gas explosion

[gonzo]

This happened at one of our shops about four months ago. A costumer brought a boat with an I/O that was hydrolocked. Assuming it was water, a mechanic took the sparkplugs out to drain the cylinders. The engine was hydrolocked with gas. The fuel pressure regulator had a ruptured diafragm. The gas in the cylinder raised the compression while cranking, which made it diesel and explode. A flame about four feet long came out too. The mechanic got only small burns. I had never heard of this happening before.

[marshmat]

Ouch.

Treat engines and their food with respect....

[tom kane]

Originally Posted by gonzo

This happened at one of our shops about four months ago. A costumer brought a boat with an I/O that was hydrolocked. Assuming it was water, a mechanic took the sparkplugs out to drain the cylinders. The engine was hydrolocked with gas. The fuel pressure regulator had a ruptured diafragm. The gas in the cylinder raised the compression while cranking, which made it diesel and explode. A flame about four feet long came out too. The mechanic got only small burns. I had never heard of this happening before.

I would be interested to know whether the boat was fueled with Gasoline or LPG.Americans seem to refer to gasoline as gas,which is confusing.

[woodboat]

Well LPG is LPG gas is short for gasoline. Who wants to type out gasoline every time. I think refering to LPG as gas is confusing. In the story the engine hydro locked. I was under the impression LPG went back to a gaseous state when not under pressure. Besides I have never seen an LPG boat.

[yipster]

hmm, in france LPG is GPL or something, gas is essence and diesel gasoline.
that way my girlfrend once put gasoline in the gas boat while i was getting icecream but at sea one after the other eng stopped.
fuelpumps got clogged, later had to be replaced, dangerous expensive and even confusing!

[Tim B]

I know, how about "Petrol" for the american's Gasoline. "Diesel" for diesel. and either "LPG" or "gas" for LPG ?

No problem.

I've never heard of big engines getting "compression locks" but I suppose it can happen (well I have, but not that badly). why was there a flame, though? if the gas (assuming it was a gas in the cylinder) expanded it would have cooled below auto-ignition temp+pressure. the only way it could burn would be either to exceed the auto ignition conditions, or for there to have been a spark.

Strange things are afoot...

Tim B.

[Mikey]

Woodboat,
You are absolutely correct and LPG does go back to a gaseous state when not under pressure.

I hope LPG does not become common in boats but I doubt it, the way demand for petrol is increasing, prices are not likely to go down. It will come.

LPG is much more volatile than petrol, with (quite) a bit of bad luck, just flipping an electrical switch can cause quicker expansion of that gas than the boat and its crew likes Nowhere to go on a boat either

It is, just like nuclear power, perfectly safe as long as it is handled correctly, maintained correctly and Sod's law doesn't kick in...

Hmmm, doesn't sound like something I want on my boat.

Am I over-reacting?
Mikey

[woodboat]

If I had to guess I would say the ingnition of fuel was not from the diesel effect. You have an engine so full of fuel that it hydro locked. You then remove the plugs and leave the spark plug wires dangling. Then crank the engine to expel the fuel wchich results in ignition. Are you sure the coil power was removed?

[gonzo]

Yes, we are all very careful about disconnecting the ignition. There are stablished safety precautions. The fuel ignited under pressure and the flame came out the sparkplug hole.

[Tim B]

because of the fluid's viscosity (the air-fuel mixture) there will be a maximum flow speed for fluid out of the sparkplug hole...you must have been cranking it at a fair rate to increase the pressure enough for ignition!!!

Tim B.

[gonzo]

Yes, with the wrong assumption that it was locked with water!

[tom kane]

It looks like much more study about LPG and other compressed fuels would help us all.You can have vapour extraction from a fuel cylinder for a carb motor,or liquid extraction from a cylinder for EFI motors.There must surely be someone in USA running compressed fuels in boats?Liquid extraction or vapour extraction,the choice is yours.Come on Gonzo give us a little more info about that motor,you have me interested.

[yokebutt]

I'm confuseded, if the cylinder is "hydro-locked" with gasoline, then there is no oxygen for the fuel to oxidize with, right? And, if the spark-plug is out, wouldn't you need one hell of a starter to build up enough pressure for compression-ignition? But even if the starter was strong enough, the fuel under pressure (in the cylinder) still doesn't have anything to oxidize with, and the fuel shooting out of the spark-plug hole is at very low pressure, (if we let our old friend Daniel Bernoulli have his say) and shouldn't ignite.

Thus, I cannot conclude anything other than that there had to be another, yet unidentified, source of ignition.

Yoke.

P.S. I'm not picking on you, it's just a curious little problem.

[woodboat]

Yokebutt, that was my thought exactly. We were trained early on in my Lineman (telephone) that you throw a hard hat next to the dead body so the widow can get death benefits. I was thinking that maybe the ignition source was disconnected prior to the investigation. Any way there are plenty of sources for ignition on a gasoline engine.

[Tim B]

there will be some oxygen in the cylinder, if not on the first cycle, then sucked in on the second. Viscosity will play a part in the pressure difference (no difference then no fuel would come out). So theoretically, it would be possible to case ignition. The piston would have to be moving pretty damn quick though. Of course, once the fuel inside the cylinder ignites, the increased heat will cause the other fuel droplets (highly flammable and plenty of O2) to ignite (above the cylinder).

It can happen, but I suspect it would need a fair piston speed. It is actually the pressure difference across the spark-plug hole that will limit the system,

Tim B.