CACOR Award at the 2017 Canada Science Fair. Featured Image Caption:
Émeric Proulx, accepting his certificate from Steve Karrel, a Director of the Board
of Youth Science Canada, at the Youth Science Fair in Regina, Saskatchewan.
CACOR is pleased to announce that Émeric Proulx, age 16, a native of Sainte-Thèrese, Québec and a student at Externat Sacré-Coeur in Rosemère, currently in Secondaire V (equivalent to Grade 11/12 in Ontario) has been awarded the CACOR Award at the 2017 Canada Science Fair. His main fields of interest are electronics, chemistry, mechanics, physics and informatics. Next year, Émeric will begin a computer science program at college.
A description of Émeric’s project — HydroPulsoRéacteur — in the form of the text that he used (en Français) in his booth at the Science Fair in Regina follows.
The problem (Le problème)
Aviation accentuates global warming. Aircraft engines emitting particles and gases that contribute to climate change cause damage to the environment. Thus, there are emissions of particles and gases such as carbon dioxide, hydrocarbons and carbon monoxide in the atmosphere. Despite the emission reductions of turbo-jet engines and turboprop engines, now more fuel-efficient and less polluting, the rapid growth of air travel in recent years has contributed to an increase in total pollution of the environment.
Like all human activities involving combustion, most forms of aviation, release of carbon dioxide and other greenhouse gases into the Earth’s atmosphere, contributes to the acceleration of global warming and (in the case of CO2) to the acidification of rivers, lakes, and oceans. In addition, the amount of fuel used increases the price of airline tickets and limits accessibility. US airlines alone burned about 61.3 billion litres of fuel, the equivalent of 50 billion US dollars in 2014. It is estimated that aviation is responsible for about 3.5% of climate change caused by humans.
The proposed solution (La solution proposée)
To remedy this problem, I suggest changing the fuel used in aviation. Commercial aircraft use kerosene, a mixture of hydrocarbons that converts to carbon dioxide after combustion. I propose to replace kerosene with hydrogen. It burns with oxygen to make water vapour only, so no carbon dioxide that is primarily responsible for the greenhouse effect. However, although hydrogen is the most abundant element in the universe, there is virtually no gaseous hydrogen on Earth. The majority of hydrogen is produced by reacting with hydrocarbons. But this process also creates pollutants, so it is not ideal.
There are other methods for making hydrogen, including the electrolysis of water. This method transforms electrical energy into chemical energy in the form of hydrogen. Hydrogen can be stored in tanks and then used by jet engines. To ensure that the electricity that generates hydrogen is environmentally friendly, I propose to use photovoltaic cells. Airports have many unused areas that can be covered. A square kilometre of photovoltaic cells can generate up to 1 Gigawatt of energy in a day. Moreover, in order to potentially increase the energy efficiency of the system, I propose to develop a pulse detonation engine instead of modern turbofans. It costs less to produce and has several advantages.
The General Concept (Le concept général)
Photovoltaic Cell (Cellule photovoltaïque)
The photovoltaic cell converts the energy of light from the sun directly into electricity by photovoltaic effect, which is a physical and chemical phenomenon. The resulting energy is transmitted to the electrolytic cell.
Electrolytic Cell (Cellule électrolytique)
The photovoltaic cell transforms its electrical energy into chemical energy in the form of hydrogen by electrolyzing water. Electrolysis of water is the decomposition of liquid water (H2O) into gaseous oxygen (O2) and gaseous hydrogen (H2) as the result of the passage of an electric current through the water.
Storing Hydrogen (Stockage de l’hydrogène)
In aircraft, heavy tanks are not a good option; therefore carbon fibre tanks are often used. These are weaker than steel hydrogen tanks (used in cars and ships) that can withstand up to 70 MPa of pressure. This limitation decreases the amount of energy that can be stored as compressed gas. Other hydrogen storage options are available: cooling to very low temperature so that it becomes liquid; or in the form of chemical compounds. Each has its advantages and disadvantages.
Jet Engine (Moteur à réaction)
A jet engine converts chemical energy into mechanical energy. These engines burn a fuel to create heat, which increases the gas pressure and generates a force. Although my concept uses a pulse detonation engine, hydrogen could also be used in most of the currently used jet engines such as turbojet and turbofan.
Further Theory (Approfondissement de la théorie)
Turbojet & Turbofan (Turboréacteur & Turbofan)
The turbojet engine has an air inlet, a compressor, a combustion chamber and a turbine (which drives the compressor). The compressed air is heated by the fuel in the combustion chamber and then allowed to expand through the turbine. Turbojets have poor efficiency at low speeds, which limits their usefulness in non-aircraft vehicles. The turbofan is quieter and has better fuel consumption than the turbojet.
A turbofan engine is the most modern variation of the basic turbojet engine. Thus, while all the air captured by a turbojet engine passes through the turbine, in a turbofan, the majority of the air bypasses the turbine. A turbofan can therefore be considered as a turbojet engine that turns a huge fan, which greatly contributes to the thrust. The latter is thus much more efficient. This is the system used in most commercial aircraft.
Pulse Detonation Engine (Moteur à ondes de détonation)
Pulse Detonation Engines are machines that produce a rapid combustion of an oxidizer (air) and a fuel through detonation. These detonations are repeated several thousand times per second. The term “detonation engine” is shortened to “PDE” for “Pulsed Detonation Engine” and I will use that term. The PDE is a propulsion system that has received considerable interest in the last decade because of the many advantages it offers compared with traditional jet engines. PDEs operate cyclically, causing detonation waves that burn the fuel-oxidant mixture in the engine, release enormous amounts of energy and develop much higher pressures than a deflagration process.
For example, the deflagration process produces a velocity of about 7 metres per second while a detonation is 1,500 metres per second. PDEs have the advantage of having a very small production cost, because the engine is very simple. Generally, it is a long tube with specialized valves. Despite this simplicity, no PDE has been put into production, as this system still needs to be developed. Theoretically, a PDE can operate from a subsonic velocity up to a hypersonic flight speed above Mach 5. Aerodynamic heating is a critical materials issue.
The difference between detonation and deflagration
Detonation is a supersonic combustion process whereas deflagration is a subsonic combustion process. Almost all engines that burn fuel use deflagration to release the energy contained in the fuel. With detonation, a shock wave compresses the gas, which is followed by a rapid release of heat and a sudden increase in pressure.
Electrolysis of Water (L’électrolyse de l’eau)
A DC power source is connected to two electrodes or two plates of inert metal such as platinum or stainless steel, which are placed in water. Hydrogen will appear at the cathode, and oxygen will appear at the anode. The amount of hydrogen should be twice the amount of oxygen. Both are proportional to the total electric charge carried by the solution. The electrolysis of pure water requires an enormous amount of energy.
The efficiency of the electrolysis is increased by the addition of an electrolyte (such as a salt, acid or base). However, some electrolytes can increase corrosion and cause undesirable chemical reactions. Also, some electrolytes, such as sodium chloride, release chlorine during electrolysis, a potentially hazardous gas. According to my experiments and research, potassium hydroxide and sodium carbonate seem to be the best electrolytes. The production of gas seems to increase with the current and bringing the electrodes together also increases the efficiency.
Storing Hydrogen (Stockage d’hydrogène)
Compressed hydrogen requires high-pressure containment tanks. In an airplane, you cannot use steel tanks so you have to store the hydrogen in a tank made of carbon fibre or made of another light material. This reduces the amount of hydrogen that can be stored and thus the energy density is low.
Cryogenic Liquefied Hydrogen
To be liquid, hydrogen must be cooled below its critical point of 33 °K (-240 °C). A common method of obtaining liquid hydrogen involves a compressor resembling a jet engine in appearance and principle. Liquid hydrogen is generally used as a concentrated form of storage of hydrogen. As with any gas, liquid storage takes up less space. Once liquefied, it can be kept in liquid form in pressurized and thermally insulated containers. In order to minimize the area and reduce boiling, liquid hydrogen must be transported inside the fuselage of the aircraft.
Metal hydrides, such as MgH2, NaAlH4, LiAlH4, LiH, may be used as a hydrogen storage medium, often reversibly. These materials have a good energy density by volume, although their energy density by weight is often worse than most hydrocarbons. These chemical compounds release hydrogen when they are reheated to a certain temperature. They work a bit like a battery. They can be “charged” with hydrogen and “discharged”.
Photovoltaics (Les photovoltaïques)
The efficiency of solar cells used in a photovoltaic system, in combination with latitude and climate, determines the annual energy output of the system. For example, a solar panel with an efficiency of 20% and an area of one square meter will produce 200 watts per hour under the sun.
v Multi-junction: 46%
Multiple junction cells consist of several thin layers, each of which is essentially one solar cell surmounted by another.
v Single junction: 29%
Single junction cells consist of a single layer of material.
v Silicon: 26%
Details of my Conception (Détails de ma conception)
The Microcontroller (Le microcontrôleur)
A microcontroller is a small computer on a single integrated circuit. A microcontroller contains one or more processors with memory and input and output devices. For my project, I use a microcontroller similar to Arduino Uno. This microcontroller provides sets of digital and analogue input and output pins that can be interfaced to other circuits. These cards can be programmed from personal computers. The reason I use a microcontroller in my system is to make sure I have flexibility on the control logic. It also allows me to ensure the stable and safe flow of hydrogen between production and storage. It also allows me to control the engine during its operation and thus start it.
Decomposition of Water (Décomposition de l’eau)
For my electrolytic cell, I had to create a model that had both good efficiency and that could ensure the separation of hydrogen and oxygen. So I found a way to separate them by using a membrane that lets the electricity pass without the fluids in the cell. I also brought the electrodes as close as possible to have a small electrical resistance. In addition, I used sodium carbonate as an electrolyte because it was easily accessible to me, it is clean and it does not release chlorine as does sodium chloride. The structure of the cell is made of PMMA (more commonly known as Plexiglass). Insulating material was required. The electrodes are made of stainless steel, a metal almost resistant to corrosion from electrolysis.
The Pulsejet (Le pulsoréacteur)
The fabrication of a pulse detonation engine is rather complex. So I decided to make a pulsoreactor instead. This one looks very much like a PDE in principle and in appearance. A pulsoreactor is a type of jet engine in which the combustion also occurs by pulsation. This can be done with few parts or without moving parts. It is also capable of operating statically unlike some jet engines. The model I designed uses a mechanical valve to control the expanding exhaust flow, forcing the expanding hot gas to exit through the rear of the engine via the exhaust pipe only, thus allowing fresh air and more fuel to enter through the valve. Pulsejets are characterized by their simplicity, low construction cost, and high noise levels. While the thrust / weight ratio is excellent, the thrust compared to fuel consumption is very low.
The pulse detonation engine is very similar to the pulsoreactor. What differentiates them is their type of combustion and their pulsation rhythm. A high frequency PDE would be very stable.
Advantages of the system (Avantages du système)
v It’s ecological:
The biggest advantage of the proposed system is probably the fact that it does not emit any greenhouse gases. If the aviation industry stopped using hydrocarbons suddenly, it could dramatically slow down global warming.
v It’s economical:
In the long term, the implementation of the system could benefit the airlines because they would no longer have to buy kerosene. By adding sufficient photovoltaic cells, airports could be energetically self-sufficient. It could also reduce costs for passengers.
v It’s efficient:
Because hydrogen has a huge specific energy the weight of a commercial aircraft could be reduced, which would make such a craft use less fuel to fly. In addition, the Pulse Detonation Engine could have a better efficiency than other jet engines used on commercial aircraft.
Graphs & Data (Tableaux & données)
v The detonation waves are typically noisier than the turbofan.
v Research needs to be done before commercial use of the system.
v The initial cost of infrastructure is costly despite being profitable over the long term.
v The tank should have a larger volume to hold the same amount of energy.
My First Jet Engine (Mon premier moteur à réaction)
The Turbojet Engine (Le turboréacteur)
At the beginning of my project, I tried to build a turbojet engine to run it with hydrogen instead of the pulsoreactor. The reason I changed the model is because I had difficulty integrating the lubrication system and because I had problems with the thermal expansion in the reactor. I would have needed more specialized tools. At the end of the design, it was functional (it was capable of transforming chemical energy into thrust) but unfortunately it was not self-sufficient (that is, the turbine did not absorb enough energy to power the turbocharger).