Technically higher is better, right up until the knocking point. 17:1 is supposed to be the limit. Practically I don’t think you’ll see much benefit over 14:1.
Some diesels now are 22:1 or better. That’s way too high and will knock.
Thanks Chris
Is the the effective compression ratio or the bore x stroke ?
Then the cylinder pressure ?
Patrick, that’s the static CR. As determined by the volume at top dead center vs volume at bottom dead center.
With various cam profiles and changing VE / throttle positions you’ll have various dynamic compression rates.
Thanks Chris
So the compression ratio is the theoretical displacement of an engine ie : at TDC it is 1ci at BDC it’s 17 ci ?
So what would be the theoretical pressure at TDC be of an engine with a 17:1 CR ?
(P1 x V1)/ T1 = (P2 x V2)/T2 ?
P1 = 1bar / atmosphere
V1 = 17 ci
T1 = 25c
P2 = ?
V2 = 1ci
T2= ?
P x V = nr x T
Thanks
Patrick
Hey PatrickJ
Math is fine for some things. For this not.
I had a 17/1 compression ratioed engine.
Measured actual compression pressure could be anywhere from 325 to 390 PSI in this engine even with the same camshaft allowed filling rates effects.
Depends on the cranking in RPM it is measured at. This will change the compression produced heat which changes the gasses heat expanded pressures.
Changes with the temperature/density of the air/gas being intaked in affecting the base beginning pressure.
Changes with the temperature of the engine intake, valve, cylinder head, pistion crown and the cylinder liner affecting base gasses temerature/pressure.
Changes with the temeratures of these as that effects the actual cylinder sealing along with ring and cylinder wall oils allowing more or less blowby in cylinder pressure reduction.
And these are all just fairly static effects. YOu could add to your equation.
The actual engine dynamic running cylinder pressures will be effected by RPM/gasses velocities/valve opening and closing effecting the effecttive true cylinder filling percentages.
The effective in cylinder dynamic running pressures will be even MORE effected by the engine loading. Listen to those manual transmissioned Dodge/Cummins diesels rattle with a poor driver! And that is even with a lot of injector timing set back factory proramed in versus auto transmission installs.
So woodgas.
17/1 was Lab Ratted maximum determined under very controlled conditions.
Swede thousands of hours of year around in-field expereinces was make it no higher than 15/1. The did note a1-2 points of difference allowable depending on the diesel engine combustion chambeing effects of a flat piston/in cylinder head Ricardo combustion chambers versus a flat cylinder head face with the combustion chamber now in a bowled out dished piston crown formed.
The Finn Vesa Mikonnen remarks about this same in his book in the diesel engine section. You need to read the “Sweedish papers” section and buy Mr Vesa’s book also for these ran in the real cold Sandinavian world experences. Nice destroyed connector rod pictures from woodgas detonation on loaded turbo running with too high of base CR.
India engine builder Pratash on thier spark converted former diesel engines list a 14/1 CR for thier BIOGAS (methane) intended gen-sets. They reduce this to 13/1 for thier BIOMASS (woodgas) intended gen-sets. They have the engineeers and must warrantee thier systems. So they must be doing this for observed reasons.
GE Jenbacher never lists thier CR’s. Again like the Pratash these are spark ignited. They use tuned in variable speed exhaust driven turbo chargers at the constant engine speeds of 1500RPM and so then you can Tune in your effective dynamic pressures to whatever the fuel will support.
ChrisKY is quite correct.
Start at 14/1 as the most liky to use maybe.
Run a lot under your actual ranges of temperatures, loads and gasifier fuel composition changing conditions first.
Observe.
Maybe you will have to adjust down a point.
Maybe you can adjust up a point.
Bet it will always end up in a mechanically base set range of 13/1 to 15/1 for real world usage.
Ha! Supercomputors and sattelites they still can’t get my weather here right better than an average of 70% of the time. Rain now. Supposed to be sunny. Smooth skined fresh younger comutor models reprorted - 60% accuracy. Old wrinkled shinned gray haired lived/experienced here 30 years perdicted - 80% accuracy. Engines/fuels; weather predicting; billards/pool - decades of expereince matters.
Regards
Steve Unruh
Here Patrick
http://www.prakash-india.com/bio-mass-pdpl.html
This one give you the pictorial of the India suppled gasifier filter train. Long train there to get the equatorial cooling and water washing.
L.H. side bar you can scroll through their different Natural Gas, BioGas and Biomass engines and generating sets.
Sadly since I looked last they have dropped listing their engines compression ratios. My old hand notes confirm the previous listed numbers that I gave.
Enjoy
Steve Unruh
Oh. The Gasification Australia folk once had a YouTube of the 3 cylinder Prakash engine genset gasified fueled on fruit pits up and running. In the alt-enrgy world the India gen heads have poor reputation for quality. Deserved? Donno. S.U.
Hi Steve
Thanks for all the info.
I have an old ford 3 cylinder diesel in the scrap heap.
I had a look at it to try convert it to spark ignition, not impossible just lots of work.
I wanted to do a compression test on it to see what she produces as a starting point.
Then may be skim the pistons to get them in to the ball park of the correct pressure.
So lets take the best for wood gas is 14:1 , what should the compression test be ? Just swing it over with the starter.
Thanks
Patrick
Be an interesting project PatrickJ. I have a working Yamnar 3T72 with a 4000 pound tractor wrapped around it. Mine is IDI with sub pre-chambers that the diesel injectors feed into. The California APL/GEK shop sponsored spark converting a big single cylinder made in India ListerCS clone engine that worked. It was an IDI engine. YouTubes up on that. First running was done on a calculated headgasket reduced 13/1? 15/1? compression ratio. 2nd year running was set up differently. ??
More inline with your project the Swede Johan Lindel (sp) spark converted an English David Brown 3 cylinder tractor and woodgas powered it. He YouTubed this and you can find his site link there. He grafted on a Volvo 6 cylinder car distributor and used every other cap post. You want to grinb back internally the unsued posts contacts to prevent spark flashover jumping.
Measuring the cranking compression will be futile as compared to anything because of your very well used engine condition. You are sure to have a lot of rings/piston skirt/cylinder walls pressure blowby. Since woodgas has proven able to run down to 6/1 compression ratio engines it should run OK. Try a measured ml or cc graduated cylinder tipped engine combustion capacity fill measurement down through an injector hole first. Piston up at top dead center careful first. Then piston lowered down to bottom dead center and refilled. Use warmed light enegine oil or a warmed vegetable oil. Done carefully you can then calculate the current set up effective CR within 10% accuracy. IF you come up with anything 17/1 or lower assuming worn pressure loss blowby as losing 2 points effective CR I’d just run it as is. JohanL never comression lowered his. Just ran it as is. I asked.
Try this for a refernce read if you’ve never seen it:
http://driveonwood.com/sites/default/pdf/record168.pdf
IISc research paper studing the effects of differet spark ignition advance setting at different compression ratios. This was done on three different former DI diesel engines so lots of combustion chamber shape, piston crown shape, stroke to bore, and rod lengh to stoke ratio factors mixed in there. This was done intentional as represenative of the actual engines they were useing out in the field for power generation and pumping. The CPGL of the IISc is only into practical use applied research. Interesting the highest produced cylinder combustion pressures at 55 bars was at the expremes of 17/1 and 11.5/1 CR’s in different engines at different ignition timing settings. Read completey to not miss the measures heats for shaft, coolant and exhaust porportions break outs. Where you get the actual engine conversion efficieny base numbers.
Search up “Cummins India Producer Gas Engines” and see if you can get some leaked out hard info. Alls I can ever find get are fluff hints.
Regards
Steve Unruh
Steve,
Do you know what type of ignition was being utilized for these conversions?
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Hello PeterC
You can find references on gasious Caterpillar, Cummins and Greeves engines as using Altronic ignition systems and the pictured componets look it.
www.altronicinc.com/products.shtml
Look here and you can see these can be an accessory geardriven CD-like triggered battery spark system; to flywheel or camshaft sensor triggered. All have individual cylinder IG coils. Don’t look to have fantastically high voltage capability. But lots of spark duration capability I am sure. And knock sensor triggered spark timing and load setback capable.
Jenbacher and Guascor installed ignitions systems look to be different than Altronics with larger squarish shaped individual IG coils. These could be higher voltages capable. They both do quote as fully electronic controllable.
http://www.guascor-usa.com/
The Prakash pictures show an actual distributor assembly being accessory geardriven in the place of the former diesel injection pump. Small cap; 7mm wires and a standard looking single oilfilled IG coil so for sure not super high voltage capable. Triggered? Could be anything from actual ignition contact points but more likely distributor internal electronic manetic triggered and amplified. NO visible external processor amplifier box.
Johan Liddel on his Volvo 6 cylinder distributor? Contact point type or electrinic? I do not know.
Altronics shows supplying a special “FashGuard” spark plug, Shielded conventional electrodes? Surface discharge type? Donno.
I’ve seen pictures of the Jennbacher spark plugs - long and skinny with conventional electrodes. I have woodgas loaded ran a Kubota high compression gasious converted engine DG972. Spark plugs - standard ND electrode type - gap set 1.1mm (0.040"). Was a flywheel magnetic triggered, individual to each cylinder coiled Denso branded system. NOT HighEnergy capable. Standerd 20KV to 35KV.
Hope this answers
Steve Unruh
Thanks Steve
Need some time to do my home work.
So I am experimenting with an oil drip system to prevent tar build up on the intake valve. 95% of the time I dont have an issue. But there is still that 5%, so to prevent this 5% from causing the head ache of a sticky intake valve, I thought of creating this drip system using waste engine oil. So two birds with one stone. However, I am trying different mixtures with the oil to thin it out and also make it last longer. The idea is just before shut down, you open the needle valve and fog the engine for 5 to 10 minutes. I wont say works at this stage as Im still testing and still too little time into it to say for certain. Every time I say something like that its not second later after I hit the reply button it proves me wrong. lol
Ok so Ill tell what I do know and why Im posting here. So I have a small tank with a needle valve to trickle in this oil mixture. Right now I am running mixture of oil, kerosene and lacquer thinner. When I run this and start to meter it in, I see my automixer system respond to it. As I trickle it in the mixture become richer and the valve opens up. The more open this valve the more power I have (generally).
So the physics;; this does not simply trickle in, as there is vacuum on this. My thinking is to add a fixed vent or an additional needle valve to the inlet to allow air in to mix with the oil; while taking off the vacuum pressure. Basically I have a gravity fed carburetor in a very simply form. With this vented then the air fuel mixture should form some what of a spray.
If this works, then theoretically you could run diesel along with the wood gas full time. you could even set it up so there is a solenoid valve that could open once fired up. Use the oil pressure switch to activate this. However, this would not be a diesel conversion, more like a spark ignition to diesel boosted woodgas conversion. But you are not limited to just diesel, oil, ethanol, kerosene, veggy oil etc I think can all be made to work.
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Sounds interesting matt rider, i am sure you can add some tuneing tricks too oil drip gasifier fuel additive features.Or gismos too make useing otherwize waiste oil work Good. I will be tuned in as it makes extra power for many uses. PS just getting the air mixture automatic ajusting, and not too rich on the compression preasure. ? COOL SCHIENCE.
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I remember reading a blast from the past article that stated some people would remove the oil valve seal to allow oil to be added.
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So far so good, Ive been running this system every day that I have run the gasifier and no issues. This does not mean this is a 100% yet it could just be the gasser is behaving and operator is doing a good job at operating the machine 
I do need to refine it a bit though or at least seal up my carburetor better. If I give it too much It is bypassing the carb gaskets and dripping all over the ground.
The next iteration Ill probably move this over to my thread.
Hi Matt , i was just giving your idea some thought and wondered if you could reduce the main jet in the carb by say 50% or more and then use the fuel solenoid on a timer to give the engine bursts of your thinned down mixture , that would then save having to drip as you could use the carburetor in a sort of conventional way maybe 1 sec on 2 secs off type of thing .
Dave
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Yes those are my thoughts too. It would be cool to just use the stock tank and dump anything in there.
I like running in this hybrid mode too, it gives me extra power. I will be testing to see if the genny can run the CNC machine along with the air compressor here soon. Before it could not run both, this is my only restriction running on wood gas. I can run everything else but it just cant run both the CNC machine and the Air compressor at the same time. When the compressor kicks on it pulls the genny down too far and the plasma cutter will shut off.
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