Mixing water with fuel is one way to reduce fire hazards in tanks and other equipment
As is known, the fuel, the reserve of which is in tank and other combat vehicles is calculated in many hundreds of liters, is an object of increased danger. When fuel tanks are damaged by shell fragments and fragments of cumulative jets, their contents can easily ignite, which in some situations leads to serious fires ending in the complete destruction of the vehicle and even its crew. Therefore, reducing the fire hazard of fuel is one of the priority areas in increasing the survivability of military equipment.
Generally speaking, there are many "classic" methods for improving the fire safety of a vehicle. These include, first of all, the installation and improvement of automatic fire extinguishing systems with a reduction in their response time and an increase in efficiency. In addition, it is of no small importance to move tanks to isolated compartments, use "self-sealing" tanks and fill fuel tanks with cellular flame-stopping elements (polyurethane foam, metal mesh, etc.).
However, most of these methods are, so to speak, symptomatic treatment, i.e. aimed at eliminating the consequences - preventing the spread of fire. In this regard, a natural question arises: is it possible to make the fuel itself safer? So that it itself has a low potential for ignition when fuel tanks are damaged. One such method is to use a water-fuel emulsion.
Water-fuel emulsion
At first glance, it may seem that the phrase "water-fuel emulsion" (WFE) simply means adding water to fuel, but in fact this is far from true. If you pour diesel fuel diluted with water into the tank, then, of course, nothing good will come of it - only problems with the engine operation are likely to arise. It is another matter if you add an emulsifier additive to the same mixture of fuel and water using a surface-active substance (SAS), which will keep the water in a bound state.
Interest in such mixtures has not waned to this day, primarily in the civilian sector. All thanks to the fact that the use of VTE allows to reduce emissions of harmful substances with exhaust gases, increase the engine life and in some cases even improve its efficiency. But emulsions have another useful property - they significantly reduce the likelihood of fire when hit by shells.
For example, a water-fuel emulsion with a 5% water content, poured into 10-liter tanks (filled to 90%) practically does not ignite when fired at by PG-9 cumulative grenades. The same, but with 10% water, does not burn stably when hit by fragments of a 23-mm steel striker flying at a speed of up to 2000 meters per second.
One of the notable types of such water-fuel mixtures is a microemulsion (there are also macroemulsions, where water envelops the fuel), in which microscopic drops of water, bound by an additive, are distributed evenly throughout the entire volume of fuel. With the correct composition and mixing, a microemulsion does not have a strong negative effect on engine performance, but it provides good fire safety, since microdrops of water seriously slow down the ignition and combustion process. And the additive itself can also act as a combustion phlegmatizer.
An example of the appearance of a fuel emulsion (left) in comparison with diesel fuel (right). Source: A.S. Ivanov. "Water-fuel emulsion for internal combustion engines". Federal State Educational Institution of Higher Professional Education "Tyumen State Agricultural Academy"
Experiments with water-fuel emulsions on armored vehicles were conducted in different countries, but one of the most indicative can be considered Soviet studies published in the late 1980s. They are notable for the fact that they include field practice with full-scale shelling, so it would be interesting to look at these studies in order to evaluate the effectiveness of emulsions. This is what we will do.
As part of these studies, a water-fuel microemulsion was produced with microscopic droplets distributed throughout the entire volume of fuel in the tank, based on the fuel-emulsion additive TEP-101. The composition of the emulsion was selected in such a way as to have a minimal effect on engine power, and did not change throughout the experiment - 77% summer diesel fuel, 15% water and 8% TEP-101 additive.
The T-80 tank was taken as a "victim" for subsequent executions, into whose tanks this water-fuel emulsion was poured - with each fuel tank filled to 90% of its capacity. In addition, the gas turbine engine was removed from the tank, and additional tanks were installed in its place in the vacated engine-transmission compartment, so to speak, to fill the target to the brim. Well, this tank was fired at from the T-64A with cumulative (BK14M) and fin-stabilized subcaliber projectiles (BM22) from a distance of 100 meters at different angles.
Unlike regular summer diesel fuel, which easily ignited when hit by cumulative and sub-caliber projectiles, the emulsion demonstrated exceptional resistance to ignition. The tanks with it, as expected, were destroyed by hydraulic shock, but combustion was not achieved during the shelling of the tank. Only during the first experiment (No. 1), when a sub-caliber projectile was fired into the area of the middle right tank, a flash occurred, but also without further combustion.
The results of the shelling are summarized in the table below. It shows the shelling angles, the temperature of pure fuel and water-fuel (MVTE in the table) microemulsion, and the impact consequences. As you can see, the water-fuel emulsion has proven its effectiveness — fuel in this form becomes much safer in terms of resistance to ignition.
Conclusions
Summarizing all of the above, we can conclude that the use of modern mixtures in the form of a microemulsion of fuel and water, especially in combination with other methods (fire extinguishing systems, filling tanks with polyurethane, their insulation, etc.), can potentially seriously improve fire safety. And this, in turn, will lead to a noticeable reduction in irretrievable losses of armored vehicles and their crews. But there are several problems.
A high-quality water-fuel emulsion can only be produced using special equipment, observing all aspects of the technological process - the principle of "just add water" does not work here. You need completely clean, ideally distilled water, and an ideal mixture of components. And that's not all.
As is known, armored vehicles must successfully perform combat missions in any climatic conditions. However, water-fuel emulsions are quite sensitive to air temperature, especially when it is very negative - the presence of water makes its own adjustments. And this already leads to a deterioration in the starting properties of the fuel or the general impossibility of using it for its intended purpose. Therefore, the search and combination of components that would allow creating an emulsion with low fire hazard, "failure-proof" and stable in any climatic conditions, will require large financial costs.
In addition, it is worth remembering that water-fuel emulsions cannot be stored for a very long time - you cannot stock up on them for years to come. At the same time, mixing water and fuel immediately before injection, as proposed in some patents for vehicles and stationary power plants, does not make sense. Based on this, again, we will have to think about creating more stable mixtures, or move to the practice of making WFE at fuel storage points or directly in the field on mobile units immediately before refueling.
In any case, all this will clearly be more expensive than using conventional fuel and, as a result, could theoretically end up in logistics "with a short leash". So, it seems that there is a great benefit, but also a lot of headaches, therefore, despite the fact that emulsions were and are still of great interest in different countries, they have not received widespread use within the framework of armored vehicles.
The source of information:
"Study of the fire hazard of fuel based on water-fuel emulsion". V.P. Antonovsky, B.M. Ginzburg, V.D. Rebrikov et al. Journal "Bulletin of Armored Equipment" No. 3 for 1989.
Information