Good day everyone, dear readers! Despite the fact that most of you are owners of four-wheeled vehicles, there are also connoisseurs of motorcycles, mopeds, and scooters among subscribers. If you don’t yet know the principle of operation of a two-stroke engine, then it’s time to familiarize yourself with this interesting topic.
This type of power unit has become the base for various types of devices and equipment due to its simplicity and reliability. In the working cycle of such a motor, there are only two strokes, unlike the 4-stroke ones that are installed on most cars. This pair of bars is compression and expansion. The reader may quite rightly ask: where do the inlet and outlet of the working mixture go. The fact is that they are combined with the compression and expansion mentioned above.
Unlike a 4-stroke engine, in a 2-stroke, the entire work cycle occurs in just one revolution of the crankshaft. This makes it possible to increase the power quality of the engine by 1.5 times or more with an equivalent displacement. However, this leads to a decrease in efficiency, otherwise all self-propelled mechanisms without exception would be equipped with such power units. But in shipbuilding they have found the widest application. A single-cylinder two-stroke engine is also an integral component of every small-engine scooter that roams our roads with might and main.
Another important feature of such mechanisms is their tendency to overheat. This is due to the release of large amounts of heat during operation. To solve this problem, forced cooling may be required. But there are also advantages to such a motor: the work of the piston is limited to 2 strokes, which means that it makes half as many movements. Due to this, wear on key parts of the power unit is reduced.
Operating principle
Let's look at how such an engine works in practice (see video):
- The piston begins to move upward from the bottom point, which is also called the “dead” point. Simultaneously with this process, fuel is delivered along with air. The exhaust window opens slightly, and exhaust gases freely escape through it. At the same time, the moment of compression of the working mixture occurs.
- As soon as compression begins, a space is formed in the crank chamber based on rarefied air. This frees up space for a fresh supply of fuel. When the piston reaches its highest point of movement, the spark plugs produce a spark that ignites the working mixture.
- Due to the ignition of the working mixture, energy arises that forces the piston to move already down. The excess pressure created in the crank chamber causes the fuel to compress. At the top point of the piston movement, the exhaust window opens, freeing the exhaust gases to exit, from where they are sent straight to the muffler.
- Further movement of the piston leads to the opening of the purge window. Fuel moves from the crank chamber to the working cylinder. As soon as the piston reaches the lowest point, this means that the full cycle of engine operation has taken place. And everything starts again, but this will be the beginning of a new cycle.
Comparison of 2 and 4 stroke engines
Since the power of an equivalent motor is two strokes greater than that of its 4-stroke counterpart, it should, in theory, be more economical. In practice, this does not happen due to additional losses that arise. Partial mixing of the exhaust gases with the newly incoming fuel occurs, and this entire mixture safely exits through the exhaust pipe. Therefore, for the same number of cycles, a two-stroke carburetor requires more fuel.
There are also differences in the lubrication system. In the case of a 2-stroke motor, it is carried out by mixing and. The 4-stroke engine has a lubrication system with a gear pump. Lubricant enters the inlet pipe of the system, and it is supplied exactly as needed.
Such engines do not have valves, which are inherent in four-stroke internal combustion engines. For them, the same work is done by a piston, which, when moving sequentially up and down, opens and closes the purge, inlet and outlet windows. Due to this, they are considered more structurally simple and easier to maintain. It is believed that their power rating is approximately 2 times higher than those designed for 4 cycles, due to the greater number of cycles passed. 
But due to insufficient use of the piston stroke, residual accumulated gases in the cylinder and partial loss of produced power for purging, the actual increase in net power will be no more than 60–70 percent. The spark on such engines appears a fraction of a second earlier than the piston reaches top dead center, and various mechanical and electronic devices are provided to change the ignition angle. On previous models, the ignition moment was set based on the optimal speed.
So, let’s summarize the main advantages of the power unit in question:
- differs in small dimensions;
- has a simple device;
- produces more power with the same displacement.
At the same time, its use is limited due to design features and significant losses. However, today this type of engine is still equipped with a large number of different mechanisms that can use both a single- and two-cylinder internal combustion engine for 2 strokes. Knowing the features and operating principle of such an engine, you can independently find problems that arise in it. In some cases, such knowledge allows you to decide between a 2-stroke and a 4-stroke power unit. 
In today's review, we tried to look at the design of a 2-stroke power unit, which is equipped with almost any modern motorcycle or moped, as well as other equipment. Friends, I will be grateful for your recommendations of my blog among your friends. In the upcoming blog releases, we will definitely look at new interesting topics in the field of cars. In the meantime, a few words about and what is the point of using them. Stay with us and see you again!
In addition to the well-known four-stroke engines that are used in cars, there are also two-stroke engines that are installed on technical units: chainsaws, motorcycles, lawn mowers, ATVs, scooters, motor boats, etc. The main difference between a two-stroke and a four-stroke engine is the operating principle of the internal combustion engine. In addition, 2-stroke engines are smaller in size, capable of developing less power and, therefore, have lower efficiency.
- The structure of a two-stroke engine.
- The operating principle of a 2-stroke internal combustion engine.
- How to increase engine power with your own hands?
- How to increase traction?
- Problem with purging after increasing power.
- Video.
Two-stroke engine design
The design of such a motor is simpler than that of a four-stroke. A two-stroke internal combustion engine does not have a gas distribution mechanism. The engine consists of a cylinder block in which the crankshaft is located on bearings.
The connecting rod head fits into a special place for it - the shaft journal. Between the connecting rod head and the shaft journal there are liners that are secured with castle nuts.
The upper part of the connecting rod is attached to the piston via a pin. A pin is a hollow cylinder that serves as a connecting element in the connecting rod-piston structure.
Compression rings are installed on the piston in special grooves around the perimeter in the upper part, on which engine compression depends.
The driving element in an internal combustion engine is the fuel-air mixture, which, when burned, creates energy that pushes the piston down. The up and down movement of the piston causes the crankshaft to rotate. A flywheel is attached to the crankshaft, which transmits rotation further, that is, to the gearbox shaft and so on.
The two-stroke engine is cooled through the fins of the outdoor unit. In addition to external cooling, some of the cooling comes from the oil contained in gasoline.
Two-stroke engines are filled with gasoline to which special motor oil has been added. For example, for a Shtil lawn mower, for 5 liters of gasoline, you need to add 100 grams, that is, the ratio of gasoline to oil is 50:1. This is exactly the amount of oil that perfectly lubricates the rubbing surfaces of the cylinder with the piston rings.
Principle of operation
One revolution of the crankshaft is one cycle of the operating process of an internal combustion engine.
Fuel (gasoline + oil) with air is supplied to the working combustion chamber of the cylinder, after which, due to the formation of a spark from the spark plug, an explosion of the combustible mixture occurs, the energy of which sharply pushes the piston down. When the piston moves down, the exhaust window opens and a little later the transition window opens through which a new portion of fuel is injected.
The fuel mixture enters the engine crankcase through a window that opens due to vacuum as the piston moves upward from bottom dead center (BDC) to top dead center (TDC). This movement also opens a window for the emission of gases of the burnt mixture. After a few milliseconds, the purge window opens. A new portion of fuel is supplied through the purge window.
How to increase power
Like 4-stroke engines, 2-stroke engines can be improved, so-called chip tuning.
To increase the power of the internal combustion engine, you can do the following:
- Ream the exhaust port so that the exhaust gases can escape completely.
- Improve the blowing effect. Purging is the removal of exhaust gases and filling the working volume of the cylinder with a new portion of the fuel mixture. It must be done so that fuel can be injected into the combustion chamber through the inlet window. If fuel does not enter the combustion chamber in the required volume, fuel will accumulate in the engine crankcase. Therefore, for high-quality filling of the working part of the cylinder with fuel, it is necessary to increase the diameter of the exhaust window opening (exhaust gas emission).
- A swirl diffuser can be used on the carburetor. A vortex diffuser is also called a zero diffuser. Due to this diffuser, more fuel will enter the cylinder in a shorter period of time.
- Mount a special resonator on the muffler, suitable for the speed of the specific engine. The resonator makes sure that the unburned fuel mixture returns back to the cylinders. This is effective when incomplete combustion of the mixture occurs in the cylinder.
In order for the part of the cylinder under the piston to be filled completely, it is necessary to inspect the inlet and outlet channels; perhaps there are scratches, burrs, or chips on the holes. Such small defects affect the speed of movement of fuel and gases.
For a better effect of increasing power, the cylinder head (cylinder head) can be milled and then ground.
How to increase cravings
The thrust of two-stroke motors depends on the opening of the throttle. With a sharp increase in engine speed, traction increases. It follows that in order to reduce the acceleration time of the internal combustion engine, it is necessary to increase the working volume of the cylinder.
When the engine operates at low speeds, high-quality traction increases throttle response and increases acceleration.
Thrust can also be increased by replacing the valves with special ones and adjusting them so that they stay open longer than regular ones.
Purge problem
The higher the crankshaft speed, the more power. But the design of two-stroke engines has this peculiarity - the faster the piston begins to move, the worse the combustion chamber of the cylinder is purged, since the exhaust gas supply and exhaust windows remain open for a very short time. 
Chamber purging is the removal of gases and injection of fuel into the cylinder from the crankcase. Fuel begins to be sucked in and remain in the crankcase as the piston moves upward. Then, when the piston goes down, the inlet port closes and the purge window opens, through which a new portion of fuel is supplied and the gases of the previous spent fuel mixture are expelled (see the figure above, in the middle).
This simple design of a two-stroke engine eliminates the need to install a gas distribution mechanism (GRM), a purge pump, valves and a lubrication unit.
Purging while a two-stroke engine is idling (idling) is carried out differently. During operation at XX, purging is carried out by opening the damper to a small angle. This kind of purging is not of high quality, so at idle speed, as many have probably noticed, the engine of a chainsaw or lawn mower does not work stably. As for a chainsaw, for example, Echo (Echo), then you need to pull the choke halfway.
A single-cylinder two-stroke engine has a contour blower, that is, a slot blower. At the bottom of the cylinder in the wall there is a special slot through which gas distribution occurs. During the compression and power strokes, that is, when the piston is up, the intake and purge ports must be closed.
Contour purge - this pre-piston volume (cylinder under the piston) is a purge pump. This design makes it possible to make engines of the smallest dimensions.
Video
Scooters are equipped with 2T or 4T two-stroke engines. Which is better?
Animation of the operation of a two-stroke engine.
Two-stroke Stihl engine (Calm) in section.
This video shows the operation of a two-stroke engine.
The internal combustion engine operates according to a long-studied principle. It is worth taking a closer look at the operation of a piston engine, since rotary and other unusual devices that convert combustion energy into kinetic energy are less common. What is the main difference between a two-stroke engine and a 4-stroke engine? The most important difference lies in the ignition mode of the combustible mixture, which can be easily understood by the reproduction of sounds. A two-stroke engine in most cases produces a shrill and also quite loud sound, while a four-stroke engine produces a calmer and more measured sound.
Operating principle of a 2-stroke engine
- More often than not, the difference also lies mainly in the purpose of the device and its overall fuel efficiency. In a two-stroke engine, the ignition process is reproduced with each revolution of the crankshaft; it is for this reason that in terms of power they are several times superior to four-stroke engines, in which there is a special mixture that flows mainly through revolutions.
- Four-stroke engines are much heavier and waste the most energy. In most cases, they are used on cars and special equipment, while on other equipment such as scooters, lawn mowers, as well as light types of boats, in most cases you can see more compact two-stroke varieties of devices.
- But a gasoline generator, for example, can easily be found in both two-stroke and four-stroke varieties. The engine in a scooter can also contain any engine at all. The operating principle of such equipment mainly involves the same processes; the difference will only be in the method and efficiency of the overall energy conversion.
What does tact mean?
The process of fuel processing in both engine models can occur through the sequential execution of all four types of processes, which are otherwise called cycles. The speed at which the main work of the engine occurs through three strokes is exactly what the main difference between a two-stroke engine and a four-stroke engine is.
The first stroke is the injection. At this time, the piston begins to move following the example of the cylinder, and the intake valve begins to open to launch the air-fuel mixture into itself and deliver it to the combustion chamber itself. Afterwards the combustion process will occur. At this time, the exhaust valve closes back, and the piston continues to move up the cylinder, compressing all the gases that are inside. The power stroke occurs when the entire mixture is ignited.
At this time, the spark from the spark plug begins to replenish all the gases compressed within itself, which provokes an explosion, the energy of which pushes the piston down to its initial position. The last stroke will be the exhaust: the piston will reach the top of the cylinder, and the exhaust valve will open again, allowing all the exhaust gases to exit the common combustion chamber so that the process can be carried out again. Reciprocating movements in the piston rotate the crankshaft, the torque at this time is transmitted to the working parts in the equipment. This is how the process of converting fuel combustion energy into forward motion can occur.
The working process of a four-stroke engine
In a conventional four-stroke device, ignition of the mixture begins at every second revolution of the shaft. The process of rotating the shaft can result in more complex forms of mechanisms that will help the user achieve successive strokes.
Opening both the intake and exhaust valves may occur thanks to the cam shaft, which presses the rocker arms over and over again. The process of returning the valve to the closed initial position is carried out under the influence of a spring. In order not to lose compression, it is worth making sure that the valve begins to fit as tightly as possible to the cylinder head.
How does the process of functioning of a push-pull device take place?
Now it’s worth considering in more detail the process of operation of a two-stroke engine, and also to distinguish its features from a four-stroke one. In a two-stroke engine, all four actions occur in one revolution of the shaft, as the piston moves from top dead center to bottom, and then up again. The release of excess gases (i.e. purging) and the injection of fuel are integrated into one stroke; ultimately, this process ignites the entire mixture, and the resulting energy pushes the piston down. This design eliminates the special need for valves in the device itself.
In place of the valves you can find several combustion chamber openings at once. At the moment when the piston is moved to the lowest point by the combustion movement, the exhaust valve will open, allowing all the exhaust gases to be eliminated, by this action the chamber will become completely empty again. During the downward movement, a vacuum is formed in the cylinder, with the help of which a certain mixture of air and additional air is drawn in through the exhaust valve located in the lower area.
As the piston moves upward, it begins to block all channels and is able to compress the gases inside the cylinder. At this time, the spark plug fires, and after that the entire process described above occurs in a new way. It is important to note that in engines of this format, the process of ignition of the mixture can occur during each subsequent revolution. Which helps extract more power from them, at least over a certain period of time.
The difference between a two-stroke engine and a four-stroke engine
Two-stroke engines will be best used in applications that require quick and sharp bursts of all the energy, rather than a steady operation over the entire length of time. For example, a jet ski accelerates much faster than a simple four-stroke truck. But at the same time it is needed for short trips, while the truck itself is capable of traveling a distance of hundreds of kilometers before it needs to rest.
The short duration of operation of the two-stroke mechanism will be compensated by the low ratio of its weight to power indicator: these types of engines in most cases weigh much less, for this reason they can start faster and reach their highest efficiency, and can also reach the maximum operating temperature. To move them to another point, much less energy is also expended.
What type of motor should you buy?
In most cases, four-stroke engines can only operate in one position. This may be due to the complexity of the moving mechanisms, as well as the designs of the oil pan.
This type of sump, which provides further lubrication of the engine, is most often found only in four-stroke devices and is of the greatest importance for the work process. A two-stroke engine most often does not have any additional sump, which is why they can be use in almost any position without the possibility of oil fluid splashing out or interrupting equipment lubrication processes. For types of equipment such as chainsaws, circular saws, and other personal tools, this flexibility indicator is considered quite important.
Fuel efficiency as well as environmental implications. In most cases, it becomes clear that compact and fast engines in devices pollute the surrounding space much faster and consume a large amount of fuel. At the lowest point of the piston movement, when the combustion chamber is completely filled with the combustible mixture, a certain amount of fuel is completely lost, ending up in an empty channel.
This can be easily seen when looking at an outboard motor. You can see multi-colored oil stains around it. It is for this reason that engines of this type are considered not very efficient and pollute the surrounding air. And although four-stroke models are heavy and slow in performance, they they burn fuel fully.
How much does it cost to repair equipment and replace components?
Smaller devices are in most cases considered the cheapest, both in terms of initial purchase and subsequent maintenance. But at the same time they are designed for a longer operating time. Although there are some oversteps, most often they are not designed for long-term use for more than two hours and are designed for a very short period of use.
The lack of a separate lubrication system can also lead to this. That even in the highest quality motor of this type, wear will occur very quickly, and then it will become unusable due to damage to the moving part.
Partly due to the lack of lubrication in gasoline, which is needed to fill a two-stroke scooter engine, for example, it is worth adding a certain amount of specialized oil. This may result in additional waste of time and money, as well as may cause equipment failure(if you ever forget to add more oil). A four-stroke engine most often requires minimal care and maintenance from the consumer.
Which motor should you choose?
Four-stroke engine main features:
Two-stroke engine features:
- One power stroke occurs for each revolution of the crankshaft.
- You should use a light bellows and the engine will begin to function quite balanced and measured, since at this time the torque will be distributed much more evenly due to the fact that the ignition process in the combustible mixture will take place during each revolution.
- The engine weight will be much higher.
- The structure of the engine is simpler due to the absence of a valve mechanism.
- The cost of a two-stroke is noticeably lower.
- High mechanical efficiency due to reduced friction due to the number of parts.
- Air cooling.
- High working amplitude.
The range of applications extends to motorized units, chainsaws, small motor boats, and motorcycles. The two-stroke engine has small dimensions, high power and low efficiency. For this type of unit, fuel efficiency is fundamentally unimportant. Nowadays, they are used as starting motors to drive large diesel internal combustion engines, for example, tractors.
Device
The two-stroke engine is distinguished by its simplicity of design, the absence of a gas distribution mechanism, and its small dimensions. Structurally, the diagram is a cylinder block, inside of which the crankshaft is located on bearings. The connecting rod head with liners rests on the shaft journal and is secured with castle nuts. The upper head of the connecting rod is connected to the piston through a metal hollow sleeve (pin). A piston with compression rings located on it prevents the penetration of burnt gases into the combustion chamber.
By moving the piston up and down, the shaft rotates. Next, the rotation is transmitted to the main gear of a particular unit.
The two-stroke engine is cooled through the outer fins of the block.
Cooling also occurs due to fuel containing a certain amount of oil. That is, the lubrication of the piston-cylinder and crankshaft-connecting rod joints is carried out with a mixture that is diluted in advance with a special oil. When it burns with fuel, it should not leave exhaust deposits under the piston.
Principle of operation
The process is based on the duty cycle that occurs per revolution of the crankshaft. The principle of operation of a two-stroke engine is that when moving upward, the piston compresses the mixture present under the piston, which got there through the inlet port. The spark from the spark plug explodes the fuel, sharply increasing the temperature and pressure of the gases. As a result of this thermal pressure, the piston is forced downwards. 
At the same time, the exhaust window and a little later the transition window open, injecting a fresh portion of fuel. By the way, the fuel in a two-stroke engine must be supplemented with oil, making up a mixture of gasoline and oil of a certain proportion. This is done to lubricate the piston, cylinder wall and crank assembly. The fuel mixture enters the crankcase through a window that opens due to the vacuum created by the movement of the piston from BDC to TDC. At the same time, the piston opens the hole, releasing the spent exhaust gases. At a certain period, a purge window is opened by means of a piston to fill the cylinder with a fresh portion of the fuel mixture.
Power boost
To increase engine power you need:
- Increase the area of the outlet opening, keeping it in the open position for a long time in order to release the maximum amount of gases.
- Increase the efficiency of blowing. This is necessary so that fuel can be injected into the combustion chamber through the inlet ports. Otherwise, an accumulation of the fuel mixture will be observed in the crankcase. To avoid this, it is recommended to enlarge the outlet windows, which will lead to high-quality filling of the cylinder.
- Use a vortex (zero) diffuser on the carburetor, which will supply more mixture in a shorter period of time.
- Install a so-called resonator on the muffler, corresponding to the engine speed. This unit helps return a portion of the mixture back to the cylinder. Similar nuances arise when a two-stroke engine throws part of the fuel out of the chamber through the outlet (window).
To completely fill the sub-piston volume, you should also examine the condition of the inlet and outlet channels to reduce all kinds of burrs, scratches, and roughness. These casting defects contribute to slowing down the flow, reducing the filling of the chamber, and reducing power.
Milling followed by fine grinding of the block head is considered to be an effective way to increase engine power. The complexity of the procedure comes down to measuring the displacement volume and selecting the octane number of the fuel.
In order to increase the power of the motor, it would be possible to reduce the weight of rotating parts, for example, the flywheel, crankshaft, by cutting off the counterweight elements. But bitter experience tells us not to go at random, since amateur performance will lead to the flywheel beating, its vibration, especially during low engine speeds. But if you really want to, you can remove thin chips, followed by mandatory balancing of the flywheel. As for the crankshaft, there is a risk of losing the center of gravity of the shaft with all the ensuing consequences.
Traction capabilities
So , two-stroke engines and their traction capabilities are correlated with the opening of the throttle valve. That is, with the acceleration of revolutions, its traction ability increases, which significantly affects acceleration. This means that in order to increase acceleration, you need to increase the working volume of the cylinder. Of course, traction can lead to top speed. Working at low speeds, good traction provides throttle response, quick acceleration with easy overcoming of road obstacles and turns. This all relates to increased traction at low revs. One of the prerequisites for increasing traction is the installation of special valves and increasing the duration of their stay in the open state.
Problem with combustion chamber purging
However, it is known that higher revs indicate more power. In two-stroke engines, due to high rotation speeds, the combustion chamber cannot be properly and quickly purged, since the windows remain open for a short time. 
The use of chamber purge involves injecting fuel into the cylinder from the crankcase. Fuel is drawn in and found in the crankcase as the piston moves upward. When moving downwards, the generated excess pressure purges the combustion chamber. This scheme is appropriate from the point of view of the small number of parts used, for example, the absence of: a gas camshaft, valves, a purge pump, and lubrication units.
Another feature of chamber purging is associated with the idle mode of the engine, in which there is a small open damper angle. This situation does not provide complete removal of exhaust gases per shaft revolution. Therefore, at idle the engine exhibits unstable operation. The fact is that a flash of the mixture leads to additional idle speed. But the mixture under the cylinder does not ignite from a spark due to the poverty of the fuel.
In engines with one piston, loop blowing (slot blowing) is widely used. The scheme provides for gas distribution through slots in the wall at the bottom of the cylinder. That is, the intake and vent holes must be in the closed position during the compression stroke and stroke of the piston. The contour purge of the combustion chamber (under-piston space) is a kind of purge pump. This factor leads to a reduction in engine components, creating the preconditions for their use on lawn mowers, walk-behind tractors, boats, and other light mobile devices.
Today it is impossible to imagine modern life without. Driving your own car, traveling by public transport, buying goods, flying on an airplane and other activities. These processes are one way or another connected with the engine.
Despite the number of various designs, and varieties of power plants, piston engines, today, are more common than others. The number of strokes to complete the work cycle divides the unit into a two-stroke and a four-stroke engine. These types of motors make up the majority among the variety of manufactured equipment.
The difference between motors arises from the application point of view. For installation on automotive equipment, a four-stroke unit is more often used, a two-stroke engine is used if dimensions and weight play a decisive role.
Suzuki RM125 motorcycle with single-cylinder two-stroke engine
Creation of a two-stroke engine
There are many speculations about who was the first to create an internal combustion engine. It is known for certain that the first two-stroke gas-powered engine was invented and designed by the Belgian Jean Joseph Etienne Lenoir, this event took place in 1858.
Lenoir engine (on display in the museum)
At that time, a steam engine had already been created, and the invention of the Belgian surpassed it in terms of performance. The engine is much lighter, simpler, and consumes less fuel. Despite the advantages, the power plant had many flaws and was inferior in reliability. After Nicholas Otto presented a four-stroke engine, which at that time was thought out in more detail, the engine operating on the principle of two cycles was forgotten, and for a long period of time it was not used anywhere.
During the Great Patriotic War, the power plant was installed on aircraft. In our region, motors are known for their use on moto equipment. Three-cylinder units that perform two strokes are used on Suzuki and Kawasaki motorcycles. Today, the engines are operated in aviation, the leader here is the Austrian company Rotax, which produces engines for use on small aircraft.
Rotax 582 UL two-stroke twin-cylinder engine
After tightening the requirements for environmental standards and emissions, the two-stroke engine was no longer used for installation in classic road vehicles. However, on light vehicles, such as: scooters, snowmobiles, boats, it is not easy to replace a small and lightweight unit. Here the two-stroke unit simply has no competitors.
Features of a two-stroke engine
A power unit that uses two strokes is good because it is simple and reliable. The difference between a two-stroke and a four-stroke engine lies in the execution of the duty cycle. This cycle consists of two strokes: compression and expansion, while in a four-stroke engine there is a stroke for the intake of new fuel and a stroke for the exhaust of spent fuel. An interesting fact is that these two cycles are also present in a two-stroke power plant, otherwise the unit could not work, but they are combined with the compression and expansion processes.
The cycle being performed clearly demonstrates the difference between a two-stroke engine and a four-stroke engine. The process of a two-stroke motor takes place per revolution of the shaft. This feature achieves installation in comparison with the opponent, one and a half times. Despite the increase in power, the return rate is underestimated, which is a negative point.
In addition, this feature leads to the release of a volume of heat during operation, which greatly overheats the motor. Two-stroke power units require intensive cooling. The positive point is that when working, the piston makes half as many movements as the piston of a four-stroke mechanism, this reduces wear on parts and elements.
The peculiarity of the unit is that there is no lubrication mechanism. Oil is supplied directly with fuel. For this purpose, a mixture of gasoline and oil is added to the gas tank, the ratio is one to fifty, or the lubricant is mixed with fuel in the pipeline at the inlet. The oil burns with gasoline and is removed with waste products.
The distinctive moment is the combustion itself. In a four-stroke unit, one cycle is allocated for this. In push-pull units, combustion occurs in a fraction of a second, so the mechanism needs adjustments to achieve the effect.
Two-stroke engines have found themselves in another industry, shipbuilding. Cylinder power plants are also used on scooters produced in large quantities.
Operating principle of a two-stroke engine
To understand why four-stroke engines have replaced their younger brothers in automotive technology, let’s look at how a two-stroke engine works.
Sequence of actions of the power plant operating cycle:
Compression stroke.
The process is accompanied by the movement of the piston from bottom to top. The movement provokes the flow of fuel through the purge holes into the unit; subsequently, the piston skirt blocks these holes. Further movement is accompanied by the closure of the exhaust channels into which combustion waste was pushed out. Between the piston and the top of the cylinder, a combustion space is formed in which excess pressure is created. At the same time, a vacuum occurs in the space under the piston, and the space is used for the flow of a renewed dose of fuel. Having reached the top point, the charge lights up.
Two-stroke engine diagram
Expansion stroke.
Having ignited, the portion creates excess pressure, which presses on the bottom of the piston and forces it to move. The process is accompanied by alternate opening of the windows, first for exhaust, then for purging. The descent creates excess pressure under the piston chamber; under its influence, fuel again enters the cylinder, squeezing out the remaining waste and filling the space to repeat the previous stroke.
The operating principle of a two-stroke engine makes it possible to do without a gas distribution system, making the design of the unit lighter and more reliable. The reverse side, the quality of the gas exchange process. The two-stroke mode is impossible without purging, the process of which is accompanied by the release of unburned fuel along with exhaust gases to the outside. This leads to excessive consumption of fuel and increased toxicity of the exhaust of the unit.
It is worth noting that the above described scheme is typical for carburetor engines. In the case of a diesel engine or, clean air is supplied to the cylinder through the purge holes. The combustible mixture is supplied by injection, this work is performed by nozzles.
Cylinder purging methods
It is obvious that the purging process, a mechanism that qualifies as complex. Properly performed purging directly affects power and efficiency indicators. To improve performance, designers are constantly trying to improve and bring the process to perfection.
How to blow out a cylinder:
- “Circuit” blowing. This type of blowing is simple and therefore widespread. The disadvantage is that the application is associated with excessive fuel consumption. Types of contour blowing: return-loop, deflector, high-altitude.
- “U-shaped” purging. The “U-shaped” principle is to be used only on engines with two cylinders. When carrying out, one cylinder participates in the process of gas intake, the second releases waste. The effect of purging is felt in fuel efficiency; the process is accompanied by uneven heating of the steam responsible for the exhaust.
- “Valve-slit” purge. It differs in that it requires a gas distribution mechanism to control the valves. The valve is used both to provide fuel and to remove exhaust vapors. Purge involves the removal of waste through a valve in the cylinder head and the flow of fuel through the holes. The advantage is that purge increases fuel efficiency and minimizes the toxicity of emitted vapors. Disadvantage, complexity of design and violation of regimes associated with an increase in the operating temperature of the unit.
- “Direct flow” blowing. Used in power plants with the number of pistons equal to two. In this case, the cylinder is located in a horizontal position. The pistons move towards each other. While moving, each piston releases and closes the valve: one piston admits a portion of fuel, the second removes a portion of waste from the cylinder. The combustion chamber is formed when the pistons approach each other. The effect of this purge option is maximum: it removes burnt gases and saves fuel. The downside is that a complex mechanism of cranks and connecting rods is required; the performance requires the use of coolers and sustainable materials for the manufacture of parts.
Two-stroke engine 5 TDF with direct-flow purge
The difference between a two-stroke engine and a four-stroke engine
Car owners are wondering: which is better, a two-stroke or a four-stroke engine. There is no definite answer; each mechanism has positive and negative sides, depending on the requirements placed on the motor.
It would seem that the power of a motor performing two strokes, in comparison with an equivalent motor performing four strokes, is greater, which means it is better. However, the reality is more complex. In practice, additional losses occur: partial ingress and mixing of waste gas with fresh fuel, release of part of the fuel during purging. The result is that when performing the same cycle, a unit that performs two cycles is inferior in terms of efficiency to a unit with four cycles.
The method of lubrication of four-stroke and two-stroke power plants is different. The two-stroke unit is lubricated by mixing engine oil and gasoline. The four-stroke unit has a lubrication mechanism using a pump, which consumes as much oil as the operation of the installation requires.
Two-stroke engines do not have valves; the role of the part is played by the piston; it opens and closes the intake and exhaust ports. The absence of gas distribution mechanisms simplifies the power unit, making maintenance simple. The power of an installation that performs two cycles is considered higher, since its cyclicity is higher. However, without fully using the piston stroke, power losses during purging and exhaust gas residues reduce the power rating.
To make it easier to determine which engine is better, two-stroke or four-stroke, we present a brief description of both power plants in the form of a table:
| Four-stroke power plant | Two-stroke power plant |
| The working process is two revolutions of the crankshaft. | The working process is one revolution of the crankshaft. |
| Ignition of the working fluid occurs every time the second revolution is made, as a result, uneven distribution of the impulse and the use of a counterweight to eliminate beats. | The ignition of the working fluid occurs every time a revolution is made, as a result, a uniform distribution of momentum, the operation of the motor is better balanced. |
| The unit is heavy. | The unit is lightweight. |
| The complex design of the power plant, there is a gas distribution mechanism. | Simple design, no valves. |
| The unit is expensive. | The cost is lower than the four-stroke. |
| Complex devices and mechanisms lead to an underestimated mechanical efficiency. | The mechanical efficiency is higher than that of a four-stroke unit. |
| Complete removal of mining fumes, resulting in increased productivity. | The remnants of mining are mixed with new fuel, which is why engine performance is lower. |
| Operating temperature is lower. | The operating temperature of the engine is higher due to a violation of mixture formation. |
| Liquid cooling. | Air cooling. |
| Fuel consumption is lower. | The fuel consumption rate is increased, due to mixture formation and purging. |
| The dimensions of the power plant have been increased. | The dimensions of the power plant are below. |
| Requires the use of complex lubrication mechanisms. | The lubrication mechanism is simple. |
| The unit operates less noisily. | The unit operates with a lot of noise. |
| Valve timing mechanism. | The function of the gas distribution mechanism is performed by the piston and channels. |
| The heat utilization rate is efficient. | The heat utilization rate is not efficient. |
| Oil consumption is underestimated. | The oil consumption rate is overestimated, since part of the lubricant is thrown out with exhaust gases. |
It is advisable to use an engine that performs two strokes during operation in moments when fuel and lubrication savings are not at issue, but the dimensions and weight of the installation come first.
At the same time, the design of a two-stroke engine contains potential that cannot be realized in practice. The calculated indicator of power and efficiency in this unit is high; the difficulty in implementing it arises due to the subtlety of the settings. Perhaps in the near future, thanks to the use of electronic sensors and control and adjustment mechanisms, two-stroke units will be able to take a leading position in the automotive market.
