TERS strategy and Wastegates.

[Vortex37]

I thought that the general consensus of opinion, was that the Mercedes ICE was relatively equal to the others, and the extra performance came from MGU-K/ES and MGU-H. Knowing what ES Mercedes have been using in the V8 era, they already had an advantage, because that particular product can take more 'abuse'. At least one of the current engines uses both a wastegate and a BOV. This makes sense to me, because it is important to keep the MGU-H at maximum allowed 'rpm' which will generate the maximum amount of electrical power. I think it is safe to assume that they are using SRM/PPMT type MGU's, which have a 97% efficiency approx. With these current hybrid units 'turbo lag' is surely irrelevant. Modern turbo units can spin up from 40k rpm to 120k rpm in <400ms. So very little energy required to spin up. Mechanical efficiency for a consumer version is claimed to be in the range of 94-97%, though I am sceptical of that figure. In the other thread somebody dismissed the idea of axial flow devices. I would challenge that. Axial flow turbochargers have a far better flow characteristic, and should be able to operate nearer the surge line. The other advantage is the rotating mass/diameter is much smaller, like for like flow can mean a >40% diameter reduction. Whilst it can be argued that a twin scroll compressor has major advantages at low ICE rpm, it would not be outside the bounds of possibility to use a hybrid turbo with radial flow turbine and axial flow compressor.

[gruntguru]

Can an axial turbine be designed with a high PR per stage? Would an F1 axial turbine need to be multi-stage?

[trinidefender]

Can an axial turbine be designed with a high PR per stage? Would an F1 axial turbine need to be multi-stage?

In modern commercial aircraft, each stage generally compresses the air to 1.1 to 1.6 atmospheres. Unfortunately not enough with F1 regulations which is just another reason why I wish F1 would loosen the regs in certain areas. Would need at least two stages to make it work in F1. Axial compressors are generally most efficient very close to the stall line.

[gruntguru]

Can an axial turbine be designed with a high PR per stage? Would an F1 axial turbine need to be multi-stage?

In modern commercial aircraft, each stage generally compresses the air to 1.1 to 1.6 atmospheres. Unfortunately not enough with F1 regulations which is just another reason why I wish F1 would loosen the regs in certain areas. Would need at least two stages to make it work in F1. Axial compressors are generally most efficient very close to the stall line.

Yes, but I was asking about turbines. Pretty sure an axial turbine is useful at PR >1.6 per stage.

[TinoBoost]

Regarding dual boost, it would be possible if rules permitted it. what would be the gain however?

there is an example.
http://turbo.honeywell.com/our-technolo ... ochargers/

lower inertia isnt worth it with the mgu-h.

[gruntguru]

Not sure if that would contravene the rules. The compressor is still single stage - just two flow paths in parallel.

[riff_raff]

If there is PM M/G coupled to the turbocharger shaft, there can be a very good reason for having an exhaust wastegate. The wastegate is a backup device to prevent the turbocharger from exceeding the safe speed limit of the PM M/G. If the safe speed of the PM M/G was exceeded, it would produce a dangerous explosive failure of the rotor assembly. The ability of the M/G to control the turbocharger speed by absorbing or adding power is a very efficient way to regulate its speed. But if the battery system cannot absorb any more power output from the M/G system, it will not have the ability to further limit the turbocharger speed.

[gruntguru]

That assumes that the MGUH is capable of harvesting more than the 120kW it is allowed to send to the MGUK. Not many people are predicting that much power from the turbine. If that was the case, it would be relatively simple to change the operating point of the engine (fuel, ignition advance, throttling) to reduce output from the MGUH to 120kW when the battery is full - perhaps even trading reduced power from the MGUH for an increase from the ICE crankshaft.

Besides, a small load bank to shed a few kW would be simpler, cheaper and lighter than a waste gate and plumbing. Not denying the waste gate may be protection from overspeed/overboost in the event of some sort of system failure - just saying it wouldn't make sense to operate it simply for boost control when the ES is full (or at any other time)

[Vortex37]

snip.....
lower inertia isnt worth it with the mgu-h.

I would take the opposite view. In a racing engine every gain is worthwhile. Remember the turbo and MGU are connected, and they have to rotate at the same RPM, so lower mass/inertia will contribute to better overall efficiency - less, if any, electrical energy required to spool up - the faster the assembly is spinning the more electrical energy is being generated - keeping a 'constant' electrical power output makes it easier to balance out power/torque to the wheels etc.

[henry]

snip.....
lower inertia isnt worth it with the mgu-h.

I would take the opposite view. In a racing engine every gain is worthwhile. Remember the turbo and MGU are connected, and they have to rotate at the same RPM, so lower mass/inertia will contribute to better overall efficiency - less, if any, electrical energy required to spool up - the faster the assembly is spinning the more electrical energy is being generated - keeping a 'constant' electrical power output makes it easier to balance out power/torque to the wheels etc.

I think your view is probably correct if the system is treated as a turbocharger with electrical assistance to spool it up when it has lost speed in off throttle conditions. However I wonder if we think of it as an electrically driven supercharger that gets assistance from the exhaust gas turbine. It might cost a little energy to keep the turbine spinning but lag could be all but eliminated. The inertia of all the components, turbine, compressor and MGU become very much less significant and they can be sized for the absolute performance.

[wuzak]

Remember the turbo and MGU are connected, and they have to rotate at the same RPM, so lower mass/inertia will contribute to better overall efficiency - less, if any, electrical energy required to spool up - the faster the assembly is spinning the more electrical energy is being generated - keeping a 'constant' electrical power output makes it easier to balance out power/torque to the wheels etc.

The MGU does not have to rotate at the same speed as the turbo - it can be geared, but it has to be a fixed ratio.

The turbo's compressor and turbine are required to spin at the same rpm.

[TinoBoost]

snip.....
lower inertia isnt worth it with the mgu-h.

I would take the opposite view. In a racing engine every gain is worthwhile. Remember the turbo and MGU are connected, and they have to rotate at the same RPM, so lower mass/inertia will contribute to better overall efficiency - less, if any, electrical energy required to spool up - the faster the assembly is spinning the more electrical energy is being generated - keeping a 'constant' electrical power output makes it easier to balance out power/torque to the wheels etc.

I think your view is probably correct if the system is treated as a turbocharger with electrical assistance to spool it up when it has lost speed in off throttle conditions. However I wonder if we think of it as an electrically driven supercharger that gets assistance from the exhaust gas turbine. It might cost a little energy to keep the turbine spinning but lag could be all but eliminated. The inertia of all the components, turbine, compressor and MGU become very much less significant and they can be sized for the absolute performance.

I am not sure there is much to gain from lower inertia. I would expect the turbo to be spinning fast all the time. Higher inertia does add a dampening factor to the turbo rpm as well, which could make controls on the MGU-H easier, and tax the electronics less.

The fact for example that Merc has a somewhat long shaft on the turbine - and a strong one, adds some inertia. I believe inertia would be a low priority on these hybrid turbochargers.

[dragvorl]

I've listened to Craig Scarborough, and if I remember well he mentioned that wastegates can help eliminating turbo lag? I don't understand that completely.

[mrluke]

Besides, a small load bank to shed a few kW would be simpler, cheaper and lighter than a waste gate and plumbing. Not denying the waste gate may be protection from overspeed/overboost in the event of some sort of system failure - just saying it wouldn't make sense to operate it simply for boost control when the ES is full (or at any other time)

Isnt this exactly what Renault / RBR did which caused them so many issues in testing?

[wuzak]

Facts only has an inetersting take on this in the Formula One 1.6l V6 turbo engine formula thread.