2014 intercooling

[ringo]

C'mon, we are talking Earth atmosphere here. You don't see people complaining about power drop in Bahrein, but you do at Interlagos! It IS about pressures.

No, i am referring to the conditions inside the system. The temperature of air is directly tied to it's pressure, no matter how small the change. The context is right before air enters the compressor to the exhuast pipe, those aren't earth's atmosphere.

Yep, you have to adjust to the same FUEL flow, not air flow.

It's an otto cycle, so you can adjust both. You adjust airflow by controlling the throttle. Both are variable. The whole idea is that i am attempting to ahcieve stoichometry.

The thermal efficiency is ONLY dependent on temperatures. You can recalculate it into pressures, or volumes, in fact pure Otto-cycle engine efficiency can be expressed thru compression ratio. However, real life performance may depend on many other things.

Yes it is determined by temperature, this is the temperature after combustion and temperature before compression. That is determined by a myriad of things.
So it cannot be looked at simply.

Fuel flow limit changes things VERY much.

Of course.

[ringo]

Hot high pressure air, or cold lower pressure air can give you the same amount of oxygen.

No it cannot, not in the same stroke. I'm talking air mass, not volume. Hot air is lighter, so it's clear there are less air molecules in the same volume. Piston engine has displacement, there is a reason it is classed by displacement, it's a volume engine. Lighter air, less oxygen, less fuel, less power.

[ringo]

Not sure what you mean here. For a given mass of fuel you need a defined mass of air. The trick is to get enough air to fully burn the fuel. There seems to be no limit for boost pressure, so you would either have higher boost and no intercooling or lower boost and intercooling.

Coulnd't have said it better myself.

[timbo]

No, i am referring to the conditions inside the system. The temperature of air is directly tied to it's pressure, no matter how small the change. The context is right before air enters the compressor to the exhuast pipe, those aren't earth's atmosphere.

So your Interlagos example was missing the point.

It's an otto cycle, so you can adjust both. You adjust airflow by controlling the throttle. Both are variable. The whole idea is that i am attempting to ahcieve stoichometry.

But I'm talking about rules. Any calculations you make should start with a set fuel flow.

So it cannot be looked at simply.

Sure, OTOH there's no clear cut advantage on using intercooler from pure thermodynamics.

I think the need for an intercooler would be mostly dictated by the combustion process.

[langwadt]

Hot high pressure air, or cold lower pressure air can give you the same amount of oxygen.

No it cannot, not in the same stroke. I'm talking air mass, not volume. Hot air is lighter, so it's clear there are less air molecules in the same volume. Piston engine has displacement, there is a reason it is classed by displacement, it's a volume engine. Lighter air, less oxygen, less fuel, less power.

agreed, if you have unlimited by fuel you want as much dense cold air in as possible and add fuel to match

but if you are limited by the amount of fuel you can add you only need to get the number oxygen molecules to match
you can get that with hot high pressure or cold low pressure

1.5bar@25C ~1.75kg/m3

2.00bar@125C ~1.75kg/m3

[riff_raff]

The engine cylinder is both a compressor and an expander. The amount of work that the engine cylinder can extract from the combustion gas is limited partially by its expansion ratio. The turbocharger can improve efficiency by performing additional air compression work outside of the cylinder using energy extracted from the exhaust gas flow. With a single stage turbo SI engine, the intercooler (or aftercooler) is primarily useful for reducing detonation. If the engine uses multiple turbo compressor stages, the intercooling also improves the performance of the latter stage compressors.

[olefud]

The engine cylinder is both a compressor and an expander. The amount of work that the engine cylinder can extract from the combustion gas is limited partially by its expansion ratio. The turbocharger can improve efficiency by performing additional air compression work outside of the cylinder using energy extracted from the exhaust gas flow. With a single stage turbo SI engine, the intercooler (or aftercooler) is primarily useful for reducing detonation. If the engine uses multiple turbo compressor stages, the intercooling also improves the performance of the latter stage compressors.

Very true. Efficiency and power is in part a function of the full compression volume relative to the expanded volume in view of blow down. Generally, if the mechanical compression ratio "just" avoids detonation the compression volume can be further reduced with yet lower temperature (more intercooling) for yet more power. The weight and volume of an intercooler at some point reaches a point of diminishing return.

[tuj]

Why are we talking about stochiometric? I would think that under torque demand, the engine will run richer than stoch to prevent detonation and produce optimal power (everything I have read suggests optimal mixture is just sort of stoch), and during the off-throttle, won't the engines be using stratified charge via DI and running somewhat-to-extremely lean?

[Tommy Cookers]

running richer than stoichiometric is throwing away fuel unburned

the benefits are trivial with this injection and fuel
the traditional benefits to CR are mostly from aromatics, these have poor specific energy and will not be used
broadly speaking .....

the partial torque running would benefit if throttling were not used, ie use modulated displacement as in recent F1
this could be combined with leaning
leaning is often wasteful of compressor work
anyway there will be 'free' fuel available via the fuel rate for this partial torque running, to the benefit of fake recovery
they won't always fight and die to go super-lean ?
the whole non-WOT area is a can of worms, given some races will be up against 100 kg of fuel, and some won't

[tuj]

I have never heard that 14.7 gives best power....where do you get that from? Because the combustion process is not complete, running a stochiometric mixture risks detonation especially under boost with high CR's. Please help me understand. I have always heard that best power occurs between 12.5:1 - 14:1.

[Tommy Cookers]

yes with unlimited fuel, as in F1 before 2014 or WW2 aircraft
no with limited fuel ie 2014 max 100kg/hr throughout

[ringo]

I think the advanced direct injection will actually reduce the issue of detonation.
The direct injection is the only reason i think not using an itercooler, though less power dense, but more aerodynamic, will be feasible.
Looking on the ferrari la ferrari with it's 13:1? compression ratio thanks to direct injection. I feel we will see engines pushing the envelop on how close they can scrape on the edge detonation.

[Cold Fussion]

I have never heard that 14.7 gives best power....where do you get that from? Because the combustion process is not complete, running a stochiometric mixture risks detonation especially under boost with high CR's. Please help me understand. I have always heard that best power occurs between 12.5:1 - 14:1.

Because you're not burning all the fuel available. In 2014, the engines have a maximum fuel flow rate, and an unlimited amount of air, so maximum power is achieved by burning all of that maximum fuel flow, which occurs at stochiometric and not running rich.

[riff_raff]

Because you're not burning all the fuel available. In 2014, the engines have a maximum fuel flow rate, and an unlimited amount of air, so maximum power is achieved by burning all of that maximum fuel flow, which occurs at stochiometric and not running rich.

Best SFC will be at the leanest A/F condition the engine can operate at without detonation. Under conditions of WOT and full load, a stoichiometric A/F mixture will usually result in the best combination of SFC and power.

Simply combusting all of the fuel existing within the intake charge is not what really matters. What matters more is the heat release rate of the fuel combustion process, and how efficiently the engine is at extracting the energy from the combustion products.

[Holm86]

I think the advanced direct injection will actually reduce the issue of detonation.
The direct injection is the only reason i think not using an itercooler, though less power dense, but more aerodynamic, will be feasible.
Looking on the ferrari la ferrari with it's 13:1? compression ratio thanks to direct injection. I feel we will see engines pushing the envelop on how close they can scrape on the edge detonation.

No doubt that direct injection allows much higher compression ratios and reduces detonation possibilities.

And Mazda's normal road car engines with SkyActiv technology runs 14:1 with both their petrol and diesel engines. (Very high for a petrol engine, relatively low for a diesel).