Why do Diesel Engines require 2 valves?

[cfellows]

I was thinking this evening, that diesel engines or any engine that uses direct fuel injection into the cylinder doesn't require a separate intake and exhaust valve. If you had only one valve, opened it to exhaust the burnt gases, then held it open to to the bottom of the stroke to suck in (mostly) fresh air, then closed it for compression and combustion, it should work. Right?

Chuck

 

[kcmillin]

Chuck, I think your Idea would work. However only for a very short time. Lesds than a minute. I have always been told, and taught that gas needs a 14 to 1 air/fuel ratio to burn properly. I think that the "Mostly" clean air would become more and more less clean and the oxygen would be spent quickly.

If you keep the exhaust/intake port short in length between the cylinder and the outside, IE no exhaust pipe, and you could keep clean air rushing past it, then it might be plausible.

Thats my two bits.

Kel

 

[Captain Jerry]

Chuck

I doubt that it would work with a turbo, and I can't begin to imagine what it would sound like?

Jerry

 

[steamer]

why not use cross scavaging with a blower....then you could use a turbo on the exhaust side...

Dave

 

[FIXIT]

Interesting thought.

i think it's probably the easy way in practically to use two because basically thinking you would still need a second valve in the inlet/exhaust tract to stop exhaust gas going up the inlet,

as suggested you could boost the inlet to scavenging the gas out of the exhaust port
but the high pressure and velocity would mean a large hi pressure pump,
which will take a lot of power from the engine.

then it's down to a very hi temp gas in the same manifold as the inlet air

but yes it could be done! i think but it's more efficient and cheaper just to have two valves

Perkins made a high speed two stroke diesel but they still used valves

So lets all put our ten-cents worth in and we might come up with something

Steve

 

[Niels Abildgaard]

Gnome monosoupape rotary aircraft engines had only one combined exhaust/inlet valve per cylinder.They was used in WW one.

 

[FIXIT]

Hi
This idea just wont leave my head, if i don't get any sleep tonight !!

Thanks Niels.
The Gnome monosoupape is a interesting engine but on looking it still uses two valves.

the early engine had it's inlet valve in the piston fed from the crankcase
and the later type was 'piston ported' if this is still classed as 'valved'

Steve

 

[Maryak]

why not use cross scavaging with a blower....then you could use a turbo on the exhaust side...

Dave

And Mr Detroit will say.................."Now why didn't I think of that." : : :

Seriously, Chuck many only have exhaust valves and use scavenge ports in the cylinder for intake.

Best Regards
Bob

 

[Admiral_dk]

Hi Chuck

Your idea will work if the engine is slow enough .... the reason is the mass of the gas (not fuel - but "air", burnt or fresh) - like all mass, it takes time and energy to accelerate. Ie : exhaust begins and the burnt gas is accelerated to a high speed out of your common intake/exhaust. It takes some time to stop again especially if you have a exhaust system / smokestak attached .... If you do attach one, it would be impossible to suck fresh gas / air into the engine - if not, it will still take time before the engine can begin to suck fresh air in.

In other words - If you keep the distance from the combustion chamber to the outside as short as possible, it will work with a diesel (as in Rudolf Diesel - injection), but not in a model diesel (compression ignition - carburator) - it will be rather slow, noisy and MESSY .... ;D

 

[lordedmond]

diesel engines slow single cylinder ones will run ok for long periods of time with the exhaust connected to the inlet manifold the only thing you would need to do is provide a small amount of oxygen into the closed loop with a small bleed of to limit the excess pressure that will develop due to the introduction of the oxygen

this unit will then run under water



so your idea if you could arrange the valve timing would work but you would need a buffer tank for the gasses and a supply of O2


Stuart

 

[cfellows]

Thanks for all the input and ideas. I was thinking primarily in the slow running, model engine category (guess I have a one track mind!). I'm still noodling over the Find Hansen model hot bulb engines. I really, really want to build a model hot bulb engine but still have so many questions, and Mr. Hansen isn't very responsive to questions, I've got to figure it all out myself.

Chuck

 

[Dan Rowe]

Chuck,
The Sulzer diesels did not use any valves until fairly recently. They are 2 strokes and used loop scavenging with intake and exhaust ports and a turbocharger. The new model Sulzers are still slow speed two strokes now they have a single exhaust valve and intake ports. The newer uniflow scavenge engines also use very large turbochargers.

It has been a while since I read Lyle Cummings book on diesel engines Volume I but I think it covered hot bulb engines. I know I have something in my library on then I will have to check my early diesel books for information.

Dan

 

[Niels Abildgaard]

Thanks for all the input and ideas. I was thinking primarily in the slow running, model engine category (guess I have a one track mind!). I'm still noodling over the Find Hansen model hot bulb engines. I really, really want to build a model hot bulb engine but still have so many questions, and Mr. Hansen isn't very responsive to questions, I've got to figure it all out myself.

Chuck

The first thing to decide is two or four-stroke.
Four stroke with one hole is possible as the Gnome monosoupape exhausted all and inhaled most through the monosoupape.The cylinder ports were for getting a very fat petrolmixture into cylinder.This will not be nessecary in a hotbulber as fuel is injected very soon after bottom deadpoint.
The exhaust will leave engine as a jet and suction will be a hemisphere so not a lot of mixing here but silencing will be difficult.
I have never even thougth of a two stroke with one hole but it could be a very exiting project.
The father of modern high power two stroke walther Kaaden once had a disc intake rotary valve engine running at full power;valve stuck in open possition and engine did not change power at all.
That means that the exhaust leaft engine so fast that a vacuum in cylinder sucked air unassisted.Again some noise problems but one piece of interesting engine.

 

[kf2qd]

Iquess the short answer is this - so it is easier to get the hot stuff out and the cool stuff in. By having seperate inlet and outlet paths you can also use some of the momentum of the gases to help purge/charge the cylinders.

It is interesting that 2-stroke diesels are falling out of favor. They have had reliability issues, long cylinder bore issues and those transfer ports are also a strenght issue. A design with the valves in the head makes for a shorter engine, shorter pistons (less weight, don't have to cover those transfer ports).

If you are thinking of cross flow 2 stroke porting you then have to deal withthe fact that the piston and rings are having to cross openings at the ports and thus a re more prone to getting damaged by carbon and whatever else may be in htat port when the piston crosses it.

Valves in the head also makes the block simple and stronger and puts all the complexity and machining in 1 place - the head.

 

[steamer]

And Mr Detroit will say.................."Now why didn't I think of that." : : :

Seriously, Chuck many only have exhaust valves and use scavenge ports in the cylinder for intake.

Best Regards
Bob

Yes he did didn't he...Hi Bob, 8V92TTA is my favorite ( blown with twin turbo's and an aftercooler, 8 cylinder V configuration 92 cubic inches/cylinder...yahooooo!)

 

[Jared]

It is interesting that 2-stroke diesels are falling out of favor. They have had reliability issues, long cylinder bore issues and those transfer ports are also a strenght issue. A design with the valves in the head makes for a shorter engine, shorter pistons (less weight, don't have to cover those transfer ports).

If you are thinking of cross flow 2 stroke porting you then have to deal withthe fact that the piston and rings are having to cross openings at the ports and thus a re more prone to getting damaged by carbon and whatever else may be in htat port when the piston crosses it.

All of my experience with 2-stroke diesels has been with Detroits, having spent a fair amount of time sleeping with two ten feet from my head. The 71 series are dang good engines, as attested to by the hundreds (thousands?) of fishing boats on the North American West Coast that use them for propulsion and generators. If they had reliability issues nobody would use them to go hundreds of miles offshore, or near shore for that matter, or in the Gulf of Alaska or the Bering Sea, all of which have a way of getting nasty when you don't want them to.
I think the main reason they are falling out of favor is they aren't quite as fuel efficient as a 4-stroke and the emissions aren't very good (at least for California). And let's not forget the oil leakage. The other brand name is Leaktroit. :big:

 

[steamer]

".. And let's not forget the oil leakage. The other brand name is Leaktroit."



My Dad, a Master Mechanic, who loved Detroits, called them " Detroit Drippers"

Dave

 

[FlyGuy2480]

An engine having only one valve is known as a monosoupape engine. The idea was first used in World War 1 in aircraft with the specific intent of making rotary engines more reliable. (At first, it sounded about right; having only one valve is more reliable than having two valves.) Gnome was one of the first companies to manufacture these monosoupape engines, and they were used by the Allied Forces in WW1. In case you don't know, a rotary engine is often used today to refer to a wankel stroke engine, but it also refers to a radial engine that essentially has its mounting inversed; the crankshaft is bolted to the aircraft, and the propeller is bolted to the engine block. (For this post, whenever I say "rotary engine," I mean this type of radial engine, NOT the wankel stroke engine.) This mounting configuration has several advantages, including improved air cooling and a strong breeze of fresh air to each valve. It also eliminated the need of a flywheel. Because of the centrifugal force on rotary engines, valves failed frequently. When only one valve occupied the space of the cylinder head, it was easier to make that one valve beefier than each of the would-be two valves.

Because the rotary engine design had a strong breeze of fresh air to the cylinders, and because it didn't need exhaust pipes, it would sound like a perfect idea to use only one valve. As the exhaust exited the valve, it would get immediately blown away so fresh air could enter. Like a two-stroke engine, fuel entered through a port in the sidewall of the cylinder from the crank case, but like a four-stroke engine, fuel entered the chamber only every other stroke.

However, there were soon discovered disadvantages to this type of engine. First, the throttle control was primitive. The ignition was turned on for full power, and turned off for no power. Cutting fuel supply would result in a very slow throttle response, so cutting ignition was preferable. If the ignition was left off during flight, unburnt gasoline would accumulate on the sidewalls of the engine cowling. Once ignition was restored, any fuel in the cowling would catch fire from the outgoing hot exhaust. This meant pilots had to keep the power off for only short periods of time, otherwise the whole plane may be engulfed in fire. Needless to say, it was also a huge waste of fuel. The idea was eventually abandoned, and engines today now have two valves.

Long story short, it is a bad idea to mix exhaust fumes and intake fumes together. This is why we segregate them into two valves. If you like to know more about monosoupape engines, do a web search of it. Other sites explain it much better than I do.

 

[Lyn S.]

I was thinking this evening, that diesel engines or any engine that uses direct fuel injection into the cylinder doesn't require a separate intake and exhaust valve. If you had only one valve, opened it to exhaust the burnt gases, then held it open to to the bottom of the stroke to suck in (mostly) fresh air, then closed it for compression and combustion, it should work. Right?

Chuck

Google up Packard radial diesel Lyn S.

 

[cfellows]

Thanks to all for your responses. I had lost track of this thread and just found it again thanks to Flyguy's response.

I am planning to only use one valve for both exhaust and intake on my hot tube engine. It will be fuel injected so there is no danger of mixing hot exhaust with a volatile intake mixture. I realize that part of the exhaust that didn't quit get out of the exhaust pipe will be sucked back in, but it should be a very small amount.

As far as silencing goes... what's that??? Isn't louder better? :big: