turbo powered pmg ?

[knighty]

as my CHP system gets closer and closer I've been thinking about other ways to feed some power into those expensive GTIs...
(engine fuel rack will be automatically controlled to vary output to meet demand)

if I can generate some "free" background power and feed it into the GTIs I would reduce the power needed from the engine and save some money/fuel...

I was thinking wind/solar....


but could I fit a turbocharger to the engine, and have it spin a PMG ?

I'm sure I read somewhere that BMW were going to do exactly this on some of there cars and do away with the alternator to make the engines more efficient ?


so I could get some pretty much free extra power out of the engine ?


if the engine is production 20kw (electrical) a few hundred watts out of the turbo should be possible ? 200w = an extra 10%.... 400=20% ?

seams like quite a big jump in power....


any thoughts/ideas anyone ?

[camillitech]

Morning Knighty,

I'm sure that it's doable but 'there's no such thing as a free lunch' so back pressure and inability of the turbo to 'spool up' quickly or sufficiently may be an issue. I suspect that BMW would use a variable geometry and oversize turbo to overcome this but I'm only guessing. Speed will be your main problem as turbo's tend to run at phenomenal speeds and gearing/belts will probably cause it to stall.

Definitely worth tinkering about with though.

Good luck, Paul

[Tombo]

Interesting idea! Of course the turbo would cause back pressure, which in turn would require the engine to do more work on the exhaust stroke. So the energy wouldn't be quite so "free" as it first appears. There are also practical considerations: like generating at such high frequency, how to attach the magnets, extreme heat, turbo bearing life span. None of which would appear to be a barrier to you from what I have read!
Personally I would get some "free" energy by ensuring the engine is in good condition, full balanced and blueprinted. Making it more efficient.
I'd also remove anything that would waste energy such as an unnecessary restriction in the exhaust.
If the engine is water cooled, could the cooling system thermosypthon? loosing a water pump and drive belt would add a horse or two.

[Countrypaul]

Why attach the PMG directly to the turbo which seems to create a number of problems. If you use the turbo to create some pressure in an air flow (which is what it does normally for an engine) and use this air to drive a fan/pmg you might avoid  problems of the turbo spinning up slowly and creating excess back pressure on the engine. It might not be as efficient though...

Paul

[SteveH]

 PMG's for this purpose are available & are used on small & medium sized standby gas turbine generating plants... They use a turbine driven pmg in the Abrahams tank as an auxiliary power supply. The main problem you will have is either finding a PMG that can cope with the rpm of a turbo charger, as the smaller car types rev at over 100,000rpm, or a reduction gear set to bring the speed down for an off the shelf PMG .

 I looked into this for a solid fuel gas-turbine generator a few years back. some of the motors used for model aircraft have a high rpm rating, but not much above 30,000rpm...

 Good luck...

 Steve.

[knighty]

well... at least I'm not totally crazy :-)


just fyi... here's the engine

click for bigger photos ! (then click on the bigger photo again for a massive photo!)

         


              


I need to run it about about 30kw electrical most of the time (new machine on the way which will pull 20kw)


I was going to sell this and go for a smaller engine to be more efficient... but the new machine means I'll need more power and I don;t want to run at high revs... (this one ticks over at 400rpm and max's out at 1800rpm)

rough plan is... a 3phase induction motor belt driven from the engine, feeding into a GTI, I'll (eventually) automatically vary the engine rpm depending on power needed... and so the voltage of the motor... and then adjust the power curve of the gti to match that voltage output....

[camillitech]

What sort of engine is that Knighty, I can't download the pics on this 2G connection.

[mespilus]

Looks like a Leyland straight 6
11 litre
with an an inline CAV DPA pump to me.




(Honesty corner:
I have not become an engine guru,
Knighty confirmed the details on another forum).

[splyn]

Scania and Volvo have been using turbo compounding on some of their truck engines for a long time. They mechanically couple the output of a second turbo to the drivechain giving a claimed 5% to 10% improvement in efficiency - definitely worthwhile. This implies you could get up to an extra 3kW out of your 30kW engine but probably rather less as you're likely to lose some efficiency when scaling down given that the Scania is probably producing 300kW or more at its peak efficiency.

However as your engine will presumably be running at a constant speed, ideally around the engine's peak torque rpm (and mostly at a constant load of 30kW?) the engineering of a turbo compound system ought to be rather easier than in Scania's truck application which has to cope with varying speeds as well as loads.

This briefly discusses some systems for extracting power from the heat of the exhaust gases, including the Scania system: http://www.heat2power.net/en__benchmark.php

This also looks to be the sort of thing you're after: http://en.wikipedia.org/wiki/Hybrid_turbocharger

Aveox make brushless motors rated up to 120K rpm http://www.aveox.com/Products-Brushless-Motors.aspx but probably expensive.

Koford also claim to make generators that run up to  200k rpm but also probably too small and expensive/hard to get.

Or you get a Dyson handheld vacuum cleaner! http://www.electronicsweekly.com/Articles/2010/08/13/46377/dyson-vacuums-104000rpm-brushless-dc-technology.htm

Apparently a Garret VNT-15 turbo (small variable vane) is rated up to 235k rpm so you might need to consider turbo speeds well in excess of 100k

Good luck, Splyn

PS. I'm no expert in thermodynamics, but I'm sure you are largely getting a 'free lunch' (in energy terms) as the majority of the power from the turbo comes from the heat of the exhaust gases - although the turbo will increase the back pressure a bit.

[knighty]

thanks for the links, only had a quick look but I'll be straight back and read through it all in the morning :-)

I *should* be running at about 10kw minimum, 30kw most of the time, and up to about 40kw depending on demand...
(we peak above that, but normally only for a few seconds as machines start up etc..)

tho I really need to run the engine, once it's all setup and see how it does and what kind of pulleys I fit to run the generator motor...

I'd be happy to cap it at 30kw if need be... once the numbers start getting high it'll be producing more hot water than I need.... so it'll be a lot less efficient (and stop saving me money)

in the end... I might cap it at less than that... it all depends on how much fuel it's using and how much noise it's making.... a bit of noise won;t be a problem... but I'd be better if it wasn't banging away loud all day long


either way... a turbo powered generator looks to be a pretty good idea !

roughly speaking... 1kwh@12p /24/7 = about £1000 a year in electricity I don't have to buy

spread over a few years, 1kw of *free* extra power adds up to quite a saving !

[camillitech]

Most interesting Splyn, and great links.

Cheers, Paul

[rogeriko]

Knighty how old is that engine? It might be worth trying to find something newer that uses much less fuel for the same power output. The modern diesels with their electronic control systems use a lot less fuel. There are a couple of hotels around here that run on diesel generators 24/7 and their fuel bills run into thousands per month. A big old diesel running full tilt and belching out the black smoke will use fuel faster than you can fill it!!

[camillitech]

Knighty how old is that engine? It might be worth trying to find something newer that uses much less fuel for the same power output. The modern diesels with their electronic control systems use a lot less fuel. There are a couple of hotels around here that run on diesel generators 24/7 and their fuel bills run into thousands per month. A big old diesel running full tilt and belching out the black smoke will use fuel faster than you can fill it!!

But they'll not run on the stuff that Knighty's using  and that smoke should smell lovely 

Cheers, Paul

[biff]

that engine looks like a perkins P6 but it could,nt be,they died out years ago.they were fitted to the seddon trucks and used to bring tears to my eyes because they were so slow,top speed was 40 to 45 mph..my old man considered them good gear and also economic on diesel. but god were they ponderous.
              biff

[Justme]

Wont you be better off just using the turbo as normal to increase the power output & taking the extra power you need off the engine directly?