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Old 07-12-2009, 07:30 PM   #11 (permalink)
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Diesels have such a low redline b/c of weight and other factors, but weight plays a major role in keeping engines running as well. A diesel engine tuned properly could idle as low as 50-75 RPM (So can 225 slant six gassers, but you'll smear the bearings.) With a properly designed oil pump that could function at a speed that slow, you'd almost never notice the fuel consumption from idling a few minutes anyway. Not to mention that under 0 load, idling, the diesel runs so insanely far from stoich that it's uncounted anyway. They literally use *just* enough fuel to keep running, and they use very little to maintain 1000 RPM or so... imagine 50RPM.

NVH is the real problem here.. you'd have to seriously balance a diesel to keep it from wiggling your eyeballs out of your head at that low engine speed.

Theory behind keeping a diesel running: They like to be hot. Hot. HOT. Hotter - better for fuel combustion, less energy necessary to heat up the air enough to combust the fuel = more efficient. That's all. It's not that you can't stop and start them, it's just that they're less efficient the cooler the motor is. Same with gassers, but more pronounced and obvious. That said, once they heat up, they don't lose that heat very quickly. Remember, most diesels are basically cast iron bricks. Sure, you'll lose a bit of efficiency each time the engine starts, for a few seconds, but you're only using it to accelerate anyway. Under load, it will heat back up very quickly. I'm sure they could insulate the engine as well, making it keep heat longer.

I still like the 50-75 RPM idling idea, though.

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Old 07-12-2009, 07:35 PM   #12 (permalink)
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petro diesel is unthinkable at this point

Ideally hybrid diesels would open the door for biodiesel or svo

creating another truly green vehicle
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Old 07-12-2009, 07:39 PM   #13 (permalink)
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Quote:
Originally Posted by alohaspirit View Post
petro diesel is unthinkable at this point

Ideally hybrid diesels would open the door for biodiesel or svo

creating another truly green vehicle
Bad... Bad.

SVO and WVO are both not very good for people... well, the exhaust from them isn't.

You're burning glycerin and triglycerides, which only burn completely at very high temperatures... higher than your engine gets them. You end up expelling very dangerous gasses, and for the time you spend with WVO filtering and blahblahblah playing with it, it's the same time you'd spend making BioDiesel out of it, at only slightly more expense, but ending up with a much higher quality fuel.

AAMOF, it's technically illegal to use WVO or SVO in cars on the road... the fine is the same as using HHO (Home Heating Oil, not that other crap) for fuel, because it's not been mandated for on-road use by the EPA or NHTSA.
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Old 07-12-2009, 08:11 PM   #14 (permalink)
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wvo is far from perfect

but alot of that oil contain no sulphur,
so SO2 gas is not present when running on those oils

CO2 emissions are also reduced
Some by as much as 80-90% when compared to petrol diesel

not to mention the metric tons of waste oil not going into a landfill somewhere



The biodiesel process is very caustic
Id rather leave that process to people who can
dedicate the proper space to its production
(ie: not my townhouse)

as far as it being illegal i think we're ok
EOC isnt exactly legal either
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Old 07-12-2009, 09:06 PM   #15 (permalink)
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Quote:
Originally Posted by alohaspirit View Post
. . .
So why is there no diesel Toyota Prius yet?
. . .
The Prius uses an Atkinson cycle engine:
  • 8-to-1 compression stroke - this is accomplished by leaving the intake valve open during nearly half of the compression stroke. Part of the charge is pushed back into the intake manifold but be drawn in by another cylinder. This also reduces the amount of energy needed to turn over the engine and reduces internal, power robbing, friction. In contrast, the diesel requires a very strong motor to overcome the 20-to-1 compression stroke.
  • 13-to-1 expansion stroke - the exhaust stroke provides a ratio that allows a very high ratio of energy extraction. A typical diesel is 20-to-1 so the Prius brake specific fuel consumption approaches diesel with the advantage of a significant reduction in NO{x} production.
  • avoiding low-power, inefficient operation - the electric part of the Prius allows the engine to run at a higher power but very efficient range than needed at slow speeds and it stores the extra energy in the battery. Then the engine shuts down and the stored electrical energy powers the car without burning any more fuel. This advanced transmission is what is missing from diesel vehicles which at lower power settings has to always deal with engine friction losses, a lower BSFC than the Atkinson engine.
  • saving brake energy - another part of the Prius is saving braking energy as battery charge for use later. This is another part missing from diesel vehicles.
What it comes down to is the diesel doesn't offer enough to compensate for its short-comings: (1) higher NO{x} emissions, (2) inefficient at low power settings, (3) absence of regenerative braking, and (4) difficulty handling start-stop engine operation. They also tend to be heavy.

It is likely that as combustion temperatures are mastered, some future engine may support super-lean yet NO{x} safe systems. Perhaps some clever combination of cooled exhaust temperature and direct fuel injection but right now, these are discussed in university labs, not really in production vehicles ... except for the 2010 Prius.

At high power settings, the 1.8L Prius engine cools part of the exhaust and feeds it into the intake manifold. This reduces the peak combustion temperature so the Prius BSFC remains high even climbing a hill at high speed. The mixture remains lean but the engine doesn't burn out the catalytic converter or overload it with NO{x} products.

The Prius also uses fuel injection but not to direct combustion. Instead, the fuel is carefully metered and there is time to achieve an optimum fuel-air mix for combustion. In contrast, the diesel is always 'lean burn', it has to be, and that leads to NO{x} and other problems. It is the Atkinson cycle, the reduced fuel charge at low power settings that gives it the "on the road" advantage.

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Old 07-12-2009, 11:30 PM   #16 (permalink)
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Apples to Apples, the gasoline engine currently in use by the prius also doesn't have regenerative braking. The electric motor stored in the housing on the back of the gasser's block is what creates that function.

Diesels have higher NOx production, yes. But there are systems in place that can work with that.

Diesels aren't inefficient at low power, they're inefficient at low LOAD... same thing with gas engines. Diesels can be run as low power as you want them, provided the engine's dynamic displacement compares to the power being created. (This is where EGR comes into play.)

At high power settings, the 1.8 Liter Prius engine uses excess EGR flow to fill the combustion chambers, which decreases dynamic displacement, keeping BSFC higher by lowering cylinder temps.

Diesels don't have difficulty handling start/stop operation as much as people like to think. Talk to a farmer some day, who runs diesel tractors.

As far as being heavy, compare the power to weight ratio (and potential power to weight) of a diesel to a gasser... they're about the same. The diesel has the potential to produce the same horsepower at the same weight (meaning smaller displacement) than a gasser.
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Old 07-12-2009, 11:51 PM   #17 (permalink)
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Its easy to find a diesel electric hybrid.
Only catch is they are all on tracks.
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Quote:
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A few months ago I returned home just as my neighbor pulled into his driveway. It was cold (around freezing) with some rain and sleet, and he yells to me: You rode your bike? In this weather?!?

So the other day we both returned home at the same time again, only now the weather is warm, sunny, with no wind. And I yell to him: You took the car? In this weather?!?
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Old 07-12-2009, 11:55 PM   #18 (permalink)
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Oh, and
Before I put on the grill block and electric fan, my temp gauge never went above the 1/4 mark.

Now it stays around the 1/2 mark.
I shut the engine to avoid idling all the time, a 2 minute stop light is not long enough for it to budge. In other words, any loss of heat from being off is negligible.

I think there are no diesel hybrid cars yet because there are very few hybrids, and also very few diesels. Someone will come out with one eventually.
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Quote:
Originally Posted by Piwoslaw View Post
A few months ago I returned home just as my neighbor pulled into his driveway. It was cold (around freezing) with some rain and sleet, and he yells to me: You rode your bike? In this weather?!?

So the other day we both returned home at the same time again, only now the weather is warm, sunny, with no wind. And I yell to him: You took the car? In this weather?!?
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Old 07-12-2009, 11:58 PM   #19 (permalink)
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One word...

ok, i lied. heres a lot of them



70 miles per gallon, a 7-speed direct shift gearbox (DSG) with a twin-clutch, minor modifications to reduce aerodynamic drag, CO2 emissions of 89 g/km (lower than a Toyota Prius hybrid), and Tier 2 Bin 5 tailpipe emissions. And of course, the ability to run on biodiesel (waste cooking oil or even algae).

But it was too good to be true. VW contradicted its earlier statement in the March 27 issue of Auto, Motor und Sport and said that the Golf turbo-diesel hybrid would be too expensive, so they're not going to make it. (A diesel that is)



R.I.P. Golf Turbo-Diesel Hybrid. We hardly knew ya.

Revealed: Volkswagen’s 69.9-MPG Diesel Hybrid | Autopia | Wired.com

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Old 07-13-2009, 12:11 AM   #20 (permalink)
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Pet Peeve #87: Idle damn diesels all the time.

They can start and stop just as well as anything. There is no reason why they can't.

Stupid *holes with diesel vehicles tend to let them idle for hours on end. Why? Damn thing has a starter right???

Only exception I can see for that is when it's -40F out. Even then, shut 'er off and restart in an hour or so for a while.

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