Turbocharger Gasoline Fuel Consumption

[ChiefWildcat]

Say a gasoline engine produces 150 HP @ 4400 rpm and 180 lb.-ft. @ 4000 rpm. Now add a turbocharger that gives it an additional 60 HP. How much more gasoline would the engine need as it cruises down the highway at 60 mph (compared to the same engine with out a turbocharger)?
I don't need an exact answer. I'm trying to get an idea of how much gas it takes to get 60 HP out of a turbocharger running at peak performance.

 

[ivymike]

If you're cruising down the highway at 60mph in both cases, the turbocharged engine will be producing the same shaft power as the n/a engine, and fuel consumption will be similar (a little higher since efficiency drops). Figure about an additional 0.75 kg/hr of fuel.

To get the additional 60hp, you'll have to burn an additional 12 to 18 kg/hr of fuel (roughly). You won't be able to cruise at 60mph while using that additional 60hp (assuming the original vehicle could cruise at 60mph)- you'll have to cruise at a higher speed to use the extra power.

 

[patprimmer]

So as to avoid detonation at the 5 or 6# boost you might require to get the extra power, you might need to reduce compression ratio. That in itself will reduce your fuel consumption. Driving the turbo at cruise (presuming the cruise is at very low throttle opening) will be negligible.

If you do not drop the compression, you might need to run a more expensive fuel. It really does all depend on a lot that you have not disclosed.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[bobqzzi04]

Assuming the engine internals haven't been changed, then the only thing requiring more fuel would be the weight of the turbocharger system.

As the others said, negligible

 

[Warpspeed]

As Pat says, if you have to reduce your compression ratio to run high turbo boost pressures, that by itself will significantly harm part throttle fuel economy.

The other aspect is slightly increased exhaust back pressure from the exhaust turbine. But, that is going to be fairly insignificant at small throttle openings, because exhaust flow will be very low. It is more a theoretical disadvantage, rather than a practical disadvantage.

 

[SBBlue]

Several observations. . . . .

First of all, unless you really have a huge car (maybe several times the size of your jumbo size hummer) your engine will not produce anywhere near 150 hp to cruise at 60 mph.

Second, the typical car (non-hybrid) at "cruise" at 60 mph is only perhaps at one-quarter or one-third throttle.

Third, in a gas engine the turbocharger doesn't really become functional until the throttle is wide open. At cruise (or one-third throttle) the only effect of the turbocharger is to slightly increase exhaust backpressure and therefore decrease fuel efficiency.

 

[rdd48856]

And slightly increase air aspiration losses...but what you should be asking is how much fuel a n/a aspirated with the extra 60hp will need in the same conditions...turbocharging coupled with direct gasoline injection in small engines(as it was done with Diesel) is the way to go on fuel economy: 1.4 liter FSI Turbo 150Hp....very small losses at 60mph...

 

[MikeHalloran]

I get the impression he was thinking of using the turbo itself as an engine. Tricky to get shaft power out of it, but Google will find hobbyists who report success building small turbojet engines from turbochargers.



Mike Halloran
Pembroke Pines, FL, USA