Can fully open valves in our engines hit the piston?
If so, ingesting a piece of ice from the inlet duct could destroy the engine.
It would have to be a colossal piece of ice (relatively speaking) to get into the combustion chamber. If chunks of ice that big are in your induction system you probably have other problems.
Also consider when the valves are opening. Let’s see you have this colossal piece of ice. It can only enter the cylinder on the intake stroke. By the time the piston comes back up, both valves will be fully closed for the compression stroke, and the temperature will be very high – so up to now it doesn’t matter how far the valves open into the cylinder because the piston has either been moving away or the valves fully closed. Then the ignition stroke, and the piston goes all the way back down and the exhaust valve opens for the piston to come up.
To destroy an engine, the chunk of ice must survive all of that intact, including the ignition event. This just doesn’t sound plausible to me.
What I was getting at is that valves are open by the camshaft and closed only by a spring. So any object which enters just as the valve is fully open could cause the valve to get stuck fully or partially open.
Ice takes a while to melt if it is a sizeable chunk. You can make bullets out of ice which work – for long enough.
You would then get “funny” combustion, or perhaps no combustion since the compression in that cylinder would be really poor. But what concerned me was the piston hitting the valve. In most car engines it would hit.
In a big-bore Lycoming, a TDC piston would crush an open valve.
Ice takes a while to melt if it is a sizeable chunk. You can make bullets out of ice which work – for long enough.
Because humans are soft. Metal is a lot harder than ice (pure aluminium, which is a very soft metal, has a value of about 3 on the Mohs hardness scale and ice has 1,5. Aluminium alloys and especially the stuff engine parts are made of are an order of magnitude harder). You can crush an ice cube with the soles of your shoes easily and they are not even metal. A valve spring will crush an ice cube as if it was a marshmellow… Chunks of ice are regularly sucked into jet engines (e.g. by turning on the anti-ice late) and leave no traces on the fan blades they hit at high speed. No need to worry.
The compressive stress applied to the ice will be the closing force of the spring divided by the contact area. The closing force is perhaps 200 lbs, and the compressive strength of ice is about 1500 psi when its cold. So you’d need more than roughly 0.13 square inches of area to be below the compressive strength of ice. Given a valve seat width of 0.1 inches width and 1.75 inches diameter, the ice would need be in full contact with about 20% of the valve seat circumference to remain intact. I think the particles of ice likely aren’t big enough to do that.
Peter wrote:
What I was getting at is that valves are open by the camshaft and closed only by a spring. So any object which enters just as the valve is fully open could cause the valve to get stuck fully or partially open.
By a very strong spring. Try compressing one by hand some time.
Any induction ice is not going to be like an ice cube you put in your margarita, it’s going to be a fuzzy collection of small pellets or rime ice. The air filter should keep hail out, and if you’re flying through hail that big, sucking one in is likely the least of your worries! Induction icing (e.g. carb ice) just won’t be able to grow into chunks that big, the engine will quit long before they get to that stage.
Why the question in the first place ? I mean with the trillions of hours that our recip engines have amassed over the last 7.5 decades and virtually zero documented incidents, why in earth would one even think it possible ?
Why the question in the first place ? I mean with the trillions of hours that our recip engines have amassed over the last 7.5 decades and virtually zero documented incidents, why in earth would one even think it possible ?
Here is one.
A DA42 does the same thing.
Here is another.
Loads of other discussions on air inlet icing.
It is easy to find the alternate door frozen solid in a layer of ice which presumably covers the whole inside of the air duct.
Lots of dual engine stoppages on twins. One I know, a Baron, descended from FL200 to 2000ft over the N Sea before it melted.
You won’t get documented incidents because the stuff melts 
Good analysis Silvaire 
I still think a large chunk could form (well that bit is obvious to me) and with bad luck could find its way it. The opening in the RSA fuel servo is about 2-3cm diameter.
The ice forms behind the air filter.
HUGE difference between Induction Icing and ICE Ingestion …
Peter wrote:
The ice forms behind the air filter.
In a fuel injected engine ? Really ?
