Intercooling diy turbojets

[mitch]

I was thinking the other day about using air to air or even water to air intercoolers on our diy turbojet/turboshaft engines. Would the chilled air/ more dense air be worth the extra weight of the intercooler itself? I was contemplating trying to build a small homemade water to air intercooler for use with my turboshaft (if I ever finish building it, lol), but wasnt sure if it is worth the time to do. Do single stage centrifugal compressor turbojets see much of a benefit to using an intercooler type device?

[racket]

Hi Mitch

Where were you going to position the "intercooler" ??

Theres no point fitting it between comp and combustor , all you'll do is cool down the air simply to heat it back up again .

If you fit it in front of the comp and chill the ingoing air then there could be a benefit .

Cheers
John

[mitch]

I was thinking about positioning it between the compressor and the combustor, however I was thinking in terms of internal combustion engines and how more dense air = more power. Now that you mention cooling the intake air before it enters the compressor, that sounds like a good idea. How would this increase efficiency or power of the engine though? Would it be mimicking the results created by a good pre compressor water injection system?

[racket]

It'd depend on what you fed into the intercooler , super cool CO2 .

[mitch]

Feeding co2 into the intercooler to cool it?
I was considering attempting to make my own water to air, and feeding it with chilled ice water using a high flow pump. Even if my intercooler was only, let's say 30% efficient, that would still mean a large temperature drop for the intake charge, given how hot the air can get when compressed to above 30 psi

[madpatty]

Isn't it goes like this?

In the brayton cycle we need the temperature to be highest before the combustor.
Intercoolers are only between compressors and not between compressor and combustor.

IC engine is a different cycle.

Cheers,
Patty

[Johansson]

It will be difficult to design a pre-compressor intercooler that doesn´t restrict air flow into the engine, even the slightest restriction will probably eliminate any gain from the cooler air charge.

A mist of water going into the compressor is the way I´ll do it, I will inject 1.5 liter of water/methanol mix per minute into the bike engine to gain a bit more power. I´ll report the results in the build thread when I´ve tried it.

[nickthesafe]

I wonder what benefits to IC engines may be obtained by pre-cooling in addition to inter-cooling..A heat pump driven by the engine and carefully controlled by the ECU running through a large area matrix placed 'aft' of the air filter in the clean air. I did a little digging and found not very much has been done, the only references I could find related to pumping heat away from oil and coolant.

[racket]

Hi Guys

Heh heh .....Now heres a scenario worth exploring ................

As our engines only burn ~30% of the oxygen in the combustor and oxygen only makes up ~20% of the air going in , we only need ~6% oxygen and the rest can be be whatever inert gas we choose to replace the nitrogen .

What if we suddenly replace the ambient air with a mix of oxygen and CO2 fed from cylinders , the sudden expansion of those gases just before entering the comp will mean they'll be super cold , the mass flow would increase , the compression would be much more efficient and there'd be a large increase in power .

I haven't thought this through , so there could be some "problems ??" , but for say a drag bike where we're only talking several seconds of max power there might be some relatively simple solutions.

CO2 has a latent heat of evaporation of 247 BTUs/lb , lets say our engine flows ~2.5 lbs/sec like Andy M's drag bike , the addition of 0.5 lbs/sec of CO2 at the intake will "release" ~ 125 BTUs of cooling , now neglecting the cooling of the liquid CO2 to gas phase change and just concentrate on the air, the air will be cooled by ~200 deg F if my maths are correct , OK , this is too much so lets look at a piddly 0.1 lbs/sec of CO2 and only ~25 BTUs/sec , that will drop the air by ~40 degrees F , now this is looking better :-)

If we only inject 0.1 lbs/sec of CO2 , thats "bugger all" when compared to the 2.5 lbs/sec of ambiant air , I doubt if the engines combustor would notice that extra bit of non combustable gas

So even just a small CO2 injection could be enough ...................your thoughts ;-)

Cheers
John

[pitciblackscotland]

I thought i might put this vid of a turbine bike using water methanol injection youtu.be/J51piuinMQc

Cheers,
Mark.

[ripcrow]

Your not the only one thinking of intercooling. A large engine manufacturer is experimenting with the idea but they are finding the intercooler dampens air flow and any any power increase is lost due to poor air flow. Although ic engines are different the principle behind intercooling air is the same. The cooler air means more air into the combustor allowing more fuel burnt equalling more power. Although 70% of a turbines air is not burnt it picks up heat and expands once oats the flame tube so denser air expanding across the exhaust turbine means less cubic metres of air need to create power. It's a win win. More fuel and greater cooling means more power but only if you get around the restriction to mass airflow