Naked Science Forum
Non Life Sciences => Technology => Topic started by: peppercorn on 03/02/2011 14:00:42
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Traditional LHB use molten salts at around 100°C to reheat a cold engine quickly. Using differing salts the temperature can be bumped up a lot higher.
So, on a vehicle - where exhaust heat runs a turbine coupled to a generator, the system needs a by-pass to stop the turbine choking the engine when the boost is low.
But what if, rather than have the temp drop by say 150°C across the turbine at an inlet of 700°C, the turbine is only dropping 110°C at inlet of 550°C - But 80% of the time as opposed to say 25% the recovery of work will far more efficiently.
In addition, heat can be used as with normal LHB systems to have a very fast warm up time, say if the vehicle has been stationary for <12hrs.
I was also thinking back an article that suggested an intercooler design that used a thermal mass of molten wax to spread the heat of compression when using a supercharger through the driving cycle. That is, so long as you are not on full boost all the time, the wax will dump heat back to the inlet air - spreading the loss of efficiency and allowing higher CRs.
I think the 'charger's temp would be too low to combine with the salt, but it is a good comparative system that also uses state change to give a better overall efficiency.
Although, coolant intercooling could be adapted as a step to transporting heat-of-compression as an intermediate stage.
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On a related note:
Engine Cooling System with a Heat Load Averaging Capability (http://lasersparkpluginc.com/uploads/engine_cooling_1.pdf)
"ABSTRACT
There is a need for an automotive engine cooling system
capable of handling increased heat load while, at the
same time, having reduced size and weight. This paper
evaluates a concept for an engine cooling system with a
passive heat accumulator that averages out peak heat
loads. Heat load averaging permits relaxation of the
cooling system requirements and allows substantial
reduction of system size and weight. This also translates
to a smaller coolant inventory allowing for faster engine
warm-up and reduced emissions of harmful pollutants
during a cold engine start."
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PC, what's a LHB?
Wiki suggests it could be the Local Health Board, or a Left Handed Batsman, but they don't seem to fit this context.
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PC, what's a LHB?
Wiki suggests it could be the Local Health Board, or a Left Handed Batsman, but they don't seem to fit this context.
latent-heat-battery
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Doh!
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Doh!
Ha Ha! - Still, does it make any more sense now you know? [:D]
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Sort of [:D].
I suspect the problem is that you can't get enough power from the turbine if you go for the 80% number to make the system worthwhile, but it's hard to be sure without doing a lot of calculations, and even then, you need to build a prototype to find out which calculations got mucked up due to underestimated practicalities.
If you are going to drive a generator, would it not be better to only run the generator at "full tilt" and couple some sort of battery/flywheel into the system to cover the time when the engine is off? The LHB could be really useful in that situation to minimize warm up time.
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If you are going to drive a generator, would it not be better to only run the generator at "full tilt" and couple some sort of battery/flywheel into the system to cover the time when the engine is off? The LHB could be really useful in that situation to minimize warm up time.
Thanks.
I suppose, in terms focusing of the question I'm asking the generator part is a bit of a distraction - I simply chose it as a load that could be maximised or minimised as necessary, and using batteries or whatever is a part of that, if needed.
The real point, like the wax-filled-intercooler example, is sometimes it's more realistic to even out the pressures on a system (in this case, heat load) than to over-engineer controlling ancillaries (in this case the cooling system) - Of course, the big driver for this is making an already useful addition (ie. an LHB) have a wider purpose (ie. waste heat recovery - to mechanical work).
LHBs seem better than say an Organic Rankine Cycle due to their simplicity and compactness of energy storage potential.
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Ah, OK.
How about this? - I think turbos rely to a significant extent on the kinetic energy they receive from the exhaust gas of the IC engine. When the IC engine is operating at low power, the air mass is greatly reduced, so post heating the exhaust, if that's what the system would do, won't be of much benefit.
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I think turbos rely to a significant extent on the kinetic energy they receive from the exhaust gas of the IC engine. When the IC engine is operating at low power, the air mass is greatly reduced, so post heating the exhaust, if that's what the system would do, won't be of much benefit.
It's a good point.
By means of exploration, may I ask a related question in response?
What would be the thermal reduction across a (well-matched) turbo, with an engine running a constant heigh-rev, lean-burn setting?
That is - it's relatively cool, but fast moving air that's exiting the cylinders... if it's all down to kinetic-energy (in the non-thermal sense) there ought to be almost as much energy available to the load on the turbo than when at stoich. mixture for the same revs... but my gut says this isn't the case, am I wrong?