2014 intercooling

[ringo]

I was going to illustrate the breyton cycle, a constant pressure combustion cycle with an otto cycle, a constant volume combustion, but it would have been difficult.

However For the piston engine you will find a 6% mass difference for the same volume of air with ten degrees Celsius difference.
The volume of the engine is more important than for a gas turbine. So you want to trap as much mass of air per stroke.

For stoichometric combustion more air will need more fuel, so you wont have improvement in fuel consumption strictly speaking.
However a more powerful engine that is the same displacement will obviously mean it can scale back performance to equal the power of the engine without the intercooler and have less mechanical losses.
And have an overall improvement in fuel efficiency.
In terms of combustion temperature:
6% more air mass per stroke is not insignificant. And you only lose about 4% of in cylinder temperature right before combustion. And this only results in a 1% difference in the flame temperature after combustion.
So in the grand scheme of creating that high heat and pressure after combustion, you don't get much returns from that higher temperature before combustion. In fact you will find that the cooler air gives higher flame pressures as well.

So it's better to have a 6% increase in air mass, than a 1% increase in overall flame temperature. And you will find your improvements in overall efficiency in that increased power density.

There is probably a 20hp difference with using an intercooler. Is it worth the aero benefit? That's an interesting discussion.

[Tommy Cookers]

the prime purpose of charge cooling SI is to get the required air massflow at a low enough temperature to allow the required CR
in our case the required massflow/mep is clear and the required CR is as high as possible
thermodynamics calculations ignore real-world factors like the temperature effect on the tradeoff of massflow and useable CR

although the lower the boost, the less racetime-efficient charge cooling would be, by degrading the aero package relatively more
surely at 2014 boost we need a charge cooler ?

the Can-Am 917 Turbo was in a power formula, not an efficiency formula
it lowered the CR to allow the required massflow without charge cooling
and no doubt used a very rich mixture in qualifying to avoid detonation at the combination of the CR and qualifying massflow
(the aromatics content of gasoline being very responsive to mixture richness)

[FW17]

the Can-Am 917 Turbo was in a power formula, not an efficiency formula

917/30 had a fuel mileage of less than 2mpg and had a 400 liter fuel tank, imagine what an F1 engine could do with such numbers.

[xpensive]

the Can-Am 917 Turbo was in a power formula, not an efficiency formula

917/30 had a fuel mileage of less than 2mpg and had a 400 liter fuel tank, imagine what an F1 engine could do with such numbers.

Right, 40 years later a modern F1 car could surely reach 3 or even 4 mpg.

[timbo]

For stoichometric combustion more air will need more fuel, so you wont have improvement in fuel consumption strictly speaking.

Yeah.

However a more powerful engine that is the same displacement will obviously mean it can scale back performance to equal the power of the engine without the intercooler and have less mechanical losses.
And have an overall improvement in fuel efficiency.

Eh? How you got more powerful engine? How you got less mechanical losses? And remember, intercooler has pressure drop.

In terms of combustion temperature:
6% more air mass per stroke is not insignificant. And you only lose about 4% of in cylinder temperature right before combustion. And this only results in a 1% difference in the flame temperature after combustion.

Eh? If we are talking a fuel flow limit, if you have your mixture at stoichiometric ratio, you have exactly same mass of air (and mixture) with or without of intercooler. With intercooler mixture is colder. (Now we can talk funny things like enthalpy variance with temperature but it must not be significant)

So in the grand scheme of creating that high heat and pressure after combustion, you don't get much returns from that higher temperature before combustion. In fact you will find that the cooler air gives higher flame pressures as well.

Pressures don't mean anything for thermal efficiency, only temps matter.

There is probably a 20hp difference with using an intercooler.

I just don't understand how you got that number

[hollus]

Where did the 6% come from?

[ringo]

I'm trying not to get into the equations. Because i'm to lazy today to post any images. I was trying to draw something up but couldnt bother. A combined cylce diagram.
Well put it this way, the same engine simulator that i used to calculate quite accurately the engine output this year, has more power from the same setup with an intercooler.
There's a 20hp difference in most cases.

You don't have exactly the same amount of air without the intercooler. You have the same flow rate, but less mass.

The mixture is colder with the intercooler, but it's also denser. Remember a compressor has an efficiency, so it will heat up the air to around 60 degrees Celcius or more. It wont compress the air without losses.

Now to illustrate to you, i will use the engine calculator. I'll show how different the power of the engine is with 60 degree air versus 40 degree air.
I had to turn down the boost pressure with the 40 degree air to have the same mass flow. You would agree with this for stoichiometry correct?

The overall pressure and temperature was reduce right before combustion process. The values were input into a flame temperature program using gasoline as the fuel. The pressures and temperatures of combustion returned are very close.

However what gives the overall package more power is the fact that there is less work done by the compressor to deliver the same mass of air to the cylinders. The engine has to do less since the air density is increased. Less compressor work, and if you'd like, less engine speed. Any how you cut it, the package with intercooler will make at least 10 more horsepower.
The whole point is less temperature before compression is better. The temperature difference has less effect on overall power than density differences. You mention tempertature difference for the cycle efficiency, however that's usually for the ideal cycle. there is more to consider when doing the breyton and otto cycle together.

in fact you will find maybe about 1% point increase in efficiency with intercooling. I want to put this calculator online, but i don't know how to make it like a web page.

[ringo]

Where did the 6% come from?

Just use the ideal gas law.

I have a spreadsheet i use for all engine power calculations, and also for intercooler and radiator sizing. So that's where the 20hp difference comes from.
You'll find the power predictions in the engine thread. They've been quite close, mustering a 588 hp prediction.

[timbo]

Well put it this way, the same engine simulator that i used to calculate quite accurately the engine output this year, has more power from the same setup with an intercooler.
There's a 20hp difference in most cases.

It can be a thing of a model.

You don't have exactly the same amount of air without the intercooler. You have the same flow rate, but less mass.

Well, I came from the idea of having stoichiometric mixture. You have to design your turbo to get that mixture, with or without intercooler. Of course, the question is whether you can, but it is different question than thermal efficiency.

The mixture is colder with the intercooler, but it's also denser. Remember a compressor has an efficiency, so it will heat up the air to around 60 degrees Celcius or more. It wont compress the air without losses.

Yeah, but with conventional setup (no fuel flow mixture) you mostly care about maximum air mass to squeeze into cylinder, so you can burn more fuel. But we have another situation.

I had to turn down the boost pressure with the 40 degree air to have the same mass flow. You would agree with this for stoichiometry correct?

Yes.

However what gives the overall package more power is the fact that there is less work done by the compressor to deliver the same mass of air to the cylinders. The engine has to do less since the air density is increased. Less compressor work, and if you'd like, less engine speed. Any how you cut it, the package with intercooler will make at least 10 more horsepower.

Well, in turbo setup the work compressor does is virtually free. It basically utilizes what would otherwise be lost, so I'm not sure what you mean.
A fair point may be that this way you can leave more energy for MGU-H (or how is it called?) to harvest.

The whole point is less temperature before compression is better.

But the intercooler is after the compressor.

You mention tempertature difference for the cycle efficiency, however that's usually for the ideal cycle. there is more to consider when doing the breyton and otto cycle together.

I'd want to see a S-T or P-V diagram for turbo setup with or without intercooling. Maybe there would be something easier to see.

Overall, I think the fuel flow limited formula makes intercooler less needed. Maybe it won't be eliminated entirely (it already looks like that) but it might be much smaller.

[turbof1]

Overall, I think the fuel flow limited formula makes intercooler less needed. Maybe it won't be eliminated entirely (it already looks like that) but it might be much smaller.

The issue with that statement is that the exhaust gasses aren't the biggest heat source which the intercooler has to cool back down; the turbo, it's turbines, are the infact generating the most heat. The limit on fuel flow isn't going to let the temperature drop a lot.

The turbo's rpm is limited at 125,000, so that could limit heat production. However, the turbo also gets spooled when not on the throttle, so without turbo lag, the heat production will be constant and might be building up. I don't know how far on either side of the balance you end up, but the way it looks you still need a fairly large intercooler.

[wuzak]

You seem to be looking at a turbocharger and applying the brayton cycle to it and it's not right, you need to look at the efficience of the otto cycle, and there cooler intake air is a good thing.

I was doing nothing of the sort.

So just tell me how lower exhaust temperature in an otto cycle is direct indication of lower thermal efficiency of said cycle.

I never said that.

I was talking about gas turbines. I made no comment about the role of intercoolers in the efficiency of otto engines.

[ringo]

The whole point is less temperature before compression is better.

But the intercooler is after the compressor.

The pistons are a compressor. Agree?
So the rule applies in the same way. Intercool between compressor stages.

It's a misconception that having an intercooler is bad, or a waste of time.

In fact i agree that efficiency gains are not significant with the exact same boost and rpm conditions, however power is greater.
What you do to improve efficiency is scale back that power to the same level as the non intercooler setup and you realize that you will have gains.

For every compressor stage, try to reduce temperatures. It always helps. Increased Mass flow with the same work is what you want. in fact it is this same density reason as to why engines lose so much power in brasil on for those hill climb cars.

And wuzak mentioned preheating with the gas turbine. If i remember correct, Honda did this with their ra168 engine. But instead of reheating the air,which would be a negative effect, they preheated the fuel instead. I'm not sure what effect that has but it was positive.

Intercoolers are very costly for gas turbines, and that's because they are water cooled and quite huge. But sometimes the price is very much worth it. Reheat with intercooling gives efficiency gains, no question about it.
But we don't have to argue this really, we've seen modern cars with direct injection using intercoolers. And if they weren't necessary makes like BMW wouldn't invest so much aerodynamics and packaging know how to place these things in their cars. Even going as far as to have water to air cooling.

[rjsa]

So just tell me how lower exhaust temperature in an otto cycle is direct indication of lower thermal efficiency of said cycle.

I never said that.

I was talking about gas turbines. I made no comment about the role of intercoolers in the efficiency of otto engines.

You're right, I didn't read it all and messed up royally. Sorry.

[FW17]

Now to illustrate to you, i will use the engine calculator. I'll show how different the power of the engine is with 60 degree air versus 40 degree air.
I had to turn down the boost pressure with the 40 degree air to have the same mass flow. You would agree with this for stoichiometry correct?

What is the point of using 40 degree and 60 degree?

If you using 45 psi as the with inlet temp 38 C outlet temp will be 256 C

The pistons are a compressor. Agree?
So the rule applies in the same way. Intercooler between compressor stages.

If there is no intercooler, the same compression ratio cannot be used

[wuzak]

If i remember correct, Honda did this with their ra168 engine. But instead of reheating the air,which would be a negative effect, they preheated the fuel instead. I'm not sure what effect that has but it was positive.

Pre-heating the fuel helps with the vapourisation of the fuel.