Preventing abnormal combustion

[Tommy Cookers]

It is always best to perform as much compression/expansion work as possible within the reciprocator, since it is a very efficient device for doing this work. The only reason for using a turbocharger to perform additional compression/expansion work of the intake/exhaust gas, is because the turbo system would have lower overall weight, and/or could give better performance under an extreme range of operating conditions.

surely ?, (IMO)
the prime advantage of any kind of supercharging is to increase power by increasing massflow by increasing induction pressure
massflow is very insensitive to increase in CR, but very sensitive to absolute induction pressure

power = massflow x TE x ME

massflow increase demands some drop in HUCR (hence TE), but can raise ME by increasing power much more than friction
and much of the power to mechanically drive an efficient supercharger is 'recovered' to the crankshaft due to the favourable 'delta P'
in this way lightly supercharged SI engines were in the 30s more efficient (32-34%) than any n/a equivalents
(granted they benefited from a small fuel advantage, the n/a equivalents were presumably not optimised for the improved fuel)
national and industrial technical policies were influenced by this (doctrine of the 'ground-boosted' aero engine)
also CI

[Tommy Cookers]

charge cooling is not primarily to benefit air density (ie massflow, hence power)
what dominates maximum power is boosting massflow by (relative to fuel quality) lowering the CR to allow increased supercharge (also some diesels do this)
this is what the supercharged aircraft engine was all about

@ Tommy What do you mean by increased supercharge?

any engine/fuel has some combination of supercharger action (possibly nil), charge cooling (possibly nil) and reciprocator HUCR
thermal efficiency is dominated by the HUCR at likely CR values
the HUCR for the given engine/fuel is determined by induction T and P (ie due to supercharge and charge cooling)
but we know that if abs induction pressure is raised eg from 1 to 2 bar, then HUCR and TE fall by a relatively small amount
(as long as there has not been a huge increase in induction temperature)
that is, in practical systems a small reduction in the recip CR allows (with alteration of the supercharging system) a large increase in induction pressure (without detonation) aka increased supercharge/increased massflow/increased mep
this would substantially increase the power despite a relatively small loss in TE
the increased air massflow would require a related increase in fuel massflow of course
increased charge cooling with the supercharging system unchanged would gain little massflow and power (in a practical engine), although TE would be better
2014 is unprecedented in forcing efficiency as the only route to power

[pgfpro]

Todays turbo 2014 engines will need IAT temps at a target temp not just the lowest temp they can reach for more air density. Todays turbo 2014 engines will need the air to be certain temp to keep the compressor in its max efficiency range and sometime a cooler charge could be going in the wrong direction.

Compressor pressure to high will take away useful energy that the turbine could of used.

Compressor pressure to low will result in a poor engine delta p. (fuel limit cause)

To low IAT will result in a lower intake pressure and hurt engine delta p. (fuel limit cause)

To high IAT will result in more intake pressure needed and pull energy away from the turbine.

Even the engines VE for the first time will be lower then normal at the higher rpm to keep the balance of the package.

[olefud]

[quote="pgfpro"]Todays turbo 2014 engines will need IAT temps at a target temp not just the lowest temp they can reach for more air density. Todays turbo 2014 engines will need the air to be certain temp to keep the compressor in its max efficiency range and sometime a cooler charge could be going in the wrong direction.quote]

Seemingly there would be several ways to skin the cat in terms of intake temp/pressure. A cooler charge would allow for a given fuel rate limited charge to be compress to a smaller combustion volume allowing a higher expansion pressure throughout the power stroke. Also, a cooler charge would further allow a leaner mixture that would extend the RPM limit with the limited fuel rate. These would be power enhancements as a result of improved TE. They will of course have some detrimental effect elsewhere and may or may not be worth that price.

[riff_raff]

When it comes to charge cooling, it is usually beneficial overall with SI engines, but not beneficial with CI engines. The fact of the matter is that intake charge coolers produce flow losses and heat energy losses. And any loss of energy in the system will reduce BTE and SFC.