How can they improve the fuel economy of the next generation Pruis?

If you modify two Prii, installing a VW Golf Diesel engine in one and a VW Golf (Otto-cycle) gasoline engine in the other, then I'd likely believe the difference you claim. I'd likely believe it even if you put in a Toyota Corolla or Matrix (Otto-cycle) gasoline engine.

But that Prius with the Golf or Corolla or Matrix gas engine won't be getting 50 mpg. Those Otto cycle engines are a serious handicap.

 

Exactly! That's why it is best to compare the same car with gas or Diesel. The Golf, being similar size to the Prius, makes an excellent like for like comparison showing Prius could gain 30% in mileage (65 mpg) with a 13% reduction in CO2 identical cars, one gas, one Diesel. That would the kind of upgrade we would hope to see in a 2015 Prius.

 

I think most of us wondered, and then concluded that diesel was not going to be a miracle jump in fuel economy if it replaced the Prius ICE. This follows simply from understanding that most of the diesel advantage is already built into a petrol hybrid --- albeit through different mechanisms.

Let's enumerate diesel's advantages:
1. 13.5% higher btu content/volume
2. High compression ratio
3. No air throttle, thus less of a partial-power efficiency problem
Disadvantages:
1. Weight
2. Cost
3. Reliability of the fuel injection system
4. Extra pollution devices

Now compare to a current gen Prius:
Advantages
1. Diesel advantage remains in terms of mpg
2. Partially duplicated with asymmetric valve timing Atkinson engine
3. Due to Prius ICE and HSD, better than diesel
Disadvantages
Adding diesel to the Prius brings along all the disadvantages of diesel.

 

No, not exactly. I was trying to point out your error in logic, but I give up. You are hopeless.

 

Keep in mind that weight has already been calculated in for the 30% gain in mpg as we see with Diesel/Gas Golf comparison. We don't really care about the "extra pollution" devices any more than we care about them (catalytic converter) on the gas vehicles, just results. In this case, 14% less CO2 emissions for the Diesel is a great result.

That leaves, reliability of fuel injection system, Diesel fuel injection system, especially the new common rail, have an excellent reliability record. Most gas and Diesel auto engines are fuel injected.

So we are left with 30% increase in mpg and 14% decrease in CO2 if Prius 2015 went Diesel.

 

Great, find a car with a choice between an Atkinson Cycle engine and a Diesel Cycle engine.

Or, using the Prius C or Auris Hybrid in Europe, compare a Otto Cycle car to a Atkinson Cycle car, THEN compare it to a Diesel Cycle Car.

Comparing Diesel to Otto tells us nothing, as no Prius has either engine. (Although the C is similar to the Yaris)

Compare Side-by-Side

 

You are nothing if not consistent. In your case wrt cars, always wrong.

Consumer Reports:

 

I thought it was more fair to compare the focus that as fuel saving technologies like di and turbocharging. The ford puts out less co2. Why would you compare a gasoline engine that gets the worst milage. The prius uses atkinson cycle, and cuts off the worst part/ low load with the hsd, and is more efficient than an otto engine in a golf. Why not add di and make the prius even more efficient with the energy in the fuel.
+1

Exactly.

 

And, the HPFP on recent VW TDI's is notoriously bad. Google for vw hpfp and vw hpfp autoblog, for example.

 

Eek!

 

Actually, the Prius ICE has VVT, offset crankshaft, EGR ... and HSD that keeps the ice running at close to maximum efficiency through the entire EPA drive cycle.

How do you think your Golf petrol ICE compares ? I'll bet it has none of the Prius ICE refinements, which is why the Golf diesel does so much better.

AG is correct here. If you find a pair of car twins that only differ by diesel and ICE, expect to find the petrol version has a primitive, crappy ICE. If the manufacturer puts in an advanced petrol ICE your will not find a diesel offering because the advantage is too small. This is doubly true for the Prius.

 

Mercedes, Audi and many others...sorry but auto Diesels are well proven products. Not sure why the jihadist attitude from some of the Prius purists but the facts are on the side of the Diesels as far as the odd complaints here from "emissions equipment" to the howler that Diesel cannot operate in hybrids.

Sounds like the prospect of a Diesel hybrid Prius is some kind of engine apostasy for the faithful.

Seems clear that a Diesel-hybrid would get the Prius the 2015 numbers it needs, 60+ mpg and 10%+ emissions improvement.

I wouldn't worry though as Toyota will likely not choose that path but more likely spend the same money on larger capacity but equal weight li-ion batteries to boost the Prius mpg.

But fact remains, the Diesel would get the job done for 2015 goals.

 

As you see, Diesel and gas the same repair record. VW's quality issues not really about the Diesel and we have lots of other auto Diesels with no issues so your own facts tend to contradict your opinions.

 

You said diesels are reliable; I picked the largest, most successful diesel auto manufacturer in the world and showed you domestic reliability data.

Not convinced ? Fine. Head over to Europe and buy yourself a diesel-hybrid. No Queue, I assure you.

 

You DO realize that a Diesel engine will differ from a Otto or Atkinson engine mostly by parts left out? An LP gas engine would also be no different, as would a E100 ethanol engine, or a wood gas engine. You show me an Otto Cycle engine with intake valves that close 30% up the intake stroke and I will admit you are right.

If you were Oldsmobile, there would be far too many parts in common between your gas and diesel engines..
Oldsmobile V8 engine - Wikipedia, the free encyclopedia

 

Is there a point the there somewhere?

Just because the two engine types use the same kinds of parts doesn't mean they are operated and managed the same way.

There is a reason Jihadist ProximalSuns didn't provide a link with that quote. It would reveal additional material that sinks his reason for posting it here. See the whole context at How an Atkinson Cycle Engine Works. (His snippet comes from page 3.)

 

I have to give PS an iota of credit. At least he looked up a tutorial on the Atkinson cycle, even if it was to just quote something out of context.

Maybe there is hope for him yet to get a clue. He should read Graham Davie's monograph, since it does a brilliant job of explaining why the Prius ICE in conjunction with an e-CVT already has most of a diesel engine's efficiency advantages, as well as other advantages the diesel lacks.

 

No the stats on auto Diesel's say that.

And your comparison showed the gas and Diesel cars had the same reliability rating which disproved your claim that auto Diesels have any more or less reliability issues than gasoline engines.

 

References ?

 

That Prius is an Otto cycle engine in construction as the Toyota engineer noted, achieving the low power efficiency of the Atkinson engine via electronically controlled variable valve timing...which can be applied to a Diesel engine if it too has the electric motor backup if it trades low end efficiency for lack of power.

You need to take lessons from your co-religionist.

"SOURCE!!!!"

Actually you provided it with the stats showing identical repair record for gas and Diesel versions of the same car.

Well done!