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Just how powerful is the explosion during the power stroke?

Blmpkn

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Like....


Hand grenades status? M-80 status?

Any idear?
 


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Twizzler09

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That depends greatly on how much power is being generated by that engine at the time. A little arithmetic.....

160 horsepower equates to 0.119 megajoule per second. For comparison, a single 30mm shot from the warthog's GAU8 cannon is roughly 0.303 megajoules at the muzzle.

A standard frag grenade is 180g of CompB.... which is slightly more potent than TNT. 180g of TNT is about 0.75 megajoules of energy. So a standard frag should sit roughly 0.8-0.85MJ
 

Blmpkn

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That depends greatly on how much power is being generated by that engine at the time. A little arithmetic.....

160 horsepower equates to 0.119 megajoule per second. For comparison, a single 30mm shot from the warthog's GAU8 cannon is roughly 0.303 megajoules at the muzzle.

A standard frag grenade is 180g of CompB.... which is slightly more potent than TNT. 180g of TNT is about 0.75 megajoules of energy. So a standard frag should sit roughly 0.8-0.85MJ
Right on.


How long is that standard hand grenade producing its .75 megajoules? Not for very long I'd imagine.

So if 160hp for 1 whole second is only .119 megajoules...

And individual power stroke on one cylinder in that 160hp motor doesn't even come close to a grenade. Definitely seems closer to "big fart" territory.
 

Twizzler09

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Well, the grenade generates that energy all at once. Then sends it literally in all directions and it weakens further due to dispersion as the pressure wave travels farther from the flashpoint. So the actual energy being imparted to target is far less.

The energy created by a 160hp motor over a second is far more akin to early armor piercing high explosive (APHE) tank rounds. They were loaded with about 20-30g of TNT or TNT equivalent. And those were quite effective at taking out tank crews.

Individual power strokes aren't generating that much energy on their own though, this is true. The amount of fuel burned in a single power cycle is just too small.
 

don4331

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It's not an explosion (or it's not supposed to be), but rather a nice rapid burn (when it explodes, you hear the nasty ping of pre-ignition).

Each cylinder of a 4.0 is making the approximate force of a .50 BMG round (48.5g @ 887 m/s = 19 kilojoules * 6 = 0.120 MJ)

Remember 2 other things:
A 4.0 only produces 160hp @ WOT @ peak power rpm. At partial throttle and cruising rpm, it might only be producing 1/8th of that.​
Only ~1/3 of the power of the burning of the gasoline was converted into useful power. 1/3 was lost to heating the anti-freeze/water in cooling system, and the other 1/3 is going out the exhaust as heat and noise.​
Considering the small amount of gasoline burned in the cylinder, pretty impressive.
 

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It is an explosion, i.e. "rapid expansion in volume associated with an extremely vigorous outward release of energy, usually with the generation of high temperatures and release of high-pressure gases"

Pinging/knocking is when there are two or more explosions in the one cylinder and the wave fronts meet up
Its why diesels sound the way they do, they have no fixed point like a spark plug where the air/fuel is ignited
It just ignites when compression and heat are high enough and often in more that one spot on the cylinder, so pingy

Its just a small explosion from very little gasoline, not even firecracker strong I would think
But it happens in an enclosed space
Its like the old saying if you hold your hand open and let a fire cracker go off ON your hand it will sting, but if you close your hand around the fire cracker tightly and it goes off you won't be using that hand for a LONG LONG TIME, lol
 

Twizzler09

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Quite true! Wasn't sure how in depth OP wanted to go, so didn't bother getting that far into it. But overall, gasoline engines are surprisingly efficient machines in a lot of ways. Inefficient, too. But nothing is perfect.

Also might want to look at 50 BMG again? Military ball ammo hits around the 12,500ft\lbs mark, which is 0.016MJ whereas the 30mm AP rounds from the GAU sit at something well over 200,000ft\lbs if memory serves. I'm doing a lot of this by memory since I'm at work right now. So I could quite easily be wrong.
 

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It is an explosion, i.e. "rapid expansion in volume associated with an extremely vigorous outward release of energy, usually with the generation of high temperatures and release of high-pressure gases"

Pinging/knocking is when there are two or more explosions in the one cylinder and the wave fronts meet up
Its why diesels sound the way they do, they have no fixed point like a spark plug where the air/fuel is ignited
It just ignites when compression and heat are high enough and often in more that one spot on the cylinder, so pingy

Its just a small explosion from very little gasoline, not even firecracker strong I would think
But it happens in an enclosed space
Its like the old saying if you hold your hand open and let a fire cracker go off ON your hand it will sting, but if you close your hand around the fire cracker tightly and it goes off you won't be using that hand for a LONG LONG TIME, lol
I believe that when he mentioned that it's not an "explosion" he may have been referring more toward the BATFE's definitions of explosive, low explosive, high explosive, etc. Where they define each of these by how fast the material burns.

Yes, to most laymen, an explosion is defined as you stated. Sorry. I had to study that years ago to get my "low explosives manufacturing" license.
 

don4331

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Also might want to look at 50 BMG again? Military ball ammo hits around the 12,500ft\lbs mark, which is 0.016MJ whereas the 30mm AP rounds from the GAU sit at something well over 200,000ft\lbs if memory serves. I'm doing a lot of this by memory since I'm at work right now. So I could quite easily be wrong.
I was using some slightly hotter numbers from Navweaps page for the M2 (0.019 MJ) * 6 cylinders = 0.120 MJ (approximately) close enough to the 0.119 MJ for the 160 hp.
 

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Oh! I got it now. That makes far more sense. I completely overlooked the x6 for six cylinders. :dunno:
 

Twizzler09

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Also out of pure boredom (my job is extremely uneventful) I decided to see how many "booms" there are in one second for the OHV 4.0L making peak power. 17 and 1/2 explodey events per second to generate .119MJ of energy.

So each bang is generating 0.0068MJ of energy. Or 5015.42 ft/lbs. A boxer's punch generates about 0.0008MJ of energy. So a single 4.0L OHV ignition event at WOT and 4,200rpm generates roughly the equivalent of a pro boxer punching something 8.5 times. Neat.

Also raises some interesting physics questions about how all that oomph manifests as a far lower amount of power at the wheels. I suspect it has something to do with conversions or the way things are measured. Or maybe I'm worse at this than I thought. :icon_rofl:

Edit: after some thinking, I might've at least partially answered that one. There's going to be a lot used to operate the compression stroke of other cylinders. As well as power lost to rotating mass all through the driveline, including driveshaft, axles, etc.
 
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Blmpkn

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Wasn't sure how in depth OP wanted to go, so didn't bother getting that far into it.

I want ALLLLL the nerdiest details lol.

Been curious for a long while 😋

Pretty satisfied with the amount of detail.
 

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you planning on destroying the world with this info?
 

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