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Diesel Hybrid?


AEB-UK
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Why do hybrid vehicles link petrol engines with electric motors?

MPG in diesel engined cars is usually better than in the equivalent petrol engined model, so linking the two might seem an obvious choice.

It should produce actual mpg figures close to those Toyota claim our cars can do :-p

There must be a practical reason why diesels aren't used - anyone from Toyota care to explain please?

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Pretty sure the Citroen DS5 hybrid is a diesel. 

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We don't know whether Toyota reads these forums, and they certainly won't respond via these forums.

Diesel is only a major seller in Europe - the rest of the world centres on petrol as regards cars. As the Prius is produced for the the American, European and Asia markets, it presumably made sense for Toyota to concentrate on petrol hybrids, as that is where the majority of sales lie.

If Toyota were to produce diesel hybrids, these would obviously have their own official consumption figures - and the difference between the official consumption figures and real world consumption would be similar to that of petrol hybrids.

PSA produce diesel hybrids, and when they were rescued by the French Government and the Chinese manufacturer Dongfeng in early 2014, as part of the recuce plan, they culled some of the diesel hybrids as they weren't profitable.

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4 hours ago, AEB-UK said:

It should produce actual mpg figures close to those Toyota claim our cars can do :-p

Our cars can produce the mpg that Toyota claim - under the conditions of the EU tests which are the only figures that they are legally allowed to publish in brochures etc. If you could drive in a way/environment that exactly matched the EU test you would get the same figures.

Given the recent furore over the real world NOx emissions of diesels I would have thought it obvious - hybrids are an attempt to be cleaner as well as more fuel efficient & diesels aren't clean (particulates & NOx).

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Diesels have a very short power band, so the gearing might not work for the Prius full hybrid transmission. 

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I think the writing`s been on the wall for diesels for a long time......it`s just been covered up by falsified tests and software...and part of the pleasure of driving a petrol hybrid, is hardly being able to tell if the ice engine is running or hear when it starts...a diesel hybrid would never be as good on NVH

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There is potential for it to work - One of the biggest advantages of diesel is it can be run at lower RPM and deliver higher torque than an equivalent petrol engine; With the CVT-like gearing of HSD, it would be possible to tune the engine to operate solely in its most optimum RPM and even optimise the clatter to a minimum. You wouldn't get that horrible red-line sound you get in current HSD's when a lot of load is put on the engine!

However, the biggest problem is heat, or lack of.

All engines have terrible efficiency when they are cold and are also at their most polluting.

Now, Petrol engines generate a LOT of waste heat, even when idling - Normally this is a bad thing, but in hybrids it helps get the engine up to operating efficiency faster and helps reduce the impact of the on-off use cycle.

Diesel engines generate far less waste heat - I think the difference in exhaust temperature is something like 200-300 degrees cooler than a petrol engine?, but this means they take absolutely ages to warm up; An idling diesel engine will take so long to reach operating temperature you'd probably get to where you're going before it happened.

Diesel engines need to be run; They like being under load - They get the heat they want, it helps drive the turbo-charger, emissions are better as more stuff is burned off and there is less oxygen to form NOx; Conversely, they tend to be very inefficient when lightly run - They lose heat and there isn't enough pressure to really get the turbo-charger really going. Worse still, particulate and NOx production tends to be worst when they are lightly run as the temps aren't high enough to burn the soot off and there is so much free oxygen that NOx formation is at its highest. All in all, the partial-load cycle that you get in hybrids just wouldn't suit them.

Maybe if you put a really really small one in that was run fairly hard, but then you may as well use it as a range extender rather than a proper hybrid unit.

 

 

I doubt it will be a thing tho' - With all the legislation pressure at this point it's just not worth the R&D - IC engines in general are being forced out; There's a lot of pressure to remove diesel engines now, and it'll be petrol's turn next.

Electric motors are better in every regard (Well, aside from the lack of a nice sound) - Their only weakness is energy storage; Batteries are still a good order of magnitude worse - even with the relative inefficiency of ICE they still provide far greater range - but once they crack that governments are going to force everyone to go electric and ICE's will have the same fate as horses as far as their use in transport goes.


 

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" governments are going to force everyone to go electric and ICE's will have the same fate as horses as far as their use in transport goes "

 

I venture to add that this isn't llikely to happen until the government has found a way to tax electric propulsion to the extent that they tax fossil fuels.

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1 hour ago, Cyker said:

...Electric motors are better in every regard (Well, aside from the lack of a nice sound)...

Some Lexus F-Sport models generate an artificial engine noise through the audio speakers to make it sound like it's changing gear! (unless you turn it off)
 

 

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1 hour ago, AEB-UK said:

" governments are going to force everyone to go electric and ICE's will have the same fate as horses as far as their use in transport goes "


 

I venture to add that this isn't llikely to happen until the government has found a way to tax electric propulsion to the extent that they tax fossil fuels.

Oh don't worry, I'm sure that won't be a problem for them! I'd wager they'll either just charge a flat fee similar to what they're moving to now, but have it affect all cars, or if they're feeling particularly arsy they could base it on the kWh of the Battery or the peak kW delivery of the electric motor(s).

I just hope they don't figure out a way of taxing 'automotive electricity' vs 'heating electricity'!!!!
 

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Yeah, I saw that; I wonder if they're going to give all their citizens driveways too so they can charge them :lol:
 

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Another factor which is sometimes overlooked is the fact that petrol electric hybrids tend to use an Atkinson cycle petrol engine rather than a conventional Otto cycle petrol engine. The Atkinson cycle engine has almost diesel-like economy, but has the disadvantages  of poor acceleration and torque, hence the reason why Atkinson engines aren't normally used conventionally in cars.

Combine an Atkinson cycle petrol engine with an electric motor however and the two tend compliment one another,  the deficiencies of one are compensated for by positive characteristics of the other in most situations. 

As a diesel engine is not actually much more fuel-efficient than an Atkinson cycle petrol engine there wouldn't be much benefit in going down the diesel route for hybrids, and there would be the added weight and emissions problems of the diesel to contend with too. 

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I dunno, I think the Atkinson (Well, really it's a Miller cycle without a turbo but now I'm just being pedantic :biggrin: ) thing is just a Toyota thing; I'm not aware of it being used in other hybrids.

But it isn't more fuel efficient than a diesel engine by a long shot - It is in a lab, but engines have to pull load in real life and that's where it falls short; The lack of torque means it can't push the car along at high speed and low RPM, which means the engine has to spin faster which means its noisier and uses more fuel and is why the HSD now has a reputation for being worse on the motorway.

They didn't fix this until the Mk3 Prius where they started using the 1.8, and it's noticeably nicer on fast long roads as the engine can put out enough baseline torque to run the car without having to trade RPM for torque like the old 1.5 did. (Although we get those complaints from the 1.5-equipped Yaris HSD instead now :laugh:)

I do wonder how much mpg the Atkinson cycle gets you; I reckon the 1.0VVTi could replace the 1.5 in the Yaris HSD with some ECU tweaks and get better mpg for extra-urban cycles.



 

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14 minutes ago, Cyker said:

I dunno, I think the Atkinson (Well, really it's a Miller cycle without a turbo but now I'm just being pedantic :biggrin: ) thing is just a Toyota thing; I'm not aware of it being used in other hybrids.

Chrysler, Ford, Honda, Hyundai/Kia, Infiniti,  Mercedes

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Are these hybrids you can buy here??? I can't believe I could have missed that many... :eek:
 

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Not forgetting that DERV's run at lower temperatures - would never get enough heat to heat the cabin most of the time in the UK or colder climates. I can't see a DERV hybrid being viable, for the reasons mentioned by others above. Although I think the Volvo plug in hybrid is a DERV?

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14 minutes ago, alan333 said:

Citroen DS5 diesel hybrid available right enough...

http://www.autoexpress.co.uk/citroen/ds5/62651/citroen-ds5-hybrid4

I've only looked at your link and not looked into it further but it sounds like its a Parallel Hybrid and not Series like the Toyota HSD, so a DERV is a viable and useable option as the engine will always be running when the car is in motion.

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18 hours ago, Cyker said:

Are these hybrids you can buy here??? I can't believe I could have missed that many... :eek:
 

Ford & Mercedes only atm in the UK, I believe. Hyundai/Kia & possibly Infiniti & Honda I would expect shortly. Also, some non-hybrid Mazdas can run their ICE in something very similar to Atkinson cycle apparently.

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