Renault Power Unit Hardware & Software

[Wayne DR]

Have they sorted out that Piston issue? If they haven't, does it mean there is something fundamentally wrong with the engine?

They have stopped making their pistons out of chocolate, and the problem went away...

[djos]

I thought I heard the sky team mention that Renault went back to last year's piston design for Spain?

[PlatinumZealot]

The mgu-h doesnt really harvest the heat energy, its basically just boost control, it works as a brake on the turbo to prevent it overboosting and feeds the electric either straight to the mgu-k or ers. It can also act as a motor to spin the turbo up when the driver is off throttle so that full boost is always available

It takes the energy that would otherwise be wasted through a waste gate as noise and uses it to power the car, if that is not harvesting I don't know what it is

That agrees with everything I said, it harvests energy but not really heat, it doesnt work like a heat pump, its really a brake on the turbine.

For the millionth time.. gas turbines do work off thermal energy. It does use the thermal energy of the gas as well as the momentum energy. The exhaust temperature of a turbocharged engine is much much lower than a naturally aspirated or supercharged engine.

Temperature is part of the internal energy of the gas. The higher the temperature, or the hotter the gas is, the faster the molecules move. And faster molecules have more energy to transfer. This energy is transferred by expansion of the gasses. You cannot do this without heat.

Pretty fundamental things. Good luck trying to extract the same amount of energy from ice-cold air!! Good luck expanding that!

[J.A.W.]

Yeah PZ.. very funny, very droll..

Hmmm..
..isn't it something about the greater the temp/density gradient in the working fluid, the higher the energy transfer?

The ICE component certainly works harder on 'ice cold' induction air.. &,
How ever do those gas-turbine powered planes manage at altitude in sub-zero temperatures?

[gruntguru]

That agrees with everything I said, it harvests energy but not really heat, it doesnt work like a heat pump, its really a brake on the turbine.

This has been discussed extensively elsewhere. The great majority of the energy extracted from the exhaust gas is heat energy.

[gruntguru]

The must be a cross over point where the energy delivered to the ES or provided to the MGU-K is less than the energy absorbed by the above losses. One way to alleviate this would be to vent excess boost from the compressor through a blow off valve, removing an additional unnecessary load from the compressor, allowing the turbine to spin faster and deliver more energy to the MGU-H.

Blow off valve = less boost = less intake mass flow = less exhaust mass flow = less turbine power.

So . . . no.

[stevesingo]

The must be a cross over point where the energy delivered to the ES or provided to the MGU-K is less than the energy absorbed by the above losses. One way to alleviate this would be to vent excess boost from the compressor through a blow off valve, removing an additional unnecessary load from the compressor, allowing the turbine to spin faster and deliver more energy to the MGU-H.

Blow off valve = less boost = less intake mass flow = less exhaust mass flow = less turbine power.

So . . . no.

Why would they want unlimited boost when they can only burn 100kg/hr of fuel?

[wuzak]

The must be a cross over point where the energy delivered to the ES or provided to the MGU-K is less than the energy absorbed by the above losses. One way to alleviate this would be to vent excess boost from the compressor through a blow off valve, removing an additional unnecessary load from the compressor, allowing the turbine to spin faster and deliver more energy to the MGU-H.

Blow off valve = less boost = less intake mass flow = less exhaust mass flow = less turbine power.

So . . . no.

Why would they want unlimited boost when they can only burn 100kg/hr of fuel?

Boost is in no way limited now.

[Cold Fussion]

The must be a cross over point where the energy delivered to the ES or provided to the MGU-K is less than the energy absorbed by the above losses. One way to alleviate this would be to vent excess boost from the compressor through a blow off valve, removing an additional unnecessary load from the compressor, allowing the turbine to spin faster and deliver more energy to the MGU-H.

Blow off valve = less boost = less intake mass flow = less exhaust mass flow = less turbine power.

So . . . no.

Why would they want unlimited boost when they can only burn 100kg/hr of fuel?

I think the point is that if you blow off compressed air you're effectively wasting turbine power compressing air needlessly which some portion of could have been recovered by having the higher exhaust mass flow.

[trinidefender]

The must be a cross over point where the energy delivered to the ES or provided to the MGU-K is less than the energy absorbed by the above losses. One way to alleviate this would be to vent excess boost from the compressor through a blow off valve, removing an additional unnecessary load from the compressor, allowing the turbine to spin faster and deliver more energy to the MGU-H.

Blow off valve = less boost = less intake mass flow = less exhaust mass flow = less turbine power.

So . . . no.

Why would they want unlimited boost when they can only burn 100kg/hr of fuel?

separate issue. GG's point was that reducing boost pressure would reduce massflow to the turbine and hence reduce energy that the turbine can get from the exhaust. As far as I'm aware all the teams have wastegates for times that they need to reduce back-pressure.

[toraabe]

The must be a cross over point where the energy delivered to the ES or provided to the MGU-K is less than the energy absorbed by the above losses. One way to alleviate this would be to vent excess boost from the compressor through a blow off valve, removing an additional unnecessary load from the compressor, allowing the turbine to spin faster and deliver more energy to the MGU-H.

Blow off valve = less boost = less intake mass flow = less exhaust mass flow = less turbine power.

So . . . no.

Why would they want unlimited boost when they can only burn 100kg/hr of fuel?

They will not. Only the optimum, BUT remember there is a significant difference in pressure loss from the compressor to the inlets the longer the pipes are. The cooler the compressor is, shorter pipes means less pressure loss hence an increase in efficiency and so on . As a result the engine runs cooler with higher thermal efficiency as the result. It also means that the engine is running under less thermal stress. I you look at the Merc turbo solution all this benefits is a result of their Turbo solution. I am sure if Renault would have implemented the Merc turbo solution the reliability also would have benefited.

[gruntguru]

There is not a significant pressure loss anywhere in the inlet manifold and runner length does not have a significant effect on pressure loss. Perhaps you are confusing "loss" with pressure wave tuning and the relationship between runner length, rpm and cylinder filling.

As a general rule, a cooler engine is less efficient in terms of "thermal efficiency" (the one that counts underthe current formula). You may be confusing volumetric efficiency, which does increase in a cooler engine but is less important under the current formula.

[stevesingo]

The way I see it is you want the turbine shaft to achieve 125k rpm as early as possible in the engine speed range. Why, If you have a higher turbine speed your MGU-H will be more able to produce more power.

This presents two problems;

1, it is likely that if the turbo is providing sufficient mass air for the engine at 7krpm with a shaft speed of 125k rpm, you could end up with a turbo speed in excess of 125krpm. We can apply load to the MGU-H to keep the turbo speed down, but this will increase exhaust back pressure.

2, it is likely that the compressor will not be able to provide sufficient air at engine speeds of 10500rpm as there is no head room in left in turbo speed.

If we need the compressor to provide sufficient mass air flow at 10.5k rpm and 125k rpm turbo speed AND we also have 125k rpm turbo speed at engine speed of 7krpm, the compressor will be delivering more air than the engine can use due to the fuel flow restriction. In this instance I would use a BOV to bleed that air air away rather than using the waste gate to reduce turbo speed and therefore HGU-H speed. The waste gate would only be used to maintain the back pressure.

[Edis]

There is not a significant pressure loss anywhere in the inlet manifold and runner length does not have a significant effect on pressure loss. Perhaps you are confusing "loss" with pressure wave tuning and the relationship between runner length, rpm and cylinder filling.

As a general rule, a cooler engine is less efficient in terms of "thermal efficiency" (the one that counts underthe current formula). You may be confusing volumetric efficiency, which does increase in a cooler engine but is less important under the current formula.

Depends on what you mean with a "cooler engine", engines will in general respond well to a lower air inlet temperature. The placement of the compressor will however have little impact in this regard, as it is mostly determined by the compressor inlet temperature, pressure ratio of the compressor, the adiabatic efficiency of the compressor and of course the charge cooling.

Renault have said they considered the turbocharger layout used by Mercedes when they developed their engine.

The way I see it is you want the turbine shaft to achieve 125k rpm as early as possible in the engine speed range. Why, If you have a higher turbine speed your MGU-H will be more able to produce more power.

This presents two problems;

1, it is likely that if the turbo is providing sufficient mass air for the engine at 7krpm with a shaft speed of 125k rpm, you could end up with a turbo speed in excess of 125krpm. We can apply load to the MGU-H to keep the turbo speed down, but this will increase exhaust back pressure.

2, it is likely that the compressor will not be able to provide sufficient air at engine speeds of 10500rpm as there is no head room in left in turbo speed.

If we need the compressor to provide sufficient mass air flow at 10.5k rpm and 125k rpm turbo speed AND we also have 125k rpm turbo speed at engine speed of 7krpm, the compressor will be delivering more air than the engine can use due to the fuel flow restriction. In this instance I would use a BOV to bleed that air air away rather than using the waste gate to reduce turbo speed and therefore HGU-H speed. The waste gate would only be used to maintain the back pressure.

No, you don't want to reach 125,000 rpm as soon as possible as that would force the compressor into surge as a centrifugal compressor can't supply pressure unless there is adequate flow and the flow depends on how much air the engine can use (engine speed, throttle position and so on). The turbocharger speed needs to be controlled depending on what boost level you want to reach, where a higher boost pressure in general means a higher turbocharger speed. So, if for instance the boost pressure is lowered at engine speeds above 10,000 rpm due to the fuel flow limit it is possible that you need to reduce the turbocharger speed above that point.

The compressors used in F1 should be somewhat similar in size to the following compressor:



The amount of power the MGU-H can produce isn't really that dependent on turbocharger speed.

If you bleed off compressed air the output of the MGU-H will be reduced as turbine power is used to compress air instead of driving the MGU-H.

[trinidefender]

The way I see it is you want the turbine shaft to achieve 125k rpm as early as possible in the engine speed range. Why, If you have a higher turbine speed your MGU-H will be more able to produce more power.

This presents two problems;

1, it is likely that if the turbo is providing sufficient mass air for the engine at 7krpm with a shaft speed of 125k rpm, you could end up with a turbo speed in excess of 125krpm. We can apply load to the MGU-H to keep the turbo speed down, but this will increase exhaust back pressure.

2, it is likely that the compressor will not be able to provide sufficient air at engine speeds of 10500rpm as there is no head room in left in turbo speed.

If we need the compressor to provide sufficient mass air flow at 10.5k rpm and 125k rpm turbo speed AND we also have 125k rpm turbo speed at engine speed of 7krpm, the compressor will be delivering more air than the engine can use due to the fuel flow restriction. In this instance I would use a BOV to bleed that air air away rather than using the waste gate to reduce turbo speed and therefore HGU-H speed. The waste gate would only be used to maintain the back pressure.

This has been discussed to quite a length much earlier in the 1.6L V6 turbo engine thread. It is the same theory behind turbo compounding. Yes, depending on the turbine design, back pressure will increase but the trade off is that electricity is generated which is then sent directly to the MGU-K providing additional power. Of course at some point the electricity generated will be less than the power reduction by increased back pressure but like everything there is a balance to find.