Exhaust heat exchanger for cold start
 

So lately I’ve been thinking about ways to improve cold start warm up times. Here’s 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 can’t think of any downside to this. You are taking heat away from the exhaust, but it’s after the turbo so there’s 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 you’re 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 wouldn’t 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. That’s already designed to handle exhaust conditions, and coolant. I haven’t quite figured out the control valve. I think there should be some way to do it mechanically, but maybe you’d have to do something electrically. For somebody that’s good with electronics, it shouldn’t be too hard.

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

I’ve attached a (crude) schematic.

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...

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.

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.

Meelis

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.

Coolant can brake down if it gets to hot, so figuring out a way to keep it from over heating seems important.

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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Exhaust brake- is that anything like a muffler belt or blinker fluid?

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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Like this?

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

No, that isn't what I had in mind. That is for heating the manifold under the carb but there's no EGR. But I have engines with those and I don't know why they aren't on everything.

Exhaust brakes work awesome for quick warm ups. The newest diesels use the VGT to create a ton of backpressure (upwards of 40 psi in the exhaust manifold at idle) during warmup to get things hot fast in order for the aftertreatment systems to work properly.

Exhaust heat exchangers, AKA EGR coolers, must have high coolant flow through them at all times. The idea of one of these being utilized for quick warm-up is sound, but you would have to bypass the exhaust once up to temp instead of valving the coolant. The instant the coolant stops flowing in an EGR cooler (at least when exhaust temps are high), it flash boils, turning the heat exchanger into a paper weight. I've seen it a hundred times when diesel engine loses its water pump belt while pulling a hill. The EGR cooler basically erupts and the engine inhales the entire contents of the cooling system through the intake. Not fun for the guy paying the bill. Fun for the guy fixing it (me).

It might be possible to use two exhaust cut out valves to remove the flow from the heat exchanger. Basically you would have two paths, one would be through the exchanger section. The reason for using two would be to completely isolate the the exchanger section. After the second valve it would flow through the normal exhaust system.

Toyota did this with their 3rd gen Prius in favor of the 2nd generation's coolant thermos. We talked about how to make our own version here:

http://ecomodder.com/forum/showthrea...very-7107.html

I was thinking the same except only one valve is needed. J.C.Whitney used to sell exhaust cut outs that would work well for this.
Add a T-stat that actuates an old heat/AC damper flapper motor.
Just remember diesel exhaust can run steady state 1200 deg +

Actually the goal is NOT to warm the coolant up ASAP. If that was the goal, I'd just go out, put the truck in neutral, and rev it a bunch of times. Or I could just drive really hard to begin with. But that defeats the goal of trying to improve FE.

My goal is to warm up the coolant faster WITHOUT having to burn more fuel to do it. Here's the way I figure it. Fuel energy goes one of 3 places: driveshaft work, coolant heat loss, exhaust heat loss. If I can use the exhaust energy to warm up the coolant faster, then I will have used exhaust heat energy to decrease the coolant heat loss (warmer coolant temps mean less temperature difference so less coolant heat loss).

I have an '07 so I already have an exhaust brake. It's actually not an exhasut brake per se (i.e., not a throttle valve in the exhaust). It's got a VG turbo. What happens is that when you engage the exhasut brake during motoring it closes down the VG so the turbo is at max capacity. That increasing the pumping work of the engine. An exhasut brake WILL cause the engine to warm up faster, but only because you're burning more fuel by making the engine work harder. I want to work the engine just the same, but warm up faster.

EGR coolers take that abuse all the time. Actually it's even worse on most diesels the EGR see pre-turbine temperatures which can be a few hundred degrees hotter than post-turbo temps, where I want to put it.

My thinking was to get a really big EGR cooler (like out of Class 8 truck or something). If it's large enough it actually wont cause much more exhaust restriction than a normal exhasut pipe. EGR coolers are also already designed with the goal of having minimal restriction. If I can't get an EGR cooler I could always just expand my exhaust pipe (say 4" up to 5") and then put a copper coil in it. That probably woudn't increase backpressure because the flow area increas (from 4" to 5") would make up for the flow area decrease from the coil.

Coolant heaters are great. I already use one. What I'm looking for is for when you can't plug in and also for "finishing the job". I'm not sure how hot exactly my coolant heater will get me, but I know it's less than 140 deg F, where my gauge starts reading. I still have to go all the way up to 190 deg F before my thermostat even starts to open. In my truck that can take over 5 miles. My commute is 25 miles so that's over 20% of my distance right there.

Excellent point. I hadn't thought of that.

One soulution would be to just leave it open all the time, but that would add more cooling load onto the radiator. Of course, especially when it's cold I don't need anywhere near as much radiator as I have.

I guess another option would be spliting the exhasut pipe (one leg normal, one leg with the heat echanger) and putting a bypass valve in, but then we're getting more complicated than I'd like.

I figured somebody around here had already thought of it. I like the thermos idea too, but it won't really help if you've been sitting a long time. In addition, even if the coolant and/or oil is warm, you still have to warm up all the metal.

Excess heat being pumped into the coolant ?

In order to work & warm up quickly, it needs to be close to the engine.
Thus it'll get pretty hot in a short while once the engine gets up to normal temperature.

Leaving the heat exchanger open on one end will boil the coolant in the heat exchanger, which then will go into the system to be replaced with colder coolant, repeating the cycle.

So you need to shut off the flow of coolant, but you can't close both ends or you'd have pressure building up - though you could possibly vent this into the radiator overflow (which might need more volume).

Putting it further back in the system will reduce its effectiveness to warm up a cold engine, as you need to wait for the exhaust system to warm up.


Another way is 2 exhaust paths - one over the coolant heat exchanger, one bypassing it.
That sort of system would need some critical pipe-work to make sure no hot exhaust gasses go over the HE when not needed.

I admit I stopped reading about halfway through the second page of replies, so forgive me if this has been suggested.

Use the air cooled VW engine defroster system.

Get a second heater core & put it in a box. Make an outer tube for your exhaust pipes, whichever ones you want. Recirculate the air from this outer tube to your aux. heater core via a small electric fan. You don't have to worry about over heating air. Shut off the fan when ever you want. Insulate anything you think is prudent. I wouldn't insulate the exhaust pipes, as that normally makes them rust something fierce.

Don

Right now I'm thinking that the best idea would be to put put a copper coil into a short piece of straight exhaust pipe. That way it can be easily moved in and out. In the winter I need nowhere near the cooling capacity of my radiator, so a little extra cooling load isn't going to matter at all. If I'm running too hot in the summer I can just take it out. I don't think that will be the cse because this summer I ran with an upper grill block in 100 F weather and never had a problem.

This also would mean that I wouldn't have to worry about any vlaves or controls--I like that. I'm thinking some heater hose, some copper tubing, a short piece of exhasust pipe and I'd be all set.

Personally, I'd just do like a marine engine, and water jacket part of the exhaust system (manifold on non-turbo engines). Then, up-size the radiator and such accordingly, so you can leave the exchanger in the loop full-time (it should be the last thing to see coolant before discharge to the radiator when the t-stat is open).

Diesel_Dave, does your Dodge have a DPF or is it a pre-DPF truck? If it has one, the last thing you want to do is cool the engine-out exhaust down. DPFs need as much heat as available, at all times. I have a feeling your truck doesn't have one, and if that's the case, never mind.

My truck came with a DPF. Your right about vehicles with a DPF--you don't want to take heat out of the exhaust. In that case you'd want to put it after the DPF. There's still quite a bit of heat there, just not as much as up bu the turbo exit.

"...Came with a DPF." Sounds like you've already done the deed (DPF delete). My buddy at work did a DPF delete on his Dodge and improved fuel ecomony by 33%, no lie. I really uncorks the 6.7s. Plus, it makes the VGT sound like a jet taking off! While doing that I would do the EGR delete as well to get a bit more. You wouldn't believe how much fuel those things dump into the exhaust to keep your DPF happy.

Now, now, I didn't say that I took it off now did I?

I can honestly say that I still have my DPF. My EGR too....whether they're actually on my truck on not I'm not going to say--but I still have them.;)

Excellent answer!