Diesel vs. Hybrid

[tripp]

Madler,

The Atkinson cycle does help somewhat, so the Prius does better than a typical 1.5L ICE. It may not approach a diesel, but it does pretty well. Driving between Denver and Omaha (and back) I got about 47.8 MPG ( 49.1 out/ 46.5 back) @ 75 mph. I'm not sure what a comparable diesel would have gotten.

[bwilson4web]

<div class='quotetop'>QUOTE(finman @ Aug 31 2007, 09:50 AM) [snapback]504877[/snapback]</div>

. . .
All cars are subject to the laws of physics and air resistance, meaning the faster you go, the more energy is need to move you...even a diesel can't escape that. I want to say the few that have done 100+MPH in the Prius reported 25 MPG. I've no idea if a diesel will do that. Some cars are designed to be for the higher-speed highways, some are designed to be a bit more all-around performers.
. . .[/b]

Bob Wilson

[micheal]

<div class='quotetop'>QUOTE(madler @ Aug 31 2007, 11:52 AM) [snapback]504878[/snapback]</div>

You might dislike the statement, but it's true. Producing and consuming electricity at constant speed on flat ground can only reduce efficiency, and therefore increase emissions. You will always lose energy when converting energy from one form to another, and then lose some more energy when you convert it back again.

The only benefit a hybrid has in those conditions is that the ICE is smaller than in most other cars. What you get from the hybrid is when you want to accelerate to pass, for example, you get the equivalent power of a larger engine from the electric motor augmentation instead. What the hybrid allows is good acceleration without having to pay for the inefficiency of an engine sized to the highest required acceleration when you are not actually accelerating.

A diesel with the same power as the gas ICE in the Prius pushing a car with the same aerodynamic drag as the Prius will have much better efficiency than the Prius at constant high speed on level ground.

Where the hybrid really shines against the non-hybrid diesel is when you are decelerating (including stopping) and accelerating a lot. I.e. normal street driving. Then you get all the advantages mentioned of running the ICE at more efficient conditions most of the time, recovering energy from the brakes, shutting down the ICE when it's not needed, and using the electric motor to augment acceleration.

Generating electricity and converting back to mechanical energy is an inefficiency that you invest, to get more dividends back in stop and go or accelerating and decelerating traffic. At constant speed on level ground, you get back no dividends.
[/b]

Sounds well and good, but why does the Prius rate 18% higher on the highway mpg than a Jetta TDI? This is from new EPA numbers for 2006 (couldn't find the TDI for 07 or 08 yet). Your argument in decreased efficiency and less hybrid improvement at higher speeds is true to some degree because the hybrid isn't as efficient on the highway. However, that doesn't mean it isn't more efficient than practically any other comparable vehicle (even a diesel). Perhaps this changes in favor of the diesels at extremely high speeds (like 90mph), but I think the point holds true even at typical interstate speeds (70-80mph).

As far as your assertion of very limited improvement, I have seen several previous posts that cited very little power is needed to maintain highway speeds once one reaches it. I want to say 20hp or less (but don't quote me). Besides, there are a lot of features of say the Prius that allows for the reduced size, more fuel-efficient, Atkinson cycle ICE. The augment from the battery is no small benefit, since the majority of the time on the highway our time is spent just maintaining speed, thereby allowing for an engine that is designed to meet say our needs 80% of the time rather than an engine designed to meet our needs 20% of the time.

BTW: It is getting dated now, but it is an apples to apples comparison of hybrids (Prius and HCH) to other frugal cars (Jetta TDI and Echo). HCH barely came out on ahead of the Prius with the TDI in 3rd. Includes both city and highway mileage. All in all, no benefit to the diesel above the hybrid and the Prius had better highway than the TDI (Doesn't say by how much). 3rd Page of Article

[patsparks]

Because EPA figures do not include much travel at 100mph.
Even with the 70mph speed limit on the UK motorways it isn't at all uncommon to be driving down the motorway at 80mph and have another car pass you like you're standing still.

At the end of the day you are preaching to the converted, it's the European diesel driver you need to convince, or rather Toyota does.
Can you blame Europeans for sticking with what they know? The benefit to risk ratio for a switch to hybrid is much worse for them than it was for a person who was already driving a petrol powered car.
I think the big advantage is quiet engine and no stink on start up plus slightly better economy.

[Stivo]

I think some of you miss some important facts/ideas:
1) The hybrid buzz in europe is way smaller than in america. Most cars here are hatchbacks or something in the size of a toyota yaris. They use much less gasoline than typical cars in the USA. Since the difference between a hybrid and a normal car isnt that big, hybrids get less attention. Check out toyota.ch to see this.
2) The prius does worse than a diesel car at 170km/h (~105mph, the maximum possible speed for it). I have read about that a lot in german forums, so trust me on this one. But since this speed is only allowed on some german speedways, I usually think of this as irrelevant.
3) There are just 4 hybrids for sale here: Prius, Lexus GS450h, Lexus RX400h (both Lexus of course very expensive) and the Honda Civic hybrid. You dont hear a lot about those, most people dont even know they exist.
4) The time of the prius is coming here, later than in the USA for before mentioned reasons, but I keep seeing them on the streets more and more.

Since switzerland does not have a single car brand I cant say anything about (the idea for the smart at least is from a swiss guy, the founder of swatch clocks) patriotic arguments to buy a car.
For some impressions of cars and their gas usage, take a look at this site:
http://www.spritmonitor.de/en/
Keep in mind that this site is used mostly by german people.

Also, the prius is quite expensive. In switzerland we pay 38950 Swiss francs for the basic version, which comes down to: 32 393.5465 Dollars, in germany even 33 939.6911 Dollars. (but could be because of low swiss franc right now)
The avensis, a very common model here, is cheaper than that and is roomier in the hatchback version.

[madler]

<div class='quotetop'>QUOTE(micheal @ Aug 31 2007, 10:46 PM) [snapback]505320[/snapback]</div>

Sounds well and good, but why does the Prius rate 18% higher on the highway mpg than a Jetta TDI?[/b]

Because the Prius has a smaller internal combustion motor, which is doing all the work at the relevant conditions. The Prius has a 76 hp ICE, the TDI is 100 hp. The bigger the engine, the more inefficient it is at a given lower power output.

You apparently missed what I said in my post -- I was making a comparison between hypothetical vehicles of equal power and drag. Diesel ICEs are more efficient than gas ICEs, and the Prius is relying entirely on its ICE at constant speed on level ground.

Also you have to be careful with mpg comparisons, since diesel fuel is denser than gasoline. It would be more fair to compare km per kg fuel or km per kg Carbon.

The augment from the battery is no small benefit, since the majority of the time on the highway our time is spent just maintaining speed, thereby allowing for an engine that is designed to meet say our needs 80% of the time rather than an engine designed to meet our needs 20% of the time.[/b]

Exactly. That is the main benefit of a hybrid. You have a smaller engine for the same overall performance experience. That's what I said in my post.

Assuming you want to maintain the benefits of the very high energy density of hydrocarbon fuels, the ideal setup would be a hybrid diesel, with measures to reduce non-CO2, non-H2O emissions, including low-sulphur fuel. That would be a good bit more efficient (I'm guessing ~20%) than our gas hybrids.

[madler]

<div class='quotetop'>QUOTE(tripp @ Aug 31 2007, 09:55 AM) [snapback]504968[/snapback]</div>

The Atkinson cycle does help somewhat, so the Prius does better than a typical 1.5L ICE. It may not approach a diesel, but it does pretty well.[/b]

Yes, that helps quite a bit. I've heard numbers like 10% over an Otto. Still short of a diesel.

By the way, I saw an article where Toyota stated it would not pursue a diesel hybrid. They said that while the emissions would be lower, there would not be a market for it. The rationale was that the consumer wouldn't want to pay a premium for both the hybrid technology and the more expensive fuel.

Of course, all of Toyota's competitors were saying the same thing about hybrids in the first place, that no one would want to pay that premium. Look who's laughing now.

[ken1784]

Just FYI...
Toyota European Hybrid Sales Accelerate Past 100,000 unit
http://www.toyota-media.com/ems_corp_v1_gl...m318-613353.pdf
"Toyota Motor Europe (TME) has announced that cumulative European sales of Toyota and Lexus hybrid vehicles have topped the 100,000 mark. Since hybrids were first launched in Europe in 2000, a total of 101,235 vehicles have been sold as of 31 July, 2007. This achievement highlights a rapid acceleration in the uptake of hybrid vehicles, with more than 50% of Toyota’s cumulative European sales achieved in the last 13 months."

The world wide sales is 1 million, so the european sales is about 10% of all Toyota/Lexus hybrids.

Ken@Japan

[gazz]

In the UK for the first time for a long time, diesel is more expensive than petrol, only about 2.5% but it eats into the diesel mpg advantage. If the demand for diesel keeps going up I wounder what will happen to the price.

[micheal]

<div class='quotetop'>QUOTE(madler @ Sep 1 2007, 01:40 PM) [snapback]505447[/snapback]</div>

Because the Prius has a smaller internal combustion motor, which is doing all the work at the relevant conditions. The Prius has a 76 hp ICE, the TDI is 100 hp. The bigger the engine, the more inefficient it is at a given lower power output.

You apparently missed what I said in my post -- I was making a comparison between hypothetical vehicles of equal power and drag. Diesel ICEs are more efficient than gas ICEs, and the Prius is relying entirely on its ICE at constant speed on level ground.


I see what you were trying to say with a a gas ICE vs diesel ICE. However, it doesn't make much sense to do that comparison. No one is comparing just an gas ICE to a diesel ICE and saying that the Prius ICE in itself is better (or more efficient) than a diesel ICE. That is because the Prius power is from Hybrid Synergy Drive not just a gas ICE.


Also you have to be careful with mpg comparisons, since diesel fuel is denser than gasoline. It would be more fair to compare km per kg fuel or km per kg Carbon.
Exactly. That is the main benefit of a hybrid. You have a smaller engine for the same overall performance experience. That's what I said in my post.
[/b]

I have never read anything that says that diesel fuel is cleaner than gas inherently. Some things are better, some are worse (particulates and NOx). Plus, since hybrids like th Prius are something around 90% cleaner than a conventional gas vehicle, the TDIs are worse than hybrids in emissions. The EPA scores show an overall pollution score of 1 and 6.4 tons a year in greenhouse emissions for the TDI. This compares to an 8-9.5 pollution score (higher is better) and only 4.0 tons a year in greenhouse emissions for the Prius. The EPA site doesn't say if this is with ULSD or not, but if you have links to show that diesels are cleaner overall in emissions, than feel free to share.

The smaller engine allows for better overall performance in terms of mpg and 0-60 times. This is based on typical US highway speeds according to the EPA estimates (18% better). (the 0-60 times are also in favor of the Prius over the Jetta TDI). The US does not have roads where one can drive 100mph legally and I don' t know of anyone that has done it for more than a short amount of time. I haven't seen comparative tests at this speed so I don't know how it will pan out. The reviews that do highway and interstate comparisons (probably speeds from 65-75mph) show the Prius coming out ahead (as mentioned in the article I linked earlier).

None of this is to say that diesels are horrible or bad. Improving fuel economy is a goal that all cars should try to do and just one technology won't do the trick. I have heard that a diesel hybrid would be hard because diesels would have a hard time with the constant stopping and starting (at least in the city). If that isn't true then I agree that a diesel hybrid would be a great solution. Diesel fuel can be hard to find and more expensive in some areas, so that could be a knock against it.