Marcus. I started thinking about something you mentioned a while back about the cam in your truck and low vacuum. Why is vacuum more important for a wood gas engine that a gasoline engine?
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Only thing I can think is on woodgas more vacuum is needed for a good idle quality, to deliver the woodgas more steadily into the intake and be breathed in. Gasolineā¦honestly I donāt know why less vacuum doesnāt change more beyond the motor sucking harder for a short moment of time as it lopes across the cam. The bigger the lift of the cam the bigger the breath, but big cams arnt meant to idle they are meant for rpm to deliver more fuel more air into the cylinder. Less efficiency in some ways unless like you and I the efficiency you are chasing is passing the guy next to you and getting where your going as fast as possible. I believe @SteveUnruh will have a interesting take on this, he knows much more about efficiency in how a motor runs then me, and can probably explain the need for vacuum better
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Vacuum from the engine is what drives the gasifier to make gas. Gasoline is already made and just needs to be injected. No?
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Vacuum from the pistons pulling in air but I always thought that the point of manifold vacuum was to draw fuel up through the idle jet. With the choke plate closed you lack the differential pressure you get from the venturi you get with it open and pulling fuel from the main jets. Thatās why low manifold vacuum causes hard starting. Of course I donāt really know what Iām talking about.
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Friends, if we talk about the vacuum in the intake manifold, it is certainly lower when running on petrol, because the throttle is also much more closed and thus the air flow is lower. In the vacuum, gasoline evaporates quickly, which is a condition for ignition. Wood gas has a lower energy density and is already gas, so the throttle must be more open for the engine to capture a sufficient amount of combustible idle mixture, so in this case the vacuum is not so deep. If we look ahead through the system, filter, refrigerator, gasifier, we know that we need to supply a smaller amount of air to the gasifier to produce wood gas, because there are heat losses and compensate for this by additional wood combustion. So, the flow of gases sucked out of the gasifier by the engine creates a lower pressure than atmospheric pressure, so fresh air can penetrates the heart of the gasifier through the nozzles.
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So the larger profile cam in the vehicle engine should not have any adverse effect on wood gas fuel which is what I expected when I started thinking about it. We concede that more compression is a benefit to wood gas but it also seems to me that an engine with more stroke than bore would also be a plus. When we are talking about lower power from wood gas are we talking about torque or horsepower? All your driving is done somewhat below peak torque and well below peak horsepower. Other than race cars, peak horsepower has very little use. More stroke produces more usable power. Horsepower is not what pulls you up a long grade. Now this is debatable but even with higher compression, the flame spread across the surface of a piston would seem to create less downward force than a smaller bore which would be off set some by greater volume of fuel. Iām just trying to figure what the optimum wood gas engine would look like.
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I donāt want to be too clever , but my understanding of the engine is that , so , a large piston stroke and a smaller diameter does not mean a higher torque engine , it is true that the surface area exposed to high temperature at ignition is smaller and thus less heat loss than in the case of a larger diameter and shorter stroke piston , but when the piston is moving downwards , the heat transfer surface area increases rapidly and eventually exceeds that of the second case. The higher frictional losses due to higher piston speeds should not be neglected, nor the higher pressure drag due to smaller valves. Somehow it seems to me that the best ratio between the cross-section and the piston stroke is a little more stroke and less cross-section, say 1,3 : 1.
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Gentlemen youāve now split onto two-three separate issues.
You most defiantly need high engine idle vacuum to be able to pull woodgas past all of the gasifier system drags for flows. Stick your loping low idle vacuum high lift camshafts up your a**.
Liquid fuel injected engine do not need manifold vacuum for the fuel delivery as such. Engines still need air sucked in!
Carbureted engines: and woodgas system supplied engines, do need manifold vacuum unless you are going to boosted pressure systems.
Engine and motor torques are to get things moving. Makes for the best changes in state.
HorsePOWER is what is needed to maintain RPM against increasing loads.
Horsepower IS what gets you up a long, long road grade.
VW van; 18-wheeler truck; old crapped out Rambler sedans; woodgassed vehicles . . . same, same. Horsepower limited. You WILL slow down. Down shifting until your speed matchās available power.
Woodgas engine optimizations?? Gums gnashing.
Use the engine that comes with the needed equipment and make the woodgas work. Adapt your usage to what woodgas can do in that equipment. Or change the equipment/engine to something that can for you on woodgas.
An engine highly optimized for one specific fuel will be unable to operate on any other fuel well. Period.
Ha! Of course, this last is my opinion.
Steve Unruh
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I hope you are happy. Your making my head hurt. Itās not used to having to think this much.
Iām asking. Does wood gas require a venturi effect ? If so then my understanding falls apart.
Carbureted engines require manifold vacuum to suck fuel out of the float bowl through differential pressure. That differential pressure is provided by the accelerated speed of the air through the venturi which then blows the liquid gasoline into a mist of much smaller droplets but not a true gas. Hopefully the percentage of air to droplets is somewhere near 14 to 1 It becomes a true gas only after it is transformed by heat in the combustion chamber.
What does the high lift cam do? Holds the valves open a little longer to allow more of some type of gas in and out of the cylinder. It enters as a gas and exits as a gas. Doesnāt need to be altered on the way in. Wood gas has a much lower stoichiometric ration. You want as much of it into the cylinder as possible. We have reached my limit. Now I want to know why that is incorrect.
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tcholton717ā āNOā; TomC
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Tom Collins answer well the one part of it. NO. Not needed.
By the way true propane and methane gas mixers do have a very slight necking down venturi.
Look down into a throttle body injection system. Virtually wide open.
A high lift long duration camshaft shifts the best flow in the intakes and into cyclinders from a balanced-usage approach to a balls-out, wide open throttle higher RPM.
This biasing: trashes the idle and low speed manifold vacuums.
An āRVā or working-equipment camshaft biases from balanced-usages too: strongly favoring maximum starting torque, and low RPM torque. At the expense of highest power and highest RPM capability.
The newer command-active camshaft systems for lobe timing and lift try to have the best usage flexible range of all. Electronics dependent.
S.U.
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Back on the DOW road again. NO More $120.00 plus fueling up to drive to work.
Bob
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Drive On Wood again, I canāt wait to Drive On Wood again
To the tune of āon the road againā
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Only plus of not dow last week was my woodpile grew up and is ready for another big chunking session
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Hey think about it.
āBreak-inā is loosening things up to work fitted.
What youāre doing is āsettling-inā. Getting ash and chars, even soots built up just right.
S.U.
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Didnāt think about that Steve, good point
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