Managing intake pulses on single cylinder engines

Anyone tried reed valves on fourstrokes? Probably not the best with sooty woodgas, but would be interesting to try, mounted in a “box” acting as a form of plenum.
I have to look up my books on gasifying of big, single cylinder hot-bulb’s, some good info about that in the book: gengas.
For the ones interested to try reed’s there are kevlar/carbon fiber material for making own reeds available, easy to cut with a dremel, and fairly cheap, and best of all: stays in shape, don’t slightly bend over time as steel-reed’s.


Goran, you only take halve of the pulse away. At max.


The no moving parts way to handle pulsing like this is to connect a long skinny pipe to a volume (like a propane tank) between the source (gasifier) and the pulsing drain (engine). The long pipe is probably already there. It’s the buffering tank that would need to be added.

The tank volume absorbs most of the pulse like a spring and then the momentum of the flowing gas in the long pipe prevents the remaining back pressure pulses from reaching the gasifier. It’s like your classic mass and spring mechanical engineering or a snubber in electronics but handles gas pulses.

The problem here is that you don’t want to have lingering mixed air and fuel. I guess you could have two tanks and two pipes… one for fuel and one for air.


Hmmm now that I have a 3D printer, I bet I could print a Tesla valve. No moving parts


You’d only need a tesla valve on the air intake to avoid losing fuel gas. The intake air is guaranteed low temp and plastic friendly. Great idea Matt! That is definitely worth a try.

I still think a small buffer tank just ahead of the mixing valve is still relevant. (1-3x engine displacement). Any reduction in the pulsing from the fuel side will reduce the performance requirements for the valve on the air intake side.

The basic problem here is that the intake stroke pulls fuel gas down a long hose, getting all that mass moving pretty fast. Then the intake valve slams shut with no other cylinders ready to pull in turn (single cylinder). The fuel gas is already moving and wants to keep moving so it spills out of the air intake. So… give it a place to go before the intake valve opens next?

Weirdly you’d want the “tank” to be more like a plastic (silicone?) bag that would deflate rather than fall below atmospheric pressure. A fixed volume tank could come into partial vacuum, sucking in air and risking pre-ignition but I’m getting ahead of myself again.


As usual, out of my pay grade. I think I understand that you are looking for ways to re-establish a more continuous flow from that which is chopped up by the blockage of the intake valve whereas in a multi cylinder engine the gas flow maintains velocity by transferring to an different cylinder. I had never heard of a Tesla valve before. For you other dummies like me, here is a video.

I don’t really grasp how this much restriction in the gas stream is a benefit.


Me too Tom. But great invention.

On the other hand, the pulses are used to increase cylinder fillings. Taking pulses away and restrict breathing further more result in less filling and less power.

Maybe bether adapt the gasifier somehow.


The Tesla Valve is a one way valve for high flow gas streams and it is esoteric. Few commercial products use them. A one way valve is useful here to prevent fuel gas from getting pushed out of the air intake… and a tesla valve might do that.

Unlike a check valve, tesla valves do not block pressure, just flow, and even then it is imperfect, though in its best use cases a tesla valve performs well. A traditional check valve blocks both flow and pressure more or less completely in the one direction but it has a moving part. In an engine that is cycling dozens of times a second traditional check valves may struggle to toggle quickly enough and may not survive long run times.

Matt’s instinct here is a good one. Tesla valves are very appropriate to the task.


Thread summary (for myself);
–Single cylinder engines have large intake (and other) pulses as the mass of air/fuel in the intake manifold is accelerating, stopping, and rebounding, with each intake valve cycle.
**The complexity of the pulsing effects is compounded if you have two independant masses of gas (air and woodgas) in unequal volumes bouncing around. In my case (and in my little video), the char gas volume is large and massive and the air volume is small. The char gas is accelerated by the engine vacuum, and when the intake valve closes, its momentum causes it to reverse the flow at the air inlet, losing some fuel gas to the atmosphere in the process.
**Another issue is large RPM related gas mixture variations. For the setup in the video, there is a large difference between a startup air setting and a run setting. The problem being, you have to switch between them almost instantly as the engine starts and RPM comes up… you are chasing a moving target. This shows up as the engine being ‘hard to start’ when it really shouldn’t be. It won’t start on the ‘run’ setting and it won’t run on the ‘start’ setting.
**A third issue is intake tuning, with a mismatch between intake resonance and engine RPM resulting in lower cylinder filling, lost power, and increased pumping losses.

Intake tuning:
Probably the least important issue, but does anyone have any idea how significant this issue might be for a small single cylinder engine? I would assume the ideal runner length would be pretty short for a small engine at higher RPM. If so, the tube from carb to filter in my setup in the video could be affecting performance.


Chuck - all that you’ve summarized looks right to me.

The simplest thing I would try is a long tube on your air intake. It would help balance the pressure pulses between the fuel gas and air intake so that the mixing is more even. It will also prevent loss of fuel gas from reverse flow because now the air supply, like the fuel gas, will be moving in one direction that doesn’t easily reverse.

You will have done nothing to prevent pulsing, just tried to get better balance between the two sides. Reducing the pressure pulses is more complex and only worth the hassle if the air hose doesn’t work well enough.

There are ways to measure the pressure difference between the fuel and air sides and be scientific about it but the simple ways wouldn’t be quick enough to see what happens over a single pulse. I have one idea but it is still more complicated than starting with a really long air hose (6 feet?) and cutting it down until the engine and gasifier is behaving well.

Six feet of hose and an hour of testing wouldn’t put you out much. Worth a try?


A good gas mixer, where the mass flow of the gas determines the air flow, eliminates most of the inconveniences during start-up and operation. I stole this video from Kristjan, where you can see that despite the vacuum cleaner working, the engine runs unhindered, but I have to admit that due to poor filtration, the moving element soon stopped. Now I have to change the construction so that it will work without any downtime.


I agree with AnthonyB., ChuckW . . . a very good summation.

On the air-in side it will help MUCH to install a motorcycle type cone air filter right off the bat.
In addition to filtering the air it will add some flow restirction to help banace the flow resriction on the fuel gas side of it. Or chargas system restiction to flow.
Tuning length?
For low-speed 91500-2500 RPM) best torque it is long on the intake side. Shorter on the exhaust side. Look at the post 2000’s big vehicle four cylinders of Honda, Nissan and Toyota for examples of this. Their big fours with variable length intakes tuned for 1800-2200 RPM freeway cruising.
Ford 90’s 302/5.0L V-8’s shows this too. Long tall individual intake ports on the pickup engines. Shorter on the passenger car applications.
I did try out to 48" once. Too heavy, bulky, clumsy.
Length added past the throttle plate does count too.

The makes it confusing is using the engine intake capable suction to flow power the gasifier/filter train.
My still-on-napkin-ideas are to start by using a constant low pressurizing electric blower sucking the gasifier and then delivering the fuel gasses. Done that a limited amount. The needed blower for a small engine single only consumes ~178 electrical watts.
Yep. How to variable meter that flows needs delivery. Various ways. Don’t know which will shake out as best yet.


I have been thinking the same way for a while but don’t know if the blower, before or after the mixer, would throw off the air/fuel ratio.


Set up the blower with a micro switch that is triggered by the governor. Just need to boost during loading. Ive done this with amtek blowers and it does work and is good for 500 to 1000 watts of output boost. But that also requires power to run the blower. So use a moderate charging system to maintain a battery storage system and only boost when needed.

Next spring Im going to 3 D print a throttle body that will replace the stock carbs with the bore opening matched to the intake runner port of the engine head. That alone I think will be one the biggest performance bolt on upgrades you could possibly make.


Ok designed up a two vain Tesla valve for 1 1/4 ID hose. Started the print just now, so hopefully it will be done by some point mid day tomorrow. Yeah that 3 D printer is a game changer, I can now custom design my fuel mixers with the servos integrated and eliminate some expenses in pipe fittings, hose adapters etc.

Ill post some pics later in the print process so we can get a real cross section view.

I think there will be some performance gains beside just letting our air mix out. Theoretically speaking I think this will create some backing presure on the intake side. So as the engine pulses back it cant go anywhere so it will produce a high presure pre charge sort of like a turbo or super charger.


The 3D printers really cover their costs when you figure in all the plastic stuff you’d have to have purchased without it.

I need to see if McMaster still has free .stl files for their items.


Oh you have no idea, just wait! Yeah Im printing out a mini 68 K-10. I might even print a WK gasifier complete with cooling rails to drop in the back!! LOL These are my first prints. This truck other than the lexan skin does not exist other than on my shelf. Yeah I litterally set up a brand floor pan for my real truck in my kitchen and scaled to 1/8th scale.


Couldn’t help but mention your guitar on the right. The body looks a lot like the one Joe Bonamassa is playing in this video. I never could see the make. I know you build your own kit guitars. Just wondering.


With exception of the Les Paul, I have three PRS style guitars. One is a real PRS (far left) and the other two are Harley Benton knock offs. The Harley Bentons are actually better than the PRS. The PRS cost almost $1000 bucks shipped and I spent days doing set up work on it. The Harley Bentons cost just over $300 shipped from Germany to my door in less than a week and I had only a few hours into each set up. I also have an Ibanez 335 style hollow body.

Cant build them for what you can just buy the Harley Bentons for and what you get is way beyond the price you pay. Id buy another in a heart beat but I think 6 guitars is enough. lol.


Here are a few pics mid way thru the print process. Yeah its still printing lol. This is one item at least in the way I designed can really only be accomplished with a 3D printer. No other way to produce it.