Posted on 12/30/2007 8:51:21 AM PST by saganite
Merging with northbound traffic on Interstate 75 just outside Auburn Hills, Mich., I punch the accelerator, quickly swing left into the passing lane and pull forcefully ahead of the cars around me. In any other ride, on any other gray morning, it’d be just another Interstate moment. But this rush hour, I’m behind the wheel of a preproduction 2009 Volkswagen Jetta, which is powered by a 2.0-liter turbo-charged, direct-injected diesel engine that, even as I leave the speed limit in tatters, is averaging nearly 50 mpg. Equally important, what’s coming out of the tailpipe is no dirtier than the emissions from the 35-mpg econoboxes I can now see in my rearview mirror. Speed, fuel efficiency and minimal emissions? These aren’t characteristics usually associated with diesel-powered vehicles. But they will be.
Most Americans have a bad impression of diesel cars. We think of them as loud, hard to start and foul-smelling. We sneer at them for lacking the get-up-and-go of their gasoline-powered cousins. And we dislike them for their perceived environmental sins, chiefly the polluting brew of sulfur and nitrogen compounds that they emit into the atmosphere. All those complaints were fair a generation ago, when the twin energy crises of the 1970s propelled diesels into national popularity and kept them there for a decade. Back then, many drivers ignored diesel’s faults, or were unaware of them, because diesel cars ran 30 percent farther on a gallon of fuel than similar gasoline-powered cars. It felt savvy to buy a diesel, even daring. Then fuel prices dropped in the mid-1980s, and drivers abandoned their clattering, odoriferous fuel sippers. They went back to gasoline.
Today, diesel powertrains are on the map again, for both car manufacturers and efficiency-minded drivers. The technology could be here to stay, even if fuel prices (improbably) decline. .
(Excerpt) Read more at popularmechanics.com ...
Are you in America? I thought the environazis have successfully kept them out of America.
The new Volkswagen Jetta Diesel is projected to get up to 60 MPG, and will be a 50 state legal car. Look for it in the summer of 08.
Rudolph Diesel originally used coal dust in his primitive engine - which exploded and nearly killed him. He later drowned in the English channel.
But still, the diesel offers a wider range of possibilities than a gasoline engine. Also, there is a grain crop that, per bushel to the acre planted, will outproduce soy, wheat, corn, or any other consumable by three to five times AND the oil (most varieties have a 40-45% oil content) is a volatile substance from the start, meaning less energy is required to distill it into fuel. That crop is mustard and the substance is mustard oil and when combined with diesel from crude and biodiesel from other grain sources, America could be on her way to retiring Arab's influences.
Canada - our close neighbor produces about 60% of the world's mustard seed. Most of America's agrarian climate could yield two harvests per year. We ought deal with them for the seed and enhance domestic production rather than continue bearing the OPEC's noose on our necks.
Nah. The ethanol racket depends purely on the consumption of gasoline, and the mandated rate at which ethanol is blended into gasoline. Right now, ethanol is replacing MTBE, and is blended into gas at 10% rates. If they want to peddle more ethanol, they merely increase the mandatory blend by 5 or 10%.
Modern diesels start very easily except in exceptionally cold weather. They’re no less “instant” than a gasoline engine in temps above 30F.
If you wanted to make one of these diesels run as smoothly as possible, well, that’s a simple matter of choosing an engine design with a multiple of 3 cylinders, and not in a V-configuration. American auto designers need to get their heads out of their V-8 obsessed posteriors and rediscover why 3 and 6 cylinder inline configurations are naturally smooth, ie, without the need for a balancing weight on the crankshaft. Most “real” diesel engines are inline-6 configurations. Most dieselheads know that most of the V-8 diesels produced were less than desirable engines from a standpoint of reliability and fuel efficiency.
If you want the engines to be particularly smooth on startup, then use compressed air to start them.
A diesel hybrid would probably get over 100 MPG in urban driving because a hybrid drive system would exploit the ability of a diesel to run most efficiently at one speed, rather than at a range of speeds. A diesel engine prefers operation in a narrow range of RPM much more than a gasoline engine; most “medium speed” diesel engines achieve their highest fuel efficiency somewhere between 1600 and 1800 RPM.
So start the diesel, bring it up to optimum speed, charge the batteries with whatever excess power is left over and shut it down when done meeting the temporary power demands.
I’m waiting, with cash in hand. They increased the torque, HP and mileage all at the same time with the new engine and transmission system.
VW is discovering the #1 issue to achieving the best fuel efficiency out of a diesel engine: keeping it in the optimum RPM range. To this end, the new Jetta has a six-speed tranny, and they have two different trannies that really differ only in the clutch system. The “automatic” tranny is really a auto variant of the powershift transmission you’d see in an ag tractor, which I’ve been advocating for years in a car.
VW’s engineers “get it.”
Detroit’s engineers still have their heads firmly lodged past their sphincters.
I don’t see why a 90 degree v8 would be any less smooth than a straight eight. The firing intervals are exactly the same. The firing order may be slightly different, but that’s all.
A straight eight should be smoother than a straight 6.
A v6 is a stupid design. It’s impossible to get an even firing interval from a v6, 90 degree or any other angle.
That is true, only when there is no mechanical device present. A turbo makes suction and pressure once the engine starts running.
There is a diesel hybrid in the works but batteries aren’t part of the plan. Instead it uses hydraulics to compress nitrogen and uses that for the initial acceleration from stop to about 20mph. It’s a great design for urban delivery type vehicles, buses etc. Ford is hopefully going to show an F-150 at the Detroit auto show in Jan with a production model for the 2009 model year although I think it may be with a gas powered engine. UPS has been testing the concept in their delivery vans.
It is a function on a four-stroke engine of how many degrees off TDC each piston/con-rod is during the four cycles.
Multiples of three cylinders are naturally balanced; multiples of four need balancing weights. Multiples of four can be made “as smooth” with the addition of the mass necessary, but if we’re trying to maximize mileage, then we want to cut out any weight possible.
In V configuration engines, most of them are over-square and have sub-optimal short piston strokes. It is better to have an under-square cylinder dimension and have long power strokes to maximize the heat/pressure extraction. The latest IH/Ford Powerstroke is a V-8 and under-square and it still sucks in fuel efficiency compared to I-6’s. The 6.0L Powerstroke was a V-8 and has cost Ford and Navistar (ie, IH) a ton of money, not to mention pissed off a lot of Ford customers.
“Real” diesels in moderate power levels (say, up to 500, perhaps 600HP) are inline sixes. In the higher power levels (say, up to 2000HP) you see V-12’s (another multiple of three).
V-8 diesels have a very poor history, regardless of the manufacturer. Cat’s 3208, the Cummins 555 and 903, the IH/Navistar 6.9 and 7.3, etc, etc. At best, they’re “acceptable.” At worst, they’re steaming dung piles. Inline eights in medium speed diesels are rare, mostly because the torque levels would require a massively thick crankshaft to withstand the torque along the length of the shaft. You do see some inline eights (and more) in the low-speed diesels, ie, max operating speed is in the range of 600 to 900 RPM.
The best diesels, the ones that are “classic” for their reliability, fuel efficiency, etc are inline sixes - the Cummins 855’s, the NH 7.5L, Perkins 354, Deere 466, Cummins B5.9, Cat 3406, etc. And then there’s the whole line of I-6 Deutz diesels. Properly cared for, I-6’s can run 10K hours and more before tear-down. I’ve seen Deere 466’s run for 12K+ hours with no new bearings, no in-frame, no nothing and still be tight. Only thing needed was gapping the valves and regular maint. I’ve never seen a V-8 diesel make it to 10K hours without at least an in-frame. I’ve seen a couple of V-8’s in farming applications here go for a little too long without the rod bearings being replaced ventilate the blocks (ie, punch a rod).
Perhaps the only V-8 diesel to have a loyal following is the 8V92 Detroit two-stroke. Most people don’t want to put up with the downsides of the Detroit two-stroke design any more, from either a noise or pollution perspective, so it isn’t something we’re going to see a lot of going forward.
I’ve run a bunch of diesels on this farm and the only V-8 diesel we have is the 7.3L Powerstroke in the pickup. When it gets run out, I’ll pull the engine completely and replace it with a Cummins B5.9. And I won’t miss a thing about the way you can’t get a feeler gauge into the engine compartment of a V-8 diesel. I’d like to pimp-slap the engineers in Detroit who insist on pushing out these stupid V-6/V-8 diesel designs when everyone who knows diesel engines well knows what they want: an inline 4, 5 or 6 cylinder engine.
Even in gasoline engines, the I-6 configuration results in outstanding engines. Perhaps the single best work pickup gasoline engine I know of is the 300 cu in. Ford I-6 industrial engine. Absolutely reliable, very fuel efficient, very good low-end torque. I’d take a 300 over any mid-sized V-8 in a pickup any day. Every day. But does Ford offer this engine in pickups? Noooooo. They’re peddling their V-8 obsessions.
Yes, I’ve seen a write-up on that hybrid design — hydraulic accumulators. A clever design.
My only reservation is this: every hydraulic system I’ve been around leaks. Every. Single. One.
I’m sure that a hydraulic system that doesn’t leak can be made. I’m not so sure it can be made by Detroit’s manufacturers.
Diesels are only good for about 30% improvement in mpg, and yes they run fine on veggie oils. The original diesel was made to use peanut oil as fuel. But magic bullet, I think not.
For efficiency, the best formula is larger displacement and fewer cylinders.
A 300 six banger is better than a 300 8 banger. A 300 4 banger is better than a 300 6 banger.
For smoothness, the opposite is true.
I don’t think I’m buying what you say about crankshafts in straight 8 motors. More main bearings equals less stiffness required in the crank. If the crank needs stiffening, just and a main or two. Of course more mains also equals more friction, greater expense, and less efficiency. The reason for the v8(instead of the straight 8) was to cut the mass of the crank in half, and the number of mains in half. Also the number of crank throws was cut in half. So the labor to construct the crankshaft was cut in half as well.
A 4 stroke engine has a 720 degree cycle(360x2). 720 is devided by 4 just as easily as it is by 3. A perfect firing interval 4 banger has the middle two pistons rising and falling together and the outside two pistons exactly opposite of the middle two. A 3 cylinder may have a slight edge over a 4 cylinder since none of it’s pistons are moving in unison, but a 3 cylinder is not going to have an edge over a straight 8 cylinder. And I would really doubt if a straight 6 would have an edge over a straight 8 either. I don’t believe a 6 banger does not need any counter weights on the crank.
I’m going to need more proof about your claim of straight 6 superiority.
I am a big fan of the ford 300-six. I also am a big fan of the old hudson hornet and it’s big six banger.
DUH! VW’s been selling TDI’s for a decade or damned close to it now... 50MPG less overall contamination than any hybrid and lower overall cost etc etc...
Hybrids, at least in their current form are a joke.
For efficiency, you want to maximize the expansion ratio on the power stroke. Going back to the ideal Carnot cycle, you want to extract as much energy as possible from the pressure/heat of the combustion gas as possible. You can do this with volume, yes, but to gain torque, you want as much mechanical advantage on the crank as possible, and that comes from longer strokes, not fatter pistons. So in general, yes, what you’re saying is true: fewer pistons with longer strokes to develop the expansion volume maximize efficiency in classic engine design.
The “more cylinders -> smoother” is the classic V-8 marketing hype from Detroit. Yes, you have more power strokes of smaller detonations, which is supposed to result in “smoother” power. Trouble is, guys like us farmers know this is Detroit marketing hype, because some of the smoothest power farmers used to have in tractors came from the old Deere “Johnny Popper” tractors with two huge cylinders and a massive flywheel. Pop-pop-miss-miss - hence the name “Johnny Popper.” Given their long, long strokes, they also had outstanding fuel efficiency and torque in their diesel versions in the days before turbocharging and I-6’s became commonplace. Deere went to I-6’s because there were simply limits to what you could get out of a two-banger, even of 505 cu in displacement at about 1100 RPM max throttle — namely, about 80HP — without going to massive crankshafts and such. Going to an I-6, higher RPM’s and turbos gave them more power in smaller displacements (eg, the original 404 cu in I-6 in the early Deere 20-series tractors) and the rest, as they say, was history.
The smoothness I’m talking about is mechanical vibration, not power strokes. Any engine with a small number of cylinders can deliver “smooth” power with a flywheel of sufficient size. I’m talking about the mechanical vibration(s) set up on an engine from end-to-end and the counter-balancing needed to even out the phase of piston mass being flung up/down throughout a four-stroke engine from end-to-end.
An inline six is in perfect primary and secondary balance and as such, requires no balance shaft (since I’m getting technical here, let’s clear up a misconception I might have started for you — these balancing weights aren’t actually part of the crank, they’re driven off the crank and balance the end-to-end vibrations of the engine - in my previously superficial explanation, I just lumped these in with the crank, because these balance shafts are usually gear-driven off the crank).
The I-6 engine is a mirror of itself from either end - ie, as the #6 cylinder is balanced by #1, #5 is balanced by #2, etc — so that there is no end-to-end rocking motion at either the primary frequency or second harmonic.
Inline 4’s, V-6’s and V-8’s usually have balance shafts in them to offset the first and/or second order end-to-end vibrations. With modern CAD/CAM and simulations, the primary/secondary end-to-end vibration issues are being reduced, to be certain, but we still see most medium-speed, medium-power diesels in inline-six configurations because it is simplest to deliver what the customer wants in an I-6 configuration.
As for the shaft stiffness: I don’t care how many bearings you have: all that increasing the number of bearings will do is eliminate shaft run-out during torsion. At some point, for a given amount of torque, as the shaft gets longer, you’re going to get some torsion flexing and distortion around the axis of rotation. Above a certain limit (which is defined by the application and the metallurgy of the steel involved), you simply need to go to a larger diameter shaft to reduce the torsion flex.
I’ll give you a completely different application example to illustrate this:
On our irrigation wells, there are motors at the top of the well. The pump is at the bottom of the well. The pump is driven by a steel shaft that runs the length of the water column, from the inside of the motor (the motor’s driveshaft is hollow) all the way down to the turbines on the pump. This can be hundreds of feet.
The driveshaft is supported every five feet by bearings inside the lubrication column.
For an application of say, 200HP, you can use a 1.25” drive shaft up to about 300 feet. More shaft length than that, and the torsion wind-up is such that you’d better be running 1.5” (or larger) shaft, or else you will eventually see the shaft snap due to work hardening as a result of startup and running torque loads on the shaft. If you have a higher HP motor, you have to reduce that length of 1.25” shaft you can run. As the length of the shaft goes up, or the HP to drive the pump goes up, you must increase the diameter of the driveline. All these drive shafts, regardless of their diameter, are supported every 5 feet by a bearing. They come in 1”, 1.25 and 1.5” shafts.
Mind you, that’s electric power, where there’s very little impulse loading on the shaft. The load is a “smooth” load (a turbine water pump) and the power source is a “smooth” application of power (a three phase induction motor).
Now kick in the issues of power impulses being transmitted to the crank and we quickly see the need for a larger, beefier crankshaft on a longer inline diesel engine.
Back to engines:
Want empirical evidence of the superiority of I-6’s in diesels? Go look at the “real diesel” market. (ie, not the Detroit pickup engine market). Look at engines for over-the-road trucks, heavy equipment, farm tractors, etc.
Pick a manufacturer - any one of them. Cummins, Detroit, Cat, Deere, Isuzu, Volvo, Deutz, Perkins, New Holland, etc. They’re all on the web. They all have their engine specs out there, and most of them will have fuel and power/torque curves out there too.
Count up the I-6’s in over-100 HP applications. Count up the number of V-8’s. Count up the number of I-8’s.
Then ponder why there are so few V-8 and I-8 diesels in “real” diesel applications — ie, applications where the customer demands longevity and won’t put up with marketing hype as a substitute for actual results on the bottom line. Big diesel customers demand reliability, performance and longevity and these customers keep records. Every diesel engine on this farm as a Hobbes hour meter on it. Every engine has a service record. I know how much I’m spending on every one of these things. I have three I-3’s (a welder and two hay balers), three I-4’s (genset, backhoe and swather), one V-8 (the F-350) and the rest (five more engines) are all I-6’s. All the highest HP engines are I-6’s.
Where customers keep records like this, the V-8 hype meets its doom. I-8’s really deliver no superior result and they have the downside of more size, mass, etc. The V-8’s that I rattled off above have long and widely known bad rep’s for their problems. The I-6’s are the engines that give the least trouble. The only reason for the I-4 is that there are simply a lot of under-100HP applications out there needing compact engines, and an I-4 is better than any V-6. An I-8 would give you nothing but a longer engine and primary/secondary vibration issues that you don’t have in an I-6. For the same HP range, you can just turn up the fuel screw, put on more turbo boost, use an intercooler, etc and get more out of an I-6 in most applications. The I-6 diesel market tops out around 700HP.
The only place you generally see I-8 diesels any more is in marine applications.
Getting back to cars, you see BMW, Mercedes, etc — using I-6’s in their EU-market high-HP, high-performance diesels. These guys know a thing or two about making smooth-running cars and their choice is the I-6. Not a V-8.
Once you reach a level of HP that you can’t get with a I-6, you generally see the big industrial engine manufacturers go up to a V-12. There are exceptions, of course, but the preponderance of industrial engines follow this trend. A v-12 has the same end-to-end vibration characteristics as the I-6’s do.
I have a ‘91 F-150 with the 300 in line 6. Great engine. The body will rust out before that engine gives out although I can’t vouch for your fuel mileage claim!
I have no idea what you’re talking. You obviously know more about the subject than I do. However I have owned a Dodge with a Cummins diesel and a Ford with the Powerstroke took both up Monarch Pass and the Powerstroke put the Cummins to shame. i wasn’t even close I had to pass my brothers Dodge going up the pass because I was losing RPMs staying behind him. He traded for a Powerstroke as soon as we got back. I don’t know the Physics of all this but I know which vehicle out performed the other.
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