h a l f b a k e r yCogito, ergo sumthin'
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Gasoline engines work best when they are at their ideal
operating temperature, for lots of reasons. The various
gaps and tolerances are designed with an operating
temperature in mind and other components, like the oil,
are optimized for a given temperature also. Furthermore,
most engine wear
occurs on startup when the oil can't do
its job.
In cold regions, people use simple plug-in resistive block
heaters to offset some of the negative effects. Why not
add this to a hybrid? Only cleverer. Some hybrids already
use electric water and oil pumps. Simply adding the heater
to the oil circuit, you could pre-heat and circulate the oil
using the not-inconsiderable battery reserve. Your engine
may then be designed to have much tighter tolerances (F1
car engines won't crank while cold, their tolerances are so
tight that they are effectively seized until warm) and the
oil could be designed with a much narrower range of
operating temperatures. The engine should then be more
efficient by not having to run on choke, which is essentially
just over fueling. It should also last longer.
It might be a bit annoying to wait for the engine to be
warmed up before it can start, but the initial portion of
most car journeys is slow speed, getting-out-of-the-
driveway type stuff, which can be done entirely on electric
anyway.
Prius Heat Storage Tank
https://www.youtube...watch?v=vpx6M8us0eU
[bs0u0155, Sep 05 2014]
[link]
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Choke? The wasted fuel is lost to heating a large lump of
metal. It might seem odd, but it actually makes sense to
use thermal losses from combustion to do that rather than
the very high order of energy found in the battery. |
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Well, I understand that using combustion heat to warm
the block is sort of neat, as it would otherwise be wasted.
I have no issue with the waste heat be used to MAINTAIN*
block temp. |
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Electrical preheating allows the initial combustion to be
as efficient as possible, for example, the 1.3l Nissan Micra
I used to own would do about 16 mpg for the first 10 mins
on a cold morning and 55 mpg when warmed up at the
same speed. That's a 1/3rd of a gallon wasted. Also, you
can make the whole engine so much tighter, much
smaller piston rings can be used, gaining efficiency. The
oil can be more specific. |
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* italics would be better here |
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Doesn't battery discharge already generate heat? You could use that heat to warm the engine block, when running electric first thing. I suspect this may already be done, as some hybrids have integrated cooling systems. |
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Also, this idea is similar to glowplugs in diesel engines. |
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//That's a 1/3rd of a gallon wasted.// Wow -
seriously? That's about £1.80... ouch. Hate to think
what it is for a 4.2 v6... |
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This would be especially good on a plug-in hybrid.
you could schedule it to preheat the engine using
grid power before you leave. Grid electricity is
even cheaper than gas. |
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I worry somewhat about this concept in a
situation where the car is stopped when the
battery is largely depleted or if the car is left
parked for along time. Currently, you can get
enough power to get the engine running in a
couple seconds with jumper cables, but you'd
need a bit more to preheat the engine. I suppose
you could design it so that another similar hybrid
could provide a jump start, though that would
require however many minutes are needed to heat
the engine. |
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How much energy does it actually take to warm up
an engine block? And if it's too cold out, and the
heater isn't powerful enough, you could end up
not being able to get it up to temperature at all. |
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Especially on a non plug-in hybrid, it seems like
you'd want some mechanism that allows you to
heat the engine by burning fuel. |
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//How much energy does it actually take to warm up
an engine block?// |
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Assuming an engine mass of 200kg (I am guessing) and
a heat capacity of about 1kJ/kg/°C, and assuming
you need to heat it by 100°C, that's
200*100*1000=20MJ, or about half a litre of petrol. |
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So, if what [bs] said is correct, it's much more
efficient to burn fuel solely to heat the engine before
starting it, than it is to run the engine from cold and
let it warm up naturally. |
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Yes, maybe, but a low-grade fuel. Liquid fuels
are too useful for vehicles to waste on simple
heating applications. A "cartridge" system
using biomass would be good. But there'd be
a significant lead time on startup. |
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Using electrical energy from the traction
battery is inherently inefficient. |
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The powerplant has a well-defined mass and
specific heat. By adding a heat reservoir in
the form of a water tank, heat could be
collected from the exhaust gases and cooling
system during normal running. When the
engine is cold, simply recirculate the coolant
through the heavily-insulated tank of hot
water. |
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A tank of liquid about 200% of the volume of
the coolant circuit should be enough. For a
small engine, that's likely to be about 20
litres. |
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Run with what 8th said, using stored warm coolant to defreeze the engine and oil, then... |
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Having previously shut down the 4-banger with all pistons at half-mast, run the injectors at very low fuel flow to hot up the cylinder and piston heads from the inside, without cranking the engine. Requires an independent valve-train and a small amount of forced induction. |
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Diesel engines like the Perkins 4.108 use an
intake air heater for starting, instead of
glowplugs. Now, with a valve lifter and an air
preheater, a small fan would be enough to
blow hot air through the pots and warm the
block and coolant for a quick and easy start. |
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//heat could be collected from the exhaust gases and
cooling system during normal running// |
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That's a very good idea, so good Toyota did it in the Prius
<link> (video warning). |
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////That's a 1/3rd of a gallon wasted.// Wow - seriously?
That's about £1.80... ouch. Hate to think what it is for a
4.2 v6...// |
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hmm. 4.2 litre V6 you say? nah. The only 4.2 litre V6 I'm
aware of is a godawful Ford unit fitted to the
F150/Explorer over here. you either have a 4.2 litre V8,
in either an Audi or a Jag. Or a 3.2 litre V6 in a VW/Audi
or possibly an oldish Honda. Either way, bigger engines
have a more optimal surface area volume ratio and heat
up faster. If you like, you can locate your OBD2 port, plug
in a laptop and get every parameter of your engine,
dumped at 10Hz. A real exercise in data wrangling after
that. Changes the way you drive... or it did me. |
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Either way, engines rarely weigh 200kg, and they're
aluminium mostly, quite a low specific heat capacity.
Also, many parts of the "Engine" are to some extent
thermally isolated when the thermostat is closed. It's
really about getting the chamber temperatures up to the
point where the fuel mixes well. |
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