Diesel fuel doubling as hybrid reactive armor?

[Algernon]

the merkava MkIV has been rumored to use it's diesel fuel, more to the point, it's placement in the vehicle as additional armor protection for the crew. this doesn't sound surprising as the merkava already does the same with it's engine/drive train and NBC equipment.

 

does it work? if so, how does it work? any estimates on the RHA equivalent of the diesel fuel per volume? could it function similarly to the israeli "hybrid" armor? i understand (vaguely) that "hybrid armor" is a type of reactive armor not akin to ERA, in that there is no high explosives or flyer plates. the hybrid armor module is comprised of an outer layer of passive armor (presumably ceramic) and an inner layer of reactive. the reactive layer is not explosive, but rather a chemical compound of unknown composition that will change it's chemical composition when exposed to sufficient chemical energy, via an explosively formed jet or presumably (in theory, i doubt such package exists) any other penetrating body exerting it's energy into the armor.

 

imagine an armor package consisting of an outer layer of passive with an inner layer of reactive, the reactive being a chemical substance that undergoes a change in it's chemical composition when exposed to CE of a certain value per unit of area or mass (IE: quantity) of the reactive substance. the CE stored in the reactive layer actively prevents penetration by reacting to the presence of CE contained in the jet. the reactive layer "reacts" to the penetrate by undergoing a chemical reaction (endothermic?), the result being the drawing in of the CE of jet and defeating/weakening of the jet. the CE released by the shape charge is used to harmlessly change the chemical composition of the armor rather than to fatigue and destroy the armor's structure resulting in penetration or perforation.

 

a simple analogy would be putting ice in your warm drink to cool it. the ice undergoes an endothermic reaction as it changes states from solid (ice) to liquid (water). this endothermic reaction needs energy and it draws it from the surrounding medium, in this case your drink and cooling it as a result. think of the reactive layer as the ice and the explosively formed jet as your warm drink.

 

i like the concept, however i question whether or not it is currently exists in any form anywhere in the world. does it? i heard israeli hybrid armor works on this principal, but i can't seem to dig up the source.

 

this is two topics combined into one, however the afore mentioned diesel fuel armor sounds a lot like "this type" of reactive armor. i do not know how the diesel fuel is structured in the tank's armor other than it is "placed near the crew for protection". presumably, the jet would have to pass trough a layer of passive ceramic before reaching the fuel, where upon reaching it heats up and boils or even ignites the fuel. the jet wastes some of it's CE heating up/boiling/ignting the diesel fuel instead of continuing on undisturbed to penetrate further into the armor

 

 

there is some evidence to suggest diesel fuel does offer some level of protection. there was a vid posted a while back here on tanktet that had shown a merk4 taking a missile hit. the missile struck the spaced armor perforated it and boiled the diesel fuel off resulting in a characteristic white smoke eminating from the tank's perforated section of spaced armor. one can only guess as to how sucsessful the diesel fuel is in disrupting the jet. however we could make some educated guesses if we had the boiling point of diesel, the quanity of energy needed to boil it and some conversion to RHA steel, right?

Edited August 10, 2006 by Algernon

[TTK Ciar]

does it work?  if so, how does it work?  any estimates on the RHA equivalent of the diesel fuel per volume?

George Herbert had this to say about it:

 

Effects of water would be like the effects of diesel fuel. [...]Particularly against shaped charges, large depths of a mildly resistant liquid are an excellent protection mechanism, with actually a higher resistance per unit weight of material than steel gives, diesel fuel having about 3.1 times as much resistance per unit weight as steel.

 

The generic formula is a square-root of the relative densities. This is based on the hydrodynamic model for shaped charge jets, which is the most accurate.

http://www.ciar.org/ttk/mbt/yam.warpragmat...dern-armor.html

 

however we could make some educated guesses if we had the boiling point of diesel, the quanity of energy needed to boil it and some conversion to RHA steel, right?

The fuel did not stop the shaped charge penetrator by cooling it off. HEAT penetrators are not very "hot", merely high velocity ("HEAT" has nothing to do with "heat"; it is an acronym for "High Explosive Anti Tank"). The shaped charge penetrator lost its velocity and cohesion from the effort of having to push the fuel out of the way at 8000m/s. At such speeds (the "hypervelocity" domain) there is little difference between interacting with liquid diesel fuel, and interacting with a solid plate that has the same density as diesel fuel (about 0.86 g/cc).

 

From the 3.1x mass efficiency George states, and the density of the fuel, we can compute the thickness efficiency of diesel fuel as 0.34 (so 10cm depth of diesel == 3.4cm depth of RHA).

 

-- TTK

[Algernon]

i see. so it's nothing more than putting the 'dead weight' fuel to use as additional protection for the crew. ignition isn't likely to occur as the temperatures and pressures needed to ignite the fuel are not present durring penetration.

 

thanks

[Ssnake]

i see.  so it's nothing more than putting the 'dead weight' fuel to use as additional protection for the crew.  ignition isn't likely to occur as the temperatures and pressures needed to ignite the fuel are not present durring penetration.

Pressures are certainly sufficient, and temperatures probably so as well. However, since gas tanks are filled with foam to suppress the development of large cavities filled with an explosive mis of fuel fumes and air it is much more difficult to set the fuel tank on fire.

I don't think that it is impossible though...

[Marek Tucan]

Very interesting article... Would it have some effect against APFSDS penetrators as well?

 

On a related note, is it possible to somehow take into account the air gap between the armour and HEAT standoff plates?

[Colin]

This concept was talked about quite abit when the Merk first came out.

[Luckyorwhat]

Do they make the tank stronger, to prevent rupture?

[lucklucky]

yeah this is around since first merkava came.

[Algernon]

link?

[Luckyorwhat]

yeah this is around since first merkava came.

357488[/snapback]

 

How do they do it? By tank I mean fuel tank, how do they strenghen it? Avoid corners, reinforce corners, design it to rupture in certain areas?

[Guest JamesG123]

How do they do it? By tank I mean fuel tank, how do they strenghen it? Avoid corners, reinforce corners, design it to rupture in certain areas?

 

On western tanks (M1, Merkava, etc) the fuel tank is sandwiched between the outer armor and another armor plate.

No such luck with T-72+, the hull fuel cells are just metal and plastic tanks in the crew compartment. They even act as ammo storage, which would be clever except for the obvious survivability problem.

[Algernon]

Pressures are certainly sufficient, and temperatures probably so as well. However, since gas tanks are filled with foam to suppress the development of large cavities filled with an explosive mis of fuel fumes and air it is much more difficult to set the fuel tank on fire.

I don't think that it is impossible though...

356057[/snapback]

 

even so, i doubt the burning does anything more to disrupt the explosively formed jet beyond passive resistance. no reactive armor here, just a "plate" of diesel fuel. i wonder if there are any additives one could add to the fuel to increase it's density per volume without any detrimental affects to the fuel system. a more dense diesel fuel would offer better ballistic resistance, correct?

 

i wonder what applications there are out there for fuel armor. could you structure the fuel in multiple fuel tanks placed in between plates of RHA to act as laminated armor, producing uneven stresses on a penetrator in hopes of breaking it up or even perforated armor with perforations of diesel fuel suspended in a RHA plate?

 

 

check out the merk 4s.

[DB]

If simple NERA can be made with rubber interlayers, might not the diesel potentially act in the same way? Rapid expansion when struck causing bulging plates to move? Are we certain we know the internal layout of the fuel tanks in these locations? One could imagine dual purpose anti-sloshing baffles that could be angled appropriately, perhaps.

 

David

[lucklucky]

That was a rumour, i dont think any new Merkava uses fuel as armour per se. Of course since the merkava by design tries to put everything in the path of the missile, some fuel tank might work as that.

[Luckyorwhat]

In 'Tank' by Patrick Wright it states that the fuel protects the crew compartment. Says that when something penetrates the fuel tank it creates pressure, and that presses fuel outward on the penetrator. I'm not sure if that is different from hitting a block of steel or not, though. Anyone?

[Guest JamesG123]

There are all kinds of hydrodynamic forces at work when you try to push a hypersonic object thru a liquid medium. The physics of which I'm sure we could debate at length.

But I think any pressure waves in a tank are minor to the effect of the sheer mass of the liquid robbing kenetic energy from the projectile.

[Sikkiyn]

I already have a thread on future items, the below being one.

 

Liquid Armor

 

Thread

Edited August 20, 2006 by Sikkiyn

[jwduquette1]

An old IDR article indicated the Israelis were indeed placing fuel cells in strategic areas around the Merkava such that the fuel could act as additional armor against shaped charge attacks. See IDR 3/1985.

 

The idea of using fuel as armor isn’t new. Naval Architects for old Dreadnought battleships and battlecruisers placed coal bunkers in strategic areas around the hull to provide additional armor to the ships vitals. Same was done with fuel oil bunkers on newer super-dreadnoughts and battleships.

 

I’ve come across a number of papers on fluids and their inherent ballistic qualities against shaped charge jets. The following is condensed from a paper by J.J White & M.J. Wahll for the 6th Symposium on Ballistics – “Shaped Charge Interaction with Liquids”.

 

The test set-up is shown in the following figure. Basically a 45mm diameter Dupont precision charge with copper liner. Stand-off was 152mm or about 3.38 CDs. Various materials were sandwiched between a 1” thick plate of RHA and a thick witness plate consisting of mild steel. The thickness of the sample material cell was 76mm. The liquid samples were also confined on the top and bottom by 0.3mm thick mild steel walls.

 

TEST SETUP

 

The black lines in the witness plate in the above figure show the amount of residual penetration by the shaped charge after passage of the 25mm RHA cap and the 76mm thick sample material cell.

 

In straight-up depth of residual penetration, steel is of course the best ballistic material. This is shown in the "Te" calculations. Numbers less than "1" imply the material is not doing as well as steel.

 

However, when you begin examining equivalent weight effectiveness (We), things begin to look very interesting. Numbers greater than "1" imply the sample material is pound for pound more effective than steel. Plexiglass does very well against shaped charge jets. Diesel fuel also has a very good weight effectiveness (We). I condensed of this into the following table.

 

TABLE 1 Condensed Test Data

 

This is where the paper sort of leaves off. Wow -- diesel is seven times better than steel. Unfortunately they stopped before taking into account the confining steel – the 25mm RHA plate plus the residual thickness of the mild steel witness plates. This all drastically effects the weight of the array as a whole. Like ceramics, "We" looks very good when the ceramic weight by itself is considered. However for max effectiveness the ceramic typically requires confinement within steel cells. This adds weight and lowers "We".

 

Let's say I was required to construct an armor array specifically designed to defeat the 45mm Dupont Shaped Charge, and I was constrained to only 76mm of non-steel material. The true weight effectiveness of the array comes a little bit more into focus. Assume that for complete ballistic protection I need the 25mm RHA cover plate + 76mm of whatever sample material I choose to employ + the depth of residual penetration in mild steel + 20mm of additional mild steel tacked onto the residual penetration depth in order to ensure complete ballistic protection. If you calculate the unit-weight of each of the various array sections, it's possible to get a better feel for weight effectiveness of all the confining material that is required. I have summarized this within the following table. Again plexiglass seems to be the the best choice with a “We” = 1.41. The array that includes 76mm of confined Diesel fuel is also better than Steel by itself. Moreover the “We” for the diesel is 1.38. Aluminum is about a wash relative to pure steel. One might ask what happens if I am allowed to use 150mm of diesel or plexiglass or whatever -- what effect would that have on our final "We"? Good question.

 

TABLE 2: Equivalent Weight Effectiveness of 1m x 1m Array

 

If RHA were employed as the witness plate rather than mild steel, the pure steel array would be somewhat more effective, and the various sample arrays and their respective “We” values would drop closer to about 1. But regardless, this does demonstrate that 3-inches of Diesel is far better armor against shaped charge jets than 3-inches of air. It’s about as effective as steel.

 

The fuel has to be somewhere – why not configure fuel cells within a tanks design such that they are pulling double-duty? Employ it as armor. Use water cans as well.

 

Regards

JD

Edited August 21, 2006 by jwduquette1

[Marsh]

Hi,

 

Just to clear up a few points.

 

1. All Merkavas since their inception have incorporated their fuel cells as part of their survivability package.

 

2. The video of a Merkava absorbing numerous hits ,was of a Merkava 2B BATASH. not a Merkava 4.

 

3. According to Israel Tal when I interviewed him in 2004, each 7cm of fuel gave the equivalent protection of 1cm of RHA against HEAT attack. He said that the protection factor against Kinetic rounds was lower but it still remains classified.

 

Cheers

Marsh

Edited August 21, 2006 by Marsh