I happened upon this news release http://www.fraunhofer.de/EN/press/pi/2008/...72008Topic6.jsp describing a fuel flap opener that operates by electrically heating a wire composed of shape-memory metal. It greatly simplifies the mechanism, but I got to wondering what would happen during a fiery car crash. Wouldn't the fuel flap open spontaneously and dump a load of heat-expanded fuel on the fire?
It'd open the flap to the fuel filler cap, but that would seem to be the least of your troubles if your car is already on-fire.
It wouldn't be good for your fuel flap to open simply because you parked your car in a parking lot in Phoenix on a late summer afternoon, so it must take a very high temperature wire to open the flap. Hmmm.... super hot wire, fuel tank.... nope, no problems there.
Answering your first post: Yes, it would. The fireball would happen instantaneously. 
Answering the OP. It would not release any additional fuel. They are referring to the external flap, the decorative piece. Not the screw cap that actually seals the tank. Current flaps are not fuel tight.
Wrong, gski. This is a heat sensory mess waiting to happen. 
QUOTE (gski+Jul 11 2008, 02:02 PM)
Answering the OP. It would not release any additional fuel. They are referring to the external flap, the decorative piece. Not the screw cap that actually seals the tank. Current flaps are not fuel tight.
Good frickin' lord, you're right. Except for the word 'decorative.' One important purpose of a fuel flap is theft prevention.
Good frickin' lord, you're right. Except for the word 'decorative.' One important purpose of a fuel flap is theft prevention.
The material used, Nitinol (really neat stuff, I'm working with it right now), has transformation temperatures roughly between -200 and 110 degrees Celsius. From the application here I would assume they're using something with a transformation temp somewhere around 60 degrees Celsius. You only need to heat the wire for a small fraction of a second, and given that the autoignition temperature of gas is about 250 degrees Celsius, you're nowhere near hot enough to ignite the fuel.
They use these wires quite frequently as actuators, there's a few sites where you can buy little actuator kits to play with (examples here). The material itself is pretty cheap, it runs around $2.50 per foot depending on the thickness of the wire, and that's a consumer price, wholesale it's much cheaper.
And gski is correct, just look at the picture from the article.
They use these wires quite frequently as actuators, there's a few sites where you can buy little actuator kits to play with (examples here). The material itself is pretty cheap, it runs around $2.50 per foot depending on the thickness of the wire, and that's a consumer price, wholesale it's much cheaper.
And gski is correct, just look at the picture from the article.
QUOTE (midwestern+Jul 11 2008, 04:19 PM)
Wrong, gski.
See, that's what I mean. You comment on what you don't know. Why is that?
See, that's what I mean. You comment on what you don't know. Why is that?
orestis: We are talking about the heat sensor, not the cosmetic flap which is flawed in design. An overheated situation can cause an explosion. Out pops the lid and BOOM goes the fuel in an accident.
QUOTE (midwestern+Jul 21 2008, 01:48 PM)
orestis: We are talking about the heat sensor, not the cosmetic flap which is flawed in design. An overheated situation can cause an explosion. Out pops the lid and BOOM goes the fuel in an accident.
If you open the door to your fuel tank (what the article was written about, read it), fuel does not come out.
If you open the door to your fuel tank (what the article was written about, read it), fuel does not come out.
True, but we are talking about a crash with a fuel spill here and BOOM!!
A crash with a fuel spill is completely irrelevant to the topic, which is opening the door to the fuel tank using shape-memory alloys. You would still need to remove the fuel cap, flip the car, and prop open the valve in order to get fuel out. Unless you want to punch a whole in the gas tank.
Not really. You have to consider this happening before you design a monstrosity. 
Are you completely stupid? You just agreed that the opening and closing of the fuel flap doesn't affect whether or not the gas comes out.
The wire opens this: http://the-gadgeteer.com//assets/diesel-gu...ing-system3.jpg
THE DOOR.
In order to get gas out, you need to unscrew the cap, flip the car over, and prop open the valve. None of those things are controlled by the memory alloy.
The wire opens this: http://the-gadgeteer.com//assets/diesel-gu...ing-system3.jpg
THE DOOR.
In order to get gas out, you need to unscrew the cap, flip the car over, and prop open the valve. None of those things are controlled by the memory alloy.
Duh bonehead. I just said in a crash the gas cap would come off and the door would be open for a spill.
QUOTE (midwestern+Jul 21 2008, 02:13 PM)
Duh bonehead. I just said in a crash the gas cap would come off and the door would be open for a spill.
The door is not fuel tight, regardless of how it opens. Gas would spill anyway if the gas cap comes off. Still irrelevant to the topic.
The door is not fuel tight, regardless of how it opens. Gas would spill anyway if the gas cap comes off. Still irrelevant to the topic.
We agree to disagree here...then...enough said. 
PhysOrg scientific forums are totally dedicated to science, physics, and technology. Besides topical forums such as nanotechnology, quantum physics, silicon and III-V technology, applied physics, materials, space and others, you can also join our news and publications discussions. We also provide an off-topic forum category. If you need specific help on a scientific problem or have a question related to physics or technology, visit the PhysOrg Forums. Here you’ll find experts from various fields online every day.
To quit out of "lo-fi" mode and return to the regular forums, please click here.