Safe Speed Forums

Some of today's diesels actually do have a throttle plate, to facilitate the function of an Exhaust Gas Recirculator (EGR) Valve.

_________________
The Rules for ALL ROAD USERS:
1) No one gets hurt
2) Nothing gets hit, except to protect others; see Rule#1
3) The Laws of Physics are invincible and immutable - so-called 'laws' of men are not
4) You are always immediately and ultimately responsible for your safety first, then proximately responsible for everyone's
Do not let other road users' mistakes become yours, nor yours become others
5) The rest, including laws of the land, is thoughtful observation, prescience, etiquette, decorum, and cooperation

I remember you!

Aren't you the same person who enthusiastically endorsed (so-called) progress? It's good to see that you are moving from the dark side. Simplicity is the answer, not towers of technology, with each layer trying to fix the defects in the ones below.

I've always believed that gentle acceleration would be best for fuel economy. I think
this was based on vague notions related to hysteresis, i.e. the property of system that,
when an input is changed, causes a lag before stable conditions are re-established.

The hysteresis (between fuel throughput and engine efficiency) might be difficult to
measure and design for, leading to efficiencies. A small change causes less
hysteresis and might be more easy to design for. I don't really know.

Anyway, that's what I thought, and I'm getting > 60 mpg from this and
other hypermiling techniques.
The hypermilers recommended it strongly.

Gentle acceleration (and braking) has many other obvious benefits over "lunging and lurching", but
they are "selfish" according to some, and would cause a flame war, so I won't elaborate on them!

The following are some quotes from the guy who coined the term 'hypermiling' ...
This is the first driving style alteration technique that goes beyond 'don't accelerate and brake wastefully, and don't drive so fast'.
Note that he mentions the safety aspect at the outset, then touches on placement as a statement to other drivers - a request for cooperation; specifically, to encourage other drivers to pass you much more quickly than they would if you drove like an oblivious jackhole, taking up more space than you needed, and denying others their right to choose a reasonable and prudent traveling speed that may be different from yours.Again, he encourages driving behaviors which encourage others to pass you whenever reasonably possible.Can he be any clearer?

By the way, it is worth noting that the vast majority of references to - and nearly every endorsement of - tailgating/wakesurfing/butt-sniffing/drafting as a hypermiling technique have been retracted. (Even if hypermiling became virulently popular, aerodynamic drag is mostly a nonfactor below 40MpH, thus platoons of hypermilers filing behind each other would yield little mileage gains, while making passing for others not only difficult, but even less fuel efficient.)

Every hypermiler, by definition, is selfish. The problem with that word is that it does not allow for the possibility that one can want more for oneself without wanting less for others.

Those who want what they want for themselves in such a way that it usurps from others are well past selfish - they are @$$h01e$. AIG executives and hypermilers who waste fuel by not riding ridges come to mind

_________________
The Rules for ALL ROAD USERS:
1) No one gets hurt
2) Nothing gets hit, except to protect others; see Rule#1
3) The Laws of Physics are invincible and immutable - so-called 'laws' of men are not
4) You are always immediately and ultimately responsible for your safety first, then proximately responsible for everyone's
Do not let other road users' mistakes become yours, nor yours become others
5) The rest, including laws of the land, is thoughtful observation, prescience, etiquette, decorum, and cooperation

Yeah, I remember you too

Unfortunately, what you DON'T seem to remember(or WANT to remember - not quite sure which!) is the detail of what I said. Just a quick refresher course:

1. I like progress that makes things better. Digital management of fuelling falls into that category.
2. I like lots of complex "toys" on a car that make it undesirable to other purchasers long before it's actually unroadworthy. That gets me cheap cars where I can choose to either fix the toys or live without them.
3. I am agnostic about "progress" that gets launched without being properly "market-ready". Dual mass flywheels are a good example of this right now. Lots of current diesels manage staggering refinement with them but then they fall apart and take the clutch with them. Clearly a good idea which works but has not yet been developed to get all the bugs out. As I don't buy new cars, I'm quite happy to let other people find these gremlins the hard way and then I just don't bother buying that model of car when it gets into my price bracket. As soon as the problems get sorted (as I'm sure they will) I'd buy one like a shot.

Getting back to my original point, most things are a compromise. You can produce a bit less CO2 and lots more CO, HC and NOx, or you can fit a cat. You can produce some diesel particulates and less CO2, OR you can fit a particulate filter and chuck out a bit more CO2. You can have good grip or low rollin resistance tyres, you can...etc etc.

Rush, maybe you can enlighten me?! I read the hypermiling stuff with a mixture of interest and bemusement. What is it about Americans and diesel cars?! If these guys want to get 60MPG (even 60 MP (IMPERIAL)G! all they need to do is go out and buy a diesel car! I've never really understood why the Prius was a petrol-electric hybrid because all that technology made it only just (in the right circumstances!) about as good as the equivalent diesel engined car.

Don't get me wrong, I happen to LIKE petrol cars because they sound and feel nicer. But I have a diesel as my everyday transport because I just can't ignore the savings to be had. Diesels are getting better (in terms of refinement) by the year and these days, other than having a rev counter with smaller numbers on it, there's little to choose between the best ones and their petrol counterparts. Certainly if I was bothered about maximising fuel economy, I'd switch to diesel LONG before I tried some of the ridiculous stunts those guys seem to be resorting to!

Just as an "aside", I'm intrigued about the "ridge riding" thing. Over here, if you did that on most of our roads, you'd be hitting all the grids, manhole covets and potholes with your nearside tyres. That all uses energy - bashing the suspension up and down like that and then disipating it as heat in the dampers! Are the nearside edges of the road a lot smoother over there? I take the point about driving in the wet, but even then, I'd have thought that when following other vehicles, it would actually be better to keep your wheels on the part of the road that had been "squeegeed" dry by the preceding car(s)?

Maybe; I can definitely answer your questions, though.Keep in mind that during the 40s, 50s, and 60s, Amerikan cars were fueled by gasoline that was either nearly as, or actually cheaper than just about any other liquid commodity I can think of. Even back in those days, most other countries paid more for fuel out of the pump than did Amerika. With gasoline so inexpensive for us, and less incentive to care about the environment at the time, why settle for a noisy, smoke belching vehicle that was so hard to start when cold?
To whatever extent that was actually true, the perception of diesel fuel was as a 'heavyduty' fuel, primarily for work vehicles. That, and the math simply didn't work out when weighed against diesel's drawbacks, perceived and real, which were both exaggerated by what the Amerikan auto industry provided its citizenry. (I know that European makers in Amerika sold many more diesel-optioned models than GM, FoMoCo, and ChrysCo., especially after the 70s, when fuel availability and cost became an issue.)By the way, I forgot the linkie. Here ya go:
Wayne Gerdes explains the basics of hypermiling.
I don't know how to provide the link to this picture, but if you care to take a look, try using maps.google.com, go to Lefrak City, Queens, NY, and drag that guy onto the Long Island Expressway so that he's between 93rd and 94th Streets.
Note that it is always at least three lanes wide, and that that usually does not include the shoulder.

When it rains, each lane features two puddles about an inch or so deep, and miles long, formed by the pressure of each car's tires passing over essentially the same path, as drivers tend to center themselves in their lanes.
Rain or shine, good hypermilers almost never center themselves in a lane (even when there is only one). Instead, they [usually] move their passengerside towards or over the painted lines, depending on their level of skill and experience, both to avoid the ruts - especially when they are filled with water - and to encourage passing. (Remember, hypermilers almost never wind up in, much less stay in, the passing lane.)

If instead, you managed to move the guy onto Horace Harding Expressway, which is the Long Island Expressway's local service road in Queens, you'll find after studying that path for a while, that we tend to put the drainage ditches on either edge, and the manhole covers pretty much anywhere; whereas the potholes tend to form where the tires have been putting their cumulative pressures - right between the dead center of a lane, and the painted lines.

For what it's worth, hypermiling never really got a foothold in New York City. The lower the automotive population density, the more likely you are to find hypermilers.

_________________
The Rules for ALL ROAD USERS:
1) No one gets hurt
2) Nothing gets hit, except to protect others; see Rule#1
3) The Laws of Physics are invincible and immutable - so-called 'laws' of men are not
4) You are always immediately and ultimately responsible for your safety first, then proximately responsible for everyone's
Do not let other road users' mistakes become yours, nor yours become others
5) The rest, including laws of the land, is thoughtful observation, prescience, etiquette, decorum, and cooperation

Thanks for that. I'm still curious though. Over here, diesel passenger cars were noisy harsh and smelly too, up until about 10 years ago. It's really only in the last decade or so that they have become good enough to be (in my view) an acceptable everyday alternative to petrol, but as soon as the public saw the improvements, they went for it in a big way. Even now, with diesel 10p a litre more expensive than petrol, they are still very popular. I would have thought that with the recent fuel price surges in the US, there would have been more inetrest in switching. As I understand it, there is currently lots of interest in the US in fuel saving and in hybrid or even fully electric vehicles, plus all the various tricks like partial cylinder shutdown, and yet a straight swap to diesel would involve much less of a change in "ordinary" motoring techniques!

Is the infrastructure in place over there? Here, petrol stations have diesel and petrol pumps right next to each other on the forecourt these days but there was a time when people with diesel cars would have to fill up in the puring rain at the "truck" pump. I could see that putting people off! I also wondered whether the cold weather in the more Northern parts of the US might have put people off with the diesel freezing. Presumably there's also a resistance within the repair trade to learning "new tricks"? That said, if they are happy to service ad maintain hybrids, a diesel can't be THAT weird, I guess!

We never really noticed those improvements, since diesel already figured less prominently in our eyes as I explained above. I also forgot to mention that when GM did not properly design a passenger car diesel engine in the '80s (they haphazardly altered a gasoline V8); those who purchased GM's diesels did not maintain them properly, either. When you couple that with the average Amerikan's nervousness at retrying technologies that failed because they were poorly executed and poorly maintained by their parents decades ago (cylinder deactivation ought to be legally mandated on all engines with more than four cylinders before I finish this, but Amerikan consumers remember Cadillac's V8-6-4) you only have one question left as to why diesel hasn't caught on as a passenger fuel alternative.

With a little margin, your figures convert to roughly 50 Amerikan cents per Amerikan gallon. That would've been nice.
When I was paying $4 per gallon, diesel was anywhere between $6 and $7 per gallon. As a %age, it went up much higher, much faster. (Presently, diesel is about $3 per gallon, to gasoline's $2 per gallon.)
Amerikans perceive the 'prices' and 'costs' of diesel - also from having learned the wrong lessons about it - as too high to allow it to enter their consciousness.

One other thing - you guys already have most of it. Most of diesel world production already winds up in Eurasia. As to whether that is the cause, or the effect, of cheaper gasoline [and more expensive diesel] in this country, I can't say.

_________________
The Rules for ALL ROAD USERS:
1) No one gets hurt
2) Nothing gets hit, except to protect others; see Rule#1
3) The Laws of Physics are invincible and immutable - so-called 'laws' of men are not
4) You are always immediately and ultimately responsible for your safety first, then proximately responsible for everyone's
Do not let other road users' mistakes become yours, nor yours become others
5) The rest, including laws of the land, is thoughtful observation, prescience, etiquette, decorum, and cooperation

They're a bit too close together. I squirted a couple of litres of petrol into my diesel last week, and then I had to fill it right up to the brim with diesel to dilute it! It's a pest.

BLIMEY! I guess that answers it then! If petrol was only 2/3 the price of diesel over here, the choice would be a lot harder - I guess it would probably tip the scales pretty firmly back towards petrol. Petrol is about £4/imperial gallon at present and diesel about £4.50

Why is it more expensive than petrol in the U.K. then?

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Malcolm W.
The views expressed in this post are personal opinions and do not represent the views of Safespeed.

still not sure i understand ridge riding.....

you want to drive a different line to everyone else.....? potentially in the grit & debris swept aside by other vehicles and away from the what (in the uk anyway) is often a bit of tarmac nicely smoothed by all the traffic.

Not that I'm a hypermiler or anything, but let me attempt to paraphrase ...

Most people, most of the time, center themselves in the lane they are driving.
Most hypermilers, most of the time, move to the right within that lane (left for the UK) so as to
a) avoid the ruts that have developed by everyone else following each other, centering themselves in a lane (in the rain, a hypermiler's tires would displace less water anyone else who centered themselves in a lane because the rain settles where the majority of the pressure on the road has been exerted by the majority of drivers)
b) alert others that they are driving slowly, sooner
c) use that unique position as a message to other drivers to overtake as soon as reasonably possible

They are trying to ride on the highest points of the road surface so that, wet or dry, their overinflated, low-rolling resistance tires are encountering as little additional resistance as possible. That said, it is far more effective in the rain.

They also tend to avoid the 'passing only' lane, since most hypermilers
a) almost never pass anyone
b) encourage others to pass them by - among other things - ridge riding

The very nature of the majority of roads in Amerika, I'm sure, means that ridge riding is probably much more common in Amerika, but the more gentle the curve of the road, the easier it is for a hypermiler to position themselves off-center in that lane, so as to avoid the grooves and encourage overtaking.

_________________
The Rules for ALL ROAD USERS:
1) No one gets hurt
2) Nothing gets hit, except to protect others; see Rule#1
3) The Laws of Physics are invincible and immutable - so-called 'laws' of men are not
4) You are always immediately and ultimately responsible for your safety first, then proximately responsible for everyone's
Do not let other road users' mistakes become yours, nor yours become others
5) The rest, including laws of the land, is thoughtful observation, prescience, etiquette, decorum, and cooperation

Presumably they end up replacing their tyres prematurely as a result of over-inflating them so some of what they save on hypermiling goes into the tyre replacement fund?

the latter two 'reasons' would be ringing plenty of alarm bells if i came across someone taking such a bizarre position.

There is an interesting article on Autospeed you might want to read.

It appears to indicate that there is a sweet spot for petrol consumption at around 2000rpm and 3/4 load. This is going to vary depending on your car as the article points out. The conclusion is that plenty of throttle at low revs is the way to go, while this is not going to give hard acceleration it will probably not be 'gentle'.

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Driving fast is for a particular time and place, I can do it I just only do it occasionally because I am a gentleman.
- James May

Good article! It's a pity they don't show similar curves for diesels and forced-induction engines though. One of the reasons I don't like petrol turbo engines is that they tend not to have this "sweet spot" because at low (off-boost) RPM, I think they fill their cylinders very poorly due to the restriction imposed by the turbine in the inlet tract which isn't really doing anything except getting in the way. Added to that, they have lower compression ratios than they need under low off-boost conditions to stop themselves grenading once the boost does arrive. This means that the gas that DOES get into the cylinders doesn't get compressed as much as it could usefully be when the piston moves up. Obviously, once they're on-boost, it's a different story, but a lot of urban or light load driving conditions don't call for that! This is where the diesels really anihilate the petrol engines. They have no throttle plate so no pumping losses (OK, Rush, I know they're starting to get them to help with EGR and particulate filter regeneration, but that's not all the time they're runniing)! Accordingly their volumetric efficiency is much higher - AND they can run much weaker anyway! Somthing I've noticed though is that at big power outputs (high revs and wide open throttle), the difference in fuel consumption between petrol and diesel is much less. I put this down to the petrol engine's throttle being open and the pumping losses therefore being much more similar to those of a diesel.


...now if only they could get a diesel that responded and sounded like a petrol engine with a wild cam and a light flywheel...

I interpret all that data to mean that it's best to keep it at 2 to 3K revs. If you're state is "low load", you HAVE to stay at 2 to 3K revs to avoid wasting fuel, and if you're state is "heavier load", revs are less important. It doesn't necessarily mean you have to adjust your load (by accelerating) so that it's not low. You could also use the gears to keep the revs at 2 to 3K, which is ALWAYS the optimal level, whatever the load. Slowpokes are OK, after all.

As it happens, that's about where my cruising spot is, when I'm in top gear. 50 to 55 on the m-way is not a sin, is it?

It means as big a throttle opening as possible for the speed you want to maintain (within reason - i.e. not labouring the engine). If the throttle plate is wide open and the pistons are moving relatively slowly, the cylinders will all get the best chance to fill properly and the "pumping losses" (as they were called in the article) will be minimised. I wouldn't get too hung up about 2000-3000RPM. As the article says, it will vary from one engine to the next. Also it doesn't cover diesels - which work differently. So far, I haven't found the most economical speed for mine, but I think it's somewhere betwen 20 and 30MPH (at which speed it most certainly is NOT doing 2000-3000RPM)! However, I'm not sufficiently into "hypermiling" to want to cause that level of disruption and chaos on the motorway!

On my big, old, and normally aspirated petrol car, I once got 37MPG sitting between the trucks at 56 for about 50 miles. I think it could probably be better still at a constant 40 (which is the lowest speed it can pull in 5th. It's doing rather less than 2000 RPM under those conditions though!