Yes, the tricky part arises when you try and quantify those differences! I am also a bit of a numbers person, so I can understand the desire to measure everything, and arrive at the “right answer.” I wholeheartedly support you in finding good hard data, but I will also say that you can follow some very basic rules of thumb, and it will still work fine. If you are going to try and compile numbers, I would suggest you figure out some form of data-logger. I tried to keep tabs on like 5 or 6 variables once, and i spent the entire run scribbling down numbers.
I did not do rigorous testing, but I did see the start of a correlation with power output and nozzle airspeed. Sadly, its easier to make a hole bigger than smaller, so I noticed it as a loss of power when I enlarged the hole in my nozzle. Your screw-in nozzles will be convenient if you decide to test different sizes. I have used that spreadsheet too, and it should apply to any configuration of nozzles. There is also a chart floating around on here that talks about CO2 to CO conversion rates based on nozzle size and gas flow (ie nozzle velocity) and the differences are not huge. At some point the added drag of the system having to breathe through tiny openings is also going to counteract the richer gas that you should in theory be creating.
I think it would run fine in the current configuration, and will maybe run a little bit better with smaller holes. Only one way to find out
Carl, Thanks for your thoughtful observations and experiences. Correlation between power output and nozzle airspeed is interesting. I here reproduce the chart floating around and some charts I made to help interpret the findings-
It seems like you need 1300°C to make it worth while. But can you reach that with only 25 to 32 m/s air speed?
Sorry if I’m over-numberizing. I like to try to understand things in a way that I can understand precisely, at least as much as possible. I’m prepared that the real world of experimentation may not match the theories, but at least I have a starting point. More later.
Where does the conversion of H2O and CO2 to make woodgas take place, at the nozzles no, to much oxygen. It’s down at the reduction zone and going past that opening. This is where the charcoal is trying to stay alive but it’s using up all the oxygen. The hot preheaded air coming out of the nozzles is moving fast, lots of heat there, the hottest area of the fire tube. Then the air slows down in the fire tube area. This area is where the cooking of the wood or charcoal is finished and it turn into charcoal and the tars are being burn up and is turn into gases. It moves into the reduction zone, the air speed increase again and the oxygen is used up. The reduction zone I feel is of more importants, this is where the cracking takes place. Sizing the reduction zone for the engine seems to be over looked even in charcoal gasification. One person who is addressing this is @KristijanL with his new down draft charcoal gasifier. He has a grate and a reduction zone after the nozzles with preheated air coming into the fire tube.
It is okay to change the nozzles size as long as you change the reduction size also to match, so the air will speed up at the reduction zone where the conversion takes place. This zone is lacking in alot of charcoal gasifiers, Like mine. They still work but take a long distance of air movement to do it because the air speed does not increase. I think Kristijan is on to something good here with his small gasifier making good quantity of gasas in a short distance. This Ben Peterson gasifier has the same make up just at a larger scale size. I am really looking forward to seeing this gasifier run on charcoal by nozzle and reduction zone resizing to run a smaller engine.
This gasifier might be able to run long durations just by shaking the grate.
Bob
Bob’s right. We aren’t looking directly at the reaction zone when we look through the nozzle. So what I’ve proposed may not be a good control strategy at all. But then, it might come a little closer than we have been before. At this point this is all just a half baked idea. I wouldn’t sink a lot of money into it.
Anywho, we must crawl before we walk. I wouldn’t automate this thing to start with. I’d just run a control cable to move a ball valve handle. If this has a positive effect then …
Rindert
I should post more clips of the tests i do…
Instead of water drip, why not use tar condensate ?
Did this last time, injected it direct in the nozzle… i should have filmed my own face, jaw dropping…
The chart I was talking about was the one i referenced in an earlier post, Nozzles for Charcoal gasifiers, part 2 - #252 by oregoncarl
Which now that I look at it, and crunch some numbers, seems to be giving a totally different picutre than the table that is talking about the 3.2mm nozzle! I looked for the text of that book, but the only place i found it wanted me to sign up. I think it is safe to say that 1300C temperatures at the nozzle are not required to make acceptable gas, although I am now starting to suspect that I do not in fact really know enough to prove it
If you change the gas coming from the gasifier, you also adjust the air mix ratio to get at the most performing mix,
at the end, the gain is minimum,
However, if you reduce restrictions, you get MORE gas EASYER in your engine = maximum gain
The smaller the nozzle = more restriction = less gas in your engine = less shaft power
In the case of gasifier / gas my opinion is: quantity over quality
The second benefit from a little less quality gas is: the higher content of CO2 that comes with a little less quality gas = VERY important to reduce NOX formation in high pressure combustion (high CR)
I am awaiting analyzer sensoric to confirm this.
The gas with higher CO2 content also provides more CO2 going in the tailpipe / more easy to use some EGR to reduce/temper the reduction zone…
so much more that could be written… so little time left then to DO the fun things in life…
Actually starting to think about this now. @KristijanL reported increased power and economy when he added exhaust gas (EGR) to his previous MBZ e230 build. Much later he admitted to making wet tarry gas at lower speeds.
I suspect that his EGR inlet valve remained in the same position except when he manually changed it from behind the car. I would have been interested to know what would have happened if he had been able to change it as he was driving.
And as I think more about it I suspect that EGR or water drip could be varied based on the engine’s mass air flow (MAF) sensor with just a ‘correction’ from the operator based on throttle response.
Rindert
This is why I am planning on using a water drip into my exhaust pipe turning the exhaust to a hot vapor exhaust mix and then use a (EGR) inlet valve to fine tune the exhaust, that can be controlled from the driver’s seat while driving with a temperature monitoring devise and alarms (for to hot) or (to cold) of temperatures in the fire tube.
When running my charcoal gasifier the white hot glow of charcoal to bright orange to red glow was guick when adding more vapor/exhaust through my (EGR) valve. And the temperature following was lagging. But thats because of the turn down ratio I built into my gasifier unit. This testing was did in the fall months when it was cold.
I need to get back on this project and all the other ones once my shoulder get heal up a little more.
Bob
Koen,
I couldn’t agree more, in theory. But aren’t TCs (or other sensors) in the reduction zone problematic? Wouldn’t they be prone to be destroyed in a high-temperature-event, and and wouldn’t they tend to increase the likelihood of constipation? @KristijanL seems to have had something working in his previous MBZ e230 build, though not perfect. I’m just trying to build on his success.
Rindert
Hi Rindert, it was a litle different actualy. When l tryed EGR, l saw a increase in economy but not gas quality. I mean it wasnt worse but it wasnt better either, wich makes sence. With egr you allso introduce loads of nitrogen and no H2O so the gas composition stays relatively unchanged.
It is true, l occasionaly got moist and even tary gas. But that was at all gasifier loads, not just low demands. The reason being charcoal quality. Updraft gasifiers are incredibly picky. That was the major reason for me to kick the updraft out and build a downdraft gasifier.
Power and trurndown ratio sake, l was wery pleased with the updraft…
Bob, you sayd the CO formation takes place in the reduction. I have a big old chemist handbook that says carbon burns in air in to CO2, but after a certain temperature, it burns straight from C to CO without the CO2 faze. If that is true or not, l dont know.
On precise gasifier temp reading, l thod a lot about it too. I was thinking what if we put a pipe and a seight glass in parts of the hearth we want to monitor, and mount photovoltaic cells on each port. As temp goes up, so does radiation, so does voltage produced. Once calibrated l think thats a rather acurate device, and above all, cheap
Hi Kristijan, I am going to open up a can of gasification worms if I start talking here. So I will start a new discussion thread titled “Gasification frequencies”. I don’t want to highjack this great discussion going on here.
Bob
Bob, Your excellent explanation of the process also appears in Ben’s book in the section on ‘Key Concepts’, page 19-27.
And in another section of the book, Ben gives several alternative nozzle sizes, depending on the engine, but the nozzle size always matches changes in the reduction tube size (along with other things), so I guess my plan to reduce only the nozzles without the reduction tube will not work. Maybe a future experiment.
If I reduced the nozzle opening to 1/8", I would be increasing restrictions on flow, producing less power (thanks, @k_vanlooken). So I’m going back to the 3/8" nozzles, which are matched to the size of the reduction tube as per Ben’s plans.
Components of this BP gasifier have been sized according to the book, for the smallest engine possible, 500 cc, using wood chunks. I figured I could run my 200 cc engine by using smaller pieces of charcoal instead of 7/8" wood chunks. Also, I have reduced the holes in the grate from 3/8" to 1/8", so the smaller ground charcoal won’t slide through.
The grate on this gasifier shakes automatically for a few seconds every approx 3 minutes.
But if the air speed could be kept the same when restrictions are increased, by increasing pressure, then maybe gas would be same quantity and better quality?
Koen, Ben’s book says the combustion zone temperature is above 1000°C, and this air goes into the reduction zone, where the heat is used up to create CO and H2, so the temp decreases to 600°C. I think it is perfect advice to use reduction zone temperature to automate the EGR or drip. Right now, I have a thermocouple (measures up to 1300°C) in the combustion zone and a thermometer (measures up to 800°C) just after the reduction tube. In future, I plan to automate the drip using a TC in the reduction zone.
Rindert, I was afraid of heat destroying my temperature sensor in the reduction zone, so I put an 800°C stove pipe thermometer just after the reduction tube, before the air gets out to the heat exchanger. The plans for my gasifier say that the temperature goes down to 600°C in the reduction tube because of the endothermic reaction that creates the H2 and the CO, so I’m hoping the gas will be less than 800°C when it reaches my thermometer.
This sounds like a good idea. Have you ever seen a photovoltaic cell calibrated for temperature? I thought it was infra red that measured temperature. Different at high temperatures?
