Only in a magical, frictionless, theoretical world. Here on Earth, it's not a zero-sum game at all. I fully admitted that more weight adds more friction. Please stop taking quotes without context.
The Prius is the single, exceptional example. It is also, I believe, the only case where a direct comparison to a conventional equivalent is not available, so we don't know exactly how much weight the Prius HSD adds. Lacking such figures, it's impossible to make any real judgements. Every single Toyota has generators with similar or more horsepower than the Prius. If you compare the Camry to the Camry hybrid, the hybrid weighs about 370 pounds more than the non-hybrid version. Total hybrid power is rated at 187hp, but I can't find what the generators are rated for. Apparently they are good for 199 ft/lbs between 0-1500rpm, while the battery is capable of 40hp, so I would say that 40hp is the appropriate power number to use. The figures are there, you just have to look for them.
That's simply "magical thinking". Electric motors and batteries have been around for much longer than internal combustion engines. You can't get electric motors to be any more efficient, battery technology isn't going to jump forward by leaps and bounds just because there's one more customer for the tech, and the drawbacks of hybrids are absolutely inherent. How is it "magical thinking"? There are still a lot of inefficiencies in the hybrids on the market today.
NiMH batteries waste a lot of energy, you only get about 67% of the power out of the that you put in. Lithium batteries will substantially improve this to over 90% efficiency once they are ready. NiMH batteries are heavy. Lithium batteries are available with 2-3 times the power to weight ratio of NiMH batteries. But they are still too expensive. They will be getting cheaper as production ramps up over the next couple years. We should start seeing them in widespread use some time after 2010. NiMH batteries can't handle extremely fast charge or discharge rates. This limits the rate of acceleration and how much regenerative braking you can use.
Once we get Lithium cells, we will see that the motor controllers and inverters start being major sources of inefficiencies. They will have to be upgraded to handle the additional current. Advances in technologies will allow further miniaturization and efficiencies.
If you didn't have the added weight of the hybrid, fuel economy wouldn't be as bad when driving uphill in the first place. And the fuel economy when going downhill in a conventional car is equally impressive... the HSD isn't giving you a net positive at all.
You are forgetting aerodynamics and the role the weight going up and *down*. The weight you carry up the hill, also helps you go down the hill. So any additional weight is not detrimental in the hills, unless that weight forces you to put the engine in to an inefficient operating state going up, or forces you to use the brakes going down. At least in a hybrid, you can recapture some of that energy on the way down if you do need to slow down.
I can't quite decipher what else you were trying to say here... The engine shuts off at freeway speeds, even though it's forced to stay on at freeway speeds?
I apologize for not being more clear. The Prius uses a planetary gear set to regulate the speed of the generators and engine instead of a conventional transmission. This allows the ECU to control the speed of the engine and generators as it sees fit. However, due to limitations on how fast the generators can spin, it forces the engine to spin over a specific speed. This doesn't necessarily mean that the engine is burning fuel - it just means that it's more likely to burn fuel since it takes some energy to spin the engine. More recent iterations of Toyot's HSD is able to alleviate this issue by adding a second planetary gearset which allows the ECU an even wider range of generator/engine/vehicle speeds.
When going down slight hills, it can stop sending fuel to the engine, open the throttle body and just let it spin. Engine braking gets in the way of a normal car. Perhaps if you had a perfect CVT you could get close to the efficiency of Toyota's HSD, but such a beast does not exist at this point in time.
The electric motors in hybrid vehicles add a minuscule amount of HP. In all hybrids that can be directly compared with a conventional alternative, it's clear that the electric motor provides a higher percentage of added weight, than it does a percent of added HP. In other words, for freeway use, it's a net HP/weight loss, not even mentioning conversion losses.
The generators in the Prius can generate up to 60hp. This is nearly equal to the 74hp that the engine is able to produce, though the combined power is limited to 110hp. I do not argue that ICEs are currently far more capable with regard to power to weight ratio. The same ICE (without the Atkinson cycle) in the Prius powers the Echo and produces 106hp, basically the same as the entire Prius drivetrain. However, it is much less efficient overall. Perhaps turbo-charging the Prius engine would restore the horsepower while maintaining the fuel economy benefits at normal loads, but that adds a bit of weight, too.
Weight makes a big difference, particularly on non-flat terrain. Remember those fuel economy figures you provided, just a few lines up? Aerodynamic drag doesn't increase as you go uphill... That difference is entirely a question of mass.
That's correct. And as I said earlier, all that weight you lugged up hill improves your fuel economy on the way down. The only drawback from the additional weight is the slight increase in road friction due to the increase in weight.
Seconds, hybrid drive trains aren't just X amount of weight in an infinitesimally small space. They take up room in the engine compartment, which means the hybrid's body needs to be designed with a larger aerodynamic footprint as well.
This is simply not true. Interior room (primarily head room and hip room) and ride height are the primary factors in determining your frontal area. How many hybrids out there have a larger frontal area than their non-hybrid counterpart?
Prius - With clever packaging, it is surprisingly roomy inside considering it's exterior dimensions. It currently is the most aerodynamic vehi
I highly doubt that even the most inefficient car comes even remotely close to filling in the vacuum left behind the car at any speed where aerodynamics is a factor.
This feature has no relevance to the driving pattern we are discussing. Why are you so focused on *only* freeway driving? And BTW, on my freeway drive home in my Prius this evening at a relatively constant 60-70mph, yes, those features (auto-stop-start, hybrid assist) came into play many times. My commute involves many small low grade hills of a few percent. On the flats at 65mph, fuel economy is a bit over 50mpg. On the way up the hills, fuel economy drops to between 28-35mpg. On the way down, fuel economy jumps to 75-99+mpg. Watching the energy monitor on some hills, the engine shuts off and the electric motor keeps me from losing speed (in other cars, I've gone in to neutral, the hill is not steep enough that you can maintain speed without some power) This is in spite of the fact that above 42mph in the Prius, the engine is forced to turn to keep motor generator 1 from spinning too fast.
The minimum size of an engine you need is determined by the top speed you wish to be able to sustain. I have yet to see an engine with a high enough HP rating to sustain a vehicle, yet which does not deliver enough torque for good acceleration. OK, so let's say you want just enough engine to sustain 75mph, since the speed limit in most states is 65-70mph and you want a bit of room for passing. But say you were traveling 65mph and needed to increase speed quickly to 75mph pass someone on a two lane road? You'd likely only have 15-20hp overhead for accelerating which will be reduced the closer you get to 75mph. I highly doubt that it's enough power for good acceleration in this case. And BTW, it's not torque that we care about (assuming we have a suitable transmission), it's horsepower that measures how fast you can accelerate. All the torque in the world wouldn't matter if you only produced it at 0 RPM.
For freeway driving, it will be lighter than the hybrid, just as fast, and no less fuel efficient. The hybrid drive train can't provide any help, so the internal combustion engine in a hybrid must necessarily be large enough for on its own. Again, why can't the hybrid drivetrain help on the freeway? I do agree that yes, the ICE must be large enough on it's own, but no, that does not mean that a hybrid drive train will not be able to improve efficiency. Unless you are talking about some mythical, 100% flat freeway that you never have to change speeds on. In which case, added weight from a hybrid drivetrain would make little difference in the efficiency of the platform, since the vast majority of drag on the freeway is from aerodynamic drag.
Since you want to talk in vague generalities and assert you are correct, rather than trying to actually prove anything, I will simply point you to the last time I discussed this instead, with someone a bit more informed: Re:Hybrids can be better at highway speeds too So now you've decided to take the discussion down a notch and call me stupid? Unless I'm mistaken, the discussion in the other thread looks surprisingly similar with raygundan making largely the same points I am. What exactly have you proven? That you are capable of losing the same argument twice to two different people?
Sorry for the formatting, could not convince Slashdot to format the table below properly, so I submitted this post as Code. I want my <pre> tag!
> I think I was thinking of the G-Wiz, which does have lead-acid cells. And they are planning on using Lithium cells soon. Lead-acid cells are a poor choice for electric cars. The only thing going for them is that they are cheap.
> Fiat Panda 1.3L diesel rates 52 mpg urban/76 hiway. Pretty impressive, what test cycle is that under? What does the Prius rate under the same test cycle?
> The dirtiness of diesels have long been solved with sulfur-free fuel > and better filters, though a lot of that hasn't come to the United > States yet. Europe does it far more intelligently. Europe emissions standards are actually *lower* than standards here in the states (Tier 2 Bin 5). Meaning they pollute more. Which is why diesels have only started trickling on to the US market again (can you buy VW's Jetta diesel or Mercedes' diesel yet?), with either complicated nitrous oxide or particulate traps or urea injection. And even then, those diesels still just squeak by under Tier 2 Bin 5 emissions levels, when most gas cars are much cleaner.
For example, let's compare the Mercedes E320 Bluetec to the E350 (only diesel I could find on the <a href="http://www.epa.gov/greenvehicles/">EPA Green Vehicles site</a>)
Model E320 diesel E320 gas Federal E320gas California Emissions Standard Tier 2 Bin 8 Tier 2 Bin 4 LEV-II SULEV NOx grams/mile 0.2 0.04 0.02 CO grams/mile 4.2 2.1 1.0 NMOG grams/mile 0.125 0.07 0.01 PM grams/mile 0.02 0.01 0.01 Smog pollution lbs year 10.75 3.64 0.99 Greenhouse gases tons year 8.15 9.65 9.65
So you can see how the gas car built to federal emissions standards, while emitting about 15% more greenhouse gases, has significantly lower emissions than the diesel, and the California model is even better than the federal car with no further reduction in fuel economy.
I am impressed with how low they got the particulate matter in the diesel with the Bluetec (urea injection), but it's still twice as high as the gas car.
Of course it does. They've designed it to be as efficient of a car as they could. The hybrid power/drive train has NOTHING to do with that, however. Why doesn't it? The hybrid powertrain lets them do these things:
1. Stop the engine at idle and use the large battery to drive accessories and air conditioning. Toyota's Hybrid Synergy Drive goes a step further and lets you stop the engine at almost any time (up to a certain vehicle speed). 2. Downsize the engine so it is more efficient at typical engine loads. Use the hybrid system for brief peak power and to augment the engine keeping it in more efficient operating ranges when required.
Indeed. Give me a car with an Atkinson cycle engine, that doesn't have the dead weight of a hybrid, and I'll be happy. And the car will still be slower and less efficient than the hybrid.
I'm not saying that hybrids are the best solution for improving efficiency, but they are the best solution that is readily available today for a reasonable cost. Down the road as battery technology improves and manufacturing capacity increases of the next generation of batteries increasing availability and reducing cost, plug-in hybrids and 100% electric vehicles will be the way of the future.
These machines are only marginally better than their purely gas powered counterparts. Real improvements, 50% to 100% can be made by re-evaluating the way we use fuel. And how do you propose we do that?
The best solution on the horizon is electric cars powered by renewable and/or low emissions power plants.
Chemical batteries will always be inefficient. Lithium batteries are very efficient - their efficiency exceeds 95%, when compared to NiMH batteries which are only about 70% efficient in a charge/discharge cycle.
Worse yet, look at the environmental impact of the a car accident involving these chemicals. Yeah, look at all those cars on the road driving around with 10s of gallons of gasoline and diesel! And those big-rigs with hundreds of gallons of fuel^H^H^H^Hexplosives! It's amazing that they don't blow up every time there is a fender bender!
Just imaging what a shard of conducting metal will do as it pierces the plates of a very low internal resistance storage battery. Anyone see the youtube images of the laptop exploding? Imagine that on an automotive scale. The tendency of a battery to catch fire has a lot to do with the specific chemistry used as well as manufacturing techniques.
Actually, the Kammback is better than a teardrop, aerodynamically and functionally. It's more aerodynamic, because it still has the same smooth flow as a teardrop, but it doesn't have all the surface drag. It's more functional because it's shaped more like a box. I know it's plastered all over the internet that in theory the Kammback is actually more aerodynamic than a teardrop, but I'm not convinced.
Otherwise all those solar racers would likely use a Kammback, airplane wings would use a Kaamback, but every single one that I've seen uses a full teardrop.
The Aptera is also a full teardrop (OK, there is a tiny flat area at the rear, but mainly for the taillights and they also vent air in to that area as well) and it was designed to be as efficient as possible.
So please - any one have any actual drag coefficients for tear drops and Kammbacks with various amounts of the tear drop chopped off?
hybrids are a joke. The only benefit is regenerative braking, short of that, batteries are terribly inefficient. If hybrids (and batteries) were terribly inefficient, how do they manage to be the most efficient vehicles on the road today?
Here are the combined fuel economy ratings from fueleconomy.gov Prius - 46mpg Civic Hybrid - 44mpg Altima Hybrid - 34mpg Camry Hybrid - 34mpg Escape Hybrid - 32mpg
Each one leads their respective classes in fuel economy - and that is still dealing with the limitations of the currently NiMH battery technology which is still fairly heavy for the capacity, is limited by peak charge/discharge rates and not all that efficient (around 70% charge/discharge efficiency).
The next-generation Lithium batteries (we should start seeing them used widespread in vehicles in a couple years once mass manufacturing starts) addresses all those issues by improving the power to weight ratio, higher peak charge/discharge rates and charge/discharge efficiencies over 95%.
mainly because I do a lot of freeway driving, where hybrids are just dead weight. No, even on the freeway a well designed hybrid does not just add dead weight.
The Civic Hybrid easily beats the non-hybrid on the freeway. The Prius is the most efficient vehicle sold today on the freeway (in the USA).
A properly designed hybrid lets you downsize the engine so that it is more efficient under the small, steady load of freeway driving. The Prius (and other hybrids) go further by utilizing the Atkinson cycle which reduces pumping losses even more.
As a bonus, the weight penalty (and price penalty) of a hybrid goes down with each generation, the next generation of hybrids due out next April from Toyota and Honda are expected to significantly reduce both by a significant margin.
IIRC, the Prius and many other electric cars still use lead-acid batteries, which is even worse. In a crash, you often have acid spilling all over the road. No, hybrids on the road today use NiMH batteries, which are classified non-toxic, but you can (and should) recycle them when they die. They do still have a 12v lead-acid battery, but in the Prius that battery is about half the size of your typical 12v lead acid battery.
In general, I agree that hybrids are a waste of effort, especially the ones with parallel drive and non-plugin recharge systems. In terms of millage, they're often beat by a pure diesel system. While on the highway, a diesel may beat a hybrid, it won't be by much. And once you compare CO2 emissions or price spent on fuel, they usually come out nearly even. But diesels also emit far more pollutants (NOx, CO and particulates) than gasoline cars and still consume significantly more fuel in city driving than hybrids.
As you say, Lithium based batteries have the potential to improve the effectiveness of hybrids by being able to handle higher currents (able to recover more power under regenerative braking), potential for more capacity at the same or less weight (plugging in to charge becomes practical). Super-caps also can help recover and deliver short bursts of power, but are currently limited by capacity.
Both Lithium and Super-caps are still more expensive than NiMH batteries and manufacturing capacity is still an issue (though both issues should be largely resolved around 2010 - at least for Lithium batteries).
A large portion is emissions controls to reduce NOx and CO emissions. My old 95 Civic (1.5l manual, basically the same as your 93 Civic but with stricter emissions on it because California has stricter emissions laws.) averaged 33mpg, a typical range depending on the driving was 31-36mpg. If you go to fueleconomy.gov you can see that Honda sold multiple Civics in the US with the 1.5l See my earlier post on the subject.
My wife's old 95 Civic (1.5l engine, CA emissions) averaged about 33mpg in mixed driving, surprisingly close to the adjusted EPA estimate of 32mpg. The 93 Civic appears to be the same as the 95.
Both are rated significantly lower than the 42mpg a 2008 Civic Hybrid is rated and lower than the 46mpg 2008 Toyota Prius that we replaced the Civic with. So far over 8 months we're averaging slightly more than 46mpg as well. The Civic Hybrid is slightly smaller and less efficient efficent (44mpg) than the Prius but costs about the same - it was a no brainer to go with the Prius over the Civic Hybrid.
The Prius has significantly more room, is more comfortable, is quieter, rides smoother, is significantly safer and travels nearly 40% further on a gallon of fuel and also emits far fewer pollutants like NOx and CO. Granted, the Prius cost about $22k vs $15k the Civic cost when new.
Now your Civic does likely get close to 40mpg, but that's because it emits far more NOx and CO than the one we had.
So I would argue that tight emissions standards have also significantly decreased fuel economy in addition to weight. If we had an efficient way to clean up NOx and CO emissions in the exhaust, we could improve fuel economy overnight by 10%+ by simply adjusting the ECU tune to use a lean-burn in light to moderate loads and even more by increasing compression ratios slightly. To obtain low NOx and CO emissions, you typically must burn much more fuel than what would otherwise be required to generate the same amount of horsepower.
We are seeing a recent surge in Exhaust Gas Recirculation (EGR) and Atkinson cycle engines (in hybrid's anyway where the lower power output of the Atkinson cycle engine can be compensated by the electric motor/generator) to offset the efficiency loss of having to run stoichiometric air/fuel ratios while still having low NOx and CO emissions.
YOU STILL KEEP A SINGLE COPY OF YOUR DCVS ON YOUR MASTER SERVER. YOU STILL MAINTAIN CENTRALIZED CONTROL!
For example, look at Linux kernel development. Linus maintains the central repository. Every single other developer regularly syncs up with Linus while working on their own tree.
If you don't want people taking it home, then you tell them not to develop on their note books. Same as when you're using a CVCS.
DCVS still has a number of advantages:
1. It's dead simple to branch off and keep track of changes to some experimental changes. If you decide to keep them, you can push all the changes to your master. If not, toss it in the bit-bin. With a CVCS, you have to make a branch and then deal with the fun of trying to merge it back into the trunk. And if it was crap, that crap gets stored in the CVCS forever (which could be a good or bad thing).
2. Concurrent development is better tracked - because you can check in every little change along the way. With your typical CVCS you end up make a lot of intrusive changes, and then check it all in in one big wallop - which means you lose the benefits of a VCS system. The DVCS system encourages you to check things in all the time.
You're pretty much screwed. Generally, the only way to extend a filesystem is to add space to the end of the partition. Extend the partition, then tell the filesystem to expand to use the newly allocated partition space.
Now, you could fake this by using LVM and multiple partitions, but the end result would not be pretty.
If you really wanted to save the planet, you wouldn't be overclocking your computer at all or buying a new car because it was hyrid. You would be beating what you have already consumed until it fell apart from overuse. Unfortunately, it isn't always better to beat what you have already consumed until it falls apart. Whether or not it's better to beat something into the ground until it is not longer usable or repairable or to buy the latest high efficiency model depends on:
1. The impact of manufacturing said item. 2. How many fewer resources said item consumes during use.
This analysis is called a life cycle analysis.
For example, your typical computer consumes much more energy during manufacture than during use. So for this case, using what you already have as long as possible is better.
Another example, your typical automobile, consumes much more energy during use than during manufacture (especially once you consider how much of your average automobile is recycled). In this case, trading in your gas guzzler for something which consumes less fuel is typically worth while, especially considering that your old vehicle is not likely to go to the scrapyard until it really is ready to fall apart from overuse or totaled.
Obviously items which do not consume energy during use are best used until unusable.
The Fedora Project's Core Principles are:
# Fedora is about the rapid progress of Free and Open Source software and content. # Fedora believes in the statement "once free, always free". Why not consolidate efforts with Fedora which has the same goals?
Is there really enough of an audience to justify a rebundled Ubuntu without the non-free bits? Or will this project slowly die as it fails to attract a community?
I highly recommend this to anyone interested in how different operating conditions affect fuel economy.
BSFC is the measurement of how much power vs how much fuel in consumed - basically measuring how efficient an engine is. In an ideal world you'd have an electronic throttle and a CVT. The throttle would directly translate into how much power you are requesting. The ECU would use a BSFC map to determine the most efficient engine RPM and throttle body position to generate that power and the CVT would allow you to maintain that RPM for as long as you are requesting that power level.
For example, if you get a Prius going a steady 20 mpg on flat land, it will transition between running solely off the battery/generator and turning the engine on to charge the battery/generator while getting over 100 mpg. To correct myself, I misread some charts when making that estimate. A Prius doing a constant 25-30 mph on flat land should get over 65-70mpg+, not 100mpg. Still pretty impressive for a midsize car, though.
Typically cramming as much air/fuel as possible in the engine is not the most efficient for a number of reasons - but primarily because doing so generates so much excess heat as waste that you must add extra fuel to try to keep things cool.
For example, your typical gas engine will produce the most power when running an air/fuel ratio around 12.5 to 1. But you could make slightly less power but do so more efficiently by running slightly leaner, around 13.5 to 1.
But realistically, most engines will run 10-12 to 1 during WOT, especially at high RPMs to keep things from melting down.
Ideally, you would run WOT all the time, and simply adjust fuel and RPMs until you had the power level you wanted. Low RPMs because friction rises more or less linearly with them and naturally the least amount of fuel possible. You know, run it like a diesel which has no throttle body. But unfortunately gas engines don't run well at extremely lean air/fuel levels and will typically misfire - not to mention generate large amounts of NOx emissions when running leaner than stoich which your typical catalytic converter will not be able to clean up.
A compromise is to run a small engine with turbocharger. This way for normal sedate driving you drive the car like a regular small car. You'll use a bit more throttle and as such, pumping losses will be lower than a larger engine with the same output capacity. And when you need the power, open the throttle and close the turbo wastegate to get that burst of power to pass that truck.
The back pressure is largely additive: its in addition to the muffler and resonator. Modern catalytic converters have very low restriction. They typically flow at least as well as your average muffler. Even if you removed the cat, muffler, resonator and associated tubing and replaced with a drag-style header, you would not see a significant increase in fuel economy - unless you possibly are driving near maximum engine load and rpms frequently. Under normal operating conditions your typical exhaust systems flows more than enough to avoid any significant restriction.
EFI does not choke the engine like a carb; it always runs at optimum fuel mix. It just might be more fuel and less air when the engine is cold. It doesn't really "waste" it. EFI or carb, you still have a throttle body which is the presents most significant pumping loss in your typical gasoline engine when running at less than wide open throttle. EFI does indeed "choke the engine like a carb" - if what you mean is running the engine rich with extra fuel when the engine is cold. The benefit of EFI is that it doesn't need to run as rich and typically quickly moves into normal operating mode.
My car, when it was new, got 38MPG(actual reading on a trip to Ohio) on the highway and generated 155Hp. You'd be VERY hard pressed to find such mileage results today. I find it extremely hard to believe that you exceeded the Old EPA MPG of 24 city/31 hwy by such a large amount without some sort of assistance - such as having a tailwind or being downhill. Perhaps if you drove the thing 45mph the whole way and you had a tailwind I'd believe it. More telling is your best mileage averaged over 3 tanks of gas.
It's really not hard to beat those mileage results. My Prius is averaging 46mpg. Civic Hybrid will average above 40mpg. Toyota Camry Hybrid will average about 35mpg - not hard to beat 38mpg if driven judiciously.
The reason is that most of the the converter takes care of is not a part of the combustion of fuel- but is rather the result of what happens to the rest of the air (nitrogen and such) in the extreme heat and such. Efficiency cannot affect that - in fact, higher operating temperatures of modern cars have made it worse. While higher operating temperatures can raise NOx emissions, I dare you to find one modern car with higher NOx emissions than it'd older counterpart - even with the catalytic converter removed. Peak operating temperatures are typically limited by the knock resistance of the gasoline - which is still 87 octane. Modern vehicles are able to raise compression and improve efficiency without knock by virtue of having highly optimized combustion chambers which quickly burn as much as possible of the air fuel mixture. If NOx was a concern, they could inject a tiny bit more fuel to compensate - the extra efficiency from being able to run higher compression should compensate.
I've heard this accusation before, but I don't grok it at all. My limited understanding was that anti-pollution devices were supposed to squelch unburned hydrocarbons emitted by inefficient engines. However, if your engine is more efficient -- if it more completely burns hydrocarbons -- then the emissions controls should be superfluous. It's not just the unburnt hydrocarbons, it's the NOX and CO emissions, too.
For example, to maintain low NOX emissions with your standard catalytic converter, you need to maintain an air/fuel ratio of approximately 14.7/1.
Under light load to minimize fuel consumption, you'd be better off leaning out the air/fuel ratio (injecting less fuel), but unfortunately NOx emissions tend to go sky high when doing so.
You can get around this by using a special exhaust devices which can trap NOx emissions, run the engine rich for a bit to burn off all the NOx emissions and then go back to lean burn operation. The Honda Insight did this, but I don't know of any others.
Diesels especially suffer from high NOx emissions since they regulate power by varying the amount of fuel injected instead of using a throttle body. This is why are only recently are a few diesel cars trickling into the market place this year with exhaust treatment systems specially designed to reduce particulate and NOx emissions to gas-car levels. Cold start fuel economy is also markedly lower for the same reason - cars intentionally burn EXTRA fuel to heat up the cats faster so that they end up emitting less overall NOx and HC emissions. If emissions weren't an issue less fuel would be burned. The Prius for example is notorious for typically delivering a meager ~25mpg during the first 5 minutes of use. The 2nd 5 minutes will be double that.
You could probably improve fuel economy 10-20% across the board in gas cars if you didn't have to worry about NOx emissions. In fact, this is one reason that hybrids improve fuel economy. Besides stopping the engine when no engine power is required, they also let you operate the engine in the most efficient and lowest polluting engine operating conditions. For example, if you get a Prius going a steady 20 mpg on flat land, it will transition between running solely off the battery/generator and turning the engine on to charge the battery/generator while getting over 100 mpg.
To clear up a common misconception with hybrid cars people often ask - why doesn't it run longer/faster/more on electric power? You have to remember that the only electric power that is "free" is the power gained through regenerative braking (that power is normally lost 100% as heat in a conventional car). You also have to remember that charging a battery and discharging a battery is not 100% efficient and most of your battery charge (except for the little bit that comes from regenerative braking) still needs to come from the gas engine. Some people will install an EV mode switch and then force their hybrid to run for extended periods of time on battery - then complain that fuel economy went down! That happens because at some point in time you have to recharge the battery - and by forcing the car to stay in EV mode you then force the car to charge the battery when it's low - no matter if it happens to be most efficient to do so at that point or not.
No, snapfs guarantees all writes will be sent to the snap filesystem, not the main file. But snapfs hasn't been maintained for 8 years. Does it even work? It says right on the homepage it is "incomplete, abandoned and unsupported" and we are talking about ways to defrag your filesystem TODAY.
Even the basic "make a copy of the file" defrag methods we've been discussing aren't even guaranteed to leave the file you are attempting to defrag in fewer fragments than the original. In a lot of my testing, often the "make a copy of the file" defrag method doesn't always help for files only moderately fragmented on an old and fragmented filesystem.
So I'll say it again: If you want to defragment files on Linux, basically your only real-world capable choice is XFS using the xfs_fsr tool.
If it were simple, someone would have written an online ext2/3 defragmenter a long time ago. There have been plenty of people asking for it, just google it.
There is an offline ext2 defragmenter, but it hasn't been maintained in ages from what I understand - I don't think it's trusted to defragment your data without risking data loss.
Both of your lsof and snapfs suggestions leave room for data loss unless you are sure that no one will be modifying the files. For that case, there is already a tool which attempts to defrag files called shake.
I call bullshit. Why is it that when someone things someone else is wrong and they reply, they must make some smart-ass comment like "I call BS?" or "You suck, I'm right you're wrong?". Come on, keep it civil. Or should I say "I call bullshit".
find / -exec (cp {} {}.defrag; rm {}; mv {}.defrag {}); Anyway, your defragmentation method is exactly the method I described. It won't defrag as well as backing it up completely, deleting all the original data and restoring because you are limited by the amount of (fragmented) free space you have. If your partition is close to empty, then it won't make much of a difference.
However, your defrag method IS NOT SAFE and WILL RESULT IN DATA LOSS on a live system (sorry to yell, but I don't want anyone trying it on a live system - it should be OK if you can guarantee that no-one else will modify the data on the partition)
There is a lot of opportunity in your script for data loss:
1. During the copy. If someone modifies part of the original that has already been copied, your.defrag file won't have those changes. 2. During the rm. Deleting files takes time, so there is more room for a file to try to write to the original. This step is actually completely unnecessary, just overwrite the original with your mv command. 3. After the mv. If a process has the original file open, it will continue writing to that original file, even after it's been deleted and "overwritten". It is very legal to continue file operations on an open file descriptor.
I suggest you actually try your defragmentation trick on a live filesystem which is actively in use. If you don't lose data, you're lucky.
So I'll say it again. The only filesystem which allows you do perform LIVE defragmentation is xfs using it's xfs_fsr utility.
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The figures are there, you just have to look for them. That's simply "magical thinking". Electric motors and batteries have been around for much longer than internal combustion engines. You can't get electric motors to be any more efficient, battery technology isn't going to jump forward by leaps and bounds just because there's one more customer for the tech, and the drawbacks of hybrids are absolutely inherent. How is it "magical thinking"? There are still a lot of inefficiencies in the hybrids on the market today.
NiMH batteries waste a lot of energy, you only get about 67% of the power out of the that you put in. Lithium batteries will substantially improve this to over 90% efficiency once they are ready.
NiMH batteries are heavy. Lithium batteries are available with 2-3 times the power to weight ratio of NiMH batteries. But they are still too expensive. They will be getting cheaper as production ramps up over the next couple years. We should start seeing them in widespread use some time after 2010.
NiMH batteries can't handle extremely fast charge or discharge rates. This limits the rate of acceleration and how much regenerative braking you can use.
Once we get Lithium cells, we will see that the motor controllers and inverters start being major sources of inefficiencies. They will have to be upgraded to handle the additional current. Advances in technologies will allow further miniaturization and efficiencies.
If you don't believe me, read this for what Delphi is planning over the next 6 years. Delphi-Led Team Developing Next-Generation Low-Cost, Compact, High-Temperature Propulsion Inverter You'll see that their roadmap has them planning to reduce both the cost and size of inverters by 50%. Or is that just "magical thinking"?
If you didn't have the added weight of the hybrid, fuel economy wouldn't be as bad when driving uphill in the first place. And the fuel economy when going downhill in a conventional car is equally impressive... the HSD isn't giving you a net positive at all.
You are forgetting aerodynamics and the role the weight going up and *down*. The weight you carry up the hill, also helps you go down the hill. So any additional weight is not detrimental in the hills, unless that weight forces you to put the engine in to an inefficient operating state going up, or forces you to use the brakes going down. At least in a hybrid, you can recapture some of that energy on the way down if you do need to slow down.
I can't quite decipher what else you were trying to say here... The engine shuts off at freeway speeds, even though it's forced to stay on at freeway speeds?
I apologize for not being more clear. The Prius uses a planetary gear set to regulate the speed of the generators and engine instead of a conventional transmission. This allows the ECU to control the speed of the engine and generators as it sees fit. However, due to limitations on how fast the generators can spin, it forces the engine to spin over a specific speed. This doesn't necessarily mean that the engine is burning fuel - it just means that it's more likely to burn fuel since it takes some energy to spin the engine. More recent iterations of Toyot's HSD is able to alleviate this issue by adding a second planetary gearset which allows the ECU an even wider range of generator/engine/vehicle speeds.
When going down slight hills, it can stop sending fuel to the engine, open the throttle body and just let it spin. Engine braking gets in the way of a normal car. Perhaps if you had a perfect CVT you could get close to the efficiency of Toyota's HSD, but such a beast does not exist at this point in time.
The electric motors in hybrid vehicles add a minuscule amount of HP. In all hybrids that can be directly compared with a conventional alternative, it's clear that the electric motor provides a higher percentage of added weight, than it does a percent of added HP. In other words, for freeway use, it's a net HP/weight loss, not even mentioning conversion losses.
The generators in the Prius can generate up to 60hp. This is nearly equal to the 74hp that the engine is able to produce, though the combined power is limited to 110hp. I do not argue that ICEs are currently far more capable with regard to power to weight ratio. The same ICE (without the Atkinson cycle) in the Prius powers the Echo and produces 106hp, basically the same as the entire Prius drivetrain. However, it is much less efficient overall. Perhaps turbo-charging the Prius engine would restore the horsepower while maintaining the fuel economy benefits at normal loads, but that adds a bit of weight, too.
Weight makes a big difference, particularly on non-flat terrain. Remember those fuel economy figures you provided, just a few lines up? Aerodynamic drag doesn't increase as you go uphill... That difference is entirely a question of mass.
That's correct. And as I said earlier, all that weight you lugged up hill improves your fuel economy on the way down. The only drawback from the additional weight is the slight increase in road friction due to the increase in weight.
Seconds, hybrid drive trains aren't just X amount of weight in an infinitesimally small space. They take up room in the engine compartment, which means the hybrid's body needs to be designed with a larger aerodynamic footprint as well.
This is simply not true. Interior room (primarily head room and hip room) and ride height are the primary factors in determining your frontal area. How many hybrids out there have a larger frontal area than their non-hybrid counterpart?
Prius - With clever packaging, it is surprisingly roomy inside considering it's exterior dimensions. It currently is the most aerodynamic vehi
I highly doubt that even the most inefficient car comes even remotely close to filling in the vacuum left behind the car at any speed where aerodynamics is a factor.
Re:Hybrids can be better at highway speeds too So now you've decided to take the discussion down a notch and call me stupid? Unless I'm mistaken, the discussion in the other thread looks surprisingly similar with raygundan making largely the same points I am. What exactly have you proven? That you are capable of losing the same argument twice to two different people?
Sorry for the formatting, could not convince Slashdot to format the table below properly, so I submitted this post as Code. I want my <pre> tag!
> I think I was thinking of the G-Wiz, which does have lead-acid cells.
And they are planning on using Lithium cells soon. Lead-acid cells are a poor choice for electric cars. The only thing going for them is that they are cheap.
> Fiat Panda 1.3L diesel rates 52 mpg urban/76 hiway.
Pretty impressive, what test cycle is that under? What does the Prius rate under the same test cycle?
> The dirtiness of diesels have long been solved with sulfur-free fuel
> and better filters, though a lot of that hasn't come to the United
> States yet. Europe does it far more intelligently.
Europe emissions standards are actually *lower* than standards here in the states (Tier 2 Bin 5). Meaning they pollute more. Which is why diesels have only started trickling on to the US market again (can you buy VW's Jetta diesel or Mercedes' diesel yet?), with either complicated nitrous oxide or particulate traps or urea injection. And even then, those diesels still just squeak by under Tier 2 Bin 5 emissions levels, when most gas cars are much cleaner.
For example, let's compare the Mercedes E320 Bluetec to the E350 (only diesel I could find on the <a href="http://www.epa.gov/greenvehicles/">EPA Green Vehicles site</a>)
Model E320 diesel E320 gas Federal E320gas California
Emissions Standard Tier 2 Bin 8 Tier 2 Bin 4 LEV-II SULEV
NOx grams/mile 0.2 0.04 0.02
CO grams/mile 4.2 2.1 1.0
NMOG grams/mile 0.125 0.07 0.01
PM grams/mile 0.02 0.01 0.01
Smog pollution lbs year 10.75 3.64 0.99
Greenhouse gases tons year 8.15 9.65 9.65
So you can see how the gas car built to federal emissions standards, while emitting about 15% more greenhouse gases, has significantly lower emissions than the diesel, and the California model is even better than the federal car with no further reduction in fuel economy.
I am impressed with how low they got the particulate matter in the diesel with the Bluetec (urea injection), but it's still twice as high as the gas car.
1. Stop the engine at idle and use the large battery to drive accessories and air conditioning. Toyota's Hybrid Synergy Drive goes a step further and lets you stop the engine at almost any time (up to a certain vehicle speed).
2. Downsize the engine so it is more efficient at typical engine loads. Use the hybrid system for brief peak power and to augment the engine keeping it in more efficient operating ranges when required. Indeed. Give me a car with an Atkinson cycle engine, that doesn't have the dead weight of a hybrid, and I'll be happy. And the car will still be slower and less efficient than the hybrid.
I'm not saying that hybrids are the best solution for improving efficiency, but they are the best solution that is readily available today for a reasonable cost. Down the road as battery technology improves and manufacturing capacity increases of the next generation of batteries increasing availability and reducing cost, plug-in hybrids and 100% electric vehicles will be the way of the future.
The best solution on the horizon is electric cars powered by renewable and/or low emissions power plants. Chemical batteries will always be inefficient. Lithium batteries are very efficient - their efficiency exceeds 95%, when compared to NiMH batteries which are only about 70% efficient in a charge/discharge cycle. Worse yet, look at the environmental impact of the a car accident involving these chemicals. Yeah, look at all those cars on the road driving around with 10s of gallons of gasoline and diesel! And those big-rigs with hundreds of gallons of fuel^H^H^H^Hexplosives! It's amazing that they don't blow up every time there is a fender bender! Just imaging what a shard of conducting metal will do as it pierces the plates of a very low internal resistance storage battery. Anyone see the youtube images of the laptop exploding? Imagine that on an automotive scale. The tendency of a battery to catch fire has a lot to do with the specific chemistry used as well as manufacturing techniques.
For example, take a look at A123Systems batteries. You can drill nails through their cells without any safety issues at all.
Otherwise all those solar racers would likely use a Kammback, airplane wings would use a Kaamback, but every single one that I've seen uses a full teardrop.
The Aptera is also a full teardrop (OK, there is a tiny flat area at the rear, but mainly for the taillights and they also vent air in to that area as well) and it was designed to be as efficient as possible.
So please - any one have any actual drag coefficients for tear drops and Kammbacks with various amounts of the tear drop chopped off?
Here are the combined fuel economy ratings from fueleconomy.gov
Prius - 46mpg
Civic Hybrid - 44mpg
Altima Hybrid - 34mpg
Camry Hybrid - 34mpg
Escape Hybrid - 32mpg
Each one leads their respective classes in fuel economy - and that is still dealing with the limitations of the currently NiMH battery technology which is still fairly heavy for the capacity, is limited by peak charge/discharge rates and not all that efficient (around 70% charge/discharge efficiency).
The next-generation Lithium batteries (we should start seeing them used widespread in vehicles in a couple years once mass manufacturing starts) addresses all those issues by improving the power to weight ratio, higher peak charge/discharge rates and charge/discharge efficiencies over 95%.
The Civic Hybrid easily beats the non-hybrid on the freeway.
The Prius is the most efficient vehicle sold today on the freeway (in the USA).
A properly designed hybrid lets you downsize the engine so that it is more efficient under the small, steady load of freeway driving. The Prius (and other hybrids) go further by utilizing the Atkinson cycle which reduces pumping losses even more.
As a bonus, the weight penalty (and price penalty) of a hybrid goes down with each generation, the next generation of hybrids due out next April from Toyota and Honda are expected to significantly reduce both by a significant margin.
As you say, Lithium based batteries have the potential to improve the effectiveness of hybrids by being able to handle higher currents (able to recover more power under regenerative braking), potential for more capacity at the same or less weight (plugging in to charge becomes practical). Super-caps also can help recover and deliver short bursts of power, but are currently limited by capacity.
Both Lithium and Super-caps are still more expensive than NiMH batteries and manufacturing capacity is still an issue (though both issues should be largely resolved around 2010 - at least for Lithium batteries).
No, it's not all due to weight.
A large portion is emissions controls to reduce NOx and CO emissions. My old 95 Civic (1.5l manual, basically the same as your 93 Civic but with stricter emissions on it because California has stricter emissions laws.) averaged 33mpg, a typical range depending on the driving was 31-36mpg. If you go to fueleconomy.gov you can see that Honda sold multiple Civics in the US with the 1.5l See my earlier post on the subject.
My wife's old 95 Civic (1.5l engine, CA emissions) averaged about 33mpg in mixed driving, surprisingly close to the adjusted EPA estimate of 32mpg. The 93 Civic appears to be the same as the 95.
Both are rated significantly lower than the 42mpg a 2008 Civic Hybrid is rated and lower than the 46mpg 2008 Toyota Prius that we replaced the Civic with. So far over 8 months we're averaging slightly more than 46mpg as well. The Civic Hybrid is slightly smaller and less efficient efficent (44mpg) than the Prius but costs about the same - it was a no brainer to go with the Prius over the Civic Hybrid.
The Prius has significantly more room, is more comfortable, is quieter, rides smoother, is significantly safer and travels nearly 40% further on a gallon of fuel and also emits far fewer pollutants like NOx and CO. Granted, the Prius cost about $22k vs $15k the Civic cost when new.
Now your Civic does likely get close to 40mpg, but that's because it emits far more NOx and CO than the one we had.
So I would argue that tight emissions standards have also significantly decreased fuel economy in addition to weight. If we had an efficient way to clean up NOx and CO emissions in the exhaust, we could improve fuel economy overnight by 10%+ by simply adjusting the ECU tune to use a lean-burn in light to moderate loads and even more by increasing compression ratios slightly. To obtain low NOx and CO emissions, you typically must burn much more fuel than what would otherwise be required to generate the same amount of horsepower.
We are seeing a recent surge in Exhaust Gas Recirculation (EGR) and Atkinson cycle engines (in hybrid's anyway where the lower power output of the Atkinson cycle engine can be compensated by the electric motor/generator) to offset the efficiency loss of having to run stoichiometric air/fuel ratios while still having low NOx and CO emissions.
You're still missing the point.
YOU STILL KEEP A SINGLE COPY OF YOUR DCVS ON YOUR MASTER SERVER. YOU STILL MAINTAIN CENTRALIZED CONTROL!
For example, look at Linux kernel development. Linus maintains the central repository. Every single other developer regularly syncs up with Linus while working on their own tree.
If you don't want people taking it home, then you tell them not to develop on their note books. Same as when you're using a CVCS.
DCVS still has a number of advantages:
1. It's dead simple to branch off and keep track of changes to some experimental changes. If you decide to keep them, you can push all the changes to your master. If not, toss it in the bit-bin. With a CVCS, you have to make a branch and then deal with the fun of trying to merge it back into the trunk. And if it was crap, that crap gets stored in the CVCS forever (which could be a good or bad thing).
2. Concurrent development is better tracked - because you can check in every little change along the way. With your typical CVCS you end up make a lot of intrusive changes, and then check it all in in one big wallop - which means you lose the benefits of a VCS system. The DVCS system encourages you to check things in all the time.
You're pretty much screwed. Generally, the only way to extend a filesystem is to add space to the end of the partition. Extend the partition, then tell the filesystem to expand to use the newly allocated partition space.
Now, you could fake this by using LVM and multiple partitions, but the end result would not be pretty.
1. The impact of manufacturing said item.
2. How many fewer resources said item consumes during use.
This analysis is called a life cycle analysis.
For example, your typical computer consumes much more energy during manufacture than during use. So for this case, using what you already have as long as possible is better.
Another example, your typical automobile, consumes much more energy during use than during manufacture (especially once you consider how much of your average automobile is recycled). In this case, trading in your gas guzzler for something which consumes less fuel is typically worth while, especially considering that your old vehicle is not likely to go to the scrapyard until it really is ready to fall apart from overuse or totaled.
Obviously items which do not consume energy during use are best used until unusable.
# Fedora believes in the statement "once free, always free". Why not consolidate efforts with Fedora which has the same goals?
Is there really enough of an audience to justify a rebundled Ubuntu without the non-free bits? Or will this project slowly die as it fails to attract a community?
Just as a follow up - AutoSpeed is running a great article on BSFC or Brake Specific Fuel Consumption.
AutoSpeed - Brake Specific Fuel Consumption
I highly recommend this to anyone interested in how different operating conditions affect fuel economy.
BSFC is the measurement of how much power vs how much fuel in consumed - basically measuring how efficient an engine is. In an ideal world you'd have an electronic throttle and a CVT. The throttle would directly translate into how much power you are requesting. The ECU would use a BSFC map to determine the most efficient engine RPM and throttle body position to generate that power and the CVT would allow you to maintain that RPM for as long as you are requesting that power level.
Data found here: Pulse & Glide vs Cruise Control - a study
You're kinda forgetting a few things.
Typically cramming as much air/fuel as possible in the engine is not the most efficient for a number of reasons - but primarily because doing so generates so much excess heat as waste that you must add extra fuel to try to keep things cool.
For example, your typical gas engine will produce the most power when running an air/fuel ratio around 12.5 to 1. But you could make slightly less power but do so more efficiently by running slightly leaner, around 13.5 to 1.
But realistically, most engines will run 10-12 to 1 during WOT, especially at high RPMs to keep things from melting down.
Ideally, you would run WOT all the time, and simply adjust fuel and RPMs until you had the power level you wanted. Low RPMs because friction rises more or less linearly with them and naturally the least amount of fuel possible. You know, run it like a diesel which has no throttle body. But unfortunately gas engines don't run well at extremely lean air/fuel levels and will typically misfire - not to mention generate large amounts of NOx emissions when running leaner than stoich which your typical catalytic converter will not be able to clean up.
A compromise is to run a small engine with turbocharger. This way for normal sedate driving you drive the car like a regular small car. You'll use a bit more throttle and as such, pumping losses will be lower than a larger engine with the same output capacity. And when you need the power, open the throttle and close the turbo wastegate to get that burst of power to pass that truck.
It's really not hard to beat those mileage results. My Prius is averaging 46mpg. Civic Hybrid will average above 40mpg. Toyota Camry Hybrid will average about 35mpg - not hard to beat 38mpg if driven judiciously. The reason is that most of the the converter takes care of is not a part of the combustion of fuel- but is rather the result of what happens to the rest of the air (nitrogen and such) in the extreme heat and such. Efficiency cannot affect that - in fact, higher operating temperatures of modern cars have made it worse. While higher operating temperatures can raise NOx emissions, I dare you to find one modern car with higher NOx emissions than it'd older counterpart - even with the catalytic converter removed. Peak operating temperatures are typically limited by the knock resistance of the gasoline - which is still 87 octane. Modern vehicles are able to raise compression and improve efficiency without knock by virtue of having highly optimized combustion chambers which quickly burn as much as possible of the air fuel mixture. If NOx was a concern, they could inject a tiny bit more fuel to compensate - the extra efficiency from being able to run higher compression should compensate.
For example, to maintain low NOX emissions with your standard catalytic converter, you need to maintain an air/fuel ratio of approximately 14.7/1.
Under light load to minimize fuel consumption, you'd be better off leaning out the air/fuel ratio (injecting less fuel), but unfortunately NOx emissions tend to go sky high when doing so.
You can get around this by using a special exhaust devices which can trap NOx emissions, run the engine rich for a bit to burn off all the NOx emissions and then go back to lean burn operation. The Honda Insight did this, but I don't know of any others.
Diesels especially suffer from high NOx emissions since they regulate power by varying the amount of fuel injected instead of using a throttle body. This is why are only recently are a few diesel cars trickling into the market place this year with exhaust treatment systems specially designed to reduce particulate and NOx emissions to gas-car levels. Cold start fuel economy is also markedly lower for the same reason - cars intentionally burn EXTRA fuel to heat up the cats faster so that they end up emitting less overall NOx and HC emissions. If emissions weren't an issue less fuel would be burned. The Prius for example is notorious for typically delivering a meager ~25mpg during the first 5 minutes of use. The 2nd 5 minutes will be double that.
You could probably improve fuel economy 10-20% across the board in gas cars if you didn't have to worry about NOx emissions. In fact, this is one reason that hybrids improve fuel economy. Besides stopping the engine when no engine power is required, they also let you operate the engine in the most efficient and lowest polluting engine operating conditions. For example, if you get a Prius going a steady 20 mpg on flat land, it will transition between running solely off the battery/generator and turning the engine on to charge the battery/generator while getting over 100 mpg.
To clear up a common misconception with hybrid cars people often ask - why doesn't it run longer/faster/more on electric power? You have to remember that the only electric power that is "free" is the power gained through regenerative braking (that power is normally lost 100% as heat in a conventional car). You also have to remember that charging a battery and discharging a battery is not 100% efficient and most of your battery charge (except for the little bit that comes from regenerative braking) still needs to come from the gas engine. Some people will install an EV mode switch and then force their hybrid to run for extended periods of time on battery - then complain that fuel economy went down! That happens because at some point in time you have to recharge the battery - and by forcing the car to stay in EV mode you then force the car to charge the battery when it's low - no matter if it happens to be most efficient to do so at that point or not.
Even the basic "make a copy of the file" defrag methods we've been discussing aren't even guaranteed to leave the file you are attempting to defrag in fewer fragments than the original. In a lot of my testing, often the "make a copy of the file" defrag method doesn't always help for files only moderately fragmented on an old and fragmented filesystem.
So I'll say it again: If you want to defragment files on Linux, basically your only real-world capable choice is XFS using the xfs_fsr tool.
If it were simple, someone would have written an online ext2/3 defragmenter a long time ago. There have been plenty of people asking for it, just google it.
There is an offline ext2 defragmenter, but it hasn't been maintained in ages from what I understand - I don't think it's trusted to defragment your data without risking data loss.
Both of your lsof and snapfs suggestions leave room for data loss unless you are sure that no one will be modifying the files. For that case, there is already a tool which attempts to defrag files called shake.
However, your defrag method IS NOT SAFE and WILL RESULT IN DATA LOSS on a live system (sorry to yell, but I don't want anyone trying it on a live system - it should be OK if you can guarantee that no-one else will modify the data on the partition)
There is a lot of opportunity in your script for data loss:
1. During the copy. If someone modifies part of the original that has already been copied, your
2. During the rm. Deleting files takes time, so there is more room for a file to try to write to the original. This step is actually completely unnecessary, just overwrite the original with your mv command.
3. After the mv. If a process has the original file open, it will continue writing to that original file, even after it's been deleted and "overwritten". It is very legal to continue file operations on an open file descriptor.
I suggest you actually try your defragmentation trick on a live filesystem which is actively in use. If you don't lose data, you're lucky.
So I'll say it again. The only filesystem which allows you do perform LIVE defragmentation is xfs using it's xfs_fsr utility.