Diesel Air Heater Theory/Installation/Operation

WilliamA

I got the last of the widgets today so I put the new tank vent in the diesel tank and properly plumbed it down and out the bottom of the tank surround:

I got my tank vent fitting and put that in today. It's a much better fit than the one in the cap, plus this one has a small filter inside the tank.

The vent is now routed down and through a brass fitting in the bottom of the toolbox. Much nicer. Of course it's cold here so the hose is about as flexible as a rake handle. It'll soften up so I can train it a bit better in time.

I'm hoping that makes it a finish on the heater job. A bit more testing and perhaps some minor re-routing of the ductwork but so far as I know it's in and done.

WilliamA

Rick67

I'm diggin the back splash a few photos up.

WilliamA

Ah yes. My olive oil 1 gallon cans. Sadly, it takes a long time to make a backsplash from those. I use a lot, but not "that" much. I am however, close to having another to work into the design.

WilliamA

WilliamA

I got my stickies made up and ready to install. I made the graphics in my Illustrator clone, printed them on regular paper, then covered both sides with packing tape. I'll put them on today...

WilliamA

WilliamA

I had my trailer out dragging it around yesterday to test the cellular modem (and wash the trailer) so while I was at it I ran the diesel heater for an hour to test the roadworthy aspects of the installation. When it first kicked in the fan was vibrating a little bit but after a couple of minutes it quieted down. Either there was a bit of debris (highly possible) from the installation in the squirrel cage or it was just cold and a bit sticky. Either way it quickly calmed down and smoothed out. It seems to be working well. I am going out camping for an overnight this weekend to give all the upgrades a good thrashing so that'll be a good test for my long list of upgrades. As I said before, if something isn't quite right but not detrimental, do nothing but continue testing. I am heading out for 3 weeks in May so I need to get in some testing before then. Campgrounds are going to be opening up around here soon so that will be the short order from here out. If the weather cooperates, I'd like to pull the diesel heater back out before my long trip just to inspect all the bits and things and put my mind at ease.

Test, test, then test some more.

WilliamA

WilliamA

I watched a recent video by Cosmo Weems. He was doing a comparison of diesel heaters, propex furnace (he has one installed) and the buddy heater. His data was impressive and sounded like he could mostly support the math, but fell a bit short on his diesel heater review. (IMHO)

The only data he had to offer on diesel heaters was anecdotal from watching YouTube videos. Not a particularly scientific analysis. I would agree with him on many of the points he made, but can't jump on board with his diesel analysis. I don't have the data or runtime yet on my own diesel heater but must disagree with his "YouTube" sources. If you post information, then it should be accurate and un-weighted. If my heater proves to be a problem, I'll let you know...

His video is still worth a look for those mulling over the heater conundrum...

WilliamA

WilliamA

Since I have plenty of time to disassemble things that are working, I decided to pull the heater out and go through it. This is for 2 reasons: I wanted to do a detailed check of all the mounts, ductwork and wiring and, also important, check and see how "field service friendly" it is. As to the former, other than a couple rivets that should be screws, it's pretty clear that things are where I put them and like it there. I found zero problems with the installation and removal was pretty much a 15 minute job. I am going to make a few minor modifications. The primary one is to replace the rivets holding the louvers on the bottom with screws and rivnuts. This will facilitate being able to quickly access the inlet side of the heater enclosure for removal of the inlet duct clamp. I can do that modification without removing the heater.

Once I had the heater out, I completely disassembled it for inspection. I was surprised at how much soot had built up inside the combustion chamber. It was super easy to clean out. I dug around and found a brass bristle brush the size of a toothbrush and just cleaned it up. Rather than being like carbon, the soot was closer to baby powder and simply fell off when I brushed it, leaving the combustion chamber clean as new. A close inspection of the glow plug and ignition chamber showed no signs of carbon buildup so I stuck it back together and slammed it back in. It's very easy to disassemble and clean. By far the most difficult part is pulling it out to service and the hardest part of that is getting the ductwork clamps off and back on. I am mostly quite happy with the installation and don't plan to make any changes to it. If I had to do it again, I would make the enclosure longer so I could get to both band clamps for the duct easier. I have a couple of ideas and may pursue it.

Now to ruminate on the sooting.... First, I changed the exhaust a bit. I re-formed the exhaust so the 90 degree turn is a much gentler radius. I then removed the muffler completely and just connected the 2 exhaust pipes together. That's a lot less back pressure for the combustion chamber. After doing those things, I ran it for an hour or so and can say that I couldn't tell any discernable difference in noise level. I do want to eliminate the waffle exhaust pipe and put in a solid steel, 1" pipe. The waffle pipe can't help but be horribly restricting and there's plenty of room to improve on it.

The other thing I want to do is make sure it's not running too rich. I don't have any way to efficiently test the exhaust to see how rich it is. I will rent/borrow a sniffer from the local auto parts store and probe it to see what the O2 counts are, but that's about as much as I'll be able to do here without more sophisticated hardware.

So there are things to pursue in order to increase efficiency and reliability. Most of it has to do with reducing obvious restrictions in the combustion air cycle and also, the heating ductwork. Most of it is pretty obvious if you just think about it. The big unknown is the fuel/air ratio, and that's going to be a little harder to parse out. As with any internal combustion device, it generally comes down to observation and adjustment.

WilliamA

Rick67

Mine got a fungus in the fuel this year. The tank got a good amount as did the fuel line in all the low spots. I ran it for couple days with a short line just to test for any fouling in pump or by glow plug. Shut it down and restarted a few hours later to smoke. I had a feeling. Didn’t pull it apart yet. May just buy another as they got cheaper and toss the old if it’s too fouled. My fault, half full tanks sweat and fuel flow is so low it may be worth blowing out for the summer. Conditioner may be an option with this newer low sulfer Diesel to sit on unused fuel.

WilliamA

I've been going through the trailer adjusting/cleaning/servicing things in preparation for the trip in April. One of the things I've been wanting to do is build a proper exhaust for the diesel heater. The one that was on there was a cheesy accordion tube that, in addition to getting rusty, had to be pretty restrictive. Since I've been wanting to lean it out some and check the burn ratio, I decided to make a proper exhaust. I picked up a 1" emt conduit 90° sweep and a short piece of 1" emt conduit. I made a double-thickness collar on the heater end to neck it down to 22mm i.d. I welded the straight conduit to the sweep, then bent it to a lateral dog-leg. I spent the afternoon yesterday testing it out and it seemed fine other than it was scavenging too hard. I modified a small muffler that came with the heater so I could pop it on and off for testing.

With the muffler on, it's running like a watch. Without it, the heater struggles (takes awhile) to start. That definitely means it is lean. The muffler fattens up the mixture with a bit of back pressure so it behaves now without weird lean noises. It also reduced the combustion outlet temperature by about 25° or so.

I also did a bunch of research and figured out how to tweak the mixture using the admin override in the controller. To do that properly, I'll need to use a wide band lambda probe. Now that I have a proper exhaust pipe, I can weld in a bung for the probe.

In the meantime, I'm happy with the results. I need to take the exhaust off (seriously...like a 2 minute job) and paint it. The emt is galvanized, but it's raw steel where I welded it so a bit of protection is called for...

WilliamA

WilliamA

I'm "mid-test" right now on a bunch of changes for the fine tuning of the heater but so far, I've been really excited with how it's going. I'm sitting in the trailer writing this on the on-board Mac while the diesel heater keeps me nice and warm. The how-to of the fine tuning is a really long story but it's been a good fun adventure with lots of research and testing. The short story for now is that I've been able to modify the injection curve on the heater to get it turned waaaaaaay lean and the heat has come down to a perfectly tolerable level. I ran it this morning while programming the ECU and, for the first time, was able to get the program changes to save in the hardware. I let it cool down for an hour and restarted it and it looks so far like the programmed changes are now sticking in the ECU. From the "out of the box" settings the ECU came with, I've been able to lean down the injection so it's not running me out of the trailer. Initial heater output, as measured at the hot air hose in the cabin, was 215 degrees more or less. It's now 154 degrees on high and 160 on low. Much better, more efficient and most important, shouldn't soot up the combustion chamber. I'll let it run tomorrow again on high for 4 hours, then pull the heater and disassemble it for complete inspection and cleaning.
I suspect that now it's running a bit TOO lean, but now that I've got the programming worked out, I should be able to bump it up in increments to see what it's doing. I'd rather it be too lean than too rich. Unlike an internal combustion engine, it won't overheat if it's too lean. It just won't start. I want it to be as lean as I can make it while still starting well.

I'll keep you posted and also put in a bunch of photos when I get them downloaded and massaged....

WilliamA

WilliamA

(Edited to remove photos)

This post might get a little way out in the weeds, technically speaking, but then that's mostly where I live. So if you're not into sorting the technical fly poop from the pepper, you might want to just move along.
I've been chasing my tail on this one for a few months now. Problem:
The diesel heater was too hot for the trailer's small space, and it was running too rich to the point that the combustion chamber was sooting up.
Now the heater is pretty easy to take apart and clean, but less maintenance is always a good goal. The big problem has been the sooting up. Now is the part where we get out in the weeds.

One needs to understand the basics of the fuel/air ratio within any combustion device, be it an internal combustion engine, propane heater, diesel heater or otherwise. They all need a proper fuel air ratio. Think of a graph: the vertical axis is the rpm's of the heater motor going from idle up the graph to full speed. The long axis is heat output from the heater. One basically needs to fiddle with two things: the amount of combustion air and the amount of fuel. The combustion air is pretty much fixed, as the fan size is fixed and only the speed changes. But other variables apply, so it's good to start with airflow. The first job is to clean up the airflow by reducing restrictions in the air in and exhaust out. Air in is a simple affair of checking to make sure there isn't anything in the inlet hose and that the filter/silencer isn't plugged. The exhaust is a bit more work, but it's also fairly straightforward. Make sure it's sized properly and doesn't have any unnecessary restrictions. I've done both of those things. Now to the fuel side:
The little diesel heater does not have a carburetor or injector. Basically, it is metered by the fuel pump. The fuel pump is a tiny electric piston-pump that puts out a metered amount of fuel for every "pulse" of the pump. In this case, it's .02ml per pulse. It would take 250 or so pulses of the pump to fill a teaspoon, so it's a tiny amount.
The "throttle" is accomplished by how fast the pump pulses, measured in hz, or how many times the pump pulses per second. 1 hz =1 pump per second etc. Both fan speed and pump hz are controlled by the ecm (electronic control module) inside the heater housing. The ecm is controlled by the heater controller. This is where it gets sticky. Both the ecm and heater controller are smart circuits. The controller keeps track of the program "ramp" (fuel/air curve vs temp) to get a good burn rate. The "ramp", however, is actually software and is stored in the ecm. That's important for the sole fact that one can unplug the controller and plug in another without changing the "ramp".
Okay. We've introduced all of the players. The basics of "tuning" the heater are simply setting the fan speed and fuel pump pulse rate. To do that, one needs to get past the lock on the controller to reset/modify the parameters. That has proven to be fairly simple. Go to the lock screen setting in the setup menu and punch in the lock code (1688. It's the same for all Chinese diesel heaters) then scroll through the menu. My heater was set at the default value of:
Fan speed, low: 1450 rpm
Fan speed, high: 4500 rpm
Fuel pump hz, low: 1.6 hz
Fuel pump hz, high: 5.5 hz.
(After MUCH fiddling) I changed those settings to:
Fan speed, low: 2050 rpm
Fan speed, high: 4000 rpm
Fuel pump hz, low: 1.0 hz
Fuel pump hz, high: 3.0 hz
I don't have a fuel/air meter, a.k.a. "wide band lambda probe" so I used a combination of my turkey temperature probe and a handheld CO (carbon monoxide) tester.
The CO tester use was a bit dodgy as it was out in the open, subject to wind and weather. I had it sitting on a bucket about 12" away from the exhaust outlet. Before I began the fiddling, the temp was over 210° at the heater hose outlet and the CO counts we're off the scale. After the adjustments/fiddling, output temp is hanging around at between 154-160°. CO counts are down to between 0-17ppm at the exhaust outlet. A household CO alarm (I think. Don't quote me on this) won't start to trigger below 50ppm for more than 30 minutes. 200 ppm is where the stuff really gets nasty. Keep in mind, this is in the exhaust stream, NOT the cabin air stream. I could not get cabin air CO readings to change from ambient (0-1ppm) with the heater running.
Now the trickiest part of the whole affair, after all the research etc, was not putting in the new ramp software parameters. It was trying to figure out how to make them stick. I tried many keystroke combos to get the new parameters to save and overwrite the old ones with no luck. In the end, it was easy. Do nothing....as in, enter the admin password, hack the parameters, then just lay the damned controller down and let it "time out". Seems that, after 30 seconds or so without input, the admin access times out and it goes back to the base menu, taking (and storing) the new parameters with it. Once the parameters are stored, one can unplug and swap controllers without messing up the settings as the ramp is stored in the ecm, not the controller.
There is a small catch:
To access the admin menu, I had to purchase a different controller.

See....
That wasn't so hard after all...
WilliamA

WilliamA

Turkey thermometer with probe in hot-air outlet at ambient temp. Pay no attention to the "212° on right. That's the set-able alarm temp.

Outlet temp pre-fiddling.

Outlet temp post-fiddling

CO meter at exhaust outlet

Simple controller

Controller used to reprogram ECU

WilliamA

Hitech

Fantastic build William!! I bought a similar heater about a year back and just now was working out the logistics of the install. I was going to use the exact area you did, minus your beautifully built box insert but didn’t like that I needed to cut the back wall of what was micro space that I long since converted to cabinetry and then also move that gas line. My other issue is that I have opened the dead space wall in a number of placed for storage on the inside of my trailer (I think you have commented on my prior posts and pics of course) I’m going with the mount a box under my trailer model as I lifted my trailer and installed a water tank above the also upgraded axle. I’ve got 8 inches of room under there to be flush with that tank and not have anything protrude in a way it will be caught and torn off. I’ve spent a week of internet searches, on and off, trying to understand how much heat might be built up in that box when after 100 YouTube videos and dozens of sites and pics I came across your build. So amazing! I like the idea of the exhaust vent, love the incorporation of the fire extinguisher, but think I have enough room for vent hoses to the plug area you note by the inverter box and was going to poke the exhaust out on the passenger side next to the stereo. All that being said, I have one question. In your experience do you think it’s necessary to draw air from inside the vehicle (running 2 vent lines) or can I have the unit draw cool air from underneath? I see so many all in a box builds with these heaters for use with rooftop tents and they all seem to just draw cool air at the heater.

WilliamA

It's a good question. Forgive me, but I need to be clear that you mean draw heater air from outside and not combustion air? It goes without saying that combustion air must be drawn from outside.

For "heating" air (think: cold air return) I think it's best to draw the air you are heating for a couple of reasons:

If you are getting both combustion air and cold air return from outside, you run the risk of having the cold air return sniff up heater exhaust. That's bad.

On a more technical note, if your cold air return is significantly colder than the heated air from the heater output, you run the risk of unbalancing. What that can potentially do is overcool the cumbustion chamber. If it's not hot enough in the combustion chamber, you run the risk of a flame-out (the combustion chamber isn't hot enough to support spontaneous combustion) or at the very least, premature sooting of the combustion pot.

I put my cold air return inside under the radio location and have had no issues with either of those. I highly recommend a cheap handheld carbon detector. It works great both for checking cabin air and also for tuning the mixture of your heater.

You've watched a lot of videos so I assume you've seen David McCluckey (spelling?) Videos on diesel heaters. If not, check out his videos on adjusting the mixture of diesel heaters.

Any Q's, just let me know. I don't come by here too often so try my wall. I'll get an email notice....

Hitech

Thanks William. Cold air intake from the heating side is definitely what I’m referring to on this. My concern with drawing cold air is that at the end of blowing nice warm air in my trailer it will finish off with cold air as it cools the unit. Was hoping to just run the heat line in, but I guess I’ll do both. I guess the heater doesn’t try and cool down to 50 degrees or anything, so it will likely not be felt inside the rv.

WilliamA

My own heater fan shuts off when the combustion chamber temp gets to about 110 degrees and is still blowing warm air so you don't get an unwelcome cold inflow at the end of cycle.