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Old 11-26-2011, 05:57 PM   #1 (permalink)
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Exhaust heat exchanger for cold start

So lately Iíve been thinking about ways to improve cold start warm up times. Hereís my latest brainchild. Why not put in a coolant-to-exhaust heat exchanger? In a cold startup (before the thermostat opens), you circulate coolant from the engine block through an exhaust heat exchanger (after the turbo) and then back to the suction side of the coolant pump. You then put in a control valve so that after the thermostat opens, no more coolant flows through the heat exchanger.

I canít think of any downside to this. You are taking heat away from the exhaust, but itís after the turbo so thereís no harm to that. At that point it truly is waste heat. After things have warmed up, the control valve would be closed, so after the thermostat opens youíre back to your original system. Depending on how you constructed the heat exchanged, there could be just a tiny bit more backpressure on the turbo, but it would be really, really small and if you sized the heat exchanger correctly there wouldnít be any additional backpressure.

As far as how it could be practically constructed, perhaps the easiest way to make the heat exchanger would be to use an EGR cooler from an engine much larger than the one being used. Thatís already designed to handle exhaust conditions, and coolant. I havenít quite figured out the control valve. I think there should be some way to do it mechanically, but maybe youíd have to do something electrically. For somebody thatís good with electronics, it shouldnít be too hard.

Has anybody else tried anything like this? Any comments or suggestions?

Iíve attached a (crude) schematic.

Attached Images
File Type: bmp Warmup2.bmp (28.3 KB, 67 views)
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Old 11-26-2011, 06:16 PM   #2 (permalink)
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I'd take the whole exchanger out of the exhaust stream after it has warmed up; no restriction, and that's gotta be an awful tough life for an exchanger that is continuously exposed.

I've been thinking of a simple butterfly valve on the exhaust that basically traps heat in the exhaust and is, well, just another EGR that traps heat in the cylinder but without looping it around in exterior (to the cylinder) plumbing. Thing is, much/any more EGR at cold probably isn't tolerable...
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Old 11-26-2011, 06:20 PM   #3 (permalink)
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I think having a coolant heater inline on the bottom rad hose would be effective enough.
I say the bottom hose so convection heats all of the coolant in the rad and possibly the motor,I have noticed mechanics install it in the easier to reach top hose which makes no sense to me.
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Old 11-26-2011, 07:32 PM   #4 (permalink)
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I am interested it also! I posted it already in some other topic but it got no attention there.

My idea is here, but no exact answers:
Basically you need to wrap copper pipe around exhaust and coolant flows through that spiral? How many wraps around exhaust? How much is it possible to make warmup time quicker? At least in normal driving (after warmup) I think that this extra heat is not a problem - your radiator should remove that heat.
Of course it woulld be better to stop that extra heating after warmup but it is not taht simple as solenoid valve - I would not want standing still coolant wrapped around exhaust - probably it starts to boil and make bad things.

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Old 11-26-2011, 07:36 PM   #5 (permalink)
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How do you deal with excess heat when you are up to temp? The exhaust will continue to dump heat into the pipework, thus boiling any non-flowing coolant.
Relief valve into the header tank maybe? Open up your grille block some? Hmm...
Bear in mind that a heat exchanger upstream of the catalytic converter might keep exhaust temps down for longer, thus reducing its effectiveness. So downstream of the cat may be the way to go?
I used to use a hot air intake on my civic and warm up times were a lot quicker than with a normal intake. No messing with coolant or valves etc.
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Old 11-26-2011, 07:52 PM   #6 (permalink)
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Coolant can brake down if it gets to hot, so figuring out a way to keep it from over heating seems important.
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Old 11-26-2011, 08:44 PM   #7 (permalink)
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I'm probably missing something. The goal is to bring the coolant to op-temp ASAP, right? So why not an exhaust brake? Most, if not all of the benefit (and others besides), but without the complications of another "cooling system". A KIMM Hotstart plus an exhaust brake plus a MOPAR winter front covers a lot. (Silicone heat pads for the rest). An ESPAR or WEBASTO otherwise.

The exhaust brake -- to expand on this -- goes directly to best & highest use as the DODGE Bodybuilders Guide states that this device is pretty much a necessity for towing trailers in excess of 10k pounds. I plan to have one on my CTD in the coming calendar year.

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Old 11-26-2011, 09:01 PM   #8 (permalink)
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Exhaust brake- is that anything like a muffler belt or blinker fluid?
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Old 11-26-2011, 09:14 PM   #9 (permalink)
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They can be used to decrease warm-up time at idle. Even a few minutes goes a long way. Not the same as a "jake brake" a compression release device used on Class 8 trucks, but the same effect in using exhaust backpressure to slow the rig in coming down to a stop. (Service brakes can last over 200k with the right driver exercising prudent use of these devices; my own experience in the oilfield with a variation of this truck type is that is unmatched for bringing a 30k+ rig to a town speed limit while on a non-Interstate highway).

Probably the reason DD wants to avoid them -- with an apparent "rule" about no engine braking while underway -- is also the "no idle" rule, etc.

Jacobs Exhaust Brake

Pacific Brake PRXB

These have been stock on CTD's since late 2007 (and a dealer option for about fifteen years before that). A CTD with the six speed manual and an exhaust brake has a wide range of stopping performance choices available to the driver. A marriage made in heaven. (Now, if only we had a seven speed manual with [2] overdrives optimal for both solo and "towing heavy").

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Last edited by slowmover; 11-26-2011 at 09:30 PM..
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Old 11-26-2011, 10:55 PM   #10 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
I've been thinking of a simple butterfly valve on the exhaust that basically traps heat in the exhaust and is, well, just another EGR that traps heat in the cylinder but without looping it around in exterior (to the cylinder) plumbing. Thing is, much/any more EGR at cold probably isn't tolerable...

Like this?

Wasn't this common at one time? I seem to recall them on many cars.

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