ROBOTS battle bunker-buster bank blast blaggers Aussies in the city of Perth have been left shaken by a wave of potentially deadly "bunker-buster" style terror explosions at ATMs as a crew of blaggers blast the machines open to rinse them of cash. Local cops, rattled by the devastating outrage rampage, have deployed police robots to battle the menace. The tally of hole-in- …
Paper money does burn, however the explosion tends to be over rather quickly if done right, and paper money in ATM's is stored inside magazines or dispensers which means only the top note is actually in the open. So with a little luck, they may well only be destroying the top note or two. Sheets of paper stacked tightly together don't actually burn very well at all.
ATMs have a front and a rear. The front is, with a wall-fitted ATM, what the general public has access to, to insert bank cards, drills and explosive gaseous mixtures. The rear, generally not freely accessible, and especially not outside opening hours (the preferred time for non-authorized withdrawals) is where the ATM operator inserts the moolah magazines. With a set of vent holes (doesn't even need big-ass fans) in that very rear, this way of ATM access is foiled. It's already been put in practice here in the Netherlands, and 'plofkraken' are now basically a thing of the past.
"Fuel-air explosions are also found in various other applications, for instance as a particularly uncompromising method of rodent control, in powerful bird-scaring/sonic-weapon equipment, and even in especially aggressive paintball guns."
And also that rare and little known application - the internal combustion engine...
'Knocking' or 'pinking' is an uncontrolled explosion, i.e. one that wasn't initiated via the desired control method.
In a petrol engine this is pre-ignition and is usually caused by a hot spot and as you state can damage the engine.
The other typical issue with pinking is the explosion is relatively uneven and can cause uneven loads on the internal components of the engine.
Diesel engines actually use this to their advantage, the shape of the pistons, head and compression ratio, are setup to ignite the fuel-air mixture at a specific timing point.
Pinking can occur in Diesels, but it usually indicates a more serious problem.
The controlled ignition of the fuel is still a form of explosion.
Diesel engines do not have a fuel-air mixture to ignite. A fine spray of fuel is injected into hot compressed air and burns as it goes in. Combustion starts when the fuel goes in: shape of pistons, head and compression ratio are irrelevant. The diesel cycle requires heat input (combustion) at constant pressure. That means a relatively slow/protracted burn as the piston descends and the easiest way to achieve that is to inject the fuel over the length of the required burn rather than have it all in there, waiting to go off.
That's proper big diesel engines. Model aircraft engines are sometimes called diesel, but they are really compression ignition, which is a different thing.
Oh, and knocking in a petrol engine is a completely different thing from pre-ignition. Knocking is when the spark starts combustion at a sub-optimal time whereas pre-ignition is when something other than the spark starts combustion.
This post has been deleted by its author
You are incorrect, sir. On so many levels.
In a Diesel engine, the ignition is caused by the compression of the fuel-air mixture by the piston as described by annodomini.
"Diesel engines do not have a fuel-air mixture to ignite" - you have heard of the fire triangle, haven't you? Without both fuel and air there can be no combustion.
There are both four-stroke (mainly vehicle) and two-stroke (mainly marine) Diesel engines, but neither of those variations operate the way you describe.
"compression ignition, which is a different thing" - It is important to note that the single defining factor of a Diesel engine is the fact that the ignition occurs by compression. I would ask you to explain where you think the ignition would come from in your idea, but there's no point.
Finally, the result required to produce power in an internal combustion engine is an explosion (see icon), not a "slow burn".
I'm not sure where you're getting your information from but I suggest you visit the topic again.
http://en.wikipedia.org/wiki/Diesel_engine
Oh dear, oh dear, oh dear.
Conventional petrol engines induct a fuel air mixture into the cylinders, compress it and then ignite it with a spark.
Diesel engines induct air, compress that and then inject a very fine spray of fuel into the hot air, where it burns. There is no fuel-air mixture involved, save at the very point of combustion.
Model aircraft "diesel" engines induct a fuel-air mixture and compress it until it ignites - often with the assistance of a glow plug which adds some heat to the mix and removes the need for very high compression ratios. That's compression ignition, and it doesn't apply to the engine in my car because the stuff which is compressed, air, does not ignite.
It's a common misconception that IC engines use explosions. To a lay observer that may seem to be the case, but at the time scales and piston velocities involved it's much better to think of it as a controlled burn. Engine designers go to huge lengths to control the speed and shape of the flame front.
The defining feature of the diesel cycle is that heat input takes place at constant pressure, as opposed to the otto cycle in which it takes place at constant volume. In practice this is implemented by using slower and longer burn of the fuel in a diesel engine. In a petrol engine the combustion happens with the piston close to the top (so at more-or-less constant volume) whereas in a diesel engine the combustion takes place as the piston moves down, keeping the pressure more constant. That's why a much less volatile fuel is used, and why it's injected. If it was mixed with the air in advance there would be much less chance of protracting the burn as much as is needed.
TL;DR: Diesel engines inject fuel into hot air.
Sorry to disappoint - the flour is the fuel here. Any dry organic powder dispersed in the air can explode if ignited, being it flour, sawdust, or coal dust. This is how many mills and sawmills were destroyed by large fires, not to mention coal mines.
Very difficult to do anything useful with it, I am afraid, as it settles down quite fast. (That being said, one of the first internal combustion engines, so called "pyroleofor" was working with a fuel in the form of a powder.)
Not too difficult; bag of flour on a string over a door, and a candle underneath; yank the string a few times, and wait for the earth-shattering kaboom! Note: the door will not fare well, and your mother will probably beat the living tar out of you for blowing up half the garage. Assuming you're not bleeding out of a dozen punctures... and maybe even then.
The Register 
Biting the hand that feeds IT
Copyright. All rights reserved © 1998–2025
