Running backwards?

[Another Ahab]

Nope, but check out Hanksdeuce's solution:

Pretty nifty.

It's simple and brilliant.

Hanksdeuce should consider taking out a patent on that idea.

And I'm not kidding about that.

 

[frodobaggins]

Commercial solutions do already exist. But his cost less than $20 total

It's simple and brilliant.

Hanksdeuce should consider taking out a patent on that idea.

And I'm not kidding about that.

 

[Another Ahab]

It's simple and brilliant.

Hanksdeuce should consider taking out a patent on that idea.

And I'm not kidding about that.

Commercial solutions do already exist. But his cost less than $20 total

Simple does not automatically mean an idea cannot be patented:

- Patent it.

- Market it to the big manufacturers.

- Sell them the patent.

And spend the rest of your life buying Green Iron!

"To Sleep/
Perchance to Dream"
- Willy S.

 

[gringeltaube]

... Hanksdeuce should consider taking out a patent on that idea.

Patent on what? Not this, or?? http://www.blastgateco.com/Cast-Aluminum-Full-Blast-Gates.php



G.

 

[Another Ahab]

Patent on what? Not this, or??
G.

I was not making myself clear, and that's my error. The patent would not be on the blast-gate (which is only one element of the idea), but on the concept of all the elements combined that make up the runaway "choke".

The only issue is, how many people in the world are going to rush to buy this better mousetrap? The deuce is popular here among the membership, but I guess we're really not talking any global-sized demand here.

 

[wanderingwillys]

I got my wrecker to do that on me - was lugging 1st gear and it started to stall - stabbed the clutch real quick and she grumbled a bit but sputtered back to life - popped it in PTO crane mode and hopped out - the smoke coming from the passenger fender area caught my attention...

Went over and stuck my hand over the intake (now the exhaust) and said "no sh!t - isn't that something" - hopped up on the fender and sure enough the exhaust pipe was sucking in fresh air...

I just shut it down with the e-stop like normal - started it right back up with no issues... Took the air cleaner out later and it seemed no worse for the wear...

I know the valve guides are pretty worn since she smokes pretty good all the time until you run for 30 - 40 min... it cleans up then

I am due for an engine overhaul but not in the cards quite yet

 

[Another Ahab]

I got my wrecker to do that on me - was lugging 1st gear and it started to stall - stabbed the clutch real quick and she grumbled a bit but sputtered back to life - popped it in PTO crane mode and hopped out - the smoke coming from the passenger fender area caught my attention...

Went over and stuck my hand over the intake (now the exhaust) and said "no sh!t - isn't that something" - hopped up on the fender and sure enough the exhaust pipe was sucking in fresh air...

I just shut it down with the e-stop like normal - started it right back up with no issues...

The impression from other stories is that any runaway transitions almost immediately to self-destruct RPM's, but your story is the first I heard that suggests there is some time to catch it all before it gets critical. That's good to know.

 

[Floridianson]

If you don't catch it in the first couple of seconds then you are not paying attention. Lets see no oil pressure would tell you right away. Exhaust coming out the intake would tell you right away. Stall the motor out as fast as you with the transmission if it's manual trans. while pulling the cut off at the same time. Do something but do it quick leave the nose picking butt scratching for later.

 

[bchauvette]

The impression from other stories is that any runaway transitions almost immediately to self-destruct RPM's, but your story is the first I heard that suggests there is some time to catch it all before it gets critical. That's good to know.

I think the question is "How long do you want to run your engine with no oil pressure?" My answer NEVER!!. I cringe waiting for oil pressure on start up.Gota believe there are other nasty stuff going on running backwards. No dout if you don't get sudden death there are long term consequences.

 

[turnkey]

Like with cars in the 80s, they would still run with key turned off...not the same as running backwards...But still can freak you out now days...

 

[wanderingwillys]

I had been running the thing for a bit so it was up to temp and well oiled - that truck sometimes takes as long as 15 to 20 sec to start showing oil pressure after starting so I doubt 30 sec of running without fresh oil supply will do it in - remember most of the oil flow is for cooling - all the bearings are hydrodynamic (minus the wrist pins) so they create their own oil wedge regardless of direction - the issue would be if the oil in the wedge overheats and the journal drops through the film...

Mine acted just like it did running forward - happily sat and idled - just the smoke was coming out the wrong hole!

I think the run-aways you mention all start stealing oil from the crankcase as fuel - then you have a problem as you have no fuel limiter and she'll just climb in RPM until the valves float and/ or something comes from togetherness...

Not much time in that situation...

I've had a few big marine diesels take off with stuck fuel racks and it's a tad terrifying when 100+ tons of rotating mass is running away next to you and you'd best get it sorted NOW!

 

[bchauvette]

I'm thinking that hydrodynamic thingy don't apply. If you look underneath there is what I call a crankcase tumor where all the oil resides. Much lower than the crank and connecting rods have to splash in. Thinking the entire engine is dependent on pressure. Not sure but some engines have scupper (pick up) tails on the connecting rod caps that would be directional. My S.E.E. also takes 10 to 15 seconds to come to pressure. Maybe the crankcase tumor thing has something to do with it.

 

[wanderingwillys]

The oil film I am talking about is the oil retained between the bearing and the journal - the oil in the sump is for cooling - the only reason you need pressure above a certain level is to assure sufficient flow to all parts of the engine. The rotation of the journal creates the wedge I am describing; the journal actually rotates slight off center in the bearing shell and acts very similar to a pump with no vanes.

The load carrying ability of the oil is based on viscosity and surface tension more than on oil pressure - if you think about it there is no way that 60 psi of oil pressure can support the journal of the shaft from contacting the bearing shell if you were relying on oil pressure alone to carry the developed loads from the gas forces applied to the piston, the con rod, and onto the crank...

A standard rod bearing in a multifuel maybe has 2 square inches of area in contact with the crank pin - I am pretty sure the firing impulse creates more than 120lbs of load

And worse yet in scavenge the piston has no opposing gas forces when it turns around at the top of the exhaust stroke - the inertia loading is huge at this point... It only gets worse with RPM and is the reason for many rod bolt failures.


The load carrying ability of the oil is affected very minimally by pressure - thermal break down from low exchange volumes and high heat will cause the oil film to fail quickly - excessive clearance will create similar problems...


HTH


Matt

 

[saddamsnightmare]

May 31st, 2015.


Most diesels do have that capability to operate in reverse, some capitalized on it (large marine engines) and had their valve gearing set up accordingly. The M-19 Fairmont Railroad trackcar with the ROC gas engine was designed to do that so the car could run in reverse......

 

[wanderingwillys]

Yep - most of the direct reversing diesels have either symmetrical cam profiles or the earlier units used two cams and a flip flop linkage to move the rockers from one cam shaft to another (it was a nightmare) - More than one ship has murdered a dock when the reversing gear failed and the astern telegraph could not be answered

I am not sure how the multifuel ended up doing it but all I know is it happened twice so far on me - the second time I got it stopped less that a few seconds after the almost stall...

 

[rchalmers3]

I think some of us are confusing a runaway condition with an engine that runs backwards. The runaway engine is turning the correct direction while consuming an external fuel source, usually lubricating oil. The reverse running engine is running on the ordinary fuel supply. In my opinion they are really two different animals altogether!

Maybe one of the engineers in our ranks can school us a bit on how a compression ignition engine will run backwards, while a spark ignition motor probably would not. I assume it has to do with the nature of the fuel timing of the long stroke diesel. Which leads me to surmise that a short stroke diesel may not run backwards???

Rick

 

[wanderingwillys]

Yep - they are indeed two very different animals - not mutually exclusive but there would be two things wrong with a unit that reverse rotated and then ran away...

The spark ignited machines will not run backwards because the ignition source is not applied when the piston would be in a position to deliver a power stroke - usually in that case what happens is you get a flame front that moves out either the exhaust or inlet valves with very little turning effort applied to the crank - in other words you get a backfire and it stalls...

Diesels are a bit unique that they just use the heat of compression to ignite the mixture; so as long as you have evaporated fuel in the chamber and the cylinder can build pressure you will get an ignition - the overlap and profile of the cams for the inlet and exhaust valves will determine if the cylinder will build enough pressure to ignite and then apply enough gas force to the crank to turn the machine - the rotary fuel pump can run backward and still operate the injectors - obviously the timing will be not very optimal and the turbocharger will not be supplying any booster pressure but most of the time this reverse rotation occurs after a stall or roll and at idle where the turbocharger does not provide much air anyhow.

Once the machine gets moving there is very minimal turning effort required to maintain an idle - apply any sort of load and the system will likely stall since all the timing elements are not optimal.

I actually had a inline 8 250mm bore machine slip several fuel cams this winter and two of the units were actually firing 360 degrees out (the lobe slipped 180 degrees) They were firing intermittently on the end of the scavenge stroke and smoking like all get out... She just wanted to keep running.

Run-away machines are usually operating in normal rotation but the RPM regulation (which is fuel based in a diesel vs. air based in gasoline machines) gets lost at some point - the machine has access to unlimited fuel reserves and becomes only air limited - this usually leads to self destruction as it will rapidly climb in RPM until physics finds the weak link on the reciprocating mass and things come from togetherness. Diesels are traditionally supplied with 2 to 2.5 times the air required for combustion as it proves very challenging to get the fuel to mix and evaporate fully in a 14.7 stoich mixture like a gasoline unit - so with unlimited fuel the unit can run well past the maximum RPM limits.

To compound this piston rings have a general speed limit - hence the RPMs on larger machines decrease - anything over 30m/s and the ring begins to lose contact with the liner wall and the resulting loss of oil control becomes a major issue... Our small diesels can happily go to 3000 or 4000 RPM with a 70mm to 120mm bore - when you get to the big boys the RPMs drop to 70 - 90 RPM max on the 800mm and 900mm machines (granted they are two stroke not four stroke but the ring speeds don't change much) The speed limit favors longer stroke engines and lower RPMs to produce maximum torque.

HTH

Matt

 

[Another Ahab]

Yep - they are indeed two very different animals - not mutually exclusive but there would be two things wrong with a unit that reverse rotated and then ran away...

Run-away machines are usually operating in normal rotation but the RPM regulation (which is fuel based in a diesel vs. air based in gasoline machines) gets lost at some point - the machine has access to unlimited fuel reserves and becomes only air limited - this usually leads to self destruction as it will rapidly climb in RPM until physics finds the weak link on the reciprocating mass and things come from togetherness. Diesels are traditionally supplied with 2 to 2.5 times the air required for combustion as it proves very challenging to get the fuel to mix and evaporate fully in a 14.7 stoich mixture like a gasoline unit - so with unlimited fuel the unit can run well past the maximum RPM limits.

That's great way to describe the resulting total destruction.

Great overall summary and explanation, Matt. Thanks for the education!

 

[Csm Davis]

Lots of this comes from the older two stroke Detroit, yes most other diesel engines can be made to do one or both but the old Detroit just seemed to love to do both. I have seen two true runaways both Detroits they will test you and separate the men from the boys. A 6-71 that split the block and had sucked the seals in there by pulling the oil in and air so that shutdown wasn't completely possible. And a big 8v-91 that shutdown as soon as I dropped the plate to cut off the air, and no damage.
The reverse thing used to be very common saw a Detroit put together backwards in a skidder and it took a few minutes to figure out why it was going the wrong way because the air was going the right way through it and it was running great. Ohhhhhh yeah don't try to use a rag to stop eather situation it probably won't do any good and will damage things, if you are able use a board or steel plate or softball anything hard and big enough to stop the air flow and cut the fuel off this should stop a 4 stroke quickly.

 

[Another Ahab]

Ohhhhhh yeah don't try to use a rag to stop eather situation it probably won't do any good and will damage things, if you are able use a board or steel plate or softball anything hard and big enough to stop the air flow and cut the fuel off this should stop a 4 stroke quickly.

I get it, the old "soap-on -a-rope" idea, hanging right off the air-intake:

- Something real simple and elegant about that solution (painted O.D., of course).

AND it would make a real conversation-starter, like "Hey, Bud; What's THAT all about!?"