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Old 16th May 2013, 08:23   #1
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Default Saving fuel, advancing technologies

Morning BHPians, another cold morning here in Yorkshire - my Merc's roof is covered in frost. Spring has been cold this year - about two days above 15C, that's all, the wood stove's been burning merrily. Anyway, here's more food for thought regarding our beloved motor car.

Cars today are much more efficient than they were forty or sixty years ago. Fact. We are told this and are convinced of it. They accelerate harder, have cleaner exhausts and have higher top speeds. Some decent-sized family cars will average 50mpg/18kmpl - such as the Skoda Octavia or VW Golf 1.9TDi - day in day out.

30/10 to 40/14 would be closer to the mark for most people, unless you own a Tata Nano. Yet back in the 1960s, figures were little different. The air was cleaner, journeys took no longer and lack of rapid acceleration was never a problem. What has happened of course is the car has become a victim of its own success, so that even though it is more powerful and less polluting, these advances offer little real improvement since cars are everywhere, clogging up the roads. And the price of fuel looks set to rise increasingly rapidly as mining it becomes increasingly expensive and the whole world aspires to live like a Lord. A Morris Minor 1000 was plenty room enough for a family of four and would easily return 45mpg in the 50s. From 20 years previously, a Citroen Traction Avant could average 30-35mpg and cover long journeys comfortably and easily. I averaged 110kph over almost 500km a few years ago in England, cruising at 130kph where possible and averaging 10kmpl.



So why aren't we offered cars which average 100mpg/35kmpl? The answer is that people can (just) afford to fuel their cars and enjoy the convenience so much, the costs are put to the back of the mind. Prestige and social standing is another reason for not only high prices but also (in the UK at least) the amazing levels of taxation placed on running a motor vehicle. As if it were the ultimate luxury, when in reality it has become a necessity with all our infrastructure built around the use of the motor car to the extent you cannot go shopping without a car in most of the British Isles.

The car engine wastes about 70% of the fuel we fuel it with, even if it is a Nano. In the UK, the fuel is taxed at close to that amount. And what starts in the West often makes its way to the rest of the world, so watch out. A lot of extra fuel is burnt through having to constantly slow down and speed up, which is one reason a light car makes sense, unless you've always got fat passengers in which case the car's weight is naturally less significant. Every time you come to a stop, the engine continues to run and fuel flows through the lines. Not only that, but an engine is running inefficiently most of the time - only within a fairly narrow rev range is it working as it likes to and wasting least fuel.

You'd think that cars would be as light as possible, the engines would run in a narrow rev band when pulling and somehow the energy used to accelerate would be recaptured as you brake. Well, mainstream cars have become much more streamlined through the air in recent years, which makes them less wasteful at steady high speeds and 'advanced' cars such as the Toyota Prius and other electric hybrid cars capture some of the energy lost in braking. They use stored braking energy to help accelerate them and other careful design to make them as efficient as possible.

Yet this state-of-the-art car achieves about the same average consumption as an efficient, conventional car - such as those mentioned above. How is this? Well, VW makes very efficeint diesel engines and also understand what makes an efficient car. So without the added complication of an electric motor, a battery pack and everything else which involves combining an internal combustion engine with an electric 'engine' and its power source, they also achieve good fuel figures in the real world.

Jeroen put his finger on an issue a couple of days ago on this forum, suggesting efficient cars were boring - he wanted something which was more exciting. I would go further and say that all cars, other than specialist cars and supercars costing way beyond what most of us can afford, are boring. It didn't used to be the case, not so long ago there were cars which were both economical and great fun to drive - chic and stylish also. I guess manufacturers have been told all too often by their cost-accountants that there is little profit in cheap cars, so why make them anything other than bland.

For a long time I have wondered about the supposed 'efficiency' of cars like the Prius - and found out that under gentle or hard braking there is little or no capture of energy. Gentle braking is too small for the electrical regeneration to work and under harder braking the limits for how rapidly a battery will recharge dictates things. Moderate braking is perfectly ok, however. In which case the best you'll do is recover 35% of braking energy.

I set thinking about this whole situation - all-electric cars are a little way off if for no other reason than cost of purchase and the batteries are going to be a problem regarding lack of range, 'refuelling' and weight for a while yet. I looked at the lawnmower, which has a hydraulic motor to power it, driven by a conventional engine. At a stroke, you could get rid of the gearbox, clutch, driveshafts and all the engine inefficiencies related to direct drive and a limited number of gear ratios. Hydraulic motors are great, lighter than electric motors and almost as efficient - you can hold a 500hp one in one hand. Instead of wires you have pipes. And instead of an electrical reservoir for (35% max efficiency) power recovery, there is the possibility of compressing a gas with the hydraulics. Which is 80-85% efficient and can be done at low braking levels as well as high.

I explored the possibilities, and discovered others had not only thought the same but gone out and done it. This link http://www.motherearthnews.com/green...#axzz2TNrdgdha could lead some of you to joke about some mad eco-warrior mislead thinking. But the figures were to be expected, even with a diy job. It turns out that the American UPS delivery network has its delivery vans running with a hybrid hydraulic system. It's all out there if you use google. Bosch are trialling refuse lorries/trucks with a similar system, and earlier this year the French automotive giant PSA announced they were intending to send such a system into production for mid-size cars. Wow! http://www.greencarcongress.com/2013...-20130305.html and http://www.greencarcongress.com/2013...-20130122.html.

I thnk electric motors are great, it's just the fact that electricity is only a means of transmitting power. The storage of it is relatively inefficient. Not only that, but a battery bank in your car is heavy (as are electric motors) and I'm not sure about such high voltages under your posterior in a flood situation. There are more benefits, some of which are mentioned in these links:

http://www.greencarcongress.com/2009...ver-messe.html

http://hydraulicspneumatics.com/200/...ydraulicPumpsM

http://www.cleanmpg.com/forums/showthread.php?t=22339
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Old 16th May 2013, 14:24   #2
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Default Re: Saving fuel, advancing technologies

Makes for a very interesting and knowledgeable read Flat Out.

Rated the thread 5 stars.
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Old 16th May 2013, 15:01   #3
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Very good information.
So there will be two parallel developments. One which tries to address the losses in the current system and the other is the development of all new alternate powertrains.

But for both, energy storage is the key and might also dictate how green the whole process is.
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Old 16th May 2013, 15:14   #4
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Still churning and digesting what you have written. Rated 5 Stars!
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Old 19th May 2013, 20:46   #5
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Quote:
Originally Posted by srishiva View Post
Very good information.
So there will be two parallel developments. One which tries to address the losses in the current system and the other is the development of all new alternate powertrains.

But for both, energy storage is the key and might also dictate how green the whole process is.
Yes, you're right. The ability of an electric hybrid to store energy in the quantities and times which cars require is very limited, at least until super-capacitors are used. Using trapped gas accumulators and hydraulics more than doubles the efficiencies and allows their use to a much greater extent.

Quote:
Originally Posted by roy_libran View Post
Still churning and digesting what you have written. Rated 5 Stars!
Thanks for the compliment, and I hope you're getting there! After 80 years the motor car has remained virtually unchanged. The next 80 years will be nothing but change, in my opinion.

Hydraulically powered cars were tested extensively post-war by a major European manufacturer over 1 million km. At the time, noise precluded productionising the technology. http://www.citroenet.org.uk/miscella...raulics-2.html (see 80% down the page). Since then, hydraulic motors have been almost silenced.

http://www.extremetech.com/extreme/146450-peugeot-unveils-hydraulic-air-hybrid-80-mpg-car says that "For city driving it is estimated that the car will be able to get up to 80% of the energy for locomotion from regenerative braking." That sounds good to me! The beauty of hydrostatic drive is that the engine can run at its most efficient at all times, rather than revving up and down with the limited number of gears. (The gearbox, differential, driveshafts etc can all be thrown away.)

The article also mentions the fully air-driven car being the extreme form of this technology - personally I don't think this is so likely except possibly for public transport vehicles and the like which spend all their time in the city, but in theory you could cover your car in solar panels and have an electric pump slowly trickling energy into the reservoir.
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Old 20th May 2013, 13:22   #6
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Default Re: Saving fuel, advancing technologies

Electric traction motors (USM) also have the ideal torque RPM curve!
At zero RPM, you get the maximum torque.

and I am pretty surprised to read that the regenerative braking only regains 35% of spent energy!
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Old 20th May 2013, 19:34   #7
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.. I am pretty surprised to read that the regenerative braking only regains 35% of spent energy!
Yes, I was too. It's all to do with batteries having a limited rate at which they can accept charge. I suppose if you had enough batteries you could improve the regen braking efficiency, but then there would be more weight. So the conventional brakes do plenty of braking. The answer (as always) is lighter cars. Bolting extra technology to an inefficient design is only one way of improving matters.

Small, lightweight cars (commuter vehicles, 2 or 3 seaters) would do best with a tiny petrol engine running as a generator for electric propulsion.

Larger vehicles, such as trucks and buses would do well with this hydraulic/hydrostatic drive and regeneration.


http://www.epa.gov/region9/air/hydraulic-hybrid/
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