[CBintheNorth]

An update on the diesel heater efficiency project...

For a proof of concept I tried running a 1" steel exhaust flex hose through a piece of 3" aluminum flex pipe and drawing intake air through the 3", over the exhaust, in an effort to cool the exhaust while preheating the intake air. This itself, actually worked surprisingly well, but wasn't very compact, and was quite fragile (prone to crushing if stepped on).

I took the same concept and expanded a bit.
I made a copper pipe exchanger which splits from a single 1" copper pipe, to (4) 1/2" copper pipes to further boost efficiency, then back to 1" copper.

A few things to note:

1) The first time I made the exchanger, I soldered the joints. The exhaust of this heater reaches 570°F, and solder typically melts @ 450°F. I didn't realize the exhaust was that hot until I saw a drip of solder hit the bench while I was testing.
A lick of JB Weld Extreme Heat over the first few solder joints seems to be holding up. After the first return bend the exhaust was cool enough that melting solder wasn't an issue.
I definitely didn't want an exhaust leak in the exchanger as the intake air would be passing directly over any leaks.

2) The heater self-regulates diesel consumption based on its burner chamber temperature. According to the built-in digital thermometer, the range it maintains internally appears to be 405°F to 435°F. (Display is in Celsius)
Not really important, and I only mention that because the description in my pictures mentions "High temp @ highest setting". That temp was taken right before the heater cut back the fuel.


When first testing the heater without the exchanger connected, discharge air temperature on highest setting was 270°F, with an intake temperature (ambient) of 73°F, and an exhaust temperature of 570°F.
Again, horribly inefficient.

With the unit again on the highest setting, and the exchanger completed and connected, the results were much, much different.
Intake air temperature (ambient) was 66.7°F
Intake air into the heater after running through the exchanger box had nearly doubled in temperature, and was now at 132.3°F going into the heater. A substantial gain.

Discharge air obviously saw substantial gains as well, and climbed from its original 270°F, to a very balmy 361.8°F.
The best part for me, as I was concerned about fires and melting fabrics, was the exhaust temperature which plummeted to well below 100°F.
Not horribly inefficient anymore...

Out of curiosity, I ran it on the lowest setting to see how much change there would be. Surprisingly, the temperatures didn't change a whole lot, but the blower fan obviously cut way back.

On the lowest setting the inlet air was being preheated to 120.7°F, and discharge air was still up there at 327.4°F.
Unfortunately I did not record the discharge temps on low without the exchanger connected to compare.

I made two modifications to the heater itself:

1) I cut a round section of the housing out of the back so I could slide the 3.5" intake tube over the air inlet snuggly.

2) I mounted some 3/4" square tube to the bottom for stability in transport. These will stay on permanently and I used two corresponding pieces on the exchanger to secure the heater to the exchanger.

Other Things...

This project likely doesn't make financial sense to most people. The copper itself cost me around $120. If I didn't have access to the the tools and materials that I do, this project would have easily cost triple what the heater did.
I wanted this heater and needed something that was going to eliminate the exhaust from becoming a fire hazard, and a way to make the unit more efficient to save fuel, and especially to conserve battery power.
With the new exchanger I think this will be able to run at a much lower setting most of the time and just sip fuel.

This unit might be really handy this spring, as I can see wood stoves being nixed with the dry conditions.
Overnight stays on the ice is where I think it's really going to shine.

Once I do some in-field use I'll post up consumption rates and overall performance.