If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Hot Starting Fuel Injected Engines
"Corky Scott" wrote in message
... With my last experience, the engine actually went into hydraulic lock without me touching the controls or using the auxiliary fuel pump. The prop barely turn half a turn before it stopped and the starter couldn't crank it anymore. I'm not sure what exactly is going on here, but I don't think it's "hydraulic lock". As a previous post hinted at, "hydraulic lock" is something that is specific to only certain kinds of engines (like radials) and not those found in C172's. It happens when oil drains into the cylinder, putting an incompressible substance into a space that wants to compress when the engine turns. If you are having trouble with the starter not being able to turn the engine on a C172, you've either got a dead battery, or something worse is going on. When you first wrote "hydraulic lock", I actually assumed you meant "vapor lock", which is what happens when the fuel in the fuel lines is heated to the point of vaporization, preventing it from being pumped to the engine. This is the usual problem when starting hot engines, especially fuel injected ones (carbureted engines usually have enough fuel in the float bowl to let things get sorted out during engine start, so even a little vapor in the fuel lines won't cause a problem with starting). But now it sounds like you did actually mean something other than "vapor lock". I'm not sure what it was, but I'm pretty certain that, given that you're talking about a C172, it wasn't "hydraulic lock". Even if hydraulic lock were possible on a C172, it wouldn't be related to a hot engine start. There are actually two fuel pumps, one works with the engine turning, the other is the electric auxiliary pump. So fuel will be pumped to the injectors the moment the engine starts turning. I'm not familiar with the new fuel-injected C172's, but it's entirely possible that with the electric fuel pump running, fuel will be pumped to the injectors and even into the engine the moment the fuel pump is turned on, regardless of whether the engine is turning or not. That's how the fuel-injection system for the Lycoming 540 engine in my plane works. Pete |
#2
|
|||
|
|||
On Tue, 14 Oct 2003 11:04:46 -0700, "Peter Duniho"
wrote: I'm not sure what exactly is going on here, but I don't think it's "hydraulic lock". As a previous post hinted at, "hydraulic lock" is something that is specific to only certain kinds of engines (like radials) and not those found in C172's. It happens when oil drains into the cylinder, putting an incompressible substance into a space that wants to compress when the engine turns. If you are having trouble with the starter not being able to turn the engine on a C172, you've either got a dead battery, or something worse is going on. When you first wrote "hydraulic lock", I actually assumed you meant "vapor lock", which is what happens when the fuel in the fuel lines is heated to the point of vaporization, preventing it from being pumped to the engine. This is the usual problem when starting hot engines, especially fuel injected ones (carbureted engines usually have enough fuel in the float bowl to let things get sorted out during engine start, so even a little vapor in the fuel lines won't cause a problem with starting). But now it sounds like you did actually mean something other than "vapor lock". I'm not sure what it was, but I'm pretty certain that, given that you're talking about a C172, it wasn't "hydraulic lock". Even if hydraulic lock were possible on a C172, it wouldn't be related to a hot engine start. There are actually two fuel pumps, one works with the engine turning, the other is the electric auxiliary pump. So fuel will be pumped to the injectors the moment the engine starts turning. I'm not familiar with the new fuel-injected C172's, but it's entirely possible that with the electric fuel pump running, fuel will be pumped to the injectors and even into the engine the moment the fuel pump is turned on, regardless of whether the engine is turning or not. That's how the fuel-injection system for the Lycoming 540 engine in my plane works. Pete Pete, I'm assuming it's hydraulic lock because the starter cranked the prop around half a turn and then jerked abruptly to a stop. I re-engaged the starter and it tried to turn the prop but wouldn't. I waited a second and tried again and it turned the prop another half to 3/4's of a turn and jerked to a stop again. I did not get out an look to see if gas was pouring out of the exhaust stacks. But once I advanced to full throttle, the starter, after a few more attempts, began to turn the engine over at a normal rate. After a few seconds of this, one of the plugs fired and I thought we'd be ok, but it still didn't start. I waited another several seconds and re-engaged the starter and this time, as it spun the prop, it actually briefly fired up on all cylinders. I moved quickly to slap the mixture in, as the engine had quit again but the prop was still windmilling, and just before the prop stopped, the engine caught for good. I was an auto mechanic in a previous life and have seen hydraulic lock before. I know no other way of describing it. Corky Scott |
#3
|
|||
|
|||
"Peter Duniho" wrote in message
... "Corky Scott" wrote in message ... With my last experience, the engine actually went into hydraulic lock without me touching the controls or using the auxiliary fuel pump. The prop barely turn half a turn before it stopped and the starter couldn't crank it anymore. If you are having trouble with the starter not being able to turn the engine on a C172, you've either got a dead battery, or something worse is going on. I had the same problem hot-starting a PA32-300 recently. Let sit for a minute or two, starter was able to crank again. It was the only hot start I've had to do (so far) in that plane, and the only one where cranking was a problem. I don't think there's anything wrong with the battery or the starter, it was some transient condition of the engine. Jeremy |
#4
|
|||
|
|||
"Corky Scott" wrote in message
... Pete, I'm assuming it's hydraulic lock because the starter cranked the prop around half a turn and then jerked abruptly to a stop. [...] I was an auto mechanic in a previous life and have seen hydraulic lock before. I know no other way of describing it. Well, like I said, I haven't flown the new C172's, so don't have any personal experience with that particular engine installation. IMHO, if that engine IS experiencing hydraulic lock, that's a problem though. Oil should not be draining into the cylinders. On the 540 engine in my airplane, excess fuel that gets into the cylinders will drain out the intake manifold, and then out a valve that leads to the outside of the airplane. I've made plenty of hot starts, including many that were really flooded starts (per the technique described by Robert Gary ), and never had any problem with the starter turning over the engine. I've never experienced anything that could be considered hydraulic lock in any of the fuel-injected horizontally opposed engines I've ever flown. That's not a huge number of different airplane/engine combinations (perhaps a dozen or two over the years), but it's enough that I'd think I'd have noticed the problem you're describing if it were common and normal. I can't think of any mechanism by which you'd experience hydraulic lock on the fuel-injected horizontally opposed engine that's in the new C172, and I would think that if you DID experience that, it would be worth discussing with the mechanic who maintains the airplane. Pete |
#5
|
|||
|
|||
"Corky Scott" wrote in message ... Pete, I'm assuming it's hydraulic lock because the starter cranked the prop around half a turn and then jerked abruptly to a stop. When you get hydraulic lock in a radial, it's not that the prop starts turning, it's that the incompressable fluid tries (and succeeds) to expand the cylinder. You can break a cylinder even pushing the prop through bu hand when oil is present. |
#6
|
|||
|
|||
"Capt. Doug" wrote in message ...
snip BTW, the Continental system won't bypass fuel back to the tank if the mixture is control is closed. Huh? Also, most TCM injection systems overhauled/new since about 1995 will also allow a small amount of fuel into the engine with the mixture at ICO (unless they've changed the specs again). TC |
#7
|
|||
|
|||
On Tue, 14 Oct 2003 15:30:32 -0400, "Ron Natalie"
wrote: "Corky Scott" wrote in message ... Pete, I'm assuming it's hydraulic lock because the starter cranked the prop around half a turn and then jerked abruptly to a stop. When you get hydraulic lock in a radial, it's not that the prop starts turning, it's that the incompressable fluid tries (and succeeds) to expand the cylinder. You can break a cylinder even pushing the prop through bu hand when oil is present. I just called the mechanic on duty for the FBO that maintains the airplane and described the situation to him. He too thought that it was probably not hydraulic lock. The time I experienced hydraulic lock as an auto mechanic was when I pulled a dead Subaru out of a snowbank where it had been abandoned for a while and dragged it back to the shop. I was a mechanic and needed a car and thought I could get the thing running so I pulled it inside and let it warm up. The starter spun a tiny bit and stopped like the pistons had hit a rock. I removed the four spark plugs and tried again. This time, geysers of water shot out of the spark plug holes. One squirt must have traveled 15 feet before it hit the shop wall ten feet up. I put the spark plugs back in and tried starting it. It did actually start, but ran so rough, with water spraying out of the radiator that I immediately shut it off. Busted head gasket, pretty common with the 73 through 76 Subaru's: They had floating cylinder liners. Anyway, the guy I was talking with claimed no one else had mentioned this. I ventured that perhaps they just hadn't written it up, since they always seem to get it running, as I did. I've never studied the Lycoming starters, but it's possible the bendix, if it has one, may be popping out prematurely, stopping the crank sequence. Engine compression would stop the prop spinning very quickly, since it's a 180 hp model. But that doesn't adaquately explain why, when I tried to re-engage the starter, it appeared to have trouble turning the prop. I had to repeatedly turn the key to "start", again and again and the prop would turn just a bit and stop. Sometimes it appeared to get over a hump and turn for one complete revolution, but would then stop again. I doubt that it's the battery, because when the starter finally managed to get going, it spun the prop as fast as I've ever seen it go. This happened the very first time I tried starting it, when the airplane had only around 38 hours on it. The older (but same model 172) has never done this. Corky Scott |
#8
|
|||
|
|||
I think he's considering the fact that the starter can't turn the engine
over makes it a hydralic lock. Similar to a hot car engine with the timing too far advanced. In that case, the spark happens so early that the crank stops or backs up before it reaches TDC. I wouldn't call that a hydralic lock though, but I think that's what he is referring to. The air in the cylinder gets hot and starts expanding as the piston is trying to compress it as well, and with enough heat, you can get a preignition from just the air fuel mixture too. Dieseling kind of. Another example is too much ether in a diesel, a ether lock. Either way, the starter is unable to overcome the compression of the engine while it is hot. Quickest way I know around it is to have an assistant, hand-prop-assist the starter. Safer overall though to just wait for it to cool. "Peter Duniho" wrote in message ... "Corky Scott" wrote in message ... Pete, I'm assuming it's hydraulic lock because the starter cranked the prop around half a turn and then jerked abruptly to a stop. [...] I was an auto mechanic in a previous life and have seen hydraulic lock before. I know no other way of describing it. Well, like I said, I haven't flown the new C172's, so don't have any personal experience with that particular engine installation. IMHO, if that engine IS experiencing hydraulic lock, that's a problem though. Oil should not be draining into the cylinders. On the 540 engine in my airplane, excess fuel that gets into the cylinders will drain out the intake manifold, and then out a valve that leads to the outside of the airplane. I've made plenty of hot starts, including many that were really flooded starts (per the technique described by Robert Gary ), and never had any problem with the starter turning over the engine. I've never experienced anything that could be considered hydraulic lock in any of the fuel-injected horizontally opposed engines I've ever flown. That's not a huge number of different airplane/engine combinations (perhaps a dozen or two over the years), but it's enough that I'd think I'd have noticed the problem you're describing if it were common and normal. I can't think of any mechanism by which you'd experience hydraulic lock on the fuel-injected horizontally opposed engine that's in the new C172, and I would think that if you DID experience that, it would be worth discussing with the mechanic who maintains the airplane. Pete |
#9
|
|||
|
|||
|
#10
|
|||
|
|||
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Replacing fuel cut-off valve with non-a/c part??? | Michael Horowitz | Owning | 46 | January 15th 05 10:20 PM |
Book Review: Converting Auto Engines for Experimental Aircraft , Finch | Paul | Home Built | 0 | October 18th 04 10:14 PM |
P-3C Ditches with Four Engines Out, All Survive! | Scet | Military Aviation | 6 | September 27th 04 01:09 AM |
Jet A / JP-4 ?? | CVBreard | General Aviation | 7 | December 8th 03 03:44 PM |
Yo! Fuel Tank! | Veeduber | Home Built | 15 | October 25th 03 02:57 AM |