zoom44

not all. My friend Bob and I were talking hypersonic flight and various propulsion systems last evening. he told me about this company http://www.interorbital.com/Rocket%2...t%20Page_1.htm (there's another one too that I cant recall just now) they are using ablative coatings on the nozzles for cooling

this allows for cheaper, lighter and less complicated engine design. of course they need to replace the nozzles but that doesnt offset the other positive aspects for their purposes

isays

yes, but how less dense? you cannot burn liquid gasoline, it must be gaseous. One reason that you want to atomize fuel when injecting it is because the rate of evaporation, as all chemical reactions, is directly proportional to the surface area of the reaction. larger surface area (many small drops) will evaporate faster. would injecting hot gas increase the rate of evaporation, allowing more gas to be evaporated before ignition creating a more even burn and faster possible time between injection and ignition? higher volumetric flow injectors will offset the increased volume of fuel due to temperature, and software can account for that "extra variable" easily because the temperature to volume relation for gasoline is well understood and simple.


if you want to, dude... i won't stop you. but do it in another thread :p
I never said this was a useful thread, if you don't want to participate, just don't post, it is easy.

isays

same with internal combustion engines.

RXeligion

Dannobre - This is either your new signature, or mine. I'll let you decide

OP:

This is all a big exercise in thought. I know nobody is ever going to do this in a car. I thought this needed to be reiterated.
Why can't you go straight to the injectors from the filter? You could go straight from the filter to the injectors, but it would require a pump (and system) with higher operating pressures, because splitting one system into two increases head loss. A booster pump for the injectors may reduce this need. (head loss results in gas in the system)
Is injecting hot fuel worse than cold fuel? Temperature is not so much as issue as Density is. Fuel density is important for tuning, and a system which uses fuel for coolant could cause this to be sporadic, especially if the load (heat input) from the engine to the fuel is constantly changing. The way to buffer this is to use an additional cooler (and/or booster pump)
In fuel injection, when the fuel gets near the injectors it is commonly exposed to large amounts of heat. Why is it that it either doesn't boil or doesn't matter if it boils? Boiling point is relative to the pressure to which the fluid is exposed. The boiling point of water is only 212F at 14.7 psi. (1 Atmosphere) but you can boil water at UNDER YOUR BODY TEMPERATURE in a vacuum. Likewise, when you pressurize water (with a pump) you increase the boiling point. This is why the coolant in your engine stays liquid. Flow is also an important factor. Flow and pressure together determine the saturation temperature of the fluid (above which, density gets REALLY sketchy.) This is why you need a high pressure system. Your question below explains this, kind of.
The coolant *must* flow fast enough *Under a given pressure* so that the effects are minimal and the bubble is taken away and condenses?

isays

I imagined the system would go like this:

tank
pump
filter
injectors (in parallel, like parallel circuits)
around engine to cool it
out to radiators
back to tank

that way you aren't splitting fuel injection and cooling into two separate systems. the pump (which would be much more powerful than a normal fuel pump) would maintain constant pressure in the system (for the fuel injectors) while moving a significant volume of fuel around. I imagine that (unless localized boiling begins to happen) a pump would be able to react fast enough to the changing pressure (from using fuel and from changes in heat) to maintain constant pressure.

fuel temperature (and thus fuel density) could be monitored and taken into account by the software that controls the metering of fuel.

what pressure are fuel injectors usually subject to? I didn't realize it was high enough to significantly alter the boiling point of the fuel (i figured it was like 0.25 atm).


so to break it down, the major obstacles to capturing heat from the engine using fuel are:
providing enough pressure and flow to prevent localized boiling, and keep it under saturation temperature, given a reasonable input temperature.
keeping constant pressure for the fuel injectors in spite of fluctuating temperatures.
monitoring fuel heat to compensate for changes to fuel density.

we can calculate the necessary flow rate if we have the following:
reasonable input temperature
pressure in the lines (therefore max fuel temperature)
volume of coolant circulating the engine at any given time
heat energy per second that must be dissipated from the engine
specific heat of gasoline

likewise if we have the flow rate, we can calculate the necessary input temperature


I'm not really sure what you mean by "head loss", so I'm not sure if that would be a big obstacle for having the fuel injectors coming off the cooling lines in parallel. Do you just mean reduction in pressure at the start of the system?

are there any other issues that you can think of that would pose problems to collection of heat using fuel?
how could we maintain constant pressure to the injectors (preferably without breaking it out into a second circuit or using a second pump)?

TeamRX8

iTrader: (25)

Be sure to check the level with a lit match so you can see where it's at ....

40w8

Why don't cars just use the AC system for engine and cabin cooling (and propane makes for good refrigeration systems)?

I'm thinking that pushing the water around takes way less power than running a compressor, so it looks like water wins for the next few years of internal combustion cooling.

Also, you can run junk car longer, and even get your coolant from the ditch or your ice chest beer if desperate!

Can you imagine the mayhem that that much gas up front could cause on every little fender bender?

monchie

First of all, water just evaporates fast. Secondly, beer is bad for your car and specially for you. Lastly, we can put a monkey in space, but we cannot find a cheaper alternative to gas.

40w8

the hell you say!

RXeligion

[quote=isays;4009163]
we can calculate the necessary flow rate if we have the following:
reasonable input temperature
pressure in the lines (therefore max fuel temperature)
volume of coolant circulating the engine at any given time
heat energy per second that must be dissipated from the engine
specific heat of gasoline

likewise if we have the flow rate, we can calculate the necessary input temperature

You're going to have to enlighten me - I'm not sure what equation you are using based on the information above. Your "Necessary Input Temp" is based on SS (Steady State) conditions of your system, not on the necessity of a certain parameter.


I'm not really sure what you mean by "head loss", so I'm not sure if that would be a big obstacle for having the fuel injectors coming off the cooling lines in parallel. Do you just mean reduction in pressure at the start of the system?

Head loss as compared to Pump Head in a hydraulic system (it has to be pressurized) Its a faily common term.

are there any other issues that you can think of that would pose problems to collection of heat using fuel?





SAFETY!This would be the engineering equivalent of putting all of your eggs in one basket. A leaky head gastet (on a piston engine) WILL result in a fire, without any questions - just like a leaky fuel buffer on a 13B. The haters who have had nothing positive to say have not been giving incorrect information, either. I wouldnt try this, and especially not without an R&D lab. (not garage) My input here has been entirely theoretical. If you catch yourself on fire or blow yourself up, I will NOT take responsibility.

how could we maintain constant pressure to the injectors (preferably without breaking it out into a second circuit or using a second pump?

I wouldn't. I've already explained how I would set it up.

isays

RXeligion:
hahaha, don't worry... i know that this is a terrible idea for a consumer car, high pressured heated fuel running all around the car is just waiting for an accident. this is all just an exercise in problem solving :p. I know I wouldn't want to drive a car like this on the street lol.
it might be useful for applications like extending the range of UAVs, though... but i don't really have any interest in that :p

I also know that the haters are (mostly) raising valid concerns. my problem is that they didn't even try to find either solutions to the problem or ways we can simply bypass the problem... so they weren't really adding much (since i had mostly already raised those concerns in my original post).

as for the "equation" i was using, there isn't really one. i was just looking at the units. it is based on steady state, but the steady state would be the worst case scenario beyond which the engine wouldn't be expected to operate.
basically, if you have pressure in the lines, you know the max temperature (ie, boiling temperature).
if you know the input and max temperature, you have a worst case delta temperature.
if you know the delta temperature, you know the specific heat of gasoline, and the mass of gasoline circulating you know how much energy it will take to achieve that delta temperature.
if you have the energy released by the engine per second, you know how much time you have to flow that coolant around the engine.
you know how much time you have and how much coolant there is, therefore you know the flow rate.

as for head loss, im not really familiar with technical terms. i started in engineering (so i have a little background) but switched to comp sci. a lot of the technical terms are things i never come across even if they're easy to understand. i should have just googled it though :p
head loss just seems to be energy lost due to the fact that moving fluids will lose energy. Wouldn't this just manifest itself as increased resistance for the pump? I'm not sure why splitting it into two circuits would reduce head losses.

40W8:
moving heat from one place to another always generates more heat than it what it removes from the system (why a room will get hotter if you leave your fridge door open for a long time).
in a fridge it takes the heat from inside and moves it to the radiators behind the fridge. if you don't cool the radiators, then the heat just goes back inside the fridge.
currently cooling systems in a car are already doing that, but since they aren't worried about bringing temperatures below ambient, they don't have to deal with compressors (which add heat to the system).

monchie

Not sure either...lol

RXeligion

I think you may have a couple of misconceptions. SS is based on the normal operating range of the system: at this point, the system can dump the heat that it creates without increasing the temperature of the system. You have to know the heat input of the engine (heat in) to know what kind of pressure and flow you will need to stay above saturation pressure. You're kind of going about this in reverse.

Headloss is CAUSED by increasing the the length of system piping and the number of bends. The problem isnt increased resistance on a pump, its the low pressure conditions caused in parts of the system (most notably before the pump, in a looped system) which can allow vapor bubbles to form.

isays

ah, i think i understand what headloss is now. its that the pressure is less the further from the pump that you go. would that be correct? so to reduce head loss you increase the number of circuits and reduce their individual length, so you're never very far from the pump.

i guess i'm going at it in reverse... i was just thinking of taking an example engine to get the data from (coolant volume and heat energy released) to figure out a flow rate...
but i guess a better question would be... after picking an achievable flow rate, an achievable and "safe" pressure, the heat/coolant-volume from an example motor... find out the required input coolant temperature (and therefore the performance required from the radiators).
which would lead to the next step of figuring out how to dump heat...

the heat energy per second would be the total energy from burning 1 second's worth of fuel at WOT, minus the energy spent in moving the car, minus the mechanical losses in the drivetrain etc, and minus the energy in the exhaust heat... sound about right?

RXeligion

I would suggest you read up a little on heat engines before attempting any equations. You may have the brain power to formulate these on your own, but A LOT more goes into these than you might have imagined. Not only heat inputs, but also work inputs, outputs for both, and then the efficiency of the system, because no heat engine is ideal.

isays

i don't have the proper vocabulary.... by circuit i mean complete loops of piping that leave the pump and goes back to the tank in parallel to the other loops of pipe. you had suggested having two circuits instead of one to reduce head loss, so i assumed the losses that come with the bit of extra piping were outweighed by never being very far from the pump. by decreasing the length of pipe you decrease the pressure difference between the start of the circuit and the end of it... or am i way off the mark about what head loss is again? lol.

i know that there is a lot more that goes on in a real engine, but since im not trying to develop this for real, i figured that it could be simplified for ballpark estimations :p.
in fact, since most engines have horrible energy efficiency, we could probably get our safety margin by assuming that ALL of the energy from combustion went directly into heat that had to be removed from the engine lol