Turbo Vs N/A economy - off boost
Discussion
Matthew-TMM said:
Imagine a p-v diagram for an N/A engine with an 8:1 compression ratio for instance, at WOT, the area inside gives the work (as you will know anyway). Then imagine the same engine with a 12:1 compression ratio at WOT and it's p-v diagram which should show a grater area and hence more work done. To reduce the output of the higher CR engine to that of the low CR engine you will need to throttle the engine (ignoring everything else you could do of course), in order to reduce the area in the trace to that of the low CR engine at WOT. When you've throttled the high CR engine to this point, the power output of both will be the same, but the mass flow of air and hence also fuel into the high CR engine will be less.
That's how I see it anyway.
Eureka, I see the light!That's how I see it anyway.
Does this make sense, to confirm my understanding;
I've been thinking of the PV diagram as a simple 2D chart, and assuming that when you throttle back the 12:1 CR engine, it ends up sat on top of the 8:1 engine for a particular power as you have the same area under the curve. But... in 2D it's specific work, ie work / flow rate
If you think of it in 3D, with mass flow as the additional axis, then for a given power, you are concerned about the volume under the PV curve (or strictly the PVM surface!), not the area.
As you throttle the high CR engine back, the CR drops, but the mass flow drops as well, so for a given power (or volume on the PVM curve) the CR of the 12:1 engine doesn't drop all the way down to 8:1, so it has retains a thermal efficiency benefit.
Still not sure how to think about turbochargers because they essentially raise the CR back up again......
Mave said:
Matthew-TMM said:
Imagine a p-v diagram for an N/A engine with an 8:1 compression ratio for instance, at WOT, the area inside gives the work (as you will know anyway). Then imagine the same engine with a 12:1 compression ratio at WOT and it's p-v diagram which should show a grater area and hence more work done. To reduce the output of the higher CR engine to that of the low CR engine you will need to throttle the engine (ignoring everything else you could do of course), in order to reduce the area in the trace to that of the low CR engine at WOT. When you've throttled the high CR engine to this point, the power output of both will be the same, but the mass flow of air and hence also fuel into the high CR engine will be less.
That's how I see it anyway.
Still not sure how to think about turbochargers because they essentially raise the CR back up again...... That's how I see it anyway.
Boosted.
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