Turbo V8 Stove Mod
In my quest to build and test various models of alcohol stoves I recently tried making AYCE's V8 stove design. I liked the very small size, light weight, simplicity, and ease to build. The problems I found with it were:
1. Priming increased fuel consumption. Priming fuel wasn't being used at all to transfer heat to the pot, only to heat fuel.
2. Pot height above the burner was too close for efficiency. Moving burner holes lower or pot higher could solve this problem.
3. If priming wasn't done properly the pot could put out the flames. No way around this with the current design.
4. it wasn't as efficient as other alcohol stoves. Mainly because it didn't create enough heat. My guess was inefficient fuel pre-heating, poor air flow to the burner because of pot placement, and conservative burner hole diameter.
So I emptied a couple of more V8 cans and started from scratch using some stuff I've learned about alcohol stoves over the months of building and playing with them.
Instructions to build my stove are now listed here. The basic model is AYCE's V8 which is simply a soda can stove made with V8 cans because they are smaller. Here are my modifications:
1. Omit the priming cup. Unnecessary with new modifications.
2. Make the burner 1 1/4" tall instead of 1 3/4" tall.
3. I added some fiberglass insulation between the two walls. I have found that the fiberglass helps in the pre-heating of the fuel, and helps to wick fuel away from the inner chamber where you add it to the outer chamber where it should burn.
4. I used a metal screw as a drill to open up the burner holes. I also added more so that there is now 24 holes around the outside just below the lip of the burner. The holes were opened until I could push a ballpoint pen tip through them. This opens up to higher fuel consumption, but also makes for a hotter burning stove.
5. Using some metal adhesive tape I taped over the seam between the burner top and the fuel reservoir. More for durability than for performance.
6. Using a 4 Square x 10 square piece of metal hardware cloth I made a raised pot stand above the burner. Cut the end off the 4th square and bend out for extra pot stability. I actually experimented holding the pot above the burner with my hand until I came up with the optimal pot height, then made the stand to that height. This allows air to get into the fuel chamber during priming while using the fuel consumed during priming to help heat the pot. After the stove has "passed its prime" the flames reach there hottest point at the bottom of the stove. If you have used this stove in the past, you will notice how much larger the flames are now.
Turbo V8 stove (cool name eh)
Weight: .6 ounce stove, .6 ounces windscreen, .6 ounces for 10 ounce fuel bottle. Total = 1.8 ounces.
Materials: 2 V8 juice cans, some fiberglass insulation, some metal tape (optional), and a 4x10 square piece of hardware cloth.
Tools: Knife, scissors, metal screw, and a pair of pliers.
2 cups of water at room temperature – 65 degrees.
Pot used is a Snow Peak 720ml titanium pot without lid.
Stove used the same windscreen as my Cat
Alcohol was tested in 6 ml increments, starting at 6 ml
Each amount was double checked using a scale. The weight of one fluid
ounce of alcohol is .82 avoirdupois ounces.
Each Test was repeated three times, the average was used.
Starting time was when the stove was lit.
Stoves were allowed to completely cool between tests.
Barometric pressure here was 30.15, the boiling point was determined to
be 212.43 degrees.
Altitude is 90 meters above
Thermometer used is an Ecko deep fat fryer thermometer, probe was ¼”
below water surface using a camera tripod. Estimated accuracy is ± 3 F.
Estimated accuracy is ± 3 F.
Air temperature was 65 degrees with the stove fan running to simulate a
13. Scale used was a
13. Scale used was a Royal EX3.
*** Notes. compared to earlier tests I added 6 ml fuel which is what I use when I just heat for some drinks and foods which don't require a full boil. I also added a column for time above 175 F which is the temperature I have found most foods to actually be cooking. Also note that the temperatures for water and room temperature are about 10 degrees colder than last time, brrr.
I am very happy with this new stove. Besides being smaller and lighter it also does the following:
1. It reaches the higher temperatures of the Cat using the same amounts of alcohol.
2. It maintains longer periods of heat, especially above 175 F than the Cat Stove which means more actual cooking time than the cat.
3. It is more efficient as well as lighter than the soda can stove.
I think a simmer cap could be made if you wanted to simmer on this stove. All you would need is a ring that covers the burner holes forcing the flames to stay in the center of the stove for a slower burn. However I recommend using a pot cozy for better fuel efficiency.
This stove isn't as stable as my other designs because of a narrower pot support. It works well with my small .72 L pot, but I wouldn't recommend it with a pot larger than 1 L. You could super glue a wider base on the bottom if you wanted to increase stability for a larger pot at the cost of about .1 to .2 ounces.
The only real test I haven't been able to do is test cold weather performance of the Turbo V8. Because of the pre-heating air jacket on the Cat it had good cold weather performance compared to other alcohol stoves. Because it lacks a pre-heater, the Turbo V8 may suffer at lower temps.
Red = Worst performer
Yellow = #3 performer
Blue = #2 performer
Green = Best performer
**Note. For purposes of this illustration I am considering my fuel bottle a 20 ounce soda bottle.
The Turbo V8 is more efficient using the numbers than the MSR pocket rocket or the Cat stove, but is worth the switch considering the amount of time it actually cooks.
Because of all the above listed information, I have decided to switch to the Turbo V8. Hopefully the cold weather doesn't screw me up.
And now for the next item. A heat exchanger. I also got this idea from the message board at Thru-Hiker.com, same place that has the V8 stove. The idea was to make a device that wraps around your pot and channels more heat to the pot. After watching the occasional flame go up the side of my pot wasting heat I decided to give it a try.
Using aluminum dryer duct I made cut two pieces 1 1/4" wide and bent them into a series of "U" shapes and then cut the top over each "U" to make a cap. Lastly I trimmed off the excess so now the heat exchangers are 3/4" wide. Hooking both together they stayed in place on the pot from tension. Total weight was .4 ounces. My wind screen was too tall, so I trimmed it down until it touched the bottoms of the heat exchanger - providing a funnel for the heat directly into the exchanger. This reduced my windscreen weight to .4 ounces.
My heat exchanger is fairly small because of my pot. If your pot had better surface area on the sides, you may give you better performance. But I think my curved pot already contributes to my pot/stove efficiency.
First test, melt 4 cups of ice using 1 ounce alcohol. 10 minutes later I had 2 cups of water at 175 F.
Now for the real tests. Using the same criteria as above this was the results:
The exchanger did improve performance at an overall .2 ounce weight gain. By improve I mean that it made the water heat faster thus allowing the stove to maintain heat above 175 F for a longer period of time.
Did it save fuel? Well, not really. It still takes 24 ml of fuel to reach boil. I suppose if I use an eye dropper to measure precise milliliters of fuel then I could say I saved X number of milliliters of fuel to achieve boil. But in field conditions 6 ml increments of fuel are easiest to meter out, so that is the standard for this test.
How about durability? Dryer duct is fairly thin aluminum. How will it stand up to constant use over many moths of trail conditions? That will take more trail and error (get it?) to determine.
So is it worth the extra .2 ounces of weight? Maybe. I'll try using it for a few hiking trips to figure that out.
I hate to delete info in case someone is looking for information about heat exchangers. So I am leaving up the update about heat exchangers.
I was looking for other ways to improve fuel performance on an alcohol burning stove. The goal was to achieve a boil with 6 ml of alcohol. I tried a variety of windscreens, heat exchangers, insulation options, etc. To test the efficiency of keeping on the lid I used a thermocouple and a multimeter to determine water temperature inside the pot, very cool!
I found that I improved max temperature by about 10° F by using the lid, but it didn't seem to increase speed to temperature significantly. I also found that over building your windscreen can have a detrimental effect by limiting air flow.
My heat exchanger was not very efficient compared to better windscreens. The problem is I could only cover a small surface of my pot with the heat exchanger, and it ended up acting like a poor windscreen at the top of my pot. By changing my windscreen and eliminating the heat exchanger, I got the same results as shown in the table on heat exchangers, but with less weight and complication.
In the end, I was able to consistently achieve a boil on my Turbo V8 stove using .66 fluid ounces of alcohol by using a good windscreen and keeping the lid on. My measure for .66 fluid ounces is the cap of an Evian 10 ounce water bottle. For some reason they make them with larger caps than the standard American soda bottle, each being .33 fluid ounces.
After working with some wind screen designs and doing some tests, I found the heat exchanger to be worthless, at least for my pot design. What I did learn was how to make a better windscreen.