Exhaust heat exchanger for cold start

[Frank Lee]

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.

[mechman600]

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).

[nemo]

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.

[Daox]

Originally Posted by Diesel_Dave

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.

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

[JasonG]

Originally Posted by nemo

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.

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 +

[Diesel_Dave]

Originally Posted by slowmover

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.

.

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.

[Diesel_Dave]

Originally Posted by Frank Lee

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.

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.

[Diesel_Dave]

Originally Posted by ecomodded

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.

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.

[Diesel_Dave]

Originally Posted by meelis11

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

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.

[Diesel_Dave]

Originally Posted by Daox

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 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.