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Compressor to 2 stroke eng.
- Thread starter mikespeed
- Start date
BrianPetersen
Mechanical
Do you mean "supercharger"?
If so, you are going to have a problem, because 2-stroke engines vent the cylinder to atmospheric pressure through the exhaust port on every rotation, so it's impossible to get (significant) boost pressure in the cylinder.
If so, you are going to have a problem, because 2-stroke engines vent the cylinder to atmospheric pressure through the exhaust port on every rotation, so it's impossible to get (significant) boost pressure in the cylinder.
- Thread starter
- #3
Hi Brian
I have been working mainly with diesel engines.
I was thinking this could give some extra power for the engine.
Normally rpm is abound 6000 depending on the boats propeller.
I meant air compressor.
Connected to flywheel and scavenging air pipe to carburetor.
A turbocharger is almost im possible to build due to small spaces.
One thing i know if this is possible that pistons need to be changed due that exhausts temperatures will increase.
I have seen that bigger Mercury engines have a TC.
I have been working mainly with diesel engines.
I was thinking this could give some extra power for the engine.
Normally rpm is abound 6000 depending on the boats propeller.
I meant air compressor.
Connected to flywheel and scavenging air pipe to carburetor.
A turbocharger is almost im possible to build due to small spaces.
One thing i know if this is possible that pistons need to be changed due that exhausts temperatures will increase.
I have seen that bigger Mercury engines have a TC.
you could alyways increase the backpressure in the exhaust system to enable the boost to be retained in the cylinder.
perhaps a turbo would work well for this, as it increases the backpressure as well as generates boost... although ot might not work at all since the backprssure increase could likely be higher than the boost it generates.
i dont know if this would work on not though. 2 strokes use expansion chambers to draw the exhaust gases out of the engine... you might be able to blow it out with boost instead though...
what if you but a pressure activated valve om the exhaust pipe and used that to regulate boost? in effect, pressurize the whole system, not just the intake.
perhaps a turbo would work well for this, as it increases the backpressure as well as generates boost... although ot might not work at all since the backprssure increase could likely be higher than the boost it generates.
i dont know if this would work on not though. 2 strokes use expansion chambers to draw the exhaust gases out of the engine... you might be able to blow it out with boost instead though...
what if you but a pressure activated valve om the exhaust pipe and used that to regulate boost? in effect, pressurize the whole system, not just the intake.
BrianPetersen
Mechanical
What do you propose to accomplish, by "scavenging the air pipe to carburetor"? You will have to explain this in better terms.
You haven't said what the engine is, but one assumes that it is a traditional crankcase-scavenged carbureted two-stroke with reed valves controlling inlet of mixture from the carb into the crankcase, probably with two cylinders.
When the piston goes up, it closes off the ports in the main cylinder and the pressure in the crankcase drops, the reed valves open and draw in mixture from the carb. When the piston goes down, the rising pressure closes the reed valves and slightly compresses the mixture in the crankcase, then it uncovers both the intake and exhaust ports. The exhaust blows out to atmosphere and the raised pressure in the crankcase transfers the mixture from the crankcase into the main cylinder.
What do you propose to change in this basic operation?
You haven't said what the engine is, but one assumes that it is a traditional crankcase-scavenged carbureted two-stroke with reed valves controlling inlet of mixture from the carb into the crankcase, probably with two cylinders.
When the piston goes up, it closes off the ports in the main cylinder and the pressure in the crankcase drops, the reed valves open and draw in mixture from the carb. When the piston goes down, the rising pressure closes the reed valves and slightly compresses the mixture in the crankcase, then it uncovers both the intake and exhaust ports. The exhaust blows out to atmosphere and the raised pressure in the crankcase transfers the mixture from the crankcase into the main cylinder.
What do you propose to change in this basic operation?
Interesting point Fireslave is making. A 2-stroke engine operating at sea level presumably makes a lot more power than the same engine operating on a mountain at 10,000 feet (for example) where the atmospheric pressure is 20 inches of Hg or thereabouts. When the engine returns to sea level it is, in a sense, being pressurised on both intake and exhaust (compared to 10,000 feet) but is making more power. FS's idea of pressurising the intake and restricting the exhaust may work.
- Thread starter
- #7
Hi
My engine is an outboard engine.
25 horsepower (20kw) SELVA engine (similar to Yamaha)
Two stroke engine with ports and 3 cylinders or old type 2 cylinders.
RPM from 6000 - 7000.
"scavenging the air pipe to carburetor" means a flexible pipe with compressed air (from Compressor) to carburetor.
I want to get more power out of the engine for racing purposes.
I know some tricks but i have not heard or seen any body build in a compressor to carburetors air intake.
You are correct Nemesis.
I have been in a race long time ago were the lake was up in the mountain and we could in the first place get so much power of the engine. Later on we find out the ambient pressure was different.
My engine is an outboard engine.
25 horsepower (20kw) SELVA engine (similar to Yamaha)
Two stroke engine with ports and 3 cylinders or old type 2 cylinders.
RPM from 6000 - 7000.
"scavenging the air pipe to carburetor" means a flexible pipe with compressed air (from Compressor) to carburetor.
I want to get more power out of the engine for racing purposes.
I know some tricks but i have not heard or seen any body build in a compressor to carburetors air intake.
You are correct Nemesis.
I have been in a race long time ago were the lake was up in the mountain and we could in the first place get so much power of the engine. Later on we find out the ambient pressure was different.
BrianPetersen
Mechanical
Okay, what you are proposing is a "supercharger".
You will have a problem because the exhaust port and intake port in the cylinder are both open at the same time, and the exhaust port is open to atmosphere, so any attempt to "supercharge" will just blow the air/fuel mixture straight out the exhaust.
Restricting the exhaust together with this might accomplish something, or it might not do enough to overcome the extra power demand of driving the supercharger. It will probably cause all sorts of other problems.
Two-strokes are fussy about air/fuel ratio. If this results in the engine running too lean, you are going to seize the engine.
You will have a problem because the exhaust port and intake port in the cylinder are both open at the same time, and the exhaust port is open to atmosphere, so any attempt to "supercharge" will just blow the air/fuel mixture straight out the exhaust.
Restricting the exhaust together with this might accomplish something, or it might not do enough to overcome the extra power demand of driving the supercharger. It will probably cause all sorts of other problems.
Two-strokes are fussy about air/fuel ratio. If this results in the engine running too lean, you are going to seize the engine.
Why not a tuned pipe? Especially since it sounds like your motor will be working at a fixed or relatively narrow RPM range.
patprimmer
New member
This link might help to establish at least an elementary understanding of two stroke operation, including some information on the necessity of some form of charge pumping (read compressor) to actually run.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
JWaterstreet
Electrical
There are so many other ways to improve HP on a 2-stroke; tuned pipe mods, increased compression with more exotic fuels, porting, etc. that it would be foolish to start with something that isn't really adaptable to 2-strokes in the first place.
But what I really want to know is this. 25 HP? Racing? On water? You might as well be talking about racing those carts that the elderly drive around the aisles at the grocery store.....
25 HP on water is pontoon boat-league stuff, anemic at best....I complain that my 130 HP stock Sea Doo is underpowered....
But what I really want to know is this. 25 HP? Racing? On water? You might as well be talking about racing those carts that the elderly drive around the aisles at the grocery store.....
25 HP on water is pontoon boat-league stuff, anemic at best....I complain that my 130 HP stock Sea Doo is underpowered....
patprimmer
New member
I think he is entitled to race whatever he likes. It's his money and his life.
I do wonder however if supercharging is allowed by the rules of the class you intend to run.
I also wonder if a change in inlet tract pressure by whatever method will require other mods to ports or piston top design.
As previously mentioned by others, and if allowed by your class rules, higher octane or energy content fuel and compression optimised to the fuel used, and ports, etc optimised to the rpm to be used will all help.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
I do wonder however if supercharging is allowed by the rules of the class you intend to run.
I also wonder if a change in inlet tract pressure by whatever method will require other mods to ports or piston top design.
As previously mentioned by others, and if allowed by your class rules, higher octane or energy content fuel and compression optimised to the fuel used, and ports, etc optimised to the rpm to be used will all help.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
patprimmer
New member
Opps
The link is actually included this time
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
The link is actually included this time
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
- Thread starter
- #14
There have been some interesting historic attempts at a hyperbaric two cycle.
The Kettering designed Detroit Diesel used a single port at the bottom of the cylinder and an exhaust valve in the head. It needed a blower or supercharger to work. This engine is no longer used because of oiling and emission issues.
The DKW 350 Speedster motorcycle used two cylinders coupled at the top and offset from the crank center. One cylinder was offset to the right of center and the other cylinder was offset to the left. The two pistons went up and down more or less together but the offset provided a phase difference. One cylinder contained the intake port and the other cylinder had the exhaust port. The phase difference made it so the exhaust port opened first and also closed first. The intake charge entered the crankcase. The crankcase was fitted with a cylinder that changed the volume of the crankcase such to supercharge the engine. The German company made this bike two years before WWII. It never reappeared after the war. The little 350 cc was reported to push the bike over 160 mph. They said over because the tires they had back then exploded about there. The bike had a tuned exhaust and could be heard miles away. It also blew most of the fuel through without burning it.
If you want to supercharge a two cycle it seems like there would be value in not using crank case induction. Use a normally sealed and oiled crankcase. No lubricant would need to be added to the fuel. This would be a big advantage since lubricants tend to destroy the octane value of the fuel.
The Kettering designed Detroit Diesel used a single port at the bottom of the cylinder and an exhaust valve in the head. It needed a blower or supercharger to work. This engine is no longer used because of oiling and emission issues.
The DKW 350 Speedster motorcycle used two cylinders coupled at the top and offset from the crank center. One cylinder was offset to the right of center and the other cylinder was offset to the left. The two pistons went up and down more or less together but the offset provided a phase difference. One cylinder contained the intake port and the other cylinder had the exhaust port. The phase difference made it so the exhaust port opened first and also closed first. The intake charge entered the crankcase. The crankcase was fitted with a cylinder that changed the volume of the crankcase such to supercharge the engine. The German company made this bike two years before WWII. It never reappeared after the war. The little 350 cc was reported to push the bike over 160 mph. They said over because the tires they had back then exploded about there. The bike had a tuned exhaust and could be heard miles away. It also blew most of the fuel through without burning it.
If you want to supercharge a two cycle it seems like there would be value in not using crank case induction. Use a normally sealed and oiled crankcase. No lubricant would need to be added to the fuel. This would be a big advantage since lubricants tend to destroy the octane value of the fuel.
thruthefence
Aerospace
CCycle, Is this anything like the Sears Allstate/Puch 250CC motorcycles from the late 60's? As I recall, they had two cylinders, and a common combustion chamber.
GregLocock
Automotive
Twingle
Cheers
Greg Locock
SIG
lease see FAQ731-376 for tips on how to make the best use of Eng-Tips.
Cheers
Greg Locock
SIG
lease see FAQ731-376 for tips on how to make the best use of Eng-Tips.
PrematureWear
Mechanical
Mikespeed,
The "compressors" you speak of, when used on an I.C. engine and driven by crankshaft power, are commonly referred to as superchargers. It is perfectly possible to supercharge a conventional two-stroke engine, but you must first solidly inform yourself as to their operating principle before attempting it. It has been done successfully, but requires throttling of the exhaust while running under boost in order to supercharge the cylinder---this is needed to prevent fresh fuel/air mixture from simply blowing out the exhaust port during the transfer event.
You'll have fun finding a compressor of suitable size for your engine... There are many options from outrageously expensive to almost free. Perhaps a large smog-pump from the largest of old-school automobile engines can be made to work when run at an appropriate speed. What drive ratio is required? How long will the pump last at that speed/pressure? For that matter, how long will the engine last at a given level of boost? Beefier pistons, connecting rods etc. may be needed to tolerate the increased power. How about pressurizing the carb float bowl to eliminate fuel blow-back and allow proper flow under boost? Maybe just place the carb on the inlet of the compressor and draw the mixture through the comp. Don't forget about exhaust throttling to prevent the pressurized mixture from blowing straight out the exhaust during transfer! The exhaust throttle must be adjusted constantly as inlet throttle and engine speed are varied. How are you going to do this? Probably a combination of carb throttle linkage, exhaust pressure operated piston or diaphragm actuator... And on and on and on.
Your in for much reading & learning about what is a perfectly feasible and very fun project.
Happy engine destroying
PrematureWear
The "compressors" you speak of, when used on an I.C. engine and driven by crankshaft power, are commonly referred to as superchargers. It is perfectly possible to supercharge a conventional two-stroke engine, but you must first solidly inform yourself as to their operating principle before attempting it. It has been done successfully, but requires throttling of the exhaust while running under boost in order to supercharge the cylinder---this is needed to prevent fresh fuel/air mixture from simply blowing out the exhaust port during the transfer event.
You'll have fun finding a compressor of suitable size for your engine... There are many options from outrageously expensive to almost free. Perhaps a large smog-pump from the largest of old-school automobile engines can be made to work when run at an appropriate speed. What drive ratio is required? How long will the pump last at that speed/pressure? For that matter, how long will the engine last at a given level of boost? Beefier pistons, connecting rods etc. may be needed to tolerate the increased power. How about pressurizing the carb float bowl to eliminate fuel blow-back and allow proper flow under boost? Maybe just place the carb on the inlet of the compressor and draw the mixture through the comp. Don't forget about exhaust throttling to prevent the pressurized mixture from blowing straight out the exhaust during transfer! The exhaust throttle must be adjusted constantly as inlet throttle and engine speed are varied. How are you going to do this? Probably a combination of carb throttle linkage, exhaust pressure operated piston or diaphragm actuator... And on and on and on.
Your in for much reading & learning about what is a perfectly feasible and very fun project.
Happy engine destroying
PrematureWear
BrianPetersen
Mechanical
Two stroke engine + air/fuel ratio even slightly too lean = seized piston or hole in piston.
Two stroke engine + power output much higher than original design specification = high heat load on piston, see above.
Hence the "happy engine destroying" comment, which I agree with ...
Two stroke engine + power output much higher than original design specification = high heat load on piston, see above.
Hence the "happy engine destroying" comment, which I agree with ...
Mr. PW - You say that supercharging of a two-stroke has been done successfully by pressurising the intake and throttling the exhaust to match the intake pressure. Do you have a reference to this somewhere? It seems like a very simple and practical method to me and I would like to actually try it - it would be an interesting experiment.
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