Turbo vs Atmospheric engine race track

[gruntguru]

Turbo engines are inherently more fuel efficient for a number of reasons, the main ones being:

- smaller displacement means less friction for a given engine output rating
- less throttling at part-load reducing pumping losses
- exhaust waste heat recovered by the turbine can return some energy to the crankshaft as intake pumping work

The reason mass-market downsized engines return poor full-load efficiency, is manufacturers have to add excess fuel to suppress detonation and thermal stress. Actually they don't HAVE to - water injection would do a better job and save a lot of fuel.

Furthermore, the fuel economy standards set around the world tend not to include full load testing. Result? Vehicles with impressive advertised fuel economy and abysmal real-world economy - especially if the vehicle has to work hard.

[etusch]

Turbo engines are inherently more fuel efficient for a number of reasons, the main ones being:

- smaller displacement means less friction for a given engine output rating
- less throttling at part-load reducing pumping losses
- exhaust waste heat recovered by the turbine can return some energy to the crankshaft as intake pumping work

The reason mass-market downsized engines return poor full-load efficiency, is manufacturers have to add excess fuel to suppress detonation and thermal stress. Actually they don't HAVE to - water injection would do a better job and save a lot of fuel.

Furthermore, the fuel economy standards set around the world tend not to include full load testing. Result? Vehicles with impressive advertised fuel economy and abysmal real-world economy - especially if the vehicle has to work hard.

aren't these advantages of small engines but not turbo. You are talking about less friction. Okey, smaller piston has lesser friction but turbo itself has additional friction and it rotates much more faster than engine itself. It adds cooling, lubricating loads to the engine. Smaller parts which makes friction gains are facing much more pressure to deal with. Smaller piston surface, smaller piston rings must deal with bigger power and bigger heats per given surface. I think smaller bore has affect on valve diameters too, so breathing also a bit harder. Direct injection and spurk plugs also need space for themselves. PreChamber systems may give space advantages in this condition.
If you are not successful at combustion then turbo's heat recovery is not that important.

[Tommy Cookers]

Turbo engines are inherently more fuel efficient for a number of reasons ...
- smaller displacement means less friction for a given engine output rating ....
- exhaust waste heat recovered by the turbine can return some energy to the crankshaft as intake pumping work

apologies for clumsy editing .... assuming track not road use .... for a given power output rating ....

smaller displacement gives smaller combustion chamber area - heat to coolant is less so heat for work is greater ... but ..

lower CR is inevitable - tending to reduce indicated TE (fraction of heat in combustion chamber turned into work on piston)
also (disadvantageously) ER is lowered by earlier EVO

additional to 1988 F1 maybe past endurance racing contains worthwhile examples ?

[sosic2121]

ER is even lower due to earlier EVO - reducing exhaust energy return via compressor

Why does EVO open early? To reduce overlap?

What effect higher exhaust back pressure and higher inlet temperature have? Hotter combustion chamber, increasing losses to coolant?

[gruntguru]

Turbo engines are inherently more fuel efficient for a number of reasons, the main ones being:

- smaller displacement means less friction for a given engine output rating
- less throttling at part-load reducing pumping losses
- exhaust waste heat recovered by the turbine can return some energy to the crankshaft as intake pumping work

The reason mass-market downsized engines return poor full-load efficiency, is manufacturers have to add excess fuel to suppress detonation and thermal stress. Actually they don't HAVE to - water injection would do a better job and save a lot of fuel.

Furthermore, the fuel economy standards set around the world tend not to include full load testing. Result? Vehicles with impressive advertised fuel economy and abysmal real-world economy - especially if the vehicle has to work hard.

aren't these advantages of small engines but not turbo. You are talking about less friction. Okey, smaller piston has lesser friction but turbo itself has additional friction and it rotates much more faster than engine itself. It adds cooling, lubricating loads to the engine. Smaller parts which makes friction gains are facing much more pressure to deal with. Smaller piston surface, smaller piston rings must deal with bigger power and bigger heats per given surface. I think smaller bore has affect on valve diameters too, so breathing also a bit harder. Direct injection and spurk plugs also need space for themselves. PreChamber systems may give space advantages in this condition.
If you are not successful at combustion then turbo's heat recovery is not that important.

- If a manufacturer wants to downsize the engine and retain the same power they need to turbo. eg 2 litre, 300 hp in a truck.
- Friction in the turbo itself dissipates only "free" energy harvested from the turbine - not the crankshaft - so doesn't add to FMEP
- Who said anything about smaller bores etc? "Downsizing" usually means fewer cylinders.

[gruntguru]

On the other hand, downsized engines are efficient(although not as efficient as small NA engine)

Incorrect. When both are designed with efficiency as the primary goal, the turbo engine is more (fuel) efficient. In the real world, downsized turbo engines are thirsty at full load for the reason I previously stated.

[gruntguru]

I guess there is a reason why Prius is NA...

The Prius engine is operated in a narrow window close to peak efficiency. Under these conditions a turbo version would:
- have only a marginal efficiency advantage
- cost a lot more
- be less suited to the frequent "engine off" operation of the hybrid transmission.

[63l8qrrfy6]

lower CR is inevitable - tending to reduce indicated TE (fraction of heat in combustion chamber turned into work on piston)
also (disadvantageously) ER is lowered by earlier EVO

Not necessarily, modern SI turbocharged engines take advantage of over-expanded cycles (Remi Taffin stated they are currently developing Miller cycle for their F1 engine) which means that very high CR is possible along with high expansion ratios. Of course volumetric efficiency takes a massive hit which would be preposterous for a N/A engine but not much of an issue for a highly turbocharged application.

[etusch]

- Friction in the turbo itself dissipates only "free" energy harvested from the turbine - not the crankshaft - so doesn't add to FMEP
- Who said anything about smaller bores etc? "Downsizing" usually means fewer cylinders.

I don't think turbo gets free energy, it has an affect on exhausting process. And my point is that, manufacturers say everything is good with what they produce no matter what it is. Tomorrow they will produce NA engine and this time they count NA advantages.

You are right with last item. I thought it by looking cars in my country. I didn't think downsizing from (for example )3.0 6 cylinder to 2.0 4 cylinder but 1.2 i4 instead of 1.6 i4. I am not against turbo. but I like bigger engines. V6 or 8 with turbo would be wonderful but it is like a dream in turkey if you are not rich who has not got problems to pay high taxes

[henry]

lower CR is inevitable - tending to reduce indicated TE (fraction of heat in combustion chamber turned into work on piston)
also (disadvantageously) ER is lowered by earlier EVO

Not necessarily, modern SI turbocharged engines take advantage of over-expanded cycles (Remi Taffin stated they are currently developing Miller cycle for their F1 engine) which means that very high CR is possible along with high expansion ratios. Of course volumetric efficiency takes a massive hit which would be preposterous for a N/A engine but not much of an issue for a highly turbocharged application.

I thought the Miller cycle reduced the effective compression ratio from the geometric compression ratio. On the current F1 engines achieving, say, an effective 15:1 from a geometric 19:1 (The limit in the regs). This would mean about 60cc of cylinder contents would be returned to the inlet tract.

[63l8qrrfy6]

Yes it does - I was referring strictly to the geometrical compression ratio.
The maximum effective compression ratio will be limited by the onset of knock but it is still higher than a N/A engine.
Also keep in mind that most of the temperature rise from compressing the air outside the cylinder has been bled off in the charge air cooler so the temperature at the end of the compression stroke will be lower.*

Another advantage of turbocharged engines is that more volumetric efficiency can be traded off for charge motion which typically results in a shorter combustion period and all associated advantages (spark timing, heat loss, etc).

*compared to a non-Miller turbo engine

[sosic2121]

Yes it does - I was referring strictly to the geometrical compression ratio.
The maximum effective compression ratio will be limited by the onset of knock but it is still higher than a N/A engine.
Also keep in mind that most of the temperature rise from compressing the air outside the cylinder has been bled off in the charge air cooler so the temperature at the end of the compression stroke will be lower.*

Another advantage of turbocharged engines is that more volumetric efficiency can be traded off for charge motion which typically results in a shorter combustion period and all associated advantages (spark timing, heat loss, etc).

*compared to a non-Miller turbo engine

This is an interesting point!

[sosic2121]

https://www.whatcar.com/news/true-mpg-m ... led/n14356
Of course this is not definitive proof of anything, but still...

[PlatinumZealot]

Toyota... Somehow has managed to remain comptetitive with naturally aspirated engines.

There was a commenter on reddit who works at an engine testing facility comparing different tech including various turbos.. Ford BMW GM Mazda SCCI etc.. There were notable behaviours from the various companies. BMW has an obsession with torque curves, mazada SCCI benefit in real world was not as big as expected... Etc etc
Very notable he said was Tthe toyota N/A plants were still among the most fuel efficient and quiet.. Just by sheer exelence in engineering.

What i gathered from his comments was just as how a Mercedes W10 can be faster than SF90 with use of less "enablers" so too can a masterfully engineering N/A engine out perform the typical low disp. turbo engine in certain metrics.

In theory turbo should be more power capable, more thermodynamically efficient. Power can even be taken off the turboshaft as we see in F1.

I had proposed a turbine N/A engine in one of these threads where the turbine has no compressor but connects to an ERS system. This turbine would be very "open" to allow N/A sound to pass through.

[gruntguru]

- Friction in the turbo itself dissipates only "free" energy harvested from the turbine - not the crankshaft - so doesn't add to FMEP
- Who said anything about smaller bores etc? "Downsizing" usually means fewer cylinders.

I don't think turbo gets free energy, it has an affect on exhausting process. And my point is that, manufacturers say everything is good with what they produce no matter what it is.

A lot of the energy Turbos extract from the exhaust is free. There is usually a small "pumping" penalty on the exhaust stroke, but an efficient turbo setup will return a similar amount as a pumping bonus during the intake stroke.

Manufacturers rely on sales and people don't buy cars based on what the manufacturer says.These days, fuel economy is all about getting a better number on the government mandated test. Manufacturers are using turbos to improve that number. Unfortunately that number doesn't include any full power (over-fuelled) testing, so manufacturers are not being encouraged to fix that problem.