Deuterium combustion within inertial fusion schemes

[artis]

Hydrogen as well as Deuterium are both flammable chemically, I read that both hydrogen as well as deuterium can ignite/combust upon compression even in ordinary ICE engines. Hydrogen has been investigated and used as fuel for internal combustion engines.

Now in a inertial fusion approach the fuel is highly compressed at a fast rate , whether it be NIF using light or other designs using a physical tamper/liner to exert force on the gas.
So before fusion conditions are reached within the gas, doesn't it combust chemically first?

It definitely undergoes the pressure rise and final pressure needed for chemical combustion along the way, a pressure that is easily attained in ICF approaches and also exists within piston engines.I also wonder , would it be beneficial to compress a cold gas to very high pressure and then ignite it chemically , I wonder how much pressure increase would that add and how could it benefit achieving fusion temperatures?
From ICE piston engines I know that the flame front travels faster if the density of fuel/air is higher, so in theory I'm not sure but wonder how would a extremely high compression gas under that high pressure react when ignited.

 

[Vanadium 50]

doesn't it combust chemically first?

Combust with what?

 

[artis]

Combust with what?

I guess I forgot that these approaches don't have oxygen in the fuel mix.

So I should have restated my question as to whether it would combust if the fuel pellet for example had been doped with oxygen.
Sure enough it would be futile for an experiment like NIF because such combustion would most likely destroy the symmetry of the compression and ruin it before it ever has a chance of reaching fusion temperatures.

 

[mfb]

Fusion happens at temperatures of several keV. Chemical reactions are irrelevant, and oxygen would just be in the way of fusion.

 

[artis]

Fusion happens at temperatures of several keV. Chemical reactions are irrelevant, and oxygen would just be in the way of fusion.

That is all true. What I was thinking is when you compress a say deuterium/oxygen mix to a super high pressure at very low temp (low so that it doesn't detonate on it's own) and then in the final stages of compression ignite it.
The pressure/temperature increase in a closed container is proportional to the gas density pre-ignition.

One could in theory calculate this and get the answer that way I'm sure, I was just wondering is it in theory possible to achieve fusion level temps with thermodynamic tricks.

 

[mfb]

The compression leads to the high temperature. That's the point of the compression.
But anyway, see above: The energy released in chemical reactions is negligible.

 

[Vanadium 50]

Where is this oxygen coming from?

And why stop there? If you are going to worry about things that aren't there, why not worry about lit sticks of dynamite in the reaction chamber? Or a pot of molasses? Or a minor Kardashian sister? Or...

 

[russ_watters]

I wonder how much pressure increase would that add and how could it benefit achieving fusion temperatures?

Google tells me if you combust a kilo of hydrogen you get 10^8 joules, and if you fuse it you get 10^14 joules. So there's a few orders of magnitude difference and the combustion doesn't add/help much.

 

[hutchphd]

That is all true. What I was thinking is when you compress a say deuterium/oxygen mix to a super high pressure at very low temp (low so that it doesn't detonate on it's own) and then in the final stages of compression ignite it.

You are comparing a V-8 engine to the interior of the sun. !

 

[Vanadium 50]

the combustion doesn't add/help much.

It hurts. If a fraction of the d collisions are with other elements, that fraction does not participate in fusion. So the effect tends to reduce energy production.

 

[artis]

I wasn't arguing about how chemical reactions could release equal amounts of energy as nuclear because I know they can't, my point was solely about taking a highly compressed mixture of gas, igniting it in a sealed container where there is a large pressure increase, but on a second thought that's probably not enough anyway so I rest my case.

PS. An imploding "liner" pretty much does the same thing in ICF approaches - it compresses the fuel much like a piston would in the v8 engine @hutchphd mentioned only faster, symmetricaly and to higher final pressure. My thought was to have a highly compressed gas/liquified and then ignition in a fixed size container would increase the pressure inside the container similarly to how a imploding liner only in one case you raise pressure/temp by compression in the other you raise it by expansion when a liquified gas ignites and turns to a burning plasma the only question is how hot would it become.
And that is why I asked.

 

[Vanadium 50]

I rest my case

That usually means that one stops talking, so it's unusual to see this 1/3 of the way down. Looks to me like you are continuing to argue.

The thing you seem to be missing (and everyone else is trying to explain) is that hydrogen does not burn in a chemical sense by itself. It needs an oxidizer, like oxygen. It doesn't matter what T and P you put it at - without an oxidizer there is no reaction.