meantime i'll keep trying to get accurate measurements of total energy released during combustion to decide if a peltier is even vaguely useful in terms of recovery (it would recover like 8% of the heat energy released at an absolute MAXIMUM, more like 3% in reality, assuming 80% energy from fuel in heat and only 3/8 of that heat recoverable with 10% efficiency).

computeralex

Still no word on the original question- how cool can the engine get before it becomes a problem?

Thanks, Alex

fatdaddy

iTrader: (4)

+ YouTube Video

c9311

For recharging battery packs couldn't you just make a small alternator?

pickle311

iTrader: (31)

Too many variables to give an accurate number. The main factor is thermal expansion. If too cold, the components aren't expanded enough. That will create more friction and excessive wear. To get the number you want, you need to know the exact makeup of the internal components and their expansion rates. What type of metal is the piston, is it CNC, cast, forged? Now you have to answer the same question with the sleeve, crank, case. Don't forget about the metal purity too, that has a major affect on thermal expansion. Just pulling a number out of a hat, anything below 180 would be too cold for optimum performance. But every motor is different. There's some that will run great at 180 and others that will run like crap.

Now also keep in mind that you can't compensate for excessive cooling by leaning your motor to keep the temps up. When you lean the motor, you are also reducing the internal lubrication. By doing so, you have just recreated the same condition as a overheated motor at a lower temperature.

I'm all for innovation and pushing things forward, but I'd say to not waste your time trying to reinvent the wheel. These motors are simple in design and there's no reason to complicate them. They are extremely efficient for what they are. Sure you could probably get a little more out of them, but at no real benifit.

Either way, have fun and I'd be interested to see the outcome.

off road god

iTrader: (13)

You have to realize that too cool an engine temp can cause more damage than too hot at times.
ABC...aluminum,brass and chrome. They all expand at different heat levels. If the expansion doesn't take place the you get excessive wear...early engine failure

You need to be around 200 degrees...but for optimum power from the engine the tune may take it higher...

Being a racer...I'll charge my pack.

computeralex

Thanks for the answers, I'll keep that in mind (and use a cheap engine to test on)

I'll probably mix some extra castor and synthetic oils to handle lubrication if temp ends up dropping dramatically

Hope to have some success to report soon enough, Alex