Print 41 comment(s) - last by m51.. on Nov 3 at 11:07 PM

You're doing it wrong.
Turbos are on 75% of new cars sold in Europe

You don't have to be a scientist or an automotive engineer to look at the fuel economy that major automakers are squeezing out of their vehicles with normal combustion engines today and wonder if we really need EVs and hybrids. More than one diesel car in Europe is able to provide fuel economy as good or better than the hybrids people generally think are so fuel thrifty.
The catch is that we rarely see diesel engines in the US inside a car, that will be changing, but the diesel car isn't common today for American drivers. One thing that is becoming very common for fuel efficiency sake is the addition of a turbocharger to allow a smaller displacement engine to produce acceptable power to provide the performance drivers expect.
The turbocharger is something that was often thought of for performance cars like the Grand National Buick in the mid to late 1980's. Today the turbo is used in a number of engines including the very popular EcoBoost line from Ford. Ford's EcoBoost engine inside the F-150 truck is selling very well and has a towing capacity on par with normal engines with larger displacement. The turbocharger is even more widely used in Europe where Reuters reports that 75% of all new cars come with one.
Craig Balis from Honeywell Turbo Technologies told Reuters in an interview, "The turbocharger is a green technology in the sense that it's helping cut emissions and raise fuel economy. It's a critical component to get more fuel efficiency out of the engine."
"Emissions regulations in Europe, the United States and worldwide are a driving force for cleaner, greener vehicles and that's a great landscape for turbocharging," said Balis. "We're confident about the continued evolution of combustion engines and the growing role turbocharging has."
Reuters reports that a diesel engine that has a turbocharger can get 40% more mileage than one without a turbo and a gas engine can go 20% further per liter of fuel than one without a turbo. With the impressive economy that normal engines with turbochargers achieve there are many that wonder if we even need EVs and hybrids.
Pierre Gaudillat, policy officer at the Transport and Environment lobby group in Brussels, was asked if we need EVs from a CO2 point of view. He said, "That's a valid question. The answer is: maybe not. Turbos are a no-brainer for cutting CO2 because the efficiency gains are really quite significant. In the near term, we don't really need and can't count on electric vehicles to deliver the CO2 savings. Maybe not until about 2030 or 2050."

Source: Reuters

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RE: Stop spreading misconceptions about Turbos
By EricMartello on 10/18/2011 12:37:49 PM , Rating: 1
You forget one aspect of a Blown engine (especially Turbocharged). The increase in Volumetric Efficiency, a boosted engine can have better than 100% Volumetric Efficiency, while an N.A. engine is rarely over 60-70%. Which means that the that the Turbocharged 2.0 @ 14.7 psi, will less air and fuel than an N.A. 4.0L engine. Further a Turbocharger actually converts some of the energy that would otherwise be lost out the tailpipe in the form of heat, Also the turbo'ed engine will have better scavenging than a N.A. engine.

Volumetric efficiency is simply a fancy way of saying "air intake" - I didn't forget any aspect, you're just using the technical term to rephrase what I originally said.

From a FUEL efficiency standpoint the bottom line is that the more air you force into an engine, the more fuel you will need to add as well. If your volumetric efficiency is above 100%, which means forced induction (i.e. nitrous, turbo or supercharger), you are adding MORE air and therefore will need to add more fuel to maintain the ideal air/fuel ratio.

To say this simplistically - your turbo 2.0L will consume the same amount of fuel as a 4.0L V8 on average assuming both the turbo engine and the V8 have similar power ratings and are driven in similar conditions by the same driver.

I am not saying that turbos do not improve engine performance - they do and they do very effectively, but they DO NOT improve fuel efficiency.

By ELGold on 10/19/2011 2:12:25 PM , Rating: 2
Right you are -- turbo mode is not efficient for fuel economy (that is, the fraction of heat content turned into mechanical work.)

The reason it is proposed as a fuel economy mod is that it allows the car to be designed with a smaller ICE yet be able to (albeit inefficiently) reach max power levels the non-turbo engine cannot. Since cars are usually operated in low power conditions, the improvement in partial power losses is thought to be an overall gain in fuel economy.

While true in theory, in practice many drivers engage turbo where it is not needed, and end up with fuel economy no better and sometimes worse than a non-turbo car. Turbo is a boon for car manufacturers, since it allows them to post fuel economy results much higher than before. Rare buyers realize the results are with turbo OFF. Once the first manufacturer gamed the fuel economy ratings with turbo, it was inevitable that everybody else would follow for marketing purposes. The ubiquity of turbo is as much for its marketing advantages as its technical merit.

RE: Stop spreading misconceptions about Turbos
By e36Jeff on 10/19/2011 10:35:41 PM , Rating: 2
Not exactly. If were to follow your example, and have a 2.0L turbo vs a 4.0L NA engine, with both engines having identical power curves, and drove them exactly the same, the turbo will come out with higher mpg. Granted, it would be a small difference, but it would still be there. The Turbo engine is almost always going to be lighter than the NA engine. Less mass requires less fuel to move it.

RE: Stop spreading misconceptions about Turbos
By EricMartello on 10/20/2011 2:17:41 PM , Rating: 2
Not exactly. If were to follow your example, and have a 2.0L turbo vs a 4.0L NA engine, with both engines having identical power curves, and drove them exactly the same, the turbo will come out with higher mpg. Granted, it would be a small difference, but it would still be there. The Turbo engine is almost always going to be lighter than the NA engine. Less mass requires less fuel to move it.

That's not an issue of engine efficiency. The mass of the vehicle is a completely separate aspect.

Not only that, but a reliable turbo engine is going to have an iron block with forged pistons so the weight savings over a typical aluminum V8 is not going to be as substantial as you think...if at all. A turbo engine also gains weight from the turbo itself, plus the intercooler and additional plumbing. On top of this, turbo engines are tuned to run rich. They must run rich to avoid detonation on pump gas, and this increases their fuel consumption.

I've had my share of cars, both turbo and NA. It never fails; once you match the power levels of the NA and Turbo engines, the fuel consumption of the turbo engine is always equal to or slightly greater than the NA engine across the board.

By Mint on 10/23/2011 3:53:03 AM , Rating: 2
This may have been true a decade ago, but now? I doubt it, or we wouldn't see so many manufacturers going to low displacement turbos.

The lower mass of smaller displacement engines help, but even 100kg (a high estimate of the savings) only gets you ~1-2% efficiency gain in rolling resistance. The main reason that they are more efficient because they have less frictional losses than bigger engines. The losses from a good turbo aren't enough to cancel that out for typical driving.

By Black1969ta on 10/25/2011 3:47:06 AM , Rating: 2
On top of this, turbo engines are tuned to run rich. They must run rich to avoid detonation on pump gas, and this increases their fuel consumption.

Hence my statement about new ECUs and better controls, such as wideband O2 sensors. Turbo engines don't have to run outside the perfect fuel ratio anymore, and a rich fuel ratio does not prevent detonation with any fuel; However, a lean ratio will ping, the rich ratios were due to the poor controls and running rich was an insurance policy to prevent a lean situation.

By McScoot on 10/31/2011 10:59:33 PM , Rating: 2
It's not at all true that reliable turbo engines have iron blocks. WRX is all alloy, even the Evo nowadays. Ford Ecoboost 4s and V6s are alloy blocks, as is the 2.5L 5 in my Ford. It's true that there are still a reasonable number of turbos using iron blocks, even ones that aren't especially extreme applications such as VW's 2L in the Golf GTI/R and the one in the Renaultsport Megane. It's just not necessary for making a reliable engine nowadays though.

Turbo engines often require higher octane fuel, it's true. There are a lot of things in a modern engine to combat the issue though, even just knock sensors and the ability to adjust valve timing, or the exhaust gas recirculation and precise combustion control possible with direct injection. You could avoid turbo and aim instead for a very high compression ratio using the same technology. Mazda is doing that with Skyactiv (though they've needed other technology for their intake manifold and things too). Knocking is not a big problem for modern turbo cars though.

Compare Ford's 1.6L Ecoboost to the 1.6L NA and the 2.0L NA available in the same car, you won't get a better comparison than that and the 2.0L NA engine isn't poor for what it is. The 1.6L is more powerful and has more torque than either (much more when you look at how it's spread over the rev range). It also gives better fuel economy than either of the others. Which would you prefer if you were buying a car in that class?

RE: Stop spreading misconceptions about Turbos
By jRaskell on 10/27/2011 8:07:21 PM , Rating: 2
Unfortunately, I simply fail to see how real world data supports such a claim. While finding separate vehicles with all other factors being equal is virtually impossible, the data is still quite revealing when looking at many of the current turbo performance vehicles vs NA performance vehicles out there:

Subaru STI: 305hp, 17/23 mileage
Subaru WRX: 265hp, 18/25 mileage
Mitsu Evo: 291hp, 17/22 mileage

Mustang V6: 305hp, 19/31 mileage (auto)
Mustang GT: 412hp, 17/26 mileage (manual)

Camaro V6: 323hp, 19/30 mileage
Camaro SS: 426hp, 16/24 mileage

In all cases, the NA cars with similar HP have significantly better fuel mileage, and the NA cars with significant HP advantages have very similar fuel mileage ratings. In the case of the Camaro, it even has a significant weight disadvantage going against it as well.

When you're comparing underpowered NA 2.0L engines to more powerful smaller displacement turbo engines, then there's compelling data that the turbos have an advantage. But when talking about amply (or even overpowered) large displacement engines, the current real world data clearly gives the fuel mileage to large displacement NA engines. Turbos may be a replacement for displacement in the power department, but that clearly doesn't carry over to fuel economy.

By McScoot on 10/31/2011 10:32:10 PM , Rating: 2
Such a comparison is not really instructive because there are too many other factors. Mainly:
1. The Japanese turbos you specify are all permanent four wheel drive, which impacts on fuel economy. Gearing and things also affect the highway economy in particular, they're not what-so-ever targeted at highway cruising.
2. There's a massive difference between a high-boost turbocharged car like the Evo and the low pressure turbos in most of those 75% of cars sold in Europe (a lot of which are probably even diesels). The Evo idles at 1500rpm. I read that the newer twin-scroll BMWs hold max torque from 1250rpm.
3. Comparing the maximum power outputs can be very inadequate. From first-hand experience, my previous car was a 4.0L inline 6, my current car a 2.5L turbocharged inline 5. The max power and torque figures are almost the same for both cars, but the 2.5L engine feels so much more powerful because that max torque is almost all available from 2000rpm below to 2500rpm above where the other engine hit that peak.

What the turbo gives you is the ability to use a smaller capacity, so you do without having the extra weight of a large engine (both in terms of components in reciprocating motion and just the block, head, etc), the extra friction, the extra pumping loss pumping a larger capacity, etc. Things like cylinder deactivation, direct injection, continuously variable valve lift, etc, are not as good as reducing the capacity and they can be applied to smaller engines anyway. With the turbo, you still have the ability to effectively scale up the engine displacement to get more power as needed. With low pressure turbos there's basically no perceptible lag, and you get the sort of low-end torque and drivability that means you don't need to rev high (which would generate a lot of friction and negate a lot of the benefits of smaller capacity). In terms of economy for petrol engines, it is quite effective at the moment. I don't really see what it has to do with hybrids though, if a turbo would be of benefit to the hybrid's ICE then they should use one, it'd still be less CO2 emissions than the non-hybrid.

If you want to see a better comparison, compare the 1.6L Ecoboost Focus engine to the 2.0L naturally aspirated petrol, both new engines from the same manufacturer in the same car. The 1.6L Ecoboost is noticeably better from a drivability perspective (270Nm torque@1900-5000rpm and 134kw versus 202Nm torque@4450rpm and 125kw@6600rpm). Even with that massive difference (looks like you really need to ring the neck of that 2L), the 1.6L is more economical (139g vs. 154g C02/km). There's also a NA version of the 1.6L to compare to if you wanted.
Make a similar comparison with the engine choices across VW's Golf, and look at their twincharge engines.
It's quite obvious that these low pressure turbos provide very substantial benefits for drivability, and for the economy you can achieve when you're targetting a specific level of performance.

By Black1969ta on 10/25/2011 4:02:25 AM , Rating: 2
Volumetric efficiency is simply a fancy way of saying "air intake" - I didn't forget any aspect, you're just using the technical term to rephrase what I originally said.

No the Volumetric efficiency effect that I was referring to does not mean that it is just a bigger air pump.

from Wiki...
Engines with higher volumetric efficiency will generally be able to run at higher speeds (commonly measured in RPM) and produce more overall power due to less parasitic power loss moving air in and out of the engine.

And I am not saying that any one benefit of a Turbo will drastically improve Fuel economy vs. a larger engine. I'm saying that the little thing add up.

By m51 on 11/3/2011 11:07:01 PM , Rating: 2
He is correct in that a properly designed turbocharged engine will be thermodynamically more efficient than the NA engine. This stems primarily from critical flow effects out of the exhaust ports that allow the turbocharger to recover additional energy from the exhaust gas stream. This energy is used to increase the intake manifold pressure which directly increases the engine torque. A quick reality check of this is the reduced exhaust temperature downstream of the Turbocharger which is evidence of the energy being recovered from the exhaust gasses and returned to the system.

This is a completely separate issue from the efficiency gains due to Volumetric efficiency, which is also real. Increase Volumetric efficiency reduces pumping losses (also called throttle losses). Pumping losses are the result of the engine pumping it's displacement every 2 revolutions from the low intake manifold pressure up to atmospheric pressure (exhaust manifold pressure). This is just wasted work. The less volume you pump and the smaller the pressure differential from input to output the lower your pumping losses will be. Although it seem non-intuitive, because of the fluid dynamics a properly designed turbocharged engine can actually achieve higher intake manifold pressures than exhaust manifold pressures (upstream of the turbo), which actually helps push the engine around.

Often though most car turbo designs are not designed for maximum efficiency but for maximum power and responsiveness. People buying a turbocharged car are looking for performance, not gas mileage, and the engine is designed accordingly.

A good place to look for Turbocharged engines designed for maximum efficiency are the huge turbo-diesels used in freighters and container ships. These can achieve thermodynamic efficiencies above 50%.

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