Difference between revisions of "Fuel tank"

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A '''fuel tank''' is a dedicated part to contain of [[fuel]]s and provide it to the appropriate [[reaction engine]]s or consumers. In the stock game there are tanks for four different fuel mixtures:
* [[Liquid fuel]] and [[oxidizer]] in the usual ratio of 9 parts liquid fuel for 11 parts oxidizer
* [[Liquid fuel]] alone usage in oxygenated atmospheres
* [[Monopropellant]] without any oxidizer usually used for [[RCS]]
* [[Xenon gas]] for [[ion engine]]s
* [[Ore]] for processing into [[liquid fuel]], [[liquid fuel]] and [[oxidizer]], or [[monopropellant]] with the [[ISRU Converter]]
The distribution through the rocket depends on the type of fuel. While xenon gas and monopropellant are available everywhere in the craft without additional plumbing, engines using liquid fuel and oxidizer needs to be attached to the tank with only fuel crossing parts between them.
== Overview ==
A liquid fuel tank can provide fuel to any engine directly attached to it. When tanks are directly connected together in a stack they will feed their contents from the top to the bottom of the stack. It is possible to mount additional fuel tanks radially with or without [[decoupler]]s, and to transfer their contents to a central tank using [[fuel line]]s. This can be used to construct an [[Tutorial:Asparagus Staging|asparagus staging]] system where outer tanks are drained first and dropped once empty, while still keeping the central tank full. This can be tricky to construct when dealing with very large rockets as the rocket engines of the outer layers have to be kept running long enough to ensure the rest of the rocket can get into orbit once they have stopped providing thrust.
=== Real world application ===
In [[w:Spacecraft|real spacecraft]], the liquid fuel is usually [[w:RP-1|highly refined kerosene]] for the first stage and/or [[w:Liquid hydrogen|liquid hydrogen (LH2)]] for subsequent stages, and the oxidizer is usually [[w:Liquid Oxygen|liquid oxygen (LOX)]]. Both the fuel and oxidizer are stored under slight pressure in [[w:Cryogenic fuel|special fuel tanks]] to keep them from vaporizing; this is because LH2 and LOX require temperatures below 20.28 K (−252.87 °C, −423.17 °F) and 90.19 K (−182.96 °C, −297.33 °F) respectively to remain in a liquid state. In comparison, jet aircraft carry only liquid fuel, as [[w:Jet engine|jet engines]] can rely solely on [[w:Atmosphere of Earth#Composition|atmospheric oxygen]] as oxidizer. Most jet engines operate using a [[w:Jet fuel|refined kerosene hydro-carbon]], similar to diesel, which can actually be used in some diesel engines. However, it is not recommended, or legal in some places, to use jet fuel as a replacement for diesel due to its high lead content and lesser lubricating ability.
Ore is a simplification for some kind of chemical which could be mined from the ground on other planets, and converted to a rocket fuel.
== List of tanks ==
=== Rocket fuel tanks ===
These tanks contain both liquid fuel and oxidizer and are designed for use with [[liquid fuel engine]]s. They can also be used for jet engines, however [[#Liquid fuel tanks|liquid fuel tanks]] are preferable, because they don't contain oxidizer, which is not used by jet engines. The oxidizer/liquid fuel ratio is exact except for the [[Oscar-B Fuel Tank]].
Their mass fully fuelled with liquid fuel and oxidizer is between 5.245 and 9.333 times higher than the dry mass. The fuel-containing Mk3 fuselages and adapters have the highest factor with 9.33 times, followed by the FL-T and Rockomax tanks at 9 times. Third are the Kerbodyne extra large tanks which have a wet mass 8.2 times that of their dry mass. The ROUND-8 Torodial Fuel Tank has a relatively low factor of only 5.44 times the dry mass and the Oscar-B Fuel Tank is the most inefficient with a mass factor of 5.245. The combined fuel and oxidizer mass compared to the dry mass is the factor reduced by one. Thus the mass of the contents in a FL-T or Rockomax tank is 8 times higher than the dry mass.
{{Stats table rocket fuel tanks}}
=== Liquid fuel tanks ===
Liquid fuel tanks can only be used with [[jet engine]]s and the [[LV-N "Nerv" Atomic Rocket Motor]], as they don't contain the oxidizer required to operate rocket engines.
{{Stats table liquid fuel tanks}}
=== Monopropellant fuel tanks ===
{{Stats Table RCS Fuel}}
=== Xenon gas tanks ===
{{Stats Table Xenon Tanks}}
=== Ore tanks ===
{{Stats Table Ore Tanks}}
<!-- That didn't work, should it be changed? -->
== Dry mass and wet mass ==
In the part configuration the dry mass is given and the resources are given in a volumetric unit. To calculate the mass of the fuel and the mass fully fueled, wet mass, the density is also required. In general the mass of one type of fuel is:
{{Formula|math=m_\text{fuel} = V_\text{fuel} \cdot \rho_\text{fuel}|where=*<math>m_\text{fuel}</math> is the mass of the fuel
* <math>V_\text{fuel}</math> is the volume of the fuel
* <math>\rho_\text{fuel}</math> is the density of the fuel}}
The total mass of the fuel is then simply the sum of all the fuels in the tank. And the wet mass is then the fuel masses added the dry mass.
  m_\text{fuel} &= \sum\limits_i (V_i \cdot \rho_i) \\
  m_\text{wet} &= m_\text{dry} + m_\text{fuel} = m_\text{dry} + \sum\limits_i (V_i \cdot \rho_i)
\end{align}|where=*<math>m_\text{fuel}</math> is the fuel mass
* <math>m_\text{wet}</math> and <math>m_\text{dry}</math> are the wet and dry mass
* <math>V_i</math> and <math>\rho_i</math> are the volume and density of each fuel}}
Because all stock tanks, except the liquid fuel and oxidizer tanks, use only one type of fuel the sum of the different fuels in the tank is not required. And because the liquid fuel and oxidizer have the same density, the volumes can be added before converted into mass.
  m_\text{fuel lf/ox} &= (V_\text{lf} + V_\text{ox}) \cdot \rho_\text{lf/ox} = (V_\text{lf} + V_\text{ox}) \cdot 0.005 \frac{\text{t} }{\text{unit} } \\
  m_\text{wet lf/ox} &= m_\text{dry} + m_\text{fuel lf/ox} = m_\text{dry} + (V_\text{lf} + V_\text{ox}) \cdot 0.005 \frac{\text{t} }{\text{unit} }
\end{align}|where=*<math>m_\text{fuel lf/ox}</math> is the fuel mass of the liquid fuel/oxidizer mixture
* <math>m_\text{wet lf/ox}</math> is the wet mass of a tank with liquid fuel/oxidizer mixture
* <math>m_\text{dry}</math> is the dry mass
* <math>V_\text{lf}</math> and <math>V_\text{ox}</math> are the volume of liquid fuel and oxidizer
* <math>\rho_\text{lf/ox}</math> is the density of liquid fuel and oxidizer (they are the same)}}
The [[Rockomax X200-16 Fuel Tank]] for example: Based on some rough in-game measurements it is approximately 0.67·1.25 meters tall with a radius of 1·1.25 meters (1.25 is the rescale factor!). This would give the tank/stage a real world volume of around 4110.9 liters (4.1109&nbsp;m³). Dividing the tank's actual in-game fuel capacity (720 unit + 880 unit = 1600 unit) with this volume, the result is 389.2&nbsp;unit/m³. If we count with 0.8 ratio for volumetric usage efficiency (real life example: 80% for the [[w:Saturn V|Saturn V's]] stages), then 1 unit = 2.0555 liters. The reason the entire volume is not used is because the actual fuel tank is a pressure vessel with rounded ends inside the cylindrical stage. The tanks itself are also insulated to keep the cryogenic fuels from boiling away to quickly. As the tanks of the liquid fuels and solid fuels has better volumetric usage efficiency, we can estimate the volume of 1 unit is about 2-2.5 liters.
== Comparison ==
The table does only contain tanks, which contain both liquid fuel and oxidizer. The height is units, where one unit is the height of the [[FL-T100 Fuel Tank]].
{| class="wikitable" style="text-align:center;"
! Height (units)
! 1
! 2
! 4
! 8
! 16
! {{Radial size|s}}
| FL-T100 Fuel Tank
| FL-T200 Fuel Tank
| FL-T400 Fuel Tank
| FL-T800 Fuel Tank
| —
! {{Radial size|l}}
| —
| Rockomax X200-8 Fuel Tank
| Rockomax X200-16 Fuel Tank
| Rockomax X200-32 Fuel Tank
| Rockomax Jumbo-64 Fuel Tank
! {{Radial size|xl}}
| —
| —
| Kerbodyne S3-3600 Tank
| Kerbodyne S3-7200 Tank
| Kerbodyne S3-14400 Tank
== Notes ==
* Before v0.18 all fuel tanks provided fuel for both rocket engines and jet engines, because there was only one type of fuel recognized in game.
* Since v0.18 fuselages cannot be used to power rocket engines anymore, as they don't contain the necessary oxidizer.
== See also ==
* [[Reaction engine]]
* [[Jet engine]]
* [[Liquid fuel]]
* [[Oxidizer]]
* [[ore]]
* [[ISRU Converter]]
* {{Wikipedia|In-situ resource utilization}}
* {{Wikipedia|Liquid hydrogen}}
* {{Wikipedia|Liquid oxygen}}
* {{Wikipedia|RP-1}}

Revision as of 18:04, 17 March 2017