MARCH: Gas Turbine Engines

In January, I studied the viability of using internal combustion engines commonly used in automobiles for my trans-dimensional rocket ship. Those types of engines ended up being too inefficient, and far too slow. But the research led me to another area of internal combustion engines—the gas turbine engine.

There are many different kinds of gas turbines, each with a slightly different design and used for different purposes, but one thing seemed common: they provide a great amount of thrust, which is exactly what I need.

Much like automobile engines, there are a lot of similar steps involved in a turbine engine’s ability to produce work; there is a compression stage, combustion stage, and a “power stage”, where the power produced by the combustion stage is turned into work by rotating the turbine. Of course, how the turbine engine achieves these stages is pretty different from piston engines, which I’ll get into shortly. I studied a turbine engine that looked most useful for my problem: the turbojet.

First, incoming air goes through the air intake. The intake acts as a sort of diffuser. This allows the air coming into the engine to maintain the speed essential for combustion. In the turbojet engine in Figure I, the air passes by to an axial compressor. An axial compressor allows the air to remain parallel to the axis of the turbine while it is being compressed. The compressor stage consists of sets of blades—powered by the turbine shaft—which act as a means to increase the pressure of the air and get it ready for the combustion stage. The air—which contains the oxygen essential to combustion—enters the combustor.

The combustor consists of a fuel nozzle that sprays fuel into the chamber. The igniter then ignites the fuel, burning the fuel and the air that is allowed to enter the chamber through inlet air holes. The air that is now energized with heat from the combustion heats up the surrounding air and then pushes the higher energy, higher pressured air to the turbine.

The turbine blades use the energy from the passing flow to spin, which—much like the crankshaft in an automobile engine—rotates to produce mechanical energy which can be used for work. This work is used for electrical generation, as well as powering the compressor. After the expanded gases pass through the turbine blades, the engine is fitted with a nozzle. Nozzles use the properties between pressure and outlet flow area to increase the velocity of the exiting gases. The gases exit the nozzle at a speed which produces a lot of thrust—hence using these engines for things like planes, some of which can go several times faster than the speed of sound!

Of course, as I mentioned, there are loads of different types of turbine engines, and each one is used in a slightly different way. For example, the turbojet engines featured here are most efficient at high speeds. Engineers are still coming up with improvements for such systems to make them even more efficient and more versatile; each system has its pros and cons. For now, I think these turbojet engines are a good look at the basic functionality of a gas turbine engine.

I think these types of engines look very promising, but they are also very complex…and require an environment with an oxygen-rich atmosphere! As far as going fast in atmosphere, this definitely looks like the way to go! But where my trans-dimensional ship is concerned, I think I’ll have to look for something that provides a lot of thrust and uses a fuel source I can actually take with me.

So the search isn’t over yet, but I feel like I’m getting closer!

– Little T

JANUARY: Internal Combustion Engines

One of the troubles of getting around from one place to another in any universe is the distribution of energy. Thanks to the laws of thermodynamics, it’s always about making a system do as much work as possible, with the most efficient use of energy.

The concept of transferring chemical energy into usable mechanical energy certainly isn’t exactly new—which brought me to my first research project: the internal combustion engine. People of this world seem to use the things to get around everywhere and have no idea how they work!

Like with any system, energy can be lost before it can be transferred into work, but a lot of years of science and engineering has produced some pretty amazing systems. And engineers continue to work on improving these systems to make them even better.

The basic concept to an internal combustion engine uses the ideal gas laws and combustion reactions to rotate a crankshaft. The rotation of the crankshaft is where the chemical energy from the reaction is transferred into mechanical energy (specifically, a type of mechanical energy called rotational energy, imagine that!), which is used by the rest of the engine to do work—in other words, the engine is able to rotate the wheels and move the vehicle.

Little T’s Research Notes: Four stroke internal combustion engine (not to scale):

Here’s the first stroke: Gas intake.
The valve opens to allow a mixture of some hydrocarbons (usually gasoline) and air (which contains oxygen) into the cylinder. The crankshaft—which has an initial rotation—will cause the piston to move vertically in the cylinder.

Second stroke: Compression.
The piston is on its way towards the top of the cylinder, with the fuel and air mixture being compressed as it goes.

At the end of the second stroke, the piston is is the top dead center position, where it and its connecting rod are parallel to the crankshaft. With the gasses fully compressed, the engine is ready to move on to the next stroke.

Third stroke: Power.
The power stroke is where the fun happens; the piston is ready to move down again, but without the energy to do it, the engine would seize. Instead, a perfectly timed spark from the spark-plug ignites the gasses in the cylinder, causing a combustion reaction. The combustion reaction is usually between the hydrocarbon octane and oxygen, and results in carbon dioxide gas and water vapor:

Since combustion reactions are exothermic—meaning the reaction gets rid of heat to the its surroundings, and heat is a form of energy—and the gases produced by the reaction expand rapidly in explosive excitement, the piston has been energized enough to give the crankshaft more rotation, and thus the rest of the engine more overall power.

Fourth stroke: Exhaust.
Now that energy has been transferred to where it needs to go, the exhaust gases aren’t so excited anymore—and they’re taking up space in the cylinder that would spoil another combustion reaction. So the exhaust valve opens. A combination of gas behavior and the motion of the piston allows the carbon dioxide and water vapor to escape.

Then engines in most vehicles have a network of these cylinders to make up the whole engine. Each cylinder fires at the right moments to provide an efficient and usable flow of energy, and over time, power. Other parts—like the transmission, radiator, and more—are also required to transfer the rotational and heat energy into work and keep the whole system running efficiently.

Unfortunately, carbon dioxide has a lot of negative effects to the atmosphere of this world, which means more research should be done to improve this type of engine, fuel, and exhaust. Maybe I can find a fuel source that doesn’t give off harmful chemicals? That’ll be research for another day!

So, I’m not sure I’ll be able use the internal combustion engine (as it is) to help me get back to my own dimension, but I definitely think it has potential to help me in other ways, while I’m here!

-Little T