40 mpg Prius vs 50 mpg European Diesel cars

There was much discussion in this thread about a diesel hybrid
It turns out that GM of all people is way ahead in devloping hybrid
diesel - in buses. the following links tell the story - diesel, hybrid, regenerative braking - the lot! 60% gain in economy.
www.shadetreemechanic.com/allison_hybrid_drive.htm
www.gm.com/company/gmability/edu_k-12/9-12/fc_energy/hybrid_allison.html
www.hybrid-vehicles.net/gm-allison-hybrid-bus.htm
I owe it to an Australian electronics magazine - Silicon Chip - which is running an article in its June issue on this GM - Allison project which is not pie in the sky - the vehicles are operating in various parts of the US.
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Still dont see it, my friend has a commonrail TD and gets 45 doing city driving, which is still above a hybrid?

Would be harder than with a petrol - re-starting a diesel requires far more cranking torque, so you'd need more powerful motors and its likely to cause a jerk, unlike a petrol car that can smoothly be 'bumped' as its low compression.
J
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"my friend has a commonrail TD and gets 45 doing city driving"
interesting, what make model car is that?
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We get mid/upper 40s in our hybrid around this hilly mountain town even with short trips and cold weather. In Phoenix it is consistently over 50 mpg in town, running A/C in a car that carries 5 adults easily and has what is effectively a perfectly smooth automatic transmission. Sitting at lights it is dead quiet most of the time and on the road it's still on the quiet side of average. In all states in the US it has the SULEV emissions rating. The merging capability is better than any of our other cars, including our 1985 turbo Volvo (gotta hate that turbo lag!) Ours is the older, less efficient version - and represents a technology in its infancy.
I give diesel its due: it has undeniable advantages as an auto fuel.
Mike
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No, it would be done the way the Prius does it: spin the engine up to speed before applying compression (that is, hold the valves open) and fuel.
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richard schumacher wrote:

So it has valve lifters. Is the only reason this is not done on regular engines the extra complexity?
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Nope. The VW diesel uses the same starter as the gasoline model, about 3 hp. A 20 to 50 kw motor will easily spin the diesel motor.
Lynn
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I would speculate that one problem with a diesel hybrid would be the extra power needed to crank the engine, remembering that this will happen quite frequently in a hybrid. This may mean more batteries (and hence weight) and a heavier engine anyway, meaning that the engine will need to run more frequently than it would in a petrol powered hybrid.
The hybrids that I have seen have clearly been designed to minimise weight, even perhaps compromising braking and cornering performance by fitting narrower tyres. With present technology, it is even possible that the extra weight required by a diesel engine would cancel out the gain in fuel economy compared to a petrol engine.
The one thing that would really make hybrids irresistable would be a means of charging the batteries from the mains. That way, even less fuel would be burned (at least by the car). But I doubt the oil companies would allow that to happen.
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wrote:

Does the hybrid engine actually stop and restart then? I had always assumed that it simply dropped to a tick over when not required. Having to restart each time must be horrendous.
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Keith Willcocks
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Yep. On rare occasions mine shudders slightly when shutting down but otherwise it's not noticeable. A common hybrid experience is sitting at a light listening to the folks around you wasting fuel for no good reason. I corrected the subject line.
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Actually, my Peugeot 406 HDI diesel (the common rail engine) averages 46mpg . This means that, to average 46, it must at times exceed 50 to counteract higher consumption in traffic. Bear in mind though that these averages are using the Imperial gallon, not the smaller US one. Factoring the US gallon into my spreadsheet shows an average of 35mpg(US). I assume that the figures quoted for the hybrid are US, not Imperial?
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Yes, the figures for the hybrid are US gallons. In the past year, my lowest mileage for a tank of gas has been 48 MPG; the highest has been 52 MPG. My highest ever was 53.4 MPG. And except for the first two tanks of gas, I have never had less than 46 MPG on a tank.
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Michelle Steiner wrote:

Were your lowest MPGs during the winter? Mine were. Other than that I was always above 50, usually 52-ish. This year my mileage is even better.
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Jean B.

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interesting, anyone know what causes better mileage in winter?
higher density of fuel due to cold? not running a/c? lower motor winding resistance due to cold?
is this a common phenomenon?
is it true for non-hybrid cars, or only hybrid cars?
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It isn't true for hybrid cars if you winter where the snow falls.
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I'm not sure that hybrid vehicles get better fuel economy in the winter than in the summer. For conventional internal combustion engines, the air is denser in cold weather so theoretically, the air-fuel mixture burns more completely. The engine takes longer to warm up in the winter so the air-fuel mixture is enriched a little longer so in the real world, most people tend to get better fuel economy in warmer weather.
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snipped-for-privacy@yahoo.com wrote:

Well, I can tell you this with a lot of certainty, large piston aircraft engines produce much more power at low temperatures than at high temperatures and the reason is that the air is much denser when cold than warm.
These engines have MAP gauges (Manifold Air Pressure...they're supercharged) and in summer they'll reach their maximum MAP before they reach their maximum 'torque', while in winter they reach max torque well before max MAP...quite a large difference...(this is at 'take-off' power)
The temp of the fuel apparently makes not much difference because we only used one weight for fuel winter and summer, it was 7.2 pounds per Imperial gallon (very high octane fuel). The aircraft held 6,640 gallons and if temp had mattered much then we'd have needed to take it into consideration in those large numbers...
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It is not true, the real thing is that the Prius has lower mpg's at winter, it is because it's main target is to be a close to zero emission vehicle, so at colder weather the catalyzer needs more gases going through it to keep at good work temperature to avoid contamination.

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Just got home. 146 miles mixed city/highway on my current tank. MPG (US) this tank 53.4.
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Mine at least is US.
Mike
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