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Alot of diesel enthusiasts don't think DWL applies to their autos.
I respectfully dissagree.
http://forums.tdiclub.com/showthread.php?p=1329812#post1329812

Note that I'm walking softly as a newish member there and since feelings can be easily hurt (Diesel vs hybrid) am taking it easy and avoiding confrontation.
I'm just another friendly voice there, trying to promote efficiency.

I believe DWL applies to all vehicles, diesel included.
I tried to explain the analogy as simply as possible.
Your thoughts?

Note that is a very long thread from the start. I've "Thumbed" through it and it seems the mentality of some members is that rolling in N is dangerous, illegal and should never be done unless you want to kill somebody. Same for increasing tire pressure over recommended levels. (32PSI)
Some are really sharp as well.

It probably all depends on how substantial the "L" actually is,
and things are probably a bit different with the turbo. I'd
love to see the efficiency curves for those engines..
.
_H*

Hi HotGeorgia:

___Be a little careful over there as you should in any non-hybrid specific forum given those guys may not yet be ready for the how’s and why’s of busting the EPA in the chops ;)

___With that, Phil has had a little experience with the TDI guys and FAS’ing while holding those turbo’s from instantly cooking off the now non-flowing lubricant and ending up as mountains of seized up metal parts headed for the garbage heap. This is one of the reasons I do not see a ton of discussion on diesel hybrids like we would have hoped for by now but there is tech to cure just about anything including electric pumps to lubricate those hot parts even after ICE-Off …

___As for DWL, you bet it would work for those guys … However, if you were to leave me without the ability to FAS every 3 - 5 miles out on the highway or FAS/P&G around town, that may hold back the FE a CI-ICE can achieve. They do not have hybrid tech and they may not be able to throw their cars into and out of conditions we can with our non-hybrid’s on a whim so just go slow with them is all. Another item … Even those guys know how supposedly inefficient a SI-ICE is at low load yet here we are creaming everything at low RPM’s and extremely low loads whenever possible.

PS: I read the following …
“I drove a Honda Insight for 50k miles. That car had a very accurate instant MPG gauge. So I could see a decrease in MPG and would add air -50psi,, then the MPG would go right back UP! Any Insight getting above 70mpg has at least 48psi in the tires.”___Maybe he needs a refresher? The following with 2 individuals, some gear, and at 44 #’s might help? CleanMPG members are about to embark ... (http://www.cleanmpg.com/forums/showthread.php?t=725)

___Good Luck

___Wayne

Here's the thing, driving slow will always produce better mileage numbers than driving fast assuming engine load is the same. By that I mean if I go up a hill at 25mph in 2nd, and go up the hill at 50mph in 3rd I'm using more fuel in 3rd hands down because the increase in energy required is the square of the velocity. In other words, if I have a 2000lb vehicle with a Cd=.3 and go up hill in 2nd @ 25mph, I expend a quarter of the energy I would traveling at 50mph in 3rd. The trade off being that I'm traveling at half the speed. But I have no problem with that if I'm using 1/4 of the fuel required.

On the other hand, the engine speed may not be the same and the engine efficiency may be less due to a decrease in rpm and volumetric efficiency. However, odds are the efficiency difference between an engine running at 2krpm and 4krpm is ~10-20%, so if even you speed up from 15mph@2krpm to 30mph@4krpm to take advantage of the ~20% increase in engine efficiency, your car has to expend ~300% more energy to cruise at 30mph. It's all in the drag equation (http://en.wikipedia.org/wiki/Drag_equation), and given the same incline, the increase in energy required to go some speed compared to another is the ratio of the sqaure of the speeds. So if I go 30mph compared to 15mph, then I'm losing (or using) (30^2)/(15^2) times more energy. Speeds costs energy, how much are you willing to put out? ;)

Something else to consider, in gas engines the engine efficiency is horrible at lower rpms and increases until the peak torque, at which the engine is running at optimum efficiency. Some gassers can be geared such that they might get the same mileage at 60mph compared to 70mph, but a diesel shouldn't exhibit this drastic change in fuel efficiency wrt engine speed. In practice I've found that a 5-10mph difference can result in 10-15% greater engine efficiency, but a 15-30% increase in energy lost due to drag, so will incur a net 10-15% efficiency penalty, so to speak.

Hi Lyeinyoureye:

___Welcome to CleanMPG and you have an interesting nick? Bio production possibly ;)

___Hot_Georgia is not speaking of the difference between 25 and 50 mph in a DWL scenario. He is speaking of a slight drop in speed of maybe 2 - 4 mph during an ascent of an overpass and a slow rebuild back to the original target before hitting the overpass on the way back down. DWL is simply holding FE as steady as possible during the ascent, crest, and descent vs. holding speed as steady as possible. Because the way DWL holds load steady, I have to believe it will work just as well in a CI-ICE, as it does in a SI one inside a hybrid or non-hybrid alike. There is no drag equation delta worth considering as the speeds are to close.

___About SI-ICE’s … there efficiencies are supposedly terrible at low throttle openings due to the pumping losses but the hypermilers live and die inside that low loaded area and guess what, the FE is a lot higher then higher RPM’s and the mechanical friction resulting from it … Let alone the aero drag after 55 - 60 + mph or so ;) The P&G technique can be seen in a different light as a somewhat faster accel with a larger throttle plate opening for a much shorter duration can and does work in some instances but we are speaking of P&G which is nothing like steady cruise.

___Good Luck

___Wayne

He is speaking of a slight drop in speed of maybe 2 - 4 mph during an ascent of an overpass.
Correct. My speed varies this small amount on the freeway, simply because of the wind resistance caused by speed and traffic requirements.

However regarding slower speeds on rural highways the difference is often much greater.
I might build to 55 before reaching that really big hill, but reach the top around 40, sometimes less especially if in FAS. But if there's an impatient driver behind then maybe only down to 47 or so :rolleyes:

Thanks Wane for the TDI suggestion.
I've been walking as softly as possible there. I think some folks there are pretty aware of driving for efficiency while others have a..It's diesel so just drive it hard mentality.
I suppose it may be difficult to take efficiency suggestions from the arch enemy- a hybrid driver. At least in a few cases.

Ah, I see... I should probably read a bit more before posting. ;)
In any event, an increase in speed will result in less efficient use of fuel due to huge losses from drag, compared to (relatively) minor losses due to engine efficiency. It's kinda like how some people can cruise through a bunch of lights without stopping and average 25mph, while someone averaging 40mph may end up stopping a few times. Not only is the slower person using their fuel more efficiently, they won't lose as much energy when they stop, and they won't stop as often (win/win).
As for my name, it's related to biodiesel production. Although I've gotta say I'm a bigger fan of home grown plant oil for the majority of my fuels, with biodiesel used during warm-up and shut-off. Ultimately, I'd like to build a plug-in EV with very low Cd/RR/FA(frontal area) and have enough battery capacity to go around town all electric (charged off solar panels) while using VO and a small trunk mounted diesel genset for highway trips. But that's at least $20k(cost of donor glider, batterys, electric motor, diesel genset, solar panels, and other misc stuff) away right now. Otoh, if I was able to do this I'd probably be totally energy independent and from that point on, nearly carbon dioxide neutral. :D

Hi Lyeinyoureye:

___So you are a Bio maker then? I wish there were more following your lead as that has got to be the best way to fuel a diesel I can think of! Thank you for taking the time to make B100 for your transportation needs.

___About getting caught in that stop light after stop light … Depending on how its handle, it can take the average 25 mpg driver up to a vastly more experienced level while pushing 75 to 100 mpg’s under the right circumstances. This is where the P&G, FAS’ing, and Rabbit timing (no pun intended ;)) portion of your FE skills can come to the forefront.

___And I can tell you would love to get your hands on a blown up Insight. Light weight, LRR RE92’s, lowest Cd of any car I could afford today, very small FA, and is just begging to be converted into an EV. Only after the motor is blown and the pack is spent however!

___You may be our first Diesel member and with that, you may see the odd question here and there in regards to Diesels that we may not be up to the chore in answering. I hope you can make the transition to CI-ICE tech as seamless as possible for all of us when and where appropriate. We will try and do the same for you from our perspective as the acronym’s can be a bit daunting at first. Your use of “low Cd/RR/FA” was practically music to my eye’s :D

___And again, thanks for joining and your Diesel Rabbit’s sig and results look spectacular!

___Good Luck

___Wayne

Please allow me to look at DWL another way. First off can we all agree that is best to be in the highest gear you can be in? None of us is driving down the freeway in 4th gear unless we only have a 4 speed. We all use top gear on the freeway correct?

Lets look at a hill steep enough to perhaps require a downshift. One method we can call the "Cruise Control" method would have you going a steady speed, say 55mph before during and after the hill. Going up the hill you load will increase and your car will downshift if you have an automatic or you will downshift yourself to maintain speed.

It is true that going faster will cause more fuel use due to air drag. When "Driving With the Load" you would also be going 55 mph on the flat before the hill. Just before the hill you would start to speed up somewhat staying in top gear to perhaps 60-65 mph. You do not do this too soon or you will lose mpg to air drag. When you hit the hill you allow the hill to slow the car down to perhaps 40-45 (traffic permitting)by the crest, remaining in top gear the entire time. You then allow the hill to speed you back up on the downside. Your average speed including the speed up to the sixties and the slow down into the forties is still 55 mph.

I submit that the loss due to the extra load and downshift of the Cruise Control method is greater than the loss due to the air drag using the DWL method.

Does a TDI or Rabbit have a real time MPG display?

___With that, Phil has had a little experience with the TDI guys and FAS’ing while holding those turbo’s from instantly cooking off the now non-flowing lubricant and ending up as mountains of seized up metal parts headed for the garbage heap. This is one of the reasons I do not see a ton of discussion on diesel hybrids like we would have hoped for by now but there is tech to cure just about anything including electric pumps to lubricate those hot parts even after ICE-Off …


not true, I've met one TDIER who gets more than 55 mpg abusing FAS on his TDI all the time. He says as long as your not abusing the turbo you don't have to worry about it cooking. Forgot his user name but I think he was the only one that actually abused bump starting and believes its just as safe as driving with NO FAS. I think he posted in the 700 mile thread, either or I know TDI's can be bump started for sure!

Hi Phil:

___I knew you would be around for this as the guy FAS’ing is the exact guy I knew you had some delings with! The rest of the TDI guys are outputting the cooked turbo info from my reads of the TDI forum last night … See the latest Honda headline on the front page ;)

___Good Luck

___Wayne

Hi Wayne! :D

I haven't started fiddling with biofuels since I'm in between houses and would rather not get into a waste oil recycling contract if I'm going to move, but I'll probably get to it within a year. I *hope. Within a couple months I'm hoping to weld up a spare tire WVO tank, get the needed solenoid/s, tank/line heaters, polyethelene tubing, storage/filtering equipment. and 100% duty cycle air compressor (I've read it's better to pump VO with compressed air than it is with a physical pump since the physical pump will wear a lot faster due to the viscosity of the WVO). I'll still be using diesel for stops/starts, but I can start getting in biodiesel production eventually and switch from using WVO/diesel in the spare/main tanks to biodiesel/WVO in the spare/main tanks, while taking care to change fuel filters 2-3 times so whatever the WVO bonds with in the main tank doesn't blow through into my injector pump.

I can't really get started on this because I'm swapping the diesel out of my current beater Rabbit (350k miles/no interior/cheap&loud exhaust, but for $400 it's paid for itself, especially with the diesel craze lately) into a nice looking, near mint interior, low mileage (100k) gasoline Rabbit. As well as refurbing my small fleet of bicycles and doing chores around the house/gardening/spending too much time online. ;)

In terms of intelligent city driving, I love it. I just wish people would get off my rear end, and I tend to drive with traffic because of this, although I should drive slower, and if I'm lucky, break 60mpg city! A dead Insight would be a perfect glider, but I should wait until I get my living situation sorted out before I get another project. My mom's not exactly happy with my bikes/cars/motorcycles as it is, another non-running vehicle might send her over the edge, although every "project" I complete does kinda get me "bonus points", so to speak. And nice little vaulted house (http://www.calearth.org/3vaults_files/3vaultInt.jpg) with a huge work shop in the San Bernardino desert is something I should get around to first.

*I have too many projects. :D

I think the cooked turbo bearings are mostly a thing of the past. Back in "the day," turbos were both lubricated and cooled by circulating engine oil. It did the job but only just, and turbos were rarely expected to last 100K miles. Now they are designed to last the full life of the engine, in part due to oil lubrication and water cooling, not to mention vastly improved bearing technology.

On older cars, like the older Volvo turbos I used to covet (and I still would love one as a project car...I'm odd), it was recommended that you idle for a minute or two before shutting down the engine in order to keep the thing from siezing. Now it doesn't really matter as long as you aren't driving like a maniac. Given the low loads that we are inclined to use, I hardly think that one of these TDIs would suffer much in a FAS-happy hypermiler's hands. That is unless they are using ancient technology, which would be surprising.

I've heard blown tdi turbos come from the vanes coking up and getting stuck wide open, which results in the turbo overboosting and frying. I don't see how coasting in N can cook it, it should just like turning the engine off when stopped. :confused:

Hi Lyeinyoureye:

___I was talking about ICE-On to ICE-Off with the key via FAS and coasting in. Nothing about a NICE-On here. In the not to distant past, you were supposed to let the turbo spool down at idle before shutting down your car. This allowed the oil pump to continue oil flow over/through the turbo journals and around the housing to remove residual exhaust heat enough so that when you finally did shut her down, the oil still left in the journal/housing wasn’t cooked off and a thick residual left in its place as well as the journals warping from thermal shock IIRC.

___What does VW, MB, Ford, Dodge, and GM do different today to prevent this issue from arising. The TDI owner I work with still lets his 04 Jetta TDI spool down and circulate oil for ~ 30 seconds before he shuts it down. A simple reservoir on top of the housing that would gravity fill the housing below once oil pump pressure bled away let alone an electric oil pump would take care of this issue without a problem … In other words, someone is doing something right or FAS would be a very destructive activity in a modern day Turbo Diesel.

___On a similar note, the latest TDI manuals describe and even expect a 1 minute idle when the car has been warmed up and ran for an extended period. What warm and extended period means is up to interpretation?

___Thanks in advance.

___Wayne

If the manual suggests idling for ~1 minute before shutdown, I'm surprised VW doesn't equip their TDIs with turbo-timers. As for why only VWs exhibit this behavior, I think it has to do with their use of VNT's and small car emission standards, especially during the first few years TDI's were available. Of couse this is a WAG based on some posts I've read in the TDIClub forums and some googling as to what kind of emissions/turbo setup other manufacturers have.
That being siad, since Ford, Dodge, and GM diesels are in a different emisisons class, they can emmit more NOx and run a leaner mixture, consequently generating less soot, and if they do use VNT's (do they?) aren't as susceptable to the turbo vanes getting stuck because of too much soot sticking the vanes wide open, which might result in too much boost until the vanes become unstuck, and a much hotter turbo.
Iirc Mercedes uses a VNT system, but the turbo vanes are controlled by electronics instead of by a vacuum actuator, and if the electronic controller exhibits undue resistence, the ECU can possibly use more force to unstick the vanes, or maybe throw a code? In any event, VW is the only small car manufacturer in the US that uses a vacuum actuated VNT, and the only manufacturer I've heard still has *turbo problems.

*At least until 2004, 2005-07 uses a different turbo design.