For more than 100 years, such a mechanism has been known as an internal combustion engine.
Engines of this type are used everywhere as the most common way of converting chemical energy into mechanical motion.
However, there is another kind of absolutely wonderful engine - which is called a linear internal combustion engine. The simplicity of the device, high speed of operation and efficiency - make such an engine very promising for use in a variety of tasks.
All internal combustion engines can be conditionally subdivided into three large types:
1) two-stroke :
in them, the process of performing useful work and filling the engine cylinder with a new portion of the mixture for combustion is carried out in 2 piston movements. When the piston moves downwards, useful work is performed, when it moves in the opposite direction, that is, upwards, the incoming mixture is compressed for its subsequent combustion;
2) four-stroke :
in them, the process of performing useful work, purging the cylinder from combustion products and filling it with a new portion of the mixture, is carried out in 4 piston movements:
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3) diesel engines : the
essence of which is that the combustion of the mixture occurs due to a sharp increase in pressure, and therefore the temperature, which actually ignites the mixture that has entered the cylinder.
In addition, there are various combinations between these three types listed above. However, despite the attempts of engineers to somehow combine these three approaches, in general, they have taken root in their "pure" form.
Despite the widespread use of internal combustion engines, there is one special subspecies of engines, which, although not widespread (which he has the right to count on), nevertheless, in some areas, it is still used.
These are internal combustion engines of the linear type : The essence of such engines is that they are much simpler than classic internal combustion engines. It is easier because in their design such a massive and complex system of parts as a "crank mechanism" is completely excluded. External compression boxer piston engine Internal compression opposite piston engine Single piston single acting engine with return mechanism Free piston engine Free piston double acting engine
In conventional engines, this mechanism serves in order to perform useful work, as well as return the piston to its original position, which it occupied before the start of movement.
The system turns out to be quite stable, predictable, and can be easily customized.
However, such a complication of the system is not in vain - it leads to the fact that the mechanism as a whole becomes much more complicated, the engine becomes heavier, various parasitic phenomena arise that lead to increased wear of the cylinder-piston group.
Among such phenomena, one can name alternating loads on the piston, which exert swinging movements to the left / right on it. These movements lead to increased wear of the piston and cylinder.
In addition, the presence of large rotating masses leads to parasitic vibrations that loosen the structure as a whole and increase the energy consumption for the movement.
Unlike such classic engines, linear internal combustion engines are devoid of all these drawbacks: in essence, they are just a piston moving in a straight line and does not have any crank mechanisms.
How, then, does the piston return to its original position? There are many schemes for this.
Among the most common approaches are:
- use of the chamber opposite to the working cylinder - as a gas spring;
- balancing one piston with another, exactly the same piston moving in the opposite direction;
- connecting two pistons moving in opposite directions - a rigid linkage;
- the absence of any balancing of the moving piston, due to the fact that the entire system is installed on a rigid massive base. This allows you to damp the resulting vibrations;
- other designs, as well as combinations of all of the above.
The linear internal combustion engine makes it very easy to realize an efficient electric current generator.
In fact, to create such a generator, you just need to quickly move a strong magnet attached to the axle connected to the piston, through the annular stator winding, for example, as in this "shaking flashlight":
Due to their simplicity, these motors can develop rather high speeds. In particular, there is information about the achievement of such engines at a frequency of 390 Hertz (390 piston movements per second and, accordingly, 23,400 - per minute).
In addition, motors of this type can be used as compact and powerful energy sources, with a fairly simple design. This is what attracts the increased attention of the defense industry around the world to these engines.
Some researchers are conducting quite interesting experiments that allow a detailed assessment of the efficiency of such engines.
In particular, a group of scientists carried out a series of works aimed at investigating the applicability of linear motors in military needs.
The researchers focused on the ability to create miniature systems and the ability to provide a high density of stored energy, despite their small size.
For this, a two-stroke linear-type engine was developed, which, to return the piston to its original position, was used in a spring with a rectangular wire section in it.
(Image source: "# 4" - in the list of used sources, under this article)
Tests have shown that generators of this type have very great potential. Namely, they can operate at a very high frequency for a long time.
Generator for 300 watts and 5 watts - in comparison with a standard battery, AA format (Image source: "No. 4" - in the list of used sources, under this article)
In the course of the experiment, the 5-10 W generator shown in the figure worked for 100 hours, operating at a frequency of 390 Hertz. In this case, the efficiency of the generator was 90%.
During testing, the following significant points were identified:
- Due to the lack of a rigid connection with the missing crank system, the generator has a variable compression ratio, which allows it to easily work with different types of fuel, in the Diesel cycle mode. In other words, the engine can easily ignite any fuel using the high temperature from compression as the ignition effect;
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The density of stored energy, in comparison with rechargeable batteries
(Image source: "No. 4" - in the list of used sources, under this article)
Why, with such obvious advantages of this type of engine, they did not become widespread and did not supplant so well known to us engines with a crank mechanism?
Probably, the answer here is that the world has become, to a certain extent, hostage to the existing infrastructure, large-scale production facilities and a network of service companies focused on working with classic internal combustion engines.
This is one side of the problem, the second is that the linear internal combustion engine is constantly at risk. This is manifested in the fact that the engines are constantly balancing on the brink of destruction.
This risk is a consequence of the fact that a rapidly moving piston does not, as a rule, have any physical limiter (engine designs that require a rigid coupling between the pistons - we will deliberately omit now, since any engineer tries to use all the advantages of this type of engine ).
And this requires abandoning any rigid couplings and making the engine work exclusively by controlling its movement using a variety of factors: compressing gas springs; synchronously moving in different directions and also synchronously converging in the center - balanced pistons, etc.
It is easy to see from this description that the implementation of accurate synchronization and controlled flow of this process is a very nontrivial task and is solved with varying degrees of success.
If this process goes out of control, this will immediately lead to the destruction of one or more pistons, as well as the cylinders (due to the impact of the pistons - into the corresponding "bottoms" of the cylinders).
If, however, completely abandon the idea of eliminating the vibrations of such an engine, using a single-cylinder scheme, this will lead to the emergence of strong vibrations, which must be extinguished by a massive base.
There is one more non-obvious problem, which concerns the complexity of starting engines of this type (we didn’t forget that we are trying to "squeeze" everything out of the engine, therefore we do not use any rigid couplings).
Typically, this type of engine is started using a compressed air pulse.
All these reasons, taken together, are holding back the widespread adoption of these engines in the commercial market.
However, recently, due to the widespread use of various microcontrollers, attempts are being made to electronically-computer control the processes taking place in an engine of the type under consideration.
In particular, the following approaches are observed:
- PWM control, when an electric generator connected to a moving piston or pistons is used to control the movement of the pistons, which is currently used as a "thruster";
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Thus, as can be seen, the use of linear internal combustion engines as generators of electric current is very interesting and promising.
However, one should not assume that linear motors are exclusively the prerogative of scientific teams and do not go beyond the "secret laboratories".
Many amateurs successfully and easily build their operating models of this type of engine, using glass tubes as cylinders, and graphite lugs as pistons.
For example, the next author, whose videos are given below, builds engines of this type, for his own pleasure.
As a spark source, an electronic board from a lighter for a gas stove is used:
A note should be made here: not all gas stove lighters use a piezoelectric or mains electrical source to generate an electrical spark. Some lighters use a low-power circuit board powered by a single AA battery that contains a voltage boosting circuit.
In addition, for a long time, some companies have been producing road rammers based on two-stroke internal combustion engines. In essence, these devices are nothing more than a linear motor, they are only used for purely utilitarian purposes, "far from high technologies":
In general, it can be summarized that the development of such linear internal combustion engines is a very promising business. In case amateurs are engaged in this, this lesson can be very exciting and you can develop your own miniature motor, literally in a pocket format (this is especially easy if you have your own metal lathe)!
Such an engine can be a good help, in obtaining electricity, while in places far from civilization.
Just remember that if this motor is to be used to generate electricity, and contains a permanent magnet generator, this device must cool very well, since the magnets have a characteristic called "Curie point" - that is, this is the temperature at which the magnet is demagnetized ...
Since the developer of an electric generator is unlikely to set as his goal “to systematically demagnetize the magnets,” he should take this essential point into account.
Sources used:
1. www.wikipedia.org
2. www.freikolben.ch/lineargeneratoren.shtml
3. www.freikolben.ch/basics-de.shtml
4. "Miniature Internal Combustion Engine-Generator For High Energy Density Portable Power"
Kurt D. Annen *, David B. Stickler, and Jim Woodroffe
Aerodyne Research, Inc
Billerica, MA 01821
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