# Difference between revisions of "Fuel tank"

A fuel tank is a dedicated part to contain of fuels and provide it to the appropriate reaction engines or consumers. In the stock game there are tanks for four different fuel mixtures:

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 decouplers, and to transfer their contents to a central tank using fuel lines. This can be used to construct an 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 real spacecraft, the liquid fuel is usually highly refined kerosene for the first stage and/or liquid hydrogen (LH2) for subsequent stages, and the oxidizer is usually liquid oxygen (LOX). Both the fuel and oxidizer are stored under slight pressure in 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 jet engines can rely solely on atmospheric oxygen as oxidizer. Most jet engines operate using a 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 engines. They can also be used for jet engines, however 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.

Liquid fuel and oxidizer density are both 5 kg/unit Mass
(t)
Liquid
Fuel

()
Oxidizer
()
()
Full Empty Max. Temp.
(K)
Tolerance
(m/s)
Tolerance
(g)
R-4 'Dumpling' External Tank Radial mounted 50
(39.90)
0.1238 0.0138 2 000 5 50 9.9 12.1
R-11 'Baguette' External Tank Radial mounted 50
(25.21)
0.3038 0.0338 2 000 5 50 24.3 29.7
R-12 'Doughnut' External Tank Small 147
(119.46)
0.3375 0.0375 2 000 6 50 27 33
Oscar-B Fuel Tank Tiny 70
(51.64)
0.225 0.025 2 000 6 50 18 22
FL-T100 Fuel Tank Small 150
(104.1)
0.5625 0.0625 2 000 6 50 45 55
FL-T200 Fuel Tank Small 275
(183.2)
1.125 0.125 2 000 6 50 90 110
FL-T400 Fuel Tank Small 500
(316.4)
2.25 0.25 2 000 6 50 180 220
FL-T800 Fuel Tank Small 800
(432.8)
4.5 0.5 2 000 6 50 360 440
Rockomax X200-8 Fuel Tank Large 800
(432.8)
4.5 0.5 2 000 6 50 360 440
Rockomax X200-16 Fuel Tank Large 1 550
(815.6)
9 1 2 000 6 50 720 880
Rockomax X200-32 Fuel Tank Large 3 000
(1 531.2)
18 2 2 000 6 50 1 440 1 760
Rockomax Jumbo-64 Fuel Tank Large 5 750
(2 812.4)
36 4 2 000 6 50 2 880 3 520
Kerbodyne S3-3600 Tank Extra large 3 250
(1 597.6)
20.25 2.25 2 000 6 50 1 620 1 980
Kerbodyne S3-7200 Tank Extra large 6 500
(3 195.2)
40.5 4.5 2 000 6 50 3 240 3 960
Kerbodyne S3-14400 Tank Extra large 13 000
(6 390.4)
81 9 2 000 6 50 6 480 7 920
Mk2 Rocket Fuel Fuselage Short Mk2 750
(566.4)
2.29 0.29 2 500 50 50 180 220
Mk2 Rocket Fuel Fuselage Mk2 1 450
(1 082.8)
4.57 0.57 2 500 50 50 360 440
Mk3 Rocket Fuel Fuselage Short Mk3 2 500
(1 352.5)
14.29 1.79 2 700 50 50 1 125 1 375
Mk3 Rocket Fuel Fuselage Mk3 5 000
(2 705)
28.57 3.57 2 700 50 50 2 250 2 750
Mk3 Rocket Fuel Fuselage Long Mk3 10 000
(5 410)
57.14 7.14 2 700 50 50 4 500 5 500
C7 Brand Adapter - 2.5m to 1.25m Small, Large 800
(433.0)
4.57 0.57 2 300 20 50 360 440
C7 Brand Adapter Slanted - 2.5m to 1.25m Small, Large 800
(433.0)
4.57 0.57 2 300 20 50 360 440
Mk2 to 1.25m Adapter Small, Mk2 550
(366.4)
2.29 0.29 2 500 50 50 180 220
Mk2 to 1.25m Adapter Long Small, Mk2 1 050
(682.8)
4.57 0.57 2 500 50 50 360 440
Mk2 Bicoupler Small, Mk2 x 2 860
(676.4)
2.29 0.29 2 500 50 50 180 220
2.5m to Mk2 Adapter Large, Mk2 800
(432.8)
4.57 0.57 2 500 50 50 360 440
Mk3 to Mk2 Adapter Mk2, Mk3 2 200
(1 282.0)
11.43 1.43 2 600 50 50 900 1 100
Mk3 to 2.5m Adapter Large, Mk3 2 500
(1 353.0)
14.29 1.79 2 600 50 50 1 125 1 375
Mk3 to 2.5m Adapter Slanted Large, Mk3 2 500
(1 353.0)
14.29 1.79 2 600 50 50 1 125 1 375
Mk3 to 3.75m Adapter Extra large, Mk3 2 500
(1 353.0)
14.29 1.79 2 600 50 50 1 125 1 375
Kerbodyne ADTP-2-3 Large, Extra large 1 623
(246.0)
16.88 1.88 2 000 6 50 1 350 1 650

### Liquid fuel tanks

Liquid fuel tanks can only be used with jet engines and the LV-N "Nerv" Atomic Rocket Motor, as they don't contain the oxidizer required to operate rocket engines.

Liquid Fuel Density is 5 kg/unit Mass
(t)
Liquid
Fuel

()
()
Full Empty Max. Temp.
(K)
Tolerance
(m/s)
Tolerance
(g)
Engine Nacelle[Note 1] Small 600
(480)
0.925 0.15 2 000 10 50 150
Engine Pre-cooler[Note 1] Small 1 650
(1 618)
0.375 0.15 2 000 10 50 40
Mk1 Diverterless Supersonic Intake[Note 1] Small 720
(560)
1.18 0.17 2 000 10 50 200
Mk0 Liquid Fuel Fuselage Tiny 200
(160)
0.275 0.025 2 000 10 50 50
Mk1 Liquid Fuel Fuselage Small 550
(230)
2.25 0.25 2 000 10 50 400
Mk2 Liquid Fuel Fuselage Short Mk2 750
(430)
2.29 0.29 2 500 50 50 400
Mk2 Liquid Fuel Fuselage Mk2 1 450
(810)
4.57 0.57 2 500 50 50 800
Mk3 Liquid Fuel Fuselage Short Mk3 4 300
(2 300)
14.29 1.79 2 700 50 50 2 500
Mk3 Liquid Fuel Fuselage Mk3 8 600
(4 600)
28.57 3.57 2 700 50 50 5 000
Mk3 Liquid Fuel Fuselage Long Mk3 17 200
(9 200)
57.14 7.14 2 700 50 50 10 000
(256)
0.5 0.1 2 400 10 50 80
FAT-455 Aeroplane Main Wing[Note 2] Radial mounted 2 800
(2 320)
3.78 0.78 1 200 15 50 600
Big-S Wing Strake[Note 2] Radial mounted 1 000
(920)
0.6 0.1 2 400 15 50 100
Big-S Delta Wing[Note 2] Radial mounted 3 000
(2 760)
2.0 0.5 2 400 15 50 300
1. The Engine Nacelle, Engine Pre-cooler, and Mk1 Diverterless Supersonic Intake are a combination of air intake and liquid fuel tank. Only the tank properties are shown. They are located in the "Aerodynamic" category in the game.
2. The FAT-455 Aeroplane Main Wing, Big-S Wing Strake, and Big-S Delta Wing are a combination of lifting surface and liquid fuel tank. Only the tank properties are shown. They are located in the "Aerodynamic" category in the game.

### Monopropellant fuel tanks

Monopropellant tanks store monopropellant gas, which is consumed by RCS maneuvering thrusters.

In real life, the term "monopropellant" is used to refer to fuels that do not require additional reactants to effect energy: although liquid fuel requires oxidizer to burn to produce thrust, monopropellants require no additional chemicals to work. A well-known real life monopropellant is hydrazine.

RCS Fuel Density is 4 kg/unit Mass
(t)
Monopropellant
()
()
Full Empty Max. Temp.
(K)
Tolerance
(m/s)
Tolerance
(g)
FL-R10 RCS Fuel Tank Tiny 200
(176)
0.10 0.02 2 000 12 50 20
FL-R25 RCS Fuel Tank Small 330
(186)
0.56 0.08 2 000 12 50 120
FL-R1 RCS Fuel Tank Large 1 800
(900)
3.4 0.4 2 000 12 50 750
Mk2 Monopropellant Tank Mk2 750
(270)
1.89 0.29 2 500 50 50 400
Mk3 Monopropellant Tank Mk3 5 040
(2 520)
9.8 1.4 2 700 50 50 2 100
Stratus-V Roundified Monopropellant Tank Radial mounted 200
(176)
0.10 0.02 2 000 12 50 20
Stratus-V Cylindrified Monopropellant Tank Radial mounted 250
(190)
0.23 0.03 2 000 12 50 50

### Xenon gas tanks

Xenon density is 0.1 kg/unit Mass
(t)
Xenon
()
()
Full Empty Max. Temp.
(K)
Tolerance
(m/s)
Tolerance
(g)
PB-X50R Xenon Container Radial mounted 2 220
(600)
0.054 0.014 2 000 12 50 405
PB-X150 Xenon Container Tiny 3 680
(800)
0.100 0.024 2 000 6 50 720
PB-X750 Xenon Container Small 24 300
(1 500)
0.76 0.19 2 000 6 50 5 700

## 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:

${\displaystyle m_{\text{fuel}}=V_{\text{fuel}}\cdot \rho _{\text{fuel}}}$
Where:
• ${\displaystyle m_{\text{fuel}}}$ is the mass of the fuel
• ${\displaystyle V_{\text{fuel}}}$ is the volume of the fuel
• ${\displaystyle \rho _{\text{fuel}}}$ 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.

{\displaystyle {\begin{aligned}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{aligned}}}
Where:
• ${\displaystyle m_{\text{fuel}}}$ is the fuel mass
• ${\displaystyle m_{\text{wet}}}$ and ${\displaystyle m_{\text{dry}}}$ are the wet and dry mass
• ${\displaystyle V_{i}}$ and ${\displaystyle \rho _{i}}$ 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.

{\displaystyle {\begin{aligned}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{aligned}}}
Where:
• ${\displaystyle m_{\text{fuel lf/ox}}}$ is the fuel mass of the liquid fuel/oxidizer mixture
• ${\displaystyle m_{\text{wet lf/ox}}}$ is the wet mass of a tank with liquid fuel/oxidizer mixture
• ${\displaystyle m_{\text{dry}}}$ is the dry mass
• ${\displaystyle V_{\text{lf}}}$ and ${\displaystyle V_{\text{ox}}}$ are the volume of liquid fuel and oxidizer
• ${\displaystyle \rho _{\text{lf/ox}}}$ 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 m³). Dividing the tank's actual in-game fuel capacity (720 unit + 880 unit = 1600 unit) with this volume, the result is 389.2 unit/m³. If we count with 0.8 ratio for volumetric usage efficiency (real life example: 80% for the 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.

Height (units) 1 2 4 8 16
Small FL-T100 Fuel Tank FL-T200 Fuel Tank FL-T400 Fuel Tank FL-T800 Fuel Tank
Large Rockomax X200-8 Fuel Tank Rockomax X200-16 Fuel Tank Rockomax X200-32 Fuel Tank Rockomax Jumbo-64 Fuel Tank
Extra large 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.