MIT Researcher Explains Why Fuel Economy is Still Low Despite Advances in Fuel Efficiency

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I wonder, has anyone......

Antilag system - Wikipedia, the free encyclopedia

 

Bunch of hobbiests decide that adding a supercharger can even out turbo lag from a big turbo. Then the car company's engineers try it out. At a minimum it generates press releases They claim more power than a 2L with 5% better efficiency.

SC get inefficient at high speeds needing a bigger innercooler.
Its a eaton roots with electomechanical clutch. But yes just using an appropriate sized engine with a turbo or supercharger makes more sense Nissan also did this on one of their cars IIRC.

Yes it would, but I believe that they simply turn it off and bypass in the twin boost application. This is the most efficient way.

Yes this is where knowledge diverges. An engine will pump out the same amount of exhaust for the same power/efficiency. A hotter exhaust will have a different pressure regulated by P =nRT/V. Since the turbine can capture exhaust energy the extra exhaust stroke in a miller application is often less efficient than a turbocharged engine. Variable lift like valvetronic can make a turbos valves reduce cylinder fill like a miller cycle while not dumping energy through a waste gate.

Whatever dude. Show me the bsfc and power levels and I might believe you, but..... I've actually driven cars that don't waste this energy. can you put this thing on a dyno and show me how its so much more efficient 99% of the time? I'm certain you have never used simulation software.

It sure does if the engine has a belt it has to drive to create this boost, versus using the waste energy in exhaust gasses. Using the engine to drive the supercharger to blow out exhaust gasses is less efficient then leaving them in, this is not true with a turbo.

yes, its been done. The super/turbo is more efficient and causes less damage. There also does not need to be any detuning of an engine if it really is off boost all the time. The system can be fitted to anything, but..... its less expensive to have a 10-11 compression and in real driving more efficient than starting out at a much higher level with gasoline. Diesels start at a higher compression.

 

I do not know how to calculate the energy cost of a turbo run off exhaust gases, but I am sure we can all agree it is not free. The turbo adds flow restriction to the exhaust, which is work the ICE must provide.

 

It's partly free, a good share of the energy a turbo uses comes from the kinetic and thermal energy of the exhaust gas. Backpressure energy is only part of it.

 

It's partly free"

This line reminds me of marketing oxymorons like "save more by shopping more"
And yes, I do understand that a turbo uses less energy than a SC.

I find the idea of using a turbo in engine design to allow ICE downsizing very smart. It has just been screwed up by drivers who do not understand that it is not a panacea for aggressive driver behavior.

 

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wwest, I leave you to AG. He seems to want to keep trying and knock some sense into you.

 

The people of the original Boston Tea Party ended up paying for their actions with muskets, bayonets, and their lives via the American Revolutuonary War when the British came looking for them.

I don't think the Tea Partiers of today are thinking about the LONG-TERM, REAL consequences of their behavior. While the tea partiers are BORROWING to pay for gasoline AND tea party Congress members are voting more and more cuts to the U.S. defense budget, China and Russia are building up their armed forces abilities.

Too bad the tea partiers can't think further than their next paycheck and credit card bill. What ever happened to planning for the long term, the future, retirement? Nope. 401K goes into the SUV.

Lions, carnivores, live fast, short lives.
Humans evolved to live slower, longer lives. Human children depend on their parents and the human brain continues to develop at least until we are 21 years old. Slow, long development.

SUV vs Prius. Who's who?
Looks like the SUV crowd is going BACKWARDS in evolution.

 

I didn't know congress' tea party membership want to cut defense spending. That is impressive, when you remember their other priority is to weaken the US from within by continuing the "cheap" fuel fiasco. I guess I'll just stop being surprised that they are even stupider than I give them credit towards.

FWIW, I want to cut defense spending too -- by not having to coddle and defend or at times bully OPEC. I just realize that there is no free lunch, and the price is decreased energy use, investment in domestic clean energy infrastructure, and transition to more mass transit.

 

Wouldn't the use of a refrigerant add power loss to the system due to the need to power the refrigeration system? Or would the savings in the lower temperature offset the power loss to the system? Just curious.

 

"...the price is decreased FOSSIL FUEL BASED energy use..."

 

They both require extra energy. The turbo is able to scavenge most of it's required energy from the waste exhaust. It's the same basic principle used in a cogen power plant. The main power turbine(the ICE) won't capture all the energy of the burning fuel. So a second, smaller turbine(the turbo) is placed down stream to capture some more of that energy.

The turbo's extra energy comes from the backpressure and turbulence in can cause in the exhaust. A supercharger's energy comes from the engine's output before it gets to the road. Even if it has a clutch, there is still loss to the belt. There's reasons why electric cooling fans are popular performance mods and Toyota went belt less.

 

The Atkinson engine design recieved a US patent in the mid-1880's. In all that time, up until now, no one has disputed it's lack of left over energy in the exhaust.

If you don't wish to WASTE exhaust energy then use the Atkinson cycle. If on the other hand you want power over FE then the use of the Otto engine mode, wasted energy out the exhaust, will be the choice for driving that turbocharger.

So yes, with an Otto engine you will have enough energy leftover in the exhaust to spin a turbine.....but off-boost FE is sacrificed.

 

Yes, but this may be in part the "tyranny of the gallon" (or the tyranny of thinking just about volume more generally).
If we are concerned with, say, CO2 emissions, it's not MPGs, but miles per unit of CO2 produced. If ethanol produces the same CO2 per mile as gasoline, I will call it a wash environmentally; if it produces the same miles per dollar as gasoline its a wash economically (beware of subsidies, though).
I don't know if ethanol does, though. In another thread (on gas vs. diesel) that I started some days ago, I found out that diesel can get you a bit further per unit CO2 produced, and this was backed up when I compared similar gas vs. diesel cars at the EPA website (however, almost all the gas comparison cars used PREMIUM--only one used regular, but it also did not go as far as a similar diesel).

Anyone know what the answer for ethanol vs. gasoline is, in terms of miles per unit CO2?

 

All this talk about turbochargers makes me want to ask another question:

Back in the old days ('70's or so), I remember hearing that turbos "wore out" quickly, but I never knew why. Now I don't hear that. Have they really gotten better, and if so, how?
(My wife is pushing to make our next car an Audi A3 turbodiesel, which is why I really want to know.)

 

Many of us are very concerned about where that carbon comes from. Ethanol from above-ground sources already in the atmospheric carbon cycle is far less destructive than fossil carbon that is mined out of its below-ground sequestration and injected back into the atmospheric carbon cycle.

From a CO2 perspective, the main problem with ethanol has been the fossil carbon used to produce it.

 

Using GREET from Argon Wheel-to-well analysis

E85 Gasoline

83,000...115,000 Approximate energy content, Btu/gallon
10,579...6,949 Btu consumed per mile (WTW basis) by typical vehicle
% 54.....23 Well-To-Tank energy use share,
% 46.....77 Tank-to-Wheel energy use share,
205g/m..577g/m Grams CO2 emitted per mile (WTW basis) by typical vehicle

 

I don't go back to the 70s, but in the bad old days they didn't cool the turbos properly and they have better materials now. They also didn't have direct injection or the variable valving, which made them much less efficient. Less efficient means more heat, which is more damage. The A3 turbo diesel has all of the modern things that makes them reliable and efficient, but you probably won't get the reliability or efficiency of a prius A modern diesel is almost always in lean burn unlike a gas engine, but has emissions control to manage the NOx.

If you want to know the nitty gritty of bad implementation, here is a guy that supercharged then turbocharged a gen 0 prius.
This talks about aftermarket turbo versus supercharging.
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rejected the supercharger then goes for a turbo
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plenty of power in the exhaust of prius

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but way too much work if toyota doesn't do it. Without toyota doing it there is no way to get the power out

When Toyota created the gen II and gen III they could add better engine tech and motor control to increase efficiency. The prius is not a tuner car.

 

Mostly over-heating.

The turbine section operates in the EXTREMELY HOT exhaust outflow and spins as high as 50,000RPM in order to bring the centrifical compressor wheel well into an efficient operating range.

Keeping that HEAT insolated from the shaft bearings, COMMON shaft bearings, and the compressor section proved to be an impossible task. The only solution was to provide a really serious level of cooling capability for the bearings, and therefore less turbine hEAT transferred to teh compressor section. The bearings also required lubrication the required cooling was often provided via the use of engine lubricating oil, pressurized with the engine oil pump.

The fly in the ointment was that when the engine was stopped the cooling flow also stopped, INSTANTLY, and the oil remaining within the turbo assembly was COOKED, literally.

Talk about SLUDGE.

One would think by "today" these problems would have been thoroughly addressed, solved, but no. Look at the extraodinarily high failure rate of the Mazda CX-7, for instance.

Enough exhaust PRESSURE at 1000F to spin that "loaded up" compressor section at ~50,000 RPM will mean a LOT of energy to be wasted "off-boost".

On the other hand for "turbodiesel" there is a completely different story line. They have been commonly accepted, and proven to be reliable, in the trucking industry for many years now.

But given a choice I would ALWAYS choose a N/A engine over a "boosted" one. Boosted engines, diesel included, must be derated/detuned except in WOT conditions. In the diesel case it FULLY compresses a FULL (atmospheric gas) cylinder FILL volume for each and EVERY compression stroke. "Off-boost" most of the energy going into that "compression" is simply lost out the exhaust.