To shake or not to shake that is the question

To shake or not to shake that is the question, when the gasifier and motor reaches an equilibrium?

Most of the time we are using the gasifier the throttle plates of the intake manifold are the bottle neck or restriction of the entire system . This includes the air entering the heat exchangers going through the complex fire tube housing, nozzles , wood , char bed and ash , grate back through the heat exchanger , cooling rails , hay filter , motor plumbing , throttle plate , intake manifold , the motor cylinders and out the exhaust .

Most of the time we are driving we can open or close the throttle to change the vacuum inside the motor as well as the vacuum in the gasifier. If we give more throttle the vacuum inside the motor decreases and the vacuum inside the gasifier increases.
There may be times when operating the gasifier that it reaches equilibrium. When opening the throttle more it changes no vacuum in the motor or the gasifier.
The gasifier can get in a state where the fine particles and the char depth can restrict the system more than the throttle settings.

One has reached this point when, for example, opening the throttle from ¼ to ¾ throttle has no effect on the system and the gauges stay the same.
This is no problem when out cruising especially on flat roads. You may be driving the speed limit or a comfortable speed. At this point the gasifier is usually making its cleanest gas and with the best efficacy.

If one has the need for speed, more power,rpms and air flow it only takes a flip of the grate shaker switch to open the restriction, but don’t over do it. If you over do it you have slipped char to the ash dump , thus wasting energy ( unless recycling the char after used) , loosened the char bed enough that oxygen might make it beyond the gate ( heater mode) and the possibility of making some tar.

My rule of thumbs are if I have enough power to do what I am doing, not to shake.

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Wayne,
If you were to fill the gasifier up and drive your truck say 20 miles down a flat state route to town at 60 MPH would you expect to have to use the grate shaker at all? That is my normal trip and I do not have a grate shaker. I stick a piece of rebar down the fire tube and tap the grate a few times before I start the unit up, but that is the extent of my grate shaking other than what naturally occurs due to highway vibrations, bumps, etc. I don’t think I’m really missing much by not having a grate shaker in this scenario but wonder what your thoughts are. I realize this is hypothetical for you since you have not driven my truck, but I am curious what you think about me not having a grate shaker nonetheless.

Hello Mr. John C,

“If you were to fill the gasifier up and drive your truck say 20 miles down a flat state route to town at 60 MPH would you expect to have to use the grate shaker at all? “

NO

“That is my normal trip and I do not have a grate shaker.”

Shouldn’t need one for those trips

“I stick a piece of rebar down the fire tube and tap the grate a few times before I start the unit up,”

Perfect

“But that is the extent of my grate shaking other than what naturally occurs due to highway vibrations, bumps, etc.”

Contrary to popular belief I have found little effect from the above loosening the char bed or grate. With the above one is also shaking the hopper and fire tube and might be packing it tighter.

“I don’t think I’m really missing much by not having a grate shaker in this scenario but wonder what your thoughts are.”

John, you are perfectly correct, in that scenario you shouldn’t need a shaker.

“I realize this is hypothetical for you since you have not driven my truck, but I am curious what you think about me not having a grate shaker nonetheless.”

John,
With these deep fire tubes there are a chance that some char will get on the grate plugging the holes and the fines start building up just above it. We may not be using the vehicle hard enough to pull the oxygen plum all the way down to the grate thus burning the char blocking the holes to let the fines purge on through the grate.

By relighting your gasifier each day with less than a hundred miles driven you are starting the fire at the grate and this relighting is giving any char that might be at the grate blocking the fines the opportunity to burn and release the fines on through the grate.

Where the grate shaker comes in handy is on long trips 400 plus miles where there is no opportunity for relights. At each refueling I can run a rod down through the char and even funnel it out some but as the gasifier is drawn on the fire is originating near the nozzles and uses the oxygen before it can get near the grate.
When I have to shake the grate I understand that very little of the char is coming through the holes. However it causes the char to fall of the side (wasted char) with some on the fines to follow. This gives the oxygen (maybe with a little over pull of the motor) an opportunity to get near the grate where it may help burn char pieces blocking the holes.

Sean may want to chime in , gasifier characteristics on long trips

To make a long story short, the gasifier is more likely to plug on long trips vs. routine operation and moderate trips if lit up each day as you describe.

One foot note. The wood I use may have a lot of small particle and saw dust mixed in that goes on in the hopper. This might make my gasifier need a little shake now and then.

Thank you Mr. Keith for such a thorough reply. That helps me understand the internal workings of the fire tube much better. I didn’t think I was missing much by not having a shaker with my driving patterns, but never hurts to ask the expert. Best regards.

Nice stuff Wayne, I have always run fixed grates and mount my gasifiers on the passenger side so I can occasionally drive off the shoulder a bit and knock things down by running on the gravel or driving over a driveway skirt. I did accidentally run over a huge pile of gravel one time with the 91 olds. The road grater had left a huge pile just over a hill and I had waved some guy by me so I could not pull left or stop … I’m surprised that rotten old car survived that bump. It was like the dukes of hazzard … I find it hard to believe how many cars and trucks I have been through. Sue asked me to list them last year and there were over 50 that I remember that I legally had on the road. I think I’ve been through around a dozen on woodgas now … Just keep an eye on that vacuum gauge. When it goes up and the power or temperature goes down, you know what to do … Occasionally I have to poke all the way to the grate and clear as much of it as I can from the top. On a few rare occasions I have had to run things right to the bottom and then reach all the way in and clean the grate. I always build my units so I can reach through the restriction with my hand and do this and even work a wrench on the bolts holding the rotors together … I swore I would never build a hopper too tall to do this again. I have a gasifier in the trailer house that is too tall and would be too tough to take apart now to change anything. I built it to take stick wood vertically … ML

Hey Wayne,
Your spot on a shaker is nice for the long rides.I remember using mine on the Ford once every 125miles heading up to your place. The longest I am driving most times on the Dakota is 100miles and still haven’t mounted my shaker motor on the gasifier wanted to see if I would miss it or not. For these short runs you really can get by without one being more efficient in the process. Sean

Wayne just loves to hit that shaker switch. It is fun to watch the vacuum gauges change when he does. Up here, the bottom of the gasifier would be so rotten after 2 years that it would just fall out :o) … I’m not joking either. The shaker motor would be rotted as well. Some times like right now, I wish I was in Dixie. I just was able to drive my survey truck back into the shed in 4wd-low. We had a real january thaw. Now there is a lot of bare ground and the frost will go down 3 or 4 feet in the next few weeks … The drought continues … ML

I remember reading Vesa’s book from Finland. He suggested running with your wheels on the side of the road. A few potholes would do the same as a shaker. Seriously!