Gasoline Webasto at altitude

[hbn7hj]

I agree with MsNomer. Good to 7500ft. It will crap out within a week at 10,000ft. It will really be nice if Velit delivers. I have the original propane furnace so I won’t freeze but I hate chasing propane.

[hbn7hj]

Originally Posted by GeorgeRa

https://www.heatso.com/espar-eberspa...200-h-kit-hak/

I noticed that the Heatso link has a reference to a Webasto high altitude kit for STC petrol heaters for $648.70. (At the bottom) That is more than I paid for my Russian Webasto but at least they are doing something.

[hbn7hj]

The Velit website now has a user manual available.

The parts diagram has a part called a compressor wheel. Maybe that is how they do it. Increasing the combustion chamber pressure would solve all problems. There is still only one motor.

The January date still holds for the moment.

[hbn7hj]

Such a simple solution. Neck down the exhaust, put a better fan on the front. Embarrassed I didn’t at least think of the possibility. If it works, all brands will adopt it and altitude coking will be a thing of the past.

[MsNomer]

ETA is now February because of China's Covid crisis.

[GeorgeRa]

Originally Posted by hbn7hj

The Velit website now has a user manual available.

The parts diagram has a part called a compressor wheel. Maybe that is how they do it. Increasing the combustion chamber pressure would solve all problems. There is still only one motor.

The January date still holds for the moment.

My Airtronics D2 has a fan to force air flow around combustion chamber heat exchanger and compressor wheel to force air into combustion chamber. Webasto is the same.

This new heater has built-in barometer to adjust fuel flow. It is likely a simple algorithm: temperature delta, barometric pressure > heater air fan RPM, fuel flow to maintain correct stochiometric oxygen to fuel ratio throughout full range of delta T and barometric pressure/elevation.

I believe that new Airtronics works the same way.

It looks like price went from $300 to $650.

[MsNomer]

Final price has always been $649. $300 is the deposit, which I have paid.

[GeorgeRa]

New third generation Airtronics is good up to 18,000' with long life and quieter brushless motor.

https://www.eberspaecher-climate.com...a_sheet_EN.pdf

"THE NEW AIRTRONIC 3 PRODUCT FAMILY With the third generation of the Airtronic, Eberspächer is launching a completely new product family of air heaters for commercial and special vehicles. It combines high heating performance with a very compact design, quiet operation, automatic altitude adjustment up to 5,500 m* and flexible installation. The Eberspächer EasyStart Pro and EasyStart Web control units offer particularly convenient and user-friendly operation for the Airtronic. All other control units are also compatible."

https://www.youtube.com/watch?v=FtmxPSs0qC0

[booster]

Originally Posted by GeorgeRa

New third generation Airtronics is good up to 18,000' with long life and quieter brushless motor.

https://www.eberspaecher-climate.com...a_sheet_EN.pdf

"THE NEW AIRTRONIC 3 PRODUCT FAMILY With the third generation of the Airtronic, Eberspächer is launching a completely new product family of air heaters for commercial and special vehicles. It combines high heating performance with a very compact design, quiet operation, automatic altitude adjustment up to 5,500 m* and flexible installation. The Eberspächer EasyStart Pro and EasyStart Web control units offer particularly convenient and user-friendly operation for the Airtronic. All other control units are also compatible."

If they are modulating the fuel then that would mean the output capacity drops also?

[GeorgeRa]

Originally Posted by booster

If they are modulating the fuel then that would mean the output capacity drops also?

I think so, maximum heater heat output will be reduced by lower oxygen content, just like lower power of internal combustion engines with altitude.

[booster]

Originally Posted by GeorgeRa

I think so, maximum heater heat output will be reduced by lower oxygen content, just like lower power of internal combustion engines with altitude.

I think that would be good for the buyers to know how much so that if they like to camp at higher elevations, they won't wind up under needed capacity. Less heat from the heater and colder because of altitude could make for a cold trip.


I just looked and a natural gas or propane home furnace derates the output by about 40% at 10,000 feet.

[GeorgeRa]

Originally Posted by booster

I think that would be good for the buyers to know how much so that if they like to camp at higher elevations, they won't wind up under needed capacity. Less heat from the heater and colder because of altitude could make for a cold trip.


I just looked and a natural gas or propane home furnace derates the output by about 40% at 10,000 feet.

Same from another site - it is about 3.5% / 1000' https://westerntransportationinstitu...l_Altitude.pdf

[hbn7hj]

Originally Posted by GeorgeRa

I think so, maximum heater heat output will be reduced by lower oxygen content, just like lower power of internal combustion engines with altitude.

Depends. If they are pressurizing the combustion chamber the BTU output will not drop.

Webasto explained they could not reduce fuel flow less than that required at 5000ft. because the flame would go out between fuel pulses. Up till now no one was pressurizing the burner chamber.

We don’t know how Espar is solving the problem. We think we know how Velit is solving the problem.

Were I trying to solve the problem I’d plumb an altimeter into the combustion chamber, neck down the exhaust and see what it would take to keep burner pressure at 3000ft when at 10,000ft. Certainly an interesting technical exercise!

I don’t know how to calculate how many watts it takes to increase the pressure of a specified air flow from 10,000ft to 3000ft. A thermodynamic problem, I think.

[GeorgeRa]

Originally Posted by hbn7hj

Depends. If they are pressurizing the combustion chamber the BTU output will not drop.

Webasto explained they could not reduce fuel flow less than that required at 5000ft. because the flame would go out between fuel pulses. Up till now no one was pressurizing the burner chamber.

We don’t know how Espar is solving the problem. We think we know how Velit is solving the problem.

Were I trying to solve the problem I’d plumb an altimeter into the combustion chamber, neck down the exhaust and see what it would take to keep burner pressure at 3000ft when at 10,000ft. Certainly an interesting technical exercise!

I don’t know how to calculate how many watts it takes to increase the pressure of a specified air flow from 10,000ft to 3000ft. A thermodynamic problem, I think.

Depends. If they are pressurizing the combustion chamber the BTU output will not drop.
Agree, but implementation could be expensive. To maintain the same pressure in the combustion chamber by compressing intake the exhaust back pressure would need to vary accordingly. A variable back pressure exhaust could be expensive.

Webasto explained they could not reduce fuel flow less than that required at 5000ft. because the flame would go out between fuel pulses. Up till now no one was pressurizing the burner chamber.
It is a matter of pulse volume and frequency, higher frequency pump at sea level should accommodate 40% lower flow with right size volume buffer while maintaining good continuous flow to an evaporator.

We don’t know how Espar is solving the problem. We think we know how Velit is solving the problem.
I think there is no difference, variable fuel flow without extinguishing at all heater outputs.

Were I trying to solve the problem I’d plumb an altimeter into the combustion chamber, neck down the exhaust and see what it would take to keep burner pressure at 3000ft when at 10,000ft. Certainly an interesting technical exercise!
A lambda sensor (level of oxygen in exhaust) could be more reliable while helping to control pollution.

Eberspächer is an old company from beautiful Esslingen which started developing automotive heaters in 1933. Their D2 version 3 is a state-of-the-art heater, I have no idea about Velit.

[hbn7hj]

I don’t think a variable back pressure exhaust is required. Variable intake pressure is easily handled with variable compressor rpm. We will see how they do it if they ever deliver.

The complication is can it be done with the same motor running the heated air fan.

The Webasto video on the VMAC website said that gasoline burned too quick to keep the flame going at lean mixture settings on the smaller heaters.

The important sensor to make it work would be combustion chamber pressure or altimeter. If Velit isn’t doing it that way it would certainly be worth a look. the important calculation is the one I don’t know how to do. How much energy does it take to compress burner air at a certain flow rate?

[GeorgeRa]

Originally Posted by hbn7hj

I don’t think a variable back pressure exhaust is required. Variable intake pressure is easily handled with variable compressor rpm. We will see how they do it if they ever deliver.

The complication is can it be done with the same motor running the heated air fan.

The Webasto video on the VMAC website said that gasoline burned too quick to keep the flame going at lean mixture settings on the smaller heaters.

The important sensor to make it work would be combustion chamber pressure or altimeter. If Velit isn’t doing it that way it would certainly be worth a look. the important calculation is the one I don’t know how to do. How much energy does it take to compress burner air at a certain flow rate?

I don’t think a variable back pressure exhaust is required. Variable intake pressure is easily handled with variable compressor rpm. We will see how they do it if they ever deliver.

To retain full heating capacity at sea level and high-altitude oxygen content would need to be the same. So, intake air pressure would need to be increase and exhaust would need have higher back pressure than high altitude ambient air would provide.

The complication is can it be done with the same motor running the heated air fan.
There is only one motor for recirculating air and for combustion air.

The Webasto video on the VMAC website said that gasoline burned too quick to keep the flame going at lean mixture settings.
It is the question of fuel pump pulse frequency, pulse volume, evaporator chamber volume and combustion chamber design.

The important sensor to make it work would be combustion chamber pressure or altimeter. If Velit isn’t doing it that way it would certainly be worth a look. the important calculation is the one I don’t know how to do. How much energy does it take to compress burner air at a certain flow rate?
Eberspacher has barometric sensor, I assume Velit as well.

[booster]

Originally Posted by hbn7hj

I don’t think a variable back pressure exhaust is required. Variable intake pressure is easily handled with variable compressor rpm. We will see how they do it if they ever deliver.

The complication is can it be done with the same motor running the heated air fan.

The Webasto video on the VMAC website said that gasoline burned too quick to keep the flame going at lean mixture settings on the smaller heaters.

The important sensor to make it work would be combustion chamber pressure or altimeter. If Velit isn’t doing it that way it would certainly be worth a look. the important calculation is the one I don’t know how to do. How much energy does it take to compress burner air at a certain flow rate?

I think you will run into issues if you try to vary the fan speed to control intake pressure because fans are too slow to react to changes in outlet pressure. Not only elevation in going to change the pressure as normal weather barometric pressure swings and pressure changes from the wind direction are also there.



Air is compressible so it can be quite hard to make it change pressure in a hurry. It is the same issue was we see in the vehicle engines. The old carburetor version constantly caused transition sagging or surging from throttle change positions. EFI engines do better because they can react much faster with the fuel rate changes, but they still have to control idle speed with the air, using a small variable orifice idle air motor.


You might get by with a pressurized box that would hold some volume to be available during quicker transitions and control the pressure in the box with a variable bypass valve. You would probably still need a variable throttle plate going into the combustion chamber.


One thing you need to remember that has not been mentioned is the any, and I mean any, time you have a pressurized combustion chamber you hugely increase the risk of CO poisoning. In furnaces in general it is against the safety rules, and probably many laws and codes, to have a positive pressure difference between the combustion chamber inside and outside. It doesn't matter if the pressure difference if from a positive chamber pressure or a negative circulation fan pressure. That is why you always see the combustion fan on the discharge end of the combustion chamber and the circulating fan on the inlet side with no restriction before the heat exchanger in you home or commercial high efficiency furnaces or water heaters.

[MsNomer]

"One thing you need to remember that has not been mentioned is the any, and I mean any, time you have a pressurized combustion chamber you hugely increase the risk of CO poisoning."

As soon as I saw the word "compressor" I started thinking increased risk. We have had a CO monitor since we installed the Webasto. Would there also be an increased fire risk?

[GeorgeRa]

Originally Posted by MsNomer

"One thing you need to remember that has not been mentioned is the any, and I mean any, time you have a pressurized combustion chamber you hugely increase the risk of CO poisoning."

As soon as I saw the word "compressor" I started thinking increased risk. We have had a CO monitor since we installed the Webasto. Would there also be an increased fire risk?

Espar, Webasto, Russian ones, Chinese ones are very similar. One end of a motor has a fan for recirculating heated air and on the other end there is a fan (compressor) to feed air into combustion chamber. As far as I know only Eberspacher is using brushless (DC) motor.

[booster]

Originally Posted by MsNomer

"One thing you need to remember that has not been mentioned is the any, and I mean any, time you have a pressurized combustion chamber you hugely increase the risk of CO poisoning."

As soon as I saw the word "compressor" I started thinking increased risk. We have had a CO monitor since we installed the Webasto. Would there also be an increased fire risk?

I don't think the fire risk would change appreciably with a pressurized combustion chamber.