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Old 09-29-2022, 07:05 AM   #1
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Default Gasoline Webasto at altitude

The Webasto 2000 STC cannot achieve complete combustion above 5000ft altitude. The reason is simple physics. Mixture is controlled by fuel pulses/minute. Gasoline is a fast burning fuel. At altitude the correct pulse per minute rate is low enough that the fuel pulse burns out before the next one arrives and the flame goes out.

At altitude (10,000ft) we cannot reduce the pulse rate so we need to add oxygen. We need a liquid that adds oxygen, something like nitrous except it is a gas and can be dangerous. Any ideas from you chemical engineers?

I don’t really expect to be successful with this and the downside is cooking my RV but I thought I’d give it some effort. Beyond that it is a bit of entertainment.

Jokes permitted!
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Old 09-29-2022, 12:14 PM   #2
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The Webasto 2000 STC cannot achieve complete combustion above 5000ft altitude. The reason is simple physics. Mixture is controlled by fuel pulses/minute. Gasoline is a fast burning fuel. At altitude the correct pulse per minute rate is low enough that the fuel pulse burns out before the next one arrives and the flame goes out.

At altitude (10,000ft) we cannot reduce the pulse rate so we need to add oxygen. We need a liquid that adds oxygen, something like nitrous except it is a gas and can be dangerous. Any ideas from you chemical engineers?

I don’t really expect to be successful with this and the downside is cooking my RV but I thought I’d give it some effort. Beyond that it is a bit of entertainment.

Jokes permitted!
In all diesel or gasoline furnaces like Webasto, Eberspacher, Russian or Chinese derivatives oxygen/air flow is constant and fixed and fuel flow is controlled by pulse frequency. I thought Webasto has built in control for pump frequency to be automatically adjusted to achieve correct stoichiometric ratio. Older models of Eberspacher needed additional device to do the same but newer ones have frequency vs elevation control built in.
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Old 09-29-2022, 02:31 PM   #3
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Maybe increase the pitch of the combustion air fan?
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Old 09-29-2022, 02:42 PM   #4
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How do they determine the air fuel ratio in these furnaces? Is it just off of barometric pressure, temp, air density calc or do they feedback from a combustion sensor (O2) to adjust the mixture and measure the air mass (MAF)?


In a land that has pure gas, ethanol laced gas in various mixes, not stellar heat content consistency, and high volatility winter gas and low volatility summer gas it would be very difficult to get accurate fueling to match the airflow to the combustion.


I also don't really understand the description of the problem. If you are burning off all the fuel before the next pulse goes in, wouldn't you need less oxygen to slow down the combustion burn time per pulse?
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Old 09-29-2022, 03:01 PM   #5
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As far as I know controls are very simplistic based on barometric pressure. Eberspacher has fixed frequency ranges starting at sea level to 5000’. Problems start at 7500”.

Pitch control could be nice but with DC invertor motors RPM control could be easier. Frequency of pulsing pumps (fixed stroke) is by far the easiest. Why Espar is asking close to $300 for it is just crazy. Wiring installation manual for these barometric modules were likely written in German, translated by Chinese to Russian and translated by Ukrainians to English. A common issue by most of buyers of these HAC modules.

https://www.heatso.com/espar-eberspa...200-h-kit-hak/
https://esparparts.com/techsupport/p...%2010-2011.pdf
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Old 09-29-2022, 03:23 PM   #6
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I also don't really understand the description of the problem. If you are burning off all the fuel before the next pulse goes in, wouldn't you need less oxygen to slow down the combustion burn time per pulse?
You have more fuel than air since you cannot reduce the frequency of fuel pulses any further. Maybe increase the rpm of the combustion air fan?

It carbons up pretty quick at 10,000ft. Cleaning takes about four hours due to removal issues. Actual cleaning is about 30 minutes.
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Old 09-29-2022, 04:10 PM   #7
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We leaned out our gas AT2000 as much as we could and run it up to about 7500 ft. No good when we're freezing at 10-12,000 ft. So we have ordered the new kid on the block:

https://velitcamping.com/products/ve...eater-17000btu

A guy I trust has fondled the heater and met with the head engineer. He was impressed. Specs are still fluid, as they are still tweaking it. They estimate I should get it by December. The bad part is I have to redo some cabinetry to accommodate the extra 3” length.
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Old 09-29-2022, 04:30 PM   #8
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We leaned out our gas AT2000 as much as we could and run it up to about 7500 ft. No good when we're freezing at 10-12,000 ft. So we have ordered the new kid on the block:

https://velitcamping.com/products/ve...eater-17000btu

A guy I trust has fondled the heater and met with the head engineer. He was impressed. Specs are still fluid, as they are still tweaking it. They estimate I should get it by December. The bad part is I have to redo some cabinetry to accommodate the extra 3” length.
I could go with that! Made in India? Velit translates to outdoor in Latin. There is a similarly named company in the UK called Velit Outdoor rather than Velit Camping.
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Old 09-29-2022, 07:18 PM   #9
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You can set your Webasto heater for high altitude and there are several videos and instructions available on how to do.

One at https://youtu.be/yL8R3yGLMII
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Old 09-29-2022, 07:34 PM   #10
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You can set your Webasto heater for high altitude and there are several videos and instructions available on how to do.

One at https://youtu.be/yL8R3yGLMII
That's how we got from 5,000 to 7,500 ft.
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Old 09-29-2022, 07:44 PM   #11
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……………..
I also don't really understand the description of the problem. If you are burning off all the fuel before the next pulse goes in, wouldn't you need less oxygen to slow down the combustion burn time per pulse?
Based on my experience combustion is continues with pump pulses in sub second range. There is sufficient buffer volume in the fuel feeding system to the combustion chamber to provide constant flow of fuel. Slight slow-down of pump frequency for higher altitude is within this buffer capacity. I really don’t think there is a problem with maintaining stoichiometric fuel to oxygen ratio by adjusting dosing frequency.

Main issue with diesel furnaces is dirty combustion often cleaned by running kerosene. I have no issues with my Airtronic and Hydronic diesel furnaces, my method is to run on high for an hour after each use.
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Old 09-29-2022, 08:15 PM   #12
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Originally Posted by MsNomer View Post
We leaned out our gas AT2000 as much as we could and run it up to about 7500 ft. No good when we're freezing at 10-12,000 ft. So we have ordered the new kid on the block:

https://velitcamping.com/products/ve...eater-17000btu

A guy I trust has fondled the heater and met with the head engineer. He was impressed. Specs are still fluid, as they are still tweaking it. They estimate I should get it by December. The bad part is I have to redo some cabinetry to accommodate the extra 3” length.
Interesting product - "the Velit air heater features a dynamically balanced blower fan and an ultra-quiet fuel pump" Continually variable air flow will keep stoichiometric ratio constant, good luck.
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Old 09-30-2022, 02:48 AM   #13
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If Velit is real then Webasto needs to up their game. Looks like combustion air flow is further increased once the lower limit of fuel pulses is reached.

I still like the idea of a shot of nitrous! That could heat your butt at 10,000ft.

Thanks MsNomer. Gives us a progress report if they ever ship it.
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Old 09-30-2022, 08:52 AM   #14
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Before pump frequency device for higher altitude Eberspacher used a pump with lower flow – shorter stroke. https://www.heatso.com/espar-eberspa...for-d2-d4-12v/ Owner had to switch correct pump for altitude from two pumps, valve and electric switch.

My experience with gas furnace from 1985 (It was either Eberspachrer or Webasto, don’t remember) was terrible. Ignition then was different, it used spark and glow plug combination. It was installed on my VW Westfalia in Germany. Failure was with the ignition system specifically the special glow/spark plug - https://www.butlertechnik.com/ebersp...3-gze201-p1225 required often changes due to fouling electrodes.

In 21st Century I would think that DC/Inverter variable motor blower with Lambda sensor (1.5A > 200mA draw), which could be active only during startup, with current positive displacement pulse pump could be a good solution. https://www.amazon.com/TAMKKEN-Downs...s%2C239&sr=8-5

I am surprised that most of the manufactures of gas power furnaces just adapted diesel furnaces without, seems as necessary, changes for high altitude.
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Old 09-30-2022, 02:58 PM   #15
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One of the major contributors to the unreliability of these heaters is cavitation in the vacuum-side of the fuel system, which causes excessively-large bubbles in the fuel, leading to flame-out, leading to fuel-rich restarts, leading to premature sooting. This happens both with diesel and petrol, but is apparently more severe with the latter. The problem is more severe at elevation. This is why the specifications for fuel lines are so strict (rigidity, run-length, pump orientation, line diameter, connection techniques, etc). It is extremely important to follow these specs exactly, which people often do not. When my van was built, GWV installed a run of too-large fuel line. As a result, the system was unreliable until the fuel line was replaced, after which it works flawlessly. Many Transit owners use the Ford factory aux fuel pickup standpipe to avoid having to modify their fuel tanks. But, the diameter of this pipe is much too large, compared with the Espar unit. I strongly suspect that these practices greatly contribute to the "these things don't work at altitude" trope.
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Old 09-30-2022, 04:24 PM   #16
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One of the major contributors to the unreliability of these heaters is cavitation in the vacuum-side of the fuel system, which causes excessively-large bubbles in the fuel, leading to flame-out, leading to fuel-rich restarts, leading to premature sooting. This happens both with diesel and petrol, but is apparently more severe with the latter. The problem is more severe at elevation. This is why the specifications for fuel lines are so strict (rigidity, run-length, pump orientation, line diameter, connection techniques, etc). It is extremely important to follow these specs exactly, which people often do not. When my van was built, GWV installed a run of too-large fuel line. As a result, the system was unreliable until the fuel line was replaced, after which it works flawlessly. Many Transit owners use the Ford factory aux fuel pickup standpipe to avoid having to modify their fuel tanks. But, the diameter of this pipe is much too large, compared with the Espar unit. I strongly suspect that these practices greatly contribute to the "these things don't work at altitude" trope.

That is the same thing that used to happen with gas vehicles that had the fuel pump by or on the engine, it sounds like.



A small booster pump at the tank would probably take care if it at all altitudes, even with a too big feed line.
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Old 09-30-2022, 04:38 PM   #17
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A small booster pump at the tank would probably take care if it at all altitudes, even with a too big feed line.
That's an interesting idea. I haven't seen it proposed before.

Sort of a band aid, since a properly set-up system works fine. However, for folks insisting on using the Ford factory standpipe, it might be a reasonable option.
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Old 09-30-2022, 04:43 PM   #18
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That's an interesting idea. I haven't seen it proposed before.

Sort of a band aid, since a properly set-up system works fine. However, for folks insisting on using the Ford factory standpipe, it might be a reasonable option.


What elevation can you get to with your unit, although diesel should not have anywhere near the issue as gas for cavitation?
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Old 09-30-2022, 05:29 PM   #19
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What elevation can you get to with your unit, although diesel should not have anywhere near the issue as gas for cavitation?
We haven't had ours higher than our place near Santa Fe -- 7100', but there are plenty of reports of successful 10K' operation.

But, our unit is extremely well-behaved everywhere we use it. Huge contrast to before our fuel line fix. My guess is that perfect behavior at low elevations is correlated with adequate behavior at altitude.
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Old 09-30-2022, 05:34 PM   #20
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I am using the Ford pickup and I have stepped down the fuel line to 1/4” and it runs to a small lawn mower fuel filter then to the Webasto fuel pump. I haven’t had any issues with air in the fuel system except if I have less than 1/8 of a tank of fuel where it will draw air as the Ford auxiliary fuel pickup is not on the bottom of the tank, so you don’t run out of fuel for the truck using the auxiliary pickup for other purposes like heaters.

If this happens I do have to reprime the system to the fuel filter and I have a boat fuel bubble line primer that I use to suck fuel into the fuel filter and the heater fuel pump keeps the rest of the fuel system primed.

I too came from the VW school of gas heaters and the current crop of heaters are way more reliable than my 69 and later 92 Westfailia gasoline heaters. You were always fixing them when the temperature was always well below freezing.

My heater has been bulletproof as long as the fuel tank is not run down less than about an 1/8 of a tank.
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