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brian Rupnow
06-14-2019, 06:45 AM
I read yesterday about a small single cylinder i.c. engine model that had a "regulator" that kept a slight negative crankcase pressure in the engine while it was running. This was a 4 cycle vertical engine with a "wet" crankcase. The negative pressure kept any oil from migrating out around the crankshaft bushings. I hadn't heard about that before and I think it is a great idea. The engine in question was the Silver Angel by Bob Shores. A visual inspection of this engine running on YouTube shows no connection from the carburetor to the crankcase. The only "oddity" I see is that the engine seems to have double oil filler caps side by side. Does anyone have more info about this?---Brian

brian Rupnow
06-14-2019, 07:03 AM
I googled this, and came up with a video showing how it is done. Seems it is a one way reed valve on the crankcase. The reed valve blocks outside air from entering the crankcase when the piston is moving away from bottom dead center, but allows air to escape from the crankcase when the piston is moving towards bottom dead center. The net effect of this is to maintain a slight negative pressure in the crankcase. I'm not sure how to apply this to a model engine, but this may be a purchased item. Any ideas?
https://www.youtube.com/watch?v=RuJqXF0Cr1M

rws
06-14-2019, 07:11 AM
Never heard of a negative pressure in a crankcase of any kind. A positive pressure is always present from piston blowby. Old engines had breather tubes which you could see it venting. Then came the PCV system that burned this off.

strokersix
06-14-2019, 07:27 AM
Commonly done for racing engines. Not only to keep the oil from passing seals and improve ring seal, but mostly to reduce losses from sloshing/pumping stuff around in the crankcase. A "dry sump" system with evacuation pump and oil separator is used.

JoeLee
06-14-2019, 07:43 AM
Isn't the purpose of a breather to vent the crankcase and keep the pressure some what neutral? I never saw any small engine that didn't have have one.

JL............

beechur johnson
06-14-2019, 07:49 AM
Sometimes on really high performance stuff, mostly dragracing cars and motorcycles they use a vacuum pump to keep a negative pressure in the crankcase. it does seem to help performance. In drag racing a couple of hundreds of a second or a tenth of a second is like light years.

Ringo
06-14-2019, 08:12 AM
I googled this, and came up with a video showing how it is done. Seems it is a one way reed valve on the crankcase. The reed valve blocks outside air from entering the crankcase when the piston is moving away from bottom dead center, but allows air to escape from the crankcase when the piston is moving towards bottom dead center. The net effect of this is to maintain a slight negative pressure in the crankcase. I'm not sure how to apply this to a model engine, but this may be a purchased item. Any ideas?
https://www.youtube.com/watch?v=RuJqXF0Cr1M

Gosh, if the reed valve lets air escape the crankcase, then it also escapes oil along with the air, right?
That's the same oil leak the breather is supposed to arrest isn't it?

A.K. Boomer
06-14-2019, 08:35 AM
It might be ok for certain applications but it does fly in the face of conventional thinking,

for one the typical seal actually functions better with slight positive pressure in fact some diesels count on it,

two is the fact that you really do not want to be drawing in outside unfiltered air directly into the crankcase as it's a good way to make abrasives in your oil, PCV systems at least run it through the air filter first before it gets to see the lower end by means of blow-bye...

im thinking it might be a handy way to keep a model engine lubed without having to build all kinds of sealing surfaces, a controlled environment (no road dirt) and minimal use and not having to make seal od's and id's for shafts and such...

RandyZ
06-14-2019, 08:51 AM
That is how the Kawasaki v twin engine in my John Deere lawn tractor works. There is a reed valve that maintains a vacuum in the crankcase.

strokersix
06-14-2019, 08:54 AM
Crankcase pressure pulses are also used to drive fuel pump on small engines.

A.K. Boomer
06-14-2019, 09:01 AM
some negative is normal even in PCV systems deceleration with a closed throttle plate while still in gear will create a vacuum inside the crankcase, generally no big whoop but in my state where there's mountains this can go on for miles as you use the engine as a brake, still generally no big whoop but dirt roads can be a little threat in this area,

the worst case scenario was the older volkwagons, rear engine - all kinds of dirt getting stirred up and they did not even have a crankcase seal around the drive pulley just a spiral cut groove that routed oil back in,,, now those systems did suck dirt directly into the crankcase even though they were in general a PCV system,

Direct injection gassers eliminate any vacuum due to no longer have a throttle plate, it's PCV even at idle or deceleration...

Glug
06-14-2019, 09:07 AM
Fwiw, auto PCV systems also prevent oil leaks, and the engine is at times put under negative pressure. That is true even on older cars. It can make the difference in whether a car leaks oil.

I had a carbureted Ford V8 with a mystery oil leak on the rear of the engine somewhere. It would leak on the headers. The factory incorrectly installed the rear intake manifold seal, which is a strip of cork. It did not leak until I disconnected the PCV to the air cleaner. Unfortunately for me and my poor diagnostics - the leak triggered a major engine upgrade (heads and cam) at a time when I would have preferred to leave it alone.

On race engines the negative crankcase pressure helps with ring sealing, reduces losses due to pushing air around, and manages oil by sucking it back to the de-aeration oil tank and keeping it off the crankshaft.

strokersix
06-14-2019, 09:15 AM
Direct injection gassers eliminate any vacuum due to no longer have a throttle plate, it's PCV even at idle or deceleration...
Please explain. I am unfamiliar. How does a spark ignited engine keep stoich without a throttle? Manipulating valve timing perhaps to limit air trapped?

A.K. Boomer
06-14-2019, 09:38 AM
They do not have to be concerned as much with stoich anymore, they are pulse controlling their injection system directly in the combustion chamber, technically it's getting to the point where it's hard to distinguish them from a diesel engine save for the type of fuel used and the burn rate, some are even dropping the almighty spark plug...

brian Rupnow
06-14-2019, 10:33 AM
I think that in the video link I posted, that one way reed valve works in combination with a filter to stop dirt from entering the crankcase. For me its rather a moot point anyways, because there is no dirt where I run my model engines.

Doozer
06-14-2019, 10:33 AM
They do not have to be concerned as much with stoich anymore, ...

OOOOOOOOOOOOOOOOOOOOkkkkkkkkkkkkkkkkkkkk.

-Doozer

A.K. Boomer
06-14-2019, 10:47 AM
OOOOOOOOOOOOOOOOOOOOkkkkkkkkkkkkkkkkkkkk.

-Doozer

If there's something you do not understand about that statement then just say so,

You think diesels are concerned with Stoichiometric ratio's ? all's they care about is if they have enough air to burn whatever their going to be injecting into the chamber -- and overkill on the air ratio is not an issue,,, actually and technically diesels are always "running lean" with way more air than fuel (unless your into "rolling coal") - they can do this due to not having to compress a pre-mix of air and fuel - yeah, kinda like what's going on with todays direct injection gas,,, you no longer have to have a perfect ratio of air and fuel... you can have and do have many times more air than what is needed like at idle - no throttle plate, full charge of air yet tiny little spritz of fuel just enough to keep it running...

ed_h
06-14-2019, 11:11 AM
My understanding of common PCV valves is that they are basically vacuum regulators, included to keep a small vacuum on the crankcase.

Even the old road draft tubes were arranged to create a small vacuum, at least at road speed.

On many vehicles using constant depression carburettors (SU, Stromberg, etc.), there was often a port on the carb that provided a relatively constant small vacuum. This port was connected to the crankcase to maintain negative pressure.

I always assumed that most modern vehicles used negative crankcase pressure.

Ed

hermetic
06-14-2019, 11:40 AM
Before egr valves most IC engines had either a breather which consisted of a small compartment full of wire mesh, linked by a tube to the intake manifold, the idea was that the oil condensed on the mesh and was sucked back into the sump on the up stroke, and any blowby gasses went into the inlet to be burnt in the cylinders. A high mileage engine would breathe heavily into this system, and all the residue would end up in the carb and manifolds. Some also had a valve which would allow pressure to escape as the piston came down, and shut when it was going up. Usually a very simple spring and disk valve.

Yondering
06-14-2019, 12:24 PM
If there's something you do not understand about that statement then just say so,

You think diesels are concerned with Stoichiometric ratio's ? all's they care about is if they have enough air to burn whatever their going to be injecting into the chamber -- and overkill on the air ratio is not an issue,,, actually and technically diesels are always "running lean" with way more air than fuel (unless your into "rolling coal") - they can do this due to not having to compress a pre-mix of air and fuel - yeah, kinda like what's going on with todays direct injection gas,,, you no longer have to have a perfect ratio of air and fuel... you can have and do have many times more air than what is needed like at idle - no throttle plate, full charge of air yet tiny little spritz of fuel just enough to keep it running...

You said gasser first, not diesel; which are you actually talking about? Stoich is very important in a gasoline engine, regardless of the type of intake system. Diesel is a completely different thing. Your post said, referring to your earlier post about "gassers", that "They do not have to be concerned as much with stoich anymore", which is completely incorrect.

Strokersix - one example of an engine not using a throttle plate is Nissan's VQ37 motor used in the 350Z and G37 cars starting in about 2008. That motor does have dual throttle bodies, but doesn't use them for air control during normal engine operation, instead it controls the intake by variable valve lift and timing. Obviously they still control the fuel mixture to be near stoichiometric, like pretty much any other gasoline engine.

Yondering
06-14-2019, 12:37 PM
I read yesterday about a small single cylinder i.c. engine model that had a "regulator" that kept a slight negative crankcase pressure in the engine while it was running. This was a 4 cycle vertical engine with a "wet" crankcase. The negative pressure kept any oil from migrating out around the crankshaft bushings. I hadn't heard about that before and I think it is a great idea. The engine in question was the Silver Angel by Bob Shores. A visual inspection of this engine running on YouTube shows no connection from the carburetor to the crankcase. The only "oddity" I see is that the engine seems to have double oil filler caps side by side. Does anyone have more info about this?---Brian

Brian, as some others pointed out, negative crankcase pressure is used in some high performance engine applications. It doesn't require a vacuum pump on a single cylinder engine, just a check valve of some sort. I use one on my dirt bike; it's a one-way check valve in the breather hose, that hose is just plumbed to the air box so it doesn't really produce any significant vacuum on it's own. The cylinder pulses in the crankcase produce the vacuum, and it helps ring seal. Several automotive applications use similar check valves, I could probably dig up some part numbers if you want.

The vacuum produced in the crankcase is noticeable when trying to drain the oil; barely any oil comes out until the filler cap is removed to break the seal, even with the engine shut off for several minutes. If you're building an engine with exposed seals that may tend to pass more air, the previously voiced concerns about dirt intrusion might be an issue depending on operating environment, but on a sealed crankcase the system works pretty well.

A.K. Boomer
06-14-2019, 01:12 PM
You said gasser first, not diesel; .

Wrong, I stated "direct injection gasser" which in fact is getting to the point of technically being called a diesel, just one that runs on gas instead...

also as stated - some are not even using spark plugs anymore...

Again - here's all you need to know, even the ones using plugs do not have a throttle plate, so it's a full charge of air even at idle,,, now how would you get an engine like this to idle without a T-plate IF you were trying to use a stoichiometric ratio of fuel and air? you could not - it would take off in an instant - so - when you know theory of operation like I do - it means you control it by fuel amount - just like a diesel and in fact just like a diesel stoichiometric is a non-issue,,, you can do whatever you please with ratio as long as there's enough air (oxygen) to burn the amount of fuel injected, so 18 to 1 is just fine - along with 100 to 1 as long as the 100 is the air part.

Yondering
06-14-2019, 02:05 PM
Sorry boomer, you're off base on this one. Gasoline internal combustion is not like diesel combustion, you're missing some important details. Diesel can be made to run really rich to produce more power, gasoline doesn't work that way. Air intake is still regulated, just not with throttles.

A.K. Boomer
06-14-2019, 02:30 PM
Sorry - and were not talking about rich here were talking lean - and air intake is not regulated anymore, it's wide open just like a diesel, all the variable cam timing in the world will not change this fact that the valves are opening and are not restricted, you need to study up on how these engines are controlling their RPM's and power and then get back to me on it. thanks

JRouche
06-14-2019, 02:36 PM
Sorry - and were not talking about rich here were talking lean - and air intake is not regulated anymore, it's wide open just like a diesel, all the variable cam timing in the world will not change this fact that the valves are opening and are not restricted, you need to study up on how these engines are controlling their RPM's and power and then get back to me on it. thanks

Yeah, the new engines are very funky compared to the old. I was working on my 2016 lexus that has two injectors per cylinder. That threw me for a loop. One "low" pressure and one high. JR

rklopp
06-14-2019, 02:40 PM
I have my Upshur Twins set up with check valves on the crankcase vents. The valves are derived from Jerry Howell's design for his V-twin, but his design combined the crankcase vent with the fuel level control. The Upshur Twins are boxers with the pistons in phase, so the crankcase volume change from TDC to BDC is quite significant. The vents seem to do a good job of keeping the oil in, because in cases when the reeds don't seat correctly due to a valve misadjustment, I get a lot of oil weep.

BCRider
06-14-2019, 02:44 PM
Brain is asking about the negative pressure in a rather specific application. Namely the use of a one way valve to maintain negative pressure in a model engine crankcase as an aid to avoiding oil leaks on an engine that has no seals on the crankshaft. The replies seem to be all over the map trying to match this application to larger multicylinder engines. I'm not sure that the comparisons apply. And in some examples they clearly don't apply.

While the PCV valve used on pretty well all automotive engines these days will likely see some slight amount of vacuum in the crankcase under some conditions I doubt it'll be anything like the suction draw that would be present in the single cylinder engine which is the topic of the thread question. A single cylinder will produce a huge volume change with every stroke due to the volume sweep of the single piston.

Brian, in this situation with only a one way valve pumping the crankcase down to a lower pressure I think I'd worry a little about oil to the main bearings. Now if the other cap has a small bleed hole or light spring loaded ball valve such that the vacuum is limited then all would be well and good. Oil viscosity and surface tension in oil is a strong factor that will ensure good lubrication. And a slight vacuum will stop the oil from gushing out the outer ends of the bearings.

And you DID say "regulator". And in such a case a simple ball valve and adjustable spring along with the one way reed would combine to regulate the case pressure (drop). And I can certainly see it eliminating the need for seals if set to just the right value.

It would be like a kid with a runny nose sniffing back the snot just before it drips out with each cycle of the piston..... .:)

Doozer
06-14-2019, 02:44 PM
Sorry - and were not talking about rich here were talking lean -....

Stoichiometric is in the middle of rich and lean.

-D

nickel-city-fab
06-14-2019, 03:37 PM
Was gonna say, isn't this similar to just about every crankcase breather system I've ever seen? Older chevys had the PCV from the valve cover to the base of the carb (where the vacuum is highest), Briggs and Stratton lawnmower systems had a similar setup with a flap valve next to the muffler, breathing into the carb. In both cases there is a one-way valve and the pressure "pulsates" slightly between positive and negative during normal (cruise) operation. Having a slight vacuum in the crankcase helps the ring seal.

brian Rupnow
06-14-2019, 04:49 PM
While everyone was yakking about diesels, the plan fairy flew up, perched on my computer, and shat out the drawing of the crankcase pressure regulator on the Silver Angel. It is a simple 3/32" diameter ball setting in a tapered seat with a very light spring holding it in place. Pressure inside the crankcase lifts the ball off it's seat and escapes. Suction in the engine pulls the ball deeper into it's tapered seat and doesn't let any air in. This gives a negative pressure in the crankcase. The engine has splash lubrication. This lubricates the main bearings, the big end of the rod, and the wrist pin. I would have to think the atmosphere inside an engine with splash lubrication must be full of a very oil heavy mist.

A.K. Boomer
06-14-2019, 05:12 PM
Stoichiometric is in the middle of rich and lean.

-D

Yes and it's needed to stay within that range on the old gassers, not the new direct injection gas, there is no "mixture" - your only compressing air - then adding whatever fuel needed to get the job done, and if that happens to be idling or low demand your not even coming close to the old school ratio's - your pulse controlling your injectors to control the flame front not using a stoichiometric mixture ratio to do the same,

the rule book for the gas engine has been re-written --- where have you guys been for the past decade???

mihit
06-14-2019, 05:18 PM
I read yesterday about a small single cylinder i.c. engine model that had a "regulator" that kept a slight negative crankcase pressure in the engine while it was running. This was a 4 cycle vertical engine with a "wet" crankcase. The negative pressure kept any oil from migrating out around the crankshaft bushings. I hadn't heard about that before and I think it is a great idea. The engine in question was the Silver Angel by Bob Shores. A visual inspection of this engine running on YouTube shows no connection from the carburetor to the crankcase. The only "oddity" I see is that the engine seems to have double oil filler caps side by side. Does anyone have more info about this?---Brian

The 193X Lister Diesel I have does this too. Not a new thing...

Yondering
06-14-2019, 06:44 PM
It is a simple 3/32" diameter ball setting in a tapered seat with a very light spring holding it in place. Pressure inside the crankcase lifts the ball off it's seat and escapes. Suction in the engine pulls the ball deeper into it's tapered seat and doesn't let any air in. This gives a negative pressure in the crankcase.

That's exactly what I was talking about with the check valve in the breather hose on my dirt bike. Mine is a factory KTM part you can buy for around $20, but there are other automotive versions too.

Yondering
06-14-2019, 06:46 PM
Yes and it's needed to stay within that range on the old gassers, not the new direct injection gas, there is no "mixture" - your only compressing air - then adding whatever fuel needed to get the job done, and if that happens to be idling or low demand your not even coming close to the old school ratio's - your pulse controlling your injectors to control the flame front not using a stoichiometric mixture ratio to do the same,

the rule book for the gas engine has been re-written --- where have you guys been for the past decade???

Combustion chemistry for gasoline engines is still different than for diesels; you seem to be missing that. Lean burn has been around for a long time, it's nothing new with direct injection. Never mind though, you're one of those guys who'll keep arguing the point all day for no real purpose. I'm out.

A.K. Boomer
06-14-2019, 06:54 PM
Combustion chemistry for gasoline engines is still different than for diesels; you seem to be missing that. Lean burn has been around for a long time, it's nothing new with direct injection. Never mind though, you're one of those guys who'll keep arguing the point all day for no real purpose. I'm out.

Your just "off the mark" with everything , of course the chemistry is different - it's different fuel, but guess what? the operating principle is actually becoming the same esp. with the gassers that are being built with no spark plugs - it's called compression/ignition, sound familiar? yeah just like diesels...

and please do not confuse what the old gassers called lean burn with what's going on today - again here's all you need to know - the direct injection gassers are compressing nothing but air so it's impossible for the "mix" to go off until the fuel is then injected... big difference between having an injector pre-intake valve VS having one INSIDE the combustion chamber (LIKE A DIESEL!)

read a book.

johansen
06-14-2019, 06:59 PM
My understanding of common PCV valves is that they are basically vacuum regulators, included to keep a small vacuum on the crankcase.
[correct]

I always assumed that most modern vehicles used negative crankcase pressure.

Ed

my brothers' 2005 honda civic does not have a pcv valve connected to the intake manifold after the throttle, but rather directly vents the valve cover to the intake after the air filter. so the maximum vacuum is the pressure difference across the intake resonator, tube, and air filter. we tried plugging up the valve cover and sucking the air out of the crankcase with a hose connected to the intake, but.. the air leaking in through the rubber seals that seal the tube used to access the spark plugs through the valve cover.. made a strange.. flock of birds type whistling resonance that.. was annoying.. not to mention the air leaking in would bring water vapor and contaminates with it.

we did a similar modification with a 1995 vw jetta and i suspect the crankcase vacuum reduced the oil leakage through the crankshaft oil seal. it also significantly reduced the water content of the oil, which was a problem with that engine (maybe very slow head gasket leak?) removing the water from the oil increased the oil pressure once the engine got up to temperature.. which was an unexpected benefit..

JRouche
06-15-2019, 05:04 AM
The only "oddity" I see is that the engine seems to have double oil filler caps side by side. Does anyone have more info about this?---Brian

Brian Rupnow. Four or two cylinder? Love your work!!! JR

JRouche
06-15-2019, 05:41 AM
Yes and it's needed to stay within that range on the old gassers, not the new direct injection gas,


Opps? The computer still likes to see what the O2 sensor is seeing !!! Heck, I put two O2 units in my 62 Nova.

Keep it stock and you are good to go.. JR

A.K. Boomer
06-15-2019, 07:43 AM
That's a damn good observation JR, my take on that is the fact that we still have cat's that we need to keep "alive",

if it were not for emissions we would be able to see yet again even more incredible gains in both horsepower and efficiencies but we are bound to certain rules and regs and systems that are incorporated into the modern day engine that have to be maintained,,,

yes we still need the dreaded oxygen sensor both upstream and downstream to know just where the catalytic converters performance is,,, if they do not coincide the dreaded "cat performance is below normal threshold" code will get thrown along with the check engine light...

all this info is being processed by the ECU, but what's incredible with todays DIG's is that we are controlling the burn rate inside the combustion chamber,,, much of this technology actually did come from the modern diesel engine doing the same due to ever increasing emission standards being inflicted upon it,,, it was inevitable that this leap over to gas engines doing the same would soon follow,
micro controlling the fuel as it's actually being burnt is a game changer - but sadly not all of it is going to better performance and efficiency - some also has to be used for needed emissions...

Edwin Dirnbeck
06-15-2019, 08:24 AM
If there's something you do not understand about that statement then just say so,

You think diesels are concerned with Stoichiometric ratio's ? all's they care about is if they have enough air to burn whatever their going to be injecting into the chamber -- and overkill on the air ratio is not an issue,,, actually and technically diesels are always "running lean" with way more air than fuel (unless your into "rolling coal") - they can do this due to not having to compress a pre-mix of air and fuel - yeah, kinda like what's going on with todays direct injection gas,,, you no longer have to have a perfect ratio of air and fuel... you can have and do have many times more air than what is needed like at idle - no throttle plate, full charge of air yet tiny little spritz of fuel just enough to keep it running...
I ,also am surprised at this info. I have a 2015 chevy equinox with direct gasoline injection.I assumed that it had a throttle plate.I do all my own repair work ,but have never had any reason to poke around in the engine. It has 70,000 miles and I only open the hood at oil change time.It is only 4 years old,but is the most perfect car that I have ever had.Edwin Dirnbeck

A.K. Boomer
06-15-2019, 08:46 AM
I ,also am surprised at this info. I have a 2015 chevy equinox with direct gasoline injection.I assumed that it had a throttle plate.I do all my own repair work ,but have never had any reason to poke around in the engine. It has 70,000 miles and I only open the hood at oil change time.It is only 4 years old,but is the most perfect car that I have ever had.Edwin Dirnbeck

I cannot speak for every system out there as there's allot of variations but know that most if not all have abandoned it,

keep a closer eye on your air filter as you are pumping allot more CFM through it if your engine is "plateless"

strokersix
06-15-2019, 11:02 AM
Boomer, please post links to specific unthrottled gasoline fueled engines. I want to know:

How does a fuel intended to NOT preignite (gasoline octane rating) work in a compression ignition direct injection engine?

A.K. Boomer
06-15-2019, 11:26 AM
Im working right now but will try to find something later,,, the thing is - is there's lots of variations going on right now and the most common is they are still using spark plugs to "compensate" and trigger the fuel going off at the same time it's being injected,,, also - keep in mind they are no longer held accountable for using higher compression and take advantage of this fact to the extreme --- compression ratio's on some of these engines are over 14:1 and climbing,,, that's with running turbos --- yesteryears gassers had to have dished pistons and run close to 7:1 or the mix would prematurely "go off" , you know if that was happening that back then-then yes indeed it is possible to get gas to "behave badly but in a good way" with todays technology - in fact if it was premixed the engines would only last minutes regardless of "mixture"...

CarlByrns
06-15-2019, 01:12 PM
Boomer, please post links to specific unthrottled gasoline fueled engines. I want to know:

How does a fuel intended to NOT preignite (gasoline octane rating) work in a compression ignition direct injection engine?

Boomer is *almost* right on this one. One or maybe more of Japan's car companies are experimenting with GDI engines that work as a normal spark-ignition engine and slide into a compression-ignition regime under certain conditions. Preignition is avoided by the simple fact there is no fuel in the cylinder. I'd imagine the injection pressure is astronomical and without diesel's lubricity, injector wear is bound to be an issue.

A.K. Boomer
06-15-2019, 01:56 PM
Boomer, please post links to specific unthrottled gasoline fueled engines. I want to know:

How does a fuel intended to NOT preignite (gasoline octane rating) work in a compression ignition direct injection engine?

Well, CarlB is *almost* right on that one; https://www.caranddriver.com/features/a14537979/hyundais-experimental-gas-engine-runs-without-spark-plugs-feature/

strokersix
06-15-2019, 02:39 PM
https://www.caranddriver.com/features/a14537979/hyundais-experimental-gas-engine-runs-without-spark-plugs-feature/

Thank you.

CarlByrns
06-15-2019, 07:13 PM
Well, CarlB is *almost* right on that one; https://www.caranddriver.com/features/a14537979/hyundais-experimental-gas-engine-runs-without-spark-plugs-feature/

Two rules when quoting car articles:
1) Never trust a five year old article.
2) Never trust an article written by Don Sherman.

The article is from 2014 and apparently Hyundai has backed off on the idea of GDCI. See :https://www.autoblog.com/2018/09/24/hyundai-spark-compression-engines-grant/. Check back in 10 years.

In other news, Mazda's Skyactiv-X, which blends spark and compression ignition, is available in Europe now and in North America 'Real Soon Now' which means 'someday, maybe'. Here ya go: https://www.motor1.com/news/346378/mazda-skyactiv-x-engine-delay/

A.K. Boomer
06-15-2019, 08:02 PM
Fair enough Carlb, but iv read about countless other variations over the years - some using a type of glow-plug just for starting but once the engine heat builds up it does not need any extra help, that's allot like certain diesels, it's just a matter of time, your concerns about injector life are warranted but Digs have been in full production for quite sometime now and I have not heard of anything out of the ordinary...

but the main thing I was stating is they really are getting immune to the old school thought of "mixture"

it's copious amounts of air and just add whatever fuel you need to it be it little or lot, they are wide open throttle all the time, they pump through many times more air then an old school gasser, to think that they are still stoichiometric would mean piss poor economy - but that's not the case because they are immune to having to match the air with the fuel ratio, they operate more like a diesel, that's what you get when you put the injector INSIDE the combustion chamber...

J Tiers
06-15-2019, 10:40 PM
..... they pump through many times more air then an old school gasser, .....

Seems like it's the same old swept volume x number of admission strokes, with an effective manifold pressure adjustment... just like always. "many times more air" would imply more displacement, or much higher rpm......

Possibly you mean "more air than the gas used would imply".... Stratified charge does that.

BTW, the gasoline engine has the potential for much higher efficiency than diesel. That comes straight from Carnot. But the EPA will not allow it, due to NOx production at the temps necessary to realize it.

A.K. Boomer
06-15-2019, 11:06 PM
Seems like it's the same old swept volume x number of admission strokes, with an effective manifold pressure adjustment... just like always. "many times more air" would imply more displacement, or much higher rpm......

JT - they don't have throttle plates - there wide open to "air" this is just like a diesel, at idle they take in many times more air possibly 10 or 100 times, they are FULL BORE WIDE OPEN and no that's not "just like always" and it does not imply "more displacement" or "higher RPM"


Possibly you mean "more air than the gas used would imply".... Stratified charge does that.

no - it blows stratified charge out of the ballpark, your talking 14+ to 1 compression ratio's WITH using a turbocharger,,, that's the miracle of micro managing the injection rate's and pulses...


BTW, the gasoline engine has the potential for much higher efficiency than diesel. That comes straight from Carnot. But the EPA will not allow it, due to NOx production at the temps necessary to realize it.

I did not know this - I always thought if we get to abandoned the emissions thing then the winner of efficiency goes to the diesel simply for carrying more BTU's per gallon... interested in what your saying so please explain...

J Tiers
06-16-2019, 12:49 AM
JT - they don't have throttle plates - there wide open to "air" this is just like a diesel, at idle they take in many times more air possibly 10 or 100 times, they are FULL BORE WIDE OPEN and no that's not "just like always" and it does not imply "more displacement" or "higher RPM" no - it blows stratified charge out of the ballpark, your talking 14+ to 1 compression ratio's WITH using a turbocharger,,, that's the miracle of micro managing the injection rate's and pulses...


I did not know this - I always thought if we get to abandoned the emissions thing then the winner of efficiency goes to the diesel simply for carrying more BTU's per gallon... interested in what your saying so please explain...

The engine may be at "full bore", but it still can take in no more air than the cylinder volume x the number of intake strokes, as modified by manifold pressure (higher if turbo,and including flow related pressure drops)....... and, it has to be stratified charge, because despite the crowing about "forget stoichiometric ratio", it still has to LOCALLY have the correct ratio, or it will not go "boom" (there are limits of flammability). That's nearly the definition of stratified charge, and I believe you said so yourself.......

As for no throttle plate, that has nothing whatever to do with it. Puts only enough fuel in to equal the power needed.... if it put in more, the engine would accelerate until the load DID equal the fuel burn power (at efficiency). Works as well as a throttle. Better, actually. Air flow is constant at a given rpm, but fuel burn is related to power needed at that rpm.

Carnot efficiency is related to the difference in temperature between starting state, and final state of the "working fluid" in the energy extraction process (power stroke, here), so long as it is used efficiently, and assuming no loss to cylinder walls etc. That's the very very short story, and no doubt one of the usual suspects will quibble and squall, but that won't make it false. It's why there was a flap about ceramic engines to work at high temps, back in the 1960s. then they discovered that NOx was a pollutant, and that anything over about 2300 deg or thereabouts made it in quantity.

The peak temp in a gas engine as traditionally made, is quite high, higher than the usual diesel, so the Carnot efficiency can be higher. It generally is not, and there are plenty of details, but it could be.

JRouche
06-16-2019, 01:59 AM
Boomer GDI engines that work as a normal spark-ignition engine and slide into a compression-ignition regime under certain conditions. Preignition is avoided by the simple fact there is no fuel in the cylinder. I'd imagine the injection pressure is astronomical and without diesel's lubricity, injector wear is bound to be an issue.

Yes Sir Carl. JR

+

strokersix
06-16-2019, 08:19 AM
Carnot efficiency is related to the difference in temperature between starting state, and final state of the "working fluid" in the energy extraction process (power stroke, here), so long as it is used efficiently, and assuming no loss to cylinder walls etc. That's the very very short story, and no doubt one of the usual suspects will quibble and squall, but that won't make it false. It's why there was a flap about ceramic engines to work at high temps, back in the 1960s. then they discovered that NOx was a pollutant, and that anything over about 2300 deg or thereabouts made it in quantity.

The peak temp in a gas engine as traditionally made, is quite high, higher than the usual diesel, so the Carnot efficiency can be higher. It generally is not, and there are plenty of details, but it could be.

Theoretical cycle for spark ignited engines is modeled as a constant volume combustion. Or in other words the combustion occurs instantaneously at TDC. Theoretical cycle for compression ignition is modeled as constant pressure combustion. Or in other words the combustion occurs on the expansion stroke. More realistic model for both is a blend of the two models. Constant volume model results in greater Carnot efficiency. Just another way to describe what Tiers is saying.

https://www.google.com/url?sa=i&source=imgres&cd=&cad=rja&uact=8&ved=2ahUKEwiPjLWU_u3iAhXMHzQIHdikC78QjRx6BAgBEAU&url=https%3A%2F%2Fen.ppt-online.org%2F181453&psig=AOvVaw2ltak9uM3ivipRcJKdfHgd&ust=1560773934123074

This subject has been of great interest to me since I was a kid. And I do have graduate level education to back it up. Enjoy the discussion!

strokersix
06-16-2019, 08:36 AM
Diesel fuel molecular structure has long straight carbon chains. This encourages autoignition quickly so the fuel starts to burn as soon as it is injected.

Gasoline is the opposite. Highly branched molecular structure to DISCOURAGE autoignition so the fuel does not start to burn until spark ignited.

Using diesel in a gas engine results in early autoignition and knocking. Using gasoline in a diesel engine results in lots of fuel injected before autoignition resulting again in knock. Very different combustion processes.

I don't understand why we don't just build diesels. This blending of the two does not make sense to me.

ed_h
06-16-2019, 09:56 AM
My understanding is that modern gasoline is composed primarily of straight chain (alkane) compnents of length up to 10 or 12 or so.

Ed

Willy
06-16-2019, 10:16 AM
[QUOTE=strokersix;1243212..................
............................

I don't understand why we don't just build diesels. This blending of the two does not make sense to me.
[/QUOTE]
It boils down to dollars and cents and the economic viability of using diesel as a fuel despite some of it's inherent advantages.
Emissions compliance has added at least 10-15,000 dollars to the cost of large truck engines. Add to this system maintenance and increased operational costs due to the complexity of these very integrated systems.

Particulate matter emissions reductions have exceeded 98% and NOX has been reduced at least 95% from pre-emission enhancement technology days but clean air comes at a cost. Gasoline being somewhat easier to clean up, either in-cylinder or by using after-treatment is becoming more of a viable option in areas where diesel used to be the first choice.

A.K. Boomer
06-16-2019, 10:26 AM
The engine may be at "full bore", but it still can take in no more air than the cylinder volume x the number of intake strokes, as modified by manifold pressure (higher if turbo,and including flow related pressure drops)....... and, it has to be stratified charge, because despite the crowing about "forget stoichiometric ratio", it still has to LOCALLY have the correct ratio, or it will not go "boom" (there are limits of flammability). That's nearly the definition of stratified charge, and I believe you said so yourself.......

Your right technically it is the definition of a highly advanced stratified charged engine - but not to be confused with yesteryears, but we were comparing the old gassers to the new Dig's, and i used idle or mild load as an example,
the old gassers do not even come close to filling up their chamber due to a throttle plate that is all but totally cutting off their air supply, the Dig's are taking in 10 fold if not 100 fold amount of air in comparison,,, this has NOTHING to do with engine displacement or turbo charging,,, one is restricted - the other is not, And yes you can "forget about stoichiometric ratio" as some kind of solid guideline throughout the engines range, unless you plan on including more flexible ratios of 60+:1

, it's why I used idle and mild load as an initial example, even the old school stratified charge engines could only make mild gains in comparison... again were talking turbo charged engines with 14:1 compression ratio's --- that's incredible... and they are now the dominant force in production vehicles... it's what everyone is going to...





As for no throttle plate, that has nothing whatever to do with it. Puts only enough fuel in to equal the power needed.... if it put in more, the engine would accelerate until the load DID equal the fuel burn power (at efficiency). Works as well as a throttle. Better, actually. Air flow is constant at a given rpm, but fuel burn is related to power needed at that rpm.

maybe this will help , the old gassers were at the mercy of controlling their flame front and burn rate by using mixture ratios's , the Dig's get to function more like diesels and are "somewhat" IMMUNE to this fact, they control their flame front and burn rate with injection...


Carnot efficiency is related to the difference in temperature between starting state, and final state of the "working fluid" in the energy extraction process (power stroke, here), so long as it is used efficiently, and assuming no loss to cylinder walls etc. That's the very very short story, and no doubt one of the usual suspects will quibble and squall, but that won't make it false. It's why there was a flap about ceramic engines to work at high temps, back in the 1960s. then they discovered that NOx was a pollutant, and that anything over about 2300 deg or thereabouts made it in quantity.

The peak temp in a gas engine as traditionally made, is quite high, higher than the usual diesel, so the Carnot efficiency can be higher. It generally is not, and there are plenty of details, but it could be.


yes im familiar with Smokey Yunicks ceramic engines and such, iv just never heard anyone use that as the holy grail for judging that Gas is more efficient then Diesel, there's no reason you can't also create a diesel to run to extreme temps, i mean if you get to toss emissions out the window then so do I, I would think tie goes to the fuel with the greater BTU rating --? heat it up and burn it and see what you get...

A.K. Boomer
06-16-2019, 10:46 AM
This discussion does make me wonder about combustion chamber "hot spots" that were so dreaded for the old gassers as they could cause the fuel to go off under compression,,, so would not the answer for the new Dig's be creating one? as in an initial glow plug to help the engine start and then it sits there out in front of the injector nozzle glowing red hot waiting for it's next "spritz" of fuel,,,
perhaps there is still an advantage to being able to control spark and injector timing and that's why it has not been done,


these newer little engines are amazing - the honda CRV for example needed a NA 2.4 liter to push it around and now it's got a 1.5 turbo that's not only faster but has about 1/3rd better fuel economy... Before Dig's you would shoot yourself in the foot expecting to do better in economy by throwing a turbo charger on an engine, in fact why honda never used them...

J Tiers
06-16-2019, 11:31 AM
.....

yes im familiar with Smokey Yunicks ceramic engines and such, iv just never heard anyone use that as the holy grail for judging that Gas is more efficient then Diesel, there's no reason you can't also create a diesel to run to extreme temps, i mean if you get to toss emissions out the window then so do I, I would think tie goes to the fuel with the greater BTU rating --? heat it up and burn it and see what you get...

Never heard of SY's ceramic engines...... talking about research engines at universities etc. SY was a tinkerer... a smart tinkerer but not a researcher. probably the whole thing is moot, since the diesel is gradually having its present advantage legislated away, and gas engine technology is improving.

if you are talking miles per gallon, or some such, you are off-base, like measuring liquid volume by wind speed........

It is nearly meaningless, and a function ONLY of the stupid american habit of measuring chemicals by volume. At the very least, you would want to measure by mass, and in reality, you would want to measure fuel by net energy content of the amount sold, because THAT is what you are buying.

The true efficiency is the amount of energy extracted, compared to the energy content of the fuel to begin with.

A.K. Boomer
06-16-2019, 11:53 AM
The true efficiency is the amount of energy extracted, compared to the energy content of the fuel to begin with.

Now that level's the playing field - then it all comes down to engine operating principle and design...

JRouche
06-16-2019, 10:30 PM
I don't understand why we don't just build diesels. This blending of the two does not make sense to me.

We tried that. Remember when they made a diesil cadillac or chevy.

Hell no. O I want my small block chevy.

I dont drive muck. My new car that is 5 years old has about 5700 miles. Yes, fifty seven hundred miles.

I dont drive much. JR

J Tiers
06-16-2019, 10:40 PM
Diesels are dirty.... particulates, unburned fuel, black smoke if poorly adjusted, etc. They often stink, and the stuff they put out is highly carcinogenic.

They are complex, tend to be heavy (Guiberson notwithstanding), and expensive.

Fixing all that reduces the efficiency advantage they currently have by a chunk. And diesel has consistently been more expensive by volume than gas....more so than the mileage advantage.

A.K. Boomer
06-16-2019, 10:42 PM
I will never "knock" a diesel for a passenger car, iv owned two silly wabbits that both achieved close to 50mpg dependably and did everything they were designed to do, my only regret is i did not get a turbo diesel Jetta - had the hots for one at the time but never got around to it cuz I entered the honda "CRX era" but that was fun and economical also... (way more fun than the wabbit's)

A.K. Boomer
06-16-2019, 10:52 PM
Diesels are dirty.... particulates, unburned fuel, black smoke if poorly adjusted, etc. They often stink, and the stuff they put out is highly carcinogenic.

.


yet just like a good barBQ if someone is generous enough to roll a little coal my way I just crank down the window and take it all in, I like the smell of diesel always have,,, pre-combustion or after,,, hate the smell of gas both burnt and un-burnt...

side note and many moons ago, there was a local coal mining operation that used to use the only IC engine vehicles that were allowed into the mine - in fact I rebuilt many of engine for them - and they were not gassers,,, they were chop top wabbit diesel pick-ups to carry gear back and forth,,,

for what it's worth they were the only vehicles that passed the "internal coal mining emissions" considered safe enough to breath the air...

Willy
06-16-2019, 11:53 PM
Diesel engines are the predominate choice of underground mining equipment power plants for a number of reasons that make sense to those that make money in such ventures. There is now a large assortment of industry approved diesel engines available. The list here of of diesel engines approved by Natural Resources Canada (https://www.nrcan.gc.ca/mining-materials/resources/approved-diesel-engines/8180) pretty much parallels that of the US and a number of other countries that share common safety goals that pertain to a large number of multinational companies.

I think the major issue with the use of gasoline engines in this safety critical application is due to the fuel itself being more dangerous in it's raw form and the fact that diesel engines emit drastically lower levels of carbon monoxide, thus reducing ventilation requirements. It's all about dollars and cents boys and girls, as usual.

Maybe I'm not using the right search criteria but try as i may I could not find a list of gasoline engines approved for underground mine use applications whether they be gassy or non-gassy mines.

J Tiers
06-17-2019, 02:00 AM
Diesel spills are not a big problem in enclosed spaces. Gasoline evaporates, and the vapor in air is actively explosive. Bad in a mine.

MattiJ
06-17-2019, 07:26 AM
I don't understand why we don't just build diesels. This blending of the two does not make sense to me.
Diesels have been extremely popular in Europe but now there is heavy decline on numbers. Latest emission standards are hard to fulfill and WV(+everyone else) software scams was the final nail in the coffin.
Over 50% of sold passenger cars were diesels in here 10 years ago and diesels were even more popular in many other European countries than here in Finland.

Edwin Dirnbeck
06-17-2019, 10:28 AM
I cannot speak for every system out there as there's allot of variations but know that most if not all have abandoned it,

keep a closer eye on your air filter as you are pumping allot more CFM through it if your engine is "plateless"
Yes,thank you. I have already changed the air filter and the cabin filter. They both looked pretty clean,we don't smoke or drive on dirt roads.It sure seems that the engine air filter and the catalytic converters would be doing extra work with a wide open throttle. Edwin Dirnbeck