why no prius diesel hybrid?!

[thepolarcrew]

"I was commenting on earlier posts that seemed to make mountains out of molehills. Agrandizing technical issues as unsurmountable impediments is pessimistic, IMO."

DaveS, you aren't alone when it comes to these thoughts. It seems like the site has a one sided approach to almost all issues. The enviroment, Ford, GM, price of fuel, etc. Nothing wrong with having pride in what you believe in.

Not trying to be a troll, rant or spew diatribe is almost imossible if you dissagree. You have people whose cars are being shot. Could it possibly have something to do with how you act or something you say. I am not condoning this sort of behavior, but when you berate and belittle people and try to cram your ideas down every-ones throat it seems to happen in the real world.

We need to face the facts, this is kill our way of life. We need use the best information, technology and resources available to date and take action NOW!

[mingoglia]

I'm not even going to touch on the argument that a comparable sized gas engine has more torque than the same displacement diesel engine. That's just false and ridiculous. Now some may be tuned for less torque by optimizing them for more horsepower.

Remember, torque is power. Horsepower isn't really measured. Horsepower is a calculation based on torque. This is why a faster revving motor will naturally have more horsepower. Horsepower and torque are equal at 5252 RPM (assuming the engine spins that fast). Because of this, a relatively low RPM diesel engine is at a disadvantage.

As was said by another poster, a system in which the diesel engine just charges batteries or provides power generation for an electric motor could work. In a hybrid system like the Prius I don't see the diesel as being an alternative. First off, the Prius requires a engine that can vary RPM quickly. The diesel engine doesn't do this. In fact a diesel is very efficient at lower RPM's, but when run at higher RPM's the fuel economy drops quickly. For example, I can pull my 12,000lb toy hauler with my '01 Dodge Cummins dually and get 14mpg. I've actually gone on a road trip WITHOUT my trailer and gotten 12mpg. When I got 12mpg, the engine was running about 3,000 RPM most of the way because I was driving fast. Yeah, part of that was wind resistance, but the point is the percentage of mpg drop on my diesel truck was far greater than it would have been if I was driving that fast with the V10 version of my truck.

The second reason why I don't believe the diesel is a good fit for a "Prius type" vehicle is diesel engines need to stay warm to be efficient. They're a compression engine and need this heat to run. Having them turn on and off at the drop of a dime isn't a good fit.... particularly in colder climates. Not only will restarting not be very smooth (a result from them being cold and the higher compression), but may potentially lead to problems such as cylinder wash where unburned fuel is forced past the piston rings and into the oil. This is a common problem with people that let their diesels idle and the reason why over the road truckers typically have their exhaust brake rigged to be able to be partially closed while idling and/or they high idle their trucks. Keeping their post turbo exhaust gas temperature above 300 degrees while idling prevents this.... This is the reason why many owners manuals for diesel powered vehicles have a idle limit of usually around 10 mins...

[Flying White Dutchman]

Originally Posted by DaveSheremata

As for CO2 emissions, I think combining PZEV with blu tech or other filtering technolgy can only be a good thing. What's more is that a diesel is a simpler design than gas engine, having a much simpler electic component.
Cheers!
Dave

the modern diesel your talking about is a commen rail variable turbo charged injected diesel and there is a lot more electronics going on then a simple todays petrol car engine.

[Dozzer]

Deisel maybe more efficient than petrol... but here are some facts about oil production...

For every 100 barrels of oil (North Sea crude) you get about 47 barrels of petroleum (gasoline) and only 28 barrels of deisel... the rest is jet fuel, heating oil etc.

In order of most profit for the oil producer:

Jet fuel (kerosene derivetives)
deisel
heating oil
petroleum (gasoline)

Apparently the company who runs North Sea Oil production here in the UK aim for a per barrel profit of 100USD
It costs around 15USD to get the barrel out of the ground.

The price of deisel will go up faster than gasoline as it's used for a lot more than just driving a family car about.

Doz

[SZ92]

Originally Posted by kevinwhite

(2) Not true - currently there are no diesel cars sold in CA because they don't meet the emission standards. There will be MY 2009 cars sold but even then they are dirtier than the best gasoline cars, and there is controversy over the impact of the very fine particulates that they do produce but will be allowed.

(4) Not true - in general a diesel of the same technology level will generate less power and torque than an equivalent gasoline engine:

For example the figures for the 2006 VW Jetta are:

Gasoline(turbo charged): 200HP @ 5500RPM, 207ft-lb @ 1800RPM
Diesel (turbo-charged): 100HP @ 4000RPM, 177ft-lb @ 1800RPM

A gasoline engine can run faster and so its power peak will be at a higher speed. In part this is because the rotating parts of a diesel engine have to be made more stronger and heavier in a diesel engine. Often the peak torque of a diesel will be at a lower speed than a gasoline engine - this may give the impression of more torque as often a gasoline engine will tend to stall at low RPM (my BMW 328 was an example of this although a fine engine in all other respects).

Although I would like for someone to produce a diesel hybrid other items to consider are that diesel costs 10-20% more (in the US) and that the refinery can get up to twice as much gasoline from crude oil compared to diesel.

kevin

Wow you dont know anything about cars do you. My 2008 Mercedes Sprinter has a 3.0 Liter 6 Cylinder diesel turbo charged and it puts out 270-285 lbs of torque whereas my Chevy Express 4.8 Liter 300 HP only put out 250 at the most so your statement about diesels is completely wrong

[kevinwhite]

Originally Posted by SZ92

Wow you dont know anything about cars do you. My 2008 Mercedes Sprinter has a 3.0 Liter 6 Cylinder diesel turbo charged and it puts out 270-285 lbs of torque whereas my Chevy Express 4.8 Liter 300 HP only put out 250 at the most so your statement about diesels is completely wrong

I don't believe you noticed my phrase "for the same technology level".

Yes - you can make a turbo-diesel have more torque than a naturally aspirated gasoline engine but if you put the same level of technology into a gasoline engine you could get even more torque than the diesel.

Now some of the recent developments by companies such as BMW and VW are doing incredible things with diesel engines and less into very high-power gasoline engines but in general a gasoline engine can give you more torque and much more power than an equivalent diesel engine for less cost.

It boils down to the fact that it is difficult to atomize the fuel well enough in a diesel engine to run it as rich as a gasoline engine - a diesel engine will smoke excessively before it gets near to stoichiometric ratio, whereas a gasoline engine can even run slightly rich. So you can get more fuel into the cylinder and thus more torque, combine that with the ability to run much faster and you get much more power.

Now a turbo-charger can help pack in the air into the cyclinder and let you put in more fuel to get more torque but it is only recently that the high inlet pressure ratios are becoming practical for everyday use. At these high pressures diesel engines don't suffer from pre-ignition that plagues turbo-charged gasoline engines so at some point they get the advantage.

kevin

[RonH]

Originally Posted by mingoglia

I

Remember, torque is power. Horsepower isn't really measured. Horsepower is a calculation based on torque. This is why a faster revving motor will naturally have more horsepower. Horsepower and torque are equal at 5252 RPM (assuming the engine spins that fast). Because of this, a relatively low RPM diesel engine is at a disadvantage.

Well I remember from my freshman physics that torque is force x lever arm length. Work is down by a torque moving the lever through an angle, thus power is torque times rpm, give or take a conversion factor or two. To say that hp = torque @ some rpm is just a coincidence of the units chosen and engine capacity and has no real meaning. Model airplane engines rev at 10K's rpms. I'm too lazy to surf the SAE site, but I'd guess hp measurement is done by measuring force via a strain gauge on the output shaft corrected to some standard diameter and multiplied by the rotation rate.

[robbyr2]

I think thinking outside the box is good, whether its a gasoline-electric hybrid, diesel-electric hybrid, electric only, electric with gasoline or diesel generator, natural gas only, hydrogen, or whatever. As long as they're clean, efficient and affordable.

Then we all just need to coexist. Sure we can have our Windows/Mac/Linux discussions, but... different strokes for different people is a good thing!

[qbee42]

work = force * distance
power = work / time
torque is a measurement of twisting force.

It doesn't matter how you measure the force, work, or power, as long as the methods are accurate.

Car people love to argue about which is more important: torque or power. Since the two are interrelated, it may seem like a silly discussion. In some ways the discussion is silly, in others it's not. Here are the facts:

1) At any given RPM, torque and power are equivalent.

2) For a given torque, if you double the RPMs, you double the power.

3) For a given RPM, if you double the torque, you double the power.

(Please don't beat me up for playing fast and loose with the term equivalent. I'm trying to make a point for the non-physicists among us.)

The above three facts are simply a restatement of the equations at the top of the page. From either, it's easy to see that there are two ways to get more power out of an engine: 1) make it bigger, so you get more torque, or 2) make it faster, so you get more RPMs.

Bigger engines are larger and weigh more, which is a disadvantage in size and weight constrained applications. High speed engines wear faster, present more frictional losses, require complex valving, and require more gearing to match the engine to the load. It's a trade off.

The whole torque vs. power thing comes down to gearing. Any engine can be geared to produce massive amounts of torque, but gears consume energy, take up space, add weight, and increase cost. This is why bicycles use a very simple and efficient gearing system.

Since we are talking about bicycles, let's look at bicycle gearing and what it does to the rider. Our human rider is able to generate a certain maximum force on the pedals. This is the maximum torque of the rider (since the pedal arms are fixed, and torque = force * distance). Our rider is also able to pedal at different speeds. These are his RPMs. Our rider can generate more power by pressing harder or pedaling faster.

Let's look at the first case: pressing harder. Going up a hill, our rider needs more power. He presses harder on the pedals. The hill gets steeper, so our rider presses even harder. As the hill steepens, he stands and puts all of his weight on the pedals. The hill steepens more, the bicycle slows and falls over. What went wrong? The rider ran out of torque. He was pressing as hard as he could, but it wasn't enough to keep the bicycle moving.

Now let's try the same hill using gears. As the hill steepens, the rider presses harder. Eventually the rider says "I need to shift", and drops to a lower gear. His feet spin faster, but he doesn't have to press as hard.

In both cases the rider increases his power output as he goes up the hill. In the first case it is done by increasing only the torque (force). In the second, he increases the RPMs. In practice you usually do both.

We already looked at the limiting case with torque, when the rider could press no harder. How about the limiting case with speed (RPMs). In this case let us look at the example of riding a bicycle down a hill. Our rider is heading downhill, and wants to ride as fast as possible. As he heads down the hill, the resistance of the pedals becomes lighter, and our rider begins to pedal faster. Eventually the pedalling speed becomes uncomfortably fast, so the rider shifts to a higer gear. This reduces the pedaling speed. Our rider presses harder and speeds up some more. Once again the pedaling speed becomes too fast, and the rider shifts again. Our hill is long and steep. Eventually the rider runs out of gears. He pedals as fast as he can, but can't make the bicycle go any faster. The pedals turn easily, but he just can't make his feet go any faster. He is pretty sure if he just had more gears he could go faster. Why couldn't he go any faster? The rider had reached his maximum speed or RPMs.

Just like an engine, our rider can develop varying amounts of torque and power at differnt speeds (RPMs). At the low end of the scale, our rider can develop maximum torque (force) at zero RPM, simply by standing on the pedal. At this point he is developing zero power, since there is no movement (power = work/time, work = force*distance, and distance=0), but maximum torque.

On the other end of the scale, our rider can pedal so fast that no force is left for moving the bicycle. In other words, it takes all of the rider's power to spin his feet, as would happen if you put him on an exercise bicycle with no drag and said "pedal as fast as you can". Once again our rider is delivering zero power. In this case the RPMs are maximum, but the force is zero.

In between these two limiting cases are the torque and power curves, which show torque and power as a function of speed. In the case of our human rider, as well as with many electric motors, the torque will be highest at zero RPM and will fall off with speed, while power will curve up to a maximum somewhere in the middle RPM range and curve back down at higher speeds, evtually reaching zero at the maximum unloaded speed. Internal combustion engines require some speed before they reach maximum torque, but that point will still be below the maximum horsepower point.

What does all this mean? It means that torque and horsepower are interrelated. All torque or all speed results in zero power. Maximum power is somewhere in between, but you need enough torque to accerate up to the maximum power point. Gearing helps with this, but also consumes power through frictional losses.

The Prius avoids most of the normal mechanical gearing by using the electric motors to provide virtual electronic gearing. The virtual gearing provides for a nearly infinite number of gears. While the virtual gearing avoids most of the normal frictional losses of mechanical gears, it does introduce electrical losses.

Tom

[skruse]

Locomotives are a good example, however, we need cleaner (low sulfur) diesel fuel. Diesel fuel is a carcinogen (not that NOx from gasoline is inert). Locomotives use diesel to support an electric motor and are actually "electric" locomotives. The current Prius uses an ICE supplemented by an electric motor.