Streamliner nose air inlet

[Glen]

Go to links and click on motorcycle link. Near the bottom is Sam Wheelers web site.
BTW, a few years back Sam was on a run when a little wind pushed him off course and Sam let it drift. During this drift he went through a mile marker split it down the middle hit the small battery and photo cell and stayed up got the chute out and stopped with no other problems. We were cleaning up the battery etc. and never found the photo cell. Later in the pits as Sam and crew were looking over the liner they found the photo cell up inside of the air intake. Some where I have pictures of it as well as the mile marker and other debris. Cool head Sam and his lots of seat time saved the day and bike.

[hotrod]

Glad you brought this up.  When the compressor side of the turbo creates pressure as we all know compressing that air creates heat.  Now let's say Sam would get 2 psi at 350.  Is that compressed air heated or just the ambient air temp.

If it is ambient temp and we wanted say 15 lbs. of final boost then it would seem to me that the turbo only has to compress the air to 13 lbs. and the other 2 would come from the boost from the speed.  Is that right?

And if that is right is the 15 lbs. of boosted air the same temp as the temp rise for 13 lbs. of boost  or 15??

The turbo only sees the inlet air density and the pressure ratio it is compressing it to.

If ambient air pressure at Bonneville was 12.5 psi and you wanted 15 psi boost for a manifold air pressure of 27.5 psi absolute, your pressure ratio would be  (12.5+15.0)/12.5

So the turbo would be operating at a pressure ratio of 2.2:1

If you were getting a ram air boost of 2 psi, then the effective inlet pressure would be 14.5. To get to that same manifold pressure of 27.5 you would need to get 13 psi boost, so your turbo would be working at a pressure ratio of (14.5+13)/14.5 = 1.89.

Since the turbo is working at a lower pressure ratio the outlet temps would in almost all cases be lower. There would be some heating due to compression in the ram boost, so the inlet temps would be slightly higher in the second case but depending on the efficiency of the ram boost recovery and the compressor efficiency of the turbo, outlet temps would very likely be lower. More importantly if the turbo was working at the limit of its efficiency that extra inlet pressure might allow you to reach boost levels that would be unattainable without the ram air effect to increase the turbo inlet density.

The efficiency on many turbo compressors falls off very quickly when they get over a 2.0 - 2.5:1 pressure ratio.

Larry

[Sumner]

..................... There would be some heating due to compression in the ram boost, so the inlet temps would be slightly higher in the second case but depending on the efficiency of the ram boost recovery and the compressor efficiency of the turbo, outlet temps would very likely be lower. More importantly if the turbo was working at the limit of its efficiency that extra inlet pressure might allow you to reach boost levels that would be unattainable without the ram air effect to increase the turbo inlet density..........Larry

Thanks Larry I understood all of that and it was explained better than the turbo books I recommended on a different post  .

If I understand the heat I think you are saying that the air would be heated somewhat from the 2 lbs. ram-boost, but not as much as if it had been compressed to 2 lbs. with the compressor on the turbo.

Thanks,

Sum

[hotrod]

Right, most turbos at their very best are only 76% -78% efficient in compression compared to ideal adiabatic compression which you would get with the perfect gas law. At maximum pressure ratios they can drop down into the 60% thermal efficiency range.

In effect the ram boost and turbo boost would be a two stage compression process. Multistage compression is almost always more efficient than a single stage compression. Especially if you have some means to cool the inlet air after the ram boost process occurs.

The other issue is for every x psi of ram boost you get, the turbo multiplies it by the pressure ratio, so even very small gains in air density in that first stage, gets magnified in that second stage of compression in the turbo.

Since by definition if you are going for a record you are probably at the very limits of all the various processes in the power making process, take every advantage you can get even if they are very small increments they add up if you take enough of them.

Larry

[hitz]

Is 2 lbs. of ram boost possible?

 Harvey

[hotrod]

Is 2 lbs. of ram boost possible?

How fast you going to be moving?

Figure in the real world you will be able to recover about 50% of the theoretical ram boost for the speed.

Larry

[Dean Los Angeles]

The formula is MPH^2*0.0000176.
Speed  PSI
100   0.18
150   0.40
200   0.70
250   1.10
300   1.58
350   2.16
400   2.82

That Larry is GOOD. I'm voting him on to my team.