LES by Xavier

In this presentation, I will show you the general design of liquid-propellant thrusters. I will then explain to you how a specific propellant is chosen for a space mission. This includes the efficiency (enthalpy change per gram), environmental impact, safety and toxicity of a propellant and an evaluation of the use of an ignition system or a catalyst.

The idea of a liquid-propellant engine is fairly simple. The fuel and the oxidizer are pumped into a combustion chamber, and there they ignite to create a high-pressure and high-velocity stream of hot gases. The high-pressure and high-velocity is caused by the high temperature (when temperature increases, kinetic energy increases and pressure increases as well). When the gas exits the rocket by the nozzle, the rocket lifts up with great acceleration and speed.

A multistage rocket is a rocket with several stages that each include an engine and a propellant. Each stage is mounted on one another, and when the propellant in a stage is fully burnt, the rocket simply ejects the stage, making place to the stage above it to thrust the rocket. Usually, the first stage is at the bottom and is usually the largest. The second stage is the one above the first stage, and is usually the second biggest stage and so on.

Having a multistage rocket for a long-range space mission is very advantageous. When the propellant is fully burnt in a stage, the rocket simply ejects the stage. This causes the rocket to be lighter, which makes the rocket go faster and gain acceleration. Not only do you gain acceleration, but you also need less gas for your trip since the engines won’t have to work as hard to propel the rocket.

A hypergolic propellant is a propellant composed of a fuel and an oxidizer that spontaneously ignite when they come in contact with each other. The advantage of using a hypergolic propellant is that there is no need of an ignition source in order to make them combust. Little energy is needed to make them react, which means they are very reliable. An example of a hypergolic propellant is the Methylhydrazine and the Nitrogen Tetraoxide. The Methylhydrazine is used as the fuel, and the Nitrogen tetraoxide is the oxidizer.

Choosing the propellant for this space adventure will not be an easy task. Many criterias will have to be evaluated. The efficiency (kJ/g), environmental impacts, safety and toxicity and the evaluation of the ignition system or catalyst will all be considered into the choice.

H2 + ½ O2 = H2O deltaH = -241.8kJ/mol H2 = 2.02 g/mol ½ O2 = 15.99 g/mol Molar Ratio: 1:2 n = m/M n = m/M 1 = m/(2.02) ½ = m/(31.98) m = 2.02g m = 15.99g 15.99 + 2.02 = 18.01g -241.8kJ/mol /18.01g = -13.43kJ/g Hydrogen and Oxygen efficiency: -13.43 kJ/g

Environmental Impact The environmental impact of the Hydrogen and Oxygen

reaction only produces water vapour, which is harmless to humans. Water vapour is the dominant greenhouse gas in the atmosphere, but it does not affect temperature by itself. It only amplifies the already warming planet.

Safety Precautions Hydrogen Gas: Hydrogen is a highly reactive gas. With only

23% air, hydrogen gas will ignite. Simple friction will cause hydrogen to ignite. Also, hydrogen fire is invisible, so you would discover the fire by simply walking into it.

Oxygen Gas: Oxygen gas supports combustion. Any

material will ignite faster into an oxygen-only environment. Do not smoke or expose an open-fire anywhere near oxygen.

Catalyst/Ignition System There are two ways to ignite hydrogen and oxygen. The first

one is to bring a little spark of 20 microjoules or let the hydrogen and oxygen autoignite at a temperature of 540 degrees Celsius at normal atmospheric pressure.

Qwater = (200)(4.19)(280-0) Qwater = 234640J -Qmethylhydrazine = Qwater -234640J = 234640J -234.64kJ H2NN(CH3)2 = 60.1 g/mol 2N2O4 = 183.92g/mol n = m/M n = m/M n = 4.8/60.1 0.16 = m/183.92 n = 0.08 m = 29.43g

234.64/0.24 = -977.66kJ/mol -977.66/34.23 = -28.56 kJ/g

Environmental Impacts Methylhadrazine produces Nitrogen gas, Carbon Dioxide and Water Vapour when it combusts. Nitrogen gas composes 78% of the air we breathe. Breathing too much nitrogen will cause suffocation. Nitrogen is often used as a fertilizer in the envrionment. Food that is rich in nitrogen elements can cause the oxygen transport of the blood to decrease. Nitrogen mixed with oxygen creates nitrous oxides, which can be harmful to the brain. Carbon Dioxide is negatively influences the quality of our air and also is one of the worst greenhouse gas. It causes extreme weather change and global temperature increase. Companies now have carbon taxes, which are taxes put on companies based on the amount of carbon dioxide released into the atmosphere. Oxygen gas supports combustion. Any material will ignite faster into an oxygen-only environment. Do not smoke or expose an open-fire anywhere near oxygen.

Safety Precautions Unsymmetrical Dimethylhydrazine is a toxic liquid that is used as a propellant. It is carcinogen and it can explode near oxidizers. Keep far away from any ignition source or any heat sources. Do not inhale. Wear proper lab equipment, because if USDM comes in contact with the skin, the skin will absorb USDM.

Catalyst/Ignition System Unsymmetrical Dimethylhydrazine

autoignites at a temperature of 248 degrees Celsius or when mixed with Nitrogen Tetraoxide in a combustion chamber with heat.

x1 C12H26 -> 12C + 13H2 ΔH = 291kJ/mol x12 12C + 12O2 -> 12CO2 ΔH = -4722kJ/mol x13 13H2 + 13/2O2 -> 13H2O ΔH = -3143.4kJ/mol C12H26 + 37/2O2 -> 12CO2 + 13H2O ΔH= -7574.4kJ/mol C12H26 37/2O2 n = m/M n = m/M 1mol = m/170.38g/mol 37/2mol = m/31.98 m = 170.38g m = 591.63g 170.38 + 591.63g -7574.4/591.63 = -12.80kJ/g N-Dodecan and Oxygen Efficiency = -12.80kJ/g

Environmental Impacts N-Dodecane and Oxygen produces carbon dioxide and water

vapour. Carbon Dioxide is negatively influences the quality of our air and also is one of the worst greenhouse gas. It causes extreme weather change and global temperature increase. Companies now have carbon taxes, which are taxes put on companies based on the amount of carbon dioxide released into the atmosphere.

Products

Safety Precautions N-Dodecane: Must be kept away from any ignition source or any

source of heat because it is a combustible liquid. It is hazardous if it is inhaled and slightly hazardous in contact of skin. Wear proper lab equipment nearby the product (glasses, apron, gloves, etc). It is hazardous to the lungs and the central nervous system if inhaled.

Oxygen Gas: Oxygen gas supports combustion. Any material will

ignite faster into an oxygen-only environment. Do not smoke or expose an open-fire anywhere near oxygen.

Catalyst/Ignition Source N-Dodecane auto-ignites at a temperature of

203 degrees Celsius. N-Dodecane also ignites when mixed with oxygen in the combustible chamber with heat. Since N-Dodecane is a cryogenic propellant, it needs an ignition source which is heat.

x1 C2H5OH -> 2C + 3H2 + ½ O2 ΔH = 291 kJ/mol

x2 2C + 2O2 -> 2CO2 ΔH = -787 kJ/mol x3 3H2 + 3/2O2 -> 3H2O ΔH = -725.4 kJ/mol C2H5OH + 3O2 -> 2CO2 + 3H2O ΔH = -1221.4 kJ/mol C2H5OH = 46.07g/mol O2 = 31.98g/mol n = m/M n = m/M 1 = m/46.07 3 = m/31.98 m = 46.07g m = 95.94g 95.94 + 46.07 = 142.01g -1221.4/142.01 = -8.6O kJ/g

Environmental Impacts Ethanol produces Carbon Dioxide and Water Vapour when it combusts with oxygen. Carbon Dioxide is negatively influences the quality of our air and also is one of the worst greenhouse gas. It causes extreme weather change and global temperature increase. Companies now have carbon taxes, which are taxes put on companies based on the amount of carbon dioxide released into the atmosphere. Oxygen gas supports combustion. Any material will ignite faster into an oxygen-only environment. Do not smoke or expose an open-fire anywhere near oxygen.

Safety Precautions Ethanol is a toxic substance that when it is ingested, it can be very harmful. Ingesting ethanol in large quantities can cause coma or death. It has similar effects as alcohol when ingested. Ethanol is a very inflammable liquid. Ethanol is also carcinogenic, which means that it can cause cancer. Needs to be sealed tightly and needs to be far from ignition sources or heat sources. Needs to be kept away from oxygen gas as well.

Catalyst/Ignition System Ethanol autoignites at a temperature of 425 degrees Celsius. It also ignites when mixed with oxygen in a combustion chamber when heat is applied to the mixture.

Even though Unsymmetrical Dimethylhydrazine and Nitrogen Tetraoxide has a better efficiency than Hydrogen and Oxygen, I chose Hydrogen and Oxygen as a propellant for the space adventure. It has an efficiency of -13.43kJ/g, has a mass of 18.01g which is the lightest and has very few environmental impacts. Hydrogen and Oxygen are also safer than the other propellants.

Liquid-Propellant Engine : http://science.howstuffworks.com/rocket5.htm Multi-Stage Rocket : http://web-solutionz.blogspot.ca/2008/10/what-is-multistage-rocket-and-its.html Hypergolic Propellants :

http://library.thinkquest.org/03oct/02144/propulsion/propellents/hypergolic.htm Water vapour greenhouse gas : http://knowledge.allianz.com/environment/climate_change/?626/global-warming-what-

role-does-water-vapor-really-play Hydrogen Safety: http://www.siei.org/hydrogensafety.html Oxygen Safety: http://irscanada.ca/main/services/home-oxygen/oxygen-safety-precautions/

Oxyhydrogen: http://en.wikipedia.org/wiki/Oxyhydrogen N-Dodecane http://feql.wsu.edu/MSDS/dodecane.pdf Ethanol http://en.wikipedia.org/wiki/Ethanol Carbon Dioxide emissions http://curiosity.discovery.com/question/how-carbon-emissions-affect-

environment Unsymmetrical Dimethylhydrazine http://en.wikipedia.org/wiki/Unsymmetrical_dimethylhydrazine