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Originally Posted by cheesehawk
Doesn't a supercharger (or turbocharger for that matter) run as a single intake, and then splits a tube towards each cylinder?
If that's the case, isn't fuel/air being routed towards each cylinder even while that cylinder isn't in its intake cycle? How could adding the fuel pre-supercharger give as precise a charge to each cylinder, when its being routed towards many cylinders that aren't prepared to accept the charge, as a direct injection which pumps it directly into the cylinder head only when the cylinder is needing it?
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Air is a mixture of gasses which have different molecular weights. But you wouldn't expect that the issues you allude to above would modify the composition of air going into the cylinders.
If the fuel has evaporated, and is in a gaseous phase, which is perfectly reasonable if the induction manifold temperature is high, the exact same argument applies; inertial separation of species within the gaseous mixture is unlikely because the forces are insufficient to overcome the diffusive tendency of the gas.
Quote:
Originally Posted by cheesehawk
All the math and numbers aside, yes, your air/fuel mix via a supercharger/turbocharger, is mixed well, but you're still backing it up against a closed valve for 3/4 of the cycle, then pushing this in when the valve opens. Also, backpressures and eddies in the airflow probably effect the droplets of fuel, allowing them to consolidate (albeit very little) before the valve opens. This might add to the compression, which might help power output, but surely can't be great for precise fuel metering.
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If the fuel is still liquid in the intake manifold then mixture distribution will be bad. This is often the case with naturally aspirated engines because the induction manifold temperature is essentially ambient.
The benefit of single point injection into the eye of the supercharger is that it improves the effective isentropic efficiency of the supercharger, and thus reduces supercharger work, increasing the brake horsepower output of the engine when compared with multi-point injection into the cylinders or ports.
I'm getting pretty tired of trying to explain this relatively simple concept.
Here's a nice big paper. It's got a lot of interesting stuff in it, but the bit that is germane to this discussion is the analysis of the effects of water injection upon compressor performance. It doesn't matter whether you're injecting fuel or water, the latent heat reduces the temperature rise through the compressor, which is analogous to an increase in compressor efficiency.
Happy reading.