There are two main types of engines: two-stroke and. In two-stroke engines, all work cycles (intake processes fuel mixture, exhaust gases, purge) occur during one revolution in two main cycles. Engines of this type do not have valves, their role is played by a piston, which, when moving, closes the inlet, outlet and purge windows. Therefore, they are simpler in design.
Power two-stroke engine at the same size cylinder and shaft speed is theoretically twice as high as a four-stroke due to a larger number of work cycles. However, the incomplete use of the piston stroke for expansion, the worst release of the cylinder from residual gases and the expenditure of a part of the generated power for blowing lead to an increase in power by only 60–70%.
The engine consists of a crankcase, in which is mounted on bearings on both sides crankshaft and cylinder. A piston moves inside the cylinder - a metal cup surrounded by spring rings (piston rings) embedded in grooves on the piston. Piston rings do not let the gases formed during the combustion of fuel in the gap between the piston and the cylinder walls. The piston is equipped with a metal rod - a pin, it connects the piston to the connecting rod. The connecting rod transfers the rectilinear reciprocating motion of the piston into rotational motion crankshaft.
Lubrication of all friction surfaces and bearings inside two-stroke engines occurs with the help of a fuel mixture in which required amount oils. The figure shows that the fuel mixture (blue) enters both the crank chamber of the engine (this is the cavity where the crankshaft is fixed and rotates) and the cylinder. There is no lubrication anywhere, and if there was, it was washed off with the fuel mixture. For this reason, oil is added in a certain proportion to gasoline. The type of oil used is special, specifically for two-stroke engines. It must withstand high temperatures and, when burned with fuel, leave a minimum of ash deposits.
Principle of operation. The entire working cycle in the engine is carried out in two cycles.
1. Compression stroke. The piston moves from the bottom dead center piston (in this position, the piston is at bottom dead center, hereinafter referred to as abbreviated BDC) to top dead piston point (hereinafter referred to as TDC), blocking first the purge and then the exhaust port. After the piston closes the outlet window in the cylinder, compression of the previously received combustible mixture. At the same time, in the crank chamber, due to its tightness and after the piston closes the purge windows, a vacuum is created under the piston, under the action of which a combustible mixture enters the crank chamber from the carburetor through the inlet window and the ajar valve.
2. Stroke stroke. When the piston is close to TDC, the compressed working mixture ignited by an electric spark from a candle, as a result of which the temperature and pressure of the gases increase sharply. Under the action of thermal expansion of gases, the piston moves to the NDC, while the expanding gases make useful work. At the same time, while descending, the piston creates a high pressure in the crank chamber (compressing air-fuel mixture in it). Under the influence of pressure, the valve closes, thus preventing the combustible mixture from entering again into intake manifold and then to the carburetor.
When the piston reaches the exhaust port, it opens and the exhaust gases are released into the atmosphere, the pressure in the cylinder decreases. With further movement, the piston opens the purge window and the combustible mixture compressed in the crank chamber enters through the channel, filling the cylinder and purging it from the remnants of exhaust gases.
Ignition principle. Since the fuel mixture needs time to ignite, a spark appears on the candle a little before the piston reaches TDC. Ideally, the faster the piston moves, the earlier the ignition should be, because the piston from the moment of the spark reaches TDC faster. There are mechanical and electronic devices that change the ignition angle depending on the engine speed. Practically for scooters up to 2000 onwards. there were no such systems and the ignition timing was set based on optimal speed.
Advantages of two-stroke engines:
No bulky lubrication and gas distribution systems
. High power in terms of 1 liter of working volume
. Easier and cheaper to manufacture
. Less weight
Disadvantages of two-stroke engines:
1. Greater fuel consumption. Recall that the approximate consumption can be calculated by the formula: for a two-stroke 300 grams per horsepower, for a four-stroke 200 grams.
2. Noise. On maximum speed 2-stroke engines tend to run a little louder than 4-stroke ones.
3. Comfort. they do not vibrate as much at low speeds (Applies only to two-cylinder engines. Single-cylinder and two- and four-stroke engines vibrate about the same) and do not smoke as much as two-stroke ones.
4. Durability. Pretty controversial point. There is an opinion that two-stroke engines are less durable. On the one hand, this is understandable, because the oil for lubricating the rubbing elements of the engine is supplied together with gasoline, which means it does not work as efficiently, unlike four-stroke engines, where the rubbing elements literally float in the oil. But on the other hand, a four-stroke engine is much more complicated in design than a competitor, it consists of a much larger number of parts, and the golden principle of mechanics “What easier themes more reliable” has not been canceled yet.
Part six: What's better?
On the previous pages we have tried to understand general principles work two- and four-stroke motors. Today we will try to approach the main thing, namely, to compare the advantages of each type of motor, of course, outboard. Therefore, fans of motorcycles and aircraft, please do not worry, as they have their own specifics.
If you look through all the catalogs, relevant literature and reference books, as well as dig a little into the theory, the following conclusions automatically arise: two-stroke outboard motors are lighter, have a smaller displacement and are more torquey. They are easier to transport (speech in this case for motors up to 40 hp. s.), and in repair they usually deliver less trouble.
Four stroke motors consume less fuel, while working emit less harmful substances and do not require constant oil consumption. These are generally accepted advantages and disadvantages. However, if you try to analyze some specific data, the picture is not so radical.
Here are the tables from which the more or less averaged difference between the "classical" two-stroke And four-stroke motors up to 40 hp s., which facilitates the choice of the type of motor (Tables 1–2). Let's try to understand everything carefully.
| Table 1. Characteristics of Yamaha motors | |||
|---|---|---|---|
| Model* | Weight, kg | ||
| "4 ACMHS" | 1/83 | 21 | 2.2 |
| "F4AMHS" | 1/112 | 22 | 1.6 |
| "8CMHS" | 2/165 | 27 | 4.5 |
| "F 8 CMHS" | 2/197 | 37 | 3.3 |
| "15 FMHS" | 2/246 | 36 | 7.3 |
| "F 15 CMHS" | 2/362 | 51.7 | 5.4 |
| "25 NMHOS" | 2/395 | 49 | 12.0 |
| "25 BMHS" | 2/496 | 53 | 10.7 |
| F 25 AMHS | 2/498 | 62 | 9.2 |
| "40 XWS" | 2/703 | 74.6 | 20.0 |
| "40 VEOS" | 3/698 | 74.5 | 18.5 |
| "F 40 BETS" | 3/747 | 86.1 | 15.0 |
| * Model brands with the letter F at the beginning refer to four-stroke engines, without a letter - to two-stroke ones. | |||
| Table 2. Characteristics of Tohatsu motors | |||
|---|---|---|---|
| Model* | Number of cylinders / displacement, cm³ | Weight, kg | Maximum fuel consumption, l/h |
| "M 3.5 B" | 1/74.6 | 13 | 1.7 |
| "MFS 3.5" | 1/85.5 | 17.5 | 1.12 |
| "M 9.8" | 2/169 | 25 | 5.1 |
| "MFS 9.8" | 2/209 | 37 | 4.9 |
| "M 18" | 2/294 | 41 | 8.5 |
| "MFS 18" | 2/328 | 52 | 5.7 |
| "M 30" | 2/429 | 52 | 15.0 |
| "MFS 30" | 2/526 | 71.5 | 10.4 |
| * M - two-stroke models, MFS - four-stroke models. | |||
Fuel consumption and weight. It is not correct to directly compare the values of the maximum consumption of Yamaha and Tohatsu engines, but the trend is clearly visible. The difference in displacement between some modern Yamaha four-stroke engines compared to their two-stroke counterparts is minimized. But this does not mean at all that volume ceases to be an advantage of two-stroke machines of this brand. In terms of weight, four-strokes are still heavier than two-strokes anyway. With Tohatsu, which has a more traditional design, these tendencies are more pronounced. The same is true for some motors with the Mercury logo, which are produced by Tohatsu.
As for fuel consumption, four-stroke engines are undoubtedly more economical than the “classic” two-stroke ones. A breakthrough in economy began with the advent of the Mercury OptiMax two-stroke, which has fuel and oil injection systems. Today, injection two-stroke engines have come close to four-stroke engines in this indicator, however, if you carefully analyze the results of fuel consumption measurements, it turns out that engines with OptiMax systems, and TLDI, and HPDI, and even with E-Tec are more economical only at medium crankshaft speeds. shaft. At the same time, the total fuel consumption is slightly (at different models differently) exceeds the consumption of some four-stroke counterparts. But we digress...
In theory, fuel consumption must be calculated each time for a specific case, since the same motor installed on different boats will show different speed. In other words, the declared maximum hourly fuel consumption, of course, will be unchanged, however, if you are interested in consumption in “liters per kilometers”, which is more common, then it will be different for different sets of “motor-boat-loading”. Those who need to cover long distances will appreciate the four-stroke engine, especially if it is not operated "in full throttle". True, it must be taken into account that its cost exceeds the cost of a two-stroke, and it will be possible to justify it in five or six years or more. This is where you think...
It should be noted that the new injection four-stroke engines equipped with “brains” turn out to be one third more economical than the “classic” two-stroke ones, that is, the gap between them and two-stroke engines in terms of fuel consumption becomes even more significant than that of carburetor versions.
So, two-stroke motors up to 40 hp. With. inclusive, lighter, have more torque at comparable crankshaft speeds (with the same displacement with a four-stroke), but less economical and more "dirty" than two-stroke. For motors of higher power, the picture is about the same, only everything is enlarged. The difference in fuel consumption “per lap” is approximately 15–30%, depending on the design of the engines, that is, there are more “gluttonous” and two-stroke and four-stroke engines.
If we compare the same motors of similar power “for acceleration”, then two-stroke motors are clearly “faster”. The difference in acceleration to 30 km / h for motors of low and medium power can reach 5–10% (in some cases, more). "Large" motors, especially those listed in the "sport" category, also spin up faster (sometimes more than 20%). In this case, do not confuse racing and sports: motors for racing, as a rule, pass special training and are not always suitable for "civilian" exploitation.
Now about what to choose? It is difficult to find a definite answer. For a number of reasons, someone prefers only two-stroke engines, while someone likes relative silence and rare refueling trips, which means four-stroke engines.
Noise. There is an opinion that two-stroke motors are very noisy, but this is true only when it comes to low and medium speeds. At maximum speed, four-stroke motors are noisy, if less, then by two or three decibels. But that's no reason to give up two stroke motor with good torque. Usually modern motors have "noise pressure" at maximum speed from 88 (very good) to 94 dB(A) (not too good). This is the noise measured in a meter from a running engine, usually on a fairly quiet boat. In fact, for the human ear, it is not so much the noise itself (total pressure) that is important, but its spectrum. Voiced noises are worse than low ones. Therefore, often a “quiet” motor is more tiring than a louder one. At low and medium speeds, four-stroke engines are usually quieter and have the “correct” noise spectrum.
Therefore, if a person plans to walk in the "about three-quarters of the gas" mode, then the four-stroke gets an advantage in this indicator. If for the most part the motor will work at a higher pace, then it makes no sense to acquire a four-stroke.
Autonomy. This is not the last factor influencing the choice of a motor, especially if it is destined to work in places remote from civilization. "Four strokes" can fill up less often, they need less oil. Owners of a four-stroke engine will also benefit in those cases when it is operated in the “track” mode. In this case, the consumption is low and, most importantly, there is no specific smell of “burnt oil”.
Weight. In most cases, the weight of a four-stroke motor is about 20% greater than that of a two-stroke of similar power. Obviously, not all boats will be able to "carry" an additional 20% of the weight. In this case, the alignment is disturbed, undesirable phenomena such as “dolphinism” occur, the level of safety decreases, etc. If the boat is designed for a 40 hp motor. and a load of, for example, 60 kg is allowed on the transom, then a motor weighing 80 kg is already too much. Sometimes even a difference of 10 kg can have a negative impact on handling on small boats (up to 4.5 m long).
Many sites may convince you that a four-stroke engine is better. In some articles you can read the opposite - they say, buy 2 cycles and forget about four altogether. But still, Which outboard motor better? We confidently intend to say that the best engine is the one that best suits your goals. For example, according to rumors and unverified data, since 2006, the sale of two-stroke engines has been banned in the EU and the USA due to increased environmental standards. But on the other hand, how many of you are going to the United States on a motorboat?
In general, unambiguously answer for you which outboard motor is better only you can. We, in turn, will try to most fully describe the comparison of two-stroke engines with four-stroke ones.
So, ecological norms and morality. Where is the truth, and where is the fiction?
Essence. Due to the design features in a two-stroke engine internal combustion, the oil that lubricates the crankshaft enters the combustion chamber. As planned by the designer, it burns there together with gasoline and the waste comes out as exhaust. The saddest thing for the environment is that not everything fits in with the plans of the designer. In fact, the injection of new fuel into the combustion chamber occurs almost simultaneously (with a small error) with the withdrawal of the spent mixture, which leads to the ingress of a certain amount of unburned or partially burned mixture into the exhaust. It is unlikely that this will lead to a mutation of tadpoles, but it is quite possible to toxic poisoning of the inhabitants of the reservoir. Although, to be honest, for quickly tangible effect pollution requires about one motorboat per square kilometer, which happens quite rarely.
Now for the rules and regulations. There are various rumors about the ban on two-stroke engines in the countries of the European Union and the USA. Some eyewitnesses say that only sales are prohibited in Finland, and everyone who managed to buy a two-stroke for themselves swims with it without bothering. Others say they saw two-strokes for sale in Germany, only the prices were too high. Presumably, these were two-stroke engines designed taking into account environmental standards. Hence the price and permission to sell. In general, how many countries, so many rules, and if you are going fishing in a particular country, then check it there. And if you want to go under the motor all over Europe, then buy four cycles. So far, no such laws have been adopted in Russia, which means that Russian Federation you can safely row in two cycles. If you think that environment you need to protect as much as possible, it is important for you what will be on the planet in five hundred years and think about how which outboard motor is better, then for you the answer is unambiguous: four cycles.
Another important aspect of the issue can be considered weight.
Every second cycle is a worker. In four-stroke, as you might guess, every fourth. That is, in theory it can be assumed that with the same combustion chamber, two-stroke engines are twice as powerful as four-stroke ones. Due to many shortcomings (for example, the ingress of an unused mixture into the exhaust and a used mixture into a fresh one), practice differs slightly from theory and in reality this figure is slightly lower - usually the difference is somewhere in 1.6-1.7 times. This means that in order to obtain the same power on the shaft (in principle, this is where it is most interesting to us), a two-stroke engine needs a smaller size than a four-stroke one. Smaller size equals less weight. That is, if, when solving a problem, which outboard motor is better Consider mass as the main parameter, then preference will strongly lean towards two-stroke.
Now, exactly, where does it matter? After all, it is quite possible that your boat is in the garage in the country and you do not care what weight the motor has. Let's look at this issue in more detail. Here the main thing to consider is what kind of boat you have and how far it is from the body of water most of the time.
If you have an inflatable boat and you go fishing in a jeep or in a passenger car with a trailer and constantly take off and put on the motor, then its weight will probably be a significant factor for you. If you have a hard hull boat and you can hang the motor on the transom forever, then what difference does it make to you how much it weighs?
The longer your boat, the less weight at the stern matters. Conversely, with a short boat, you will have to constantly additional load the bow as soon as you want to approach the motor.
If you have a large inflatable boat and you put, for example, 15 horses on it, then a difference of 20 kg will be noticeable - 30 kg can be hooked on the transom yourself with some effort, but 50 ... for this you need to swing in advance or call friends for help... If you are just fishing in quiet places and your motor has a mass of up to 20-25 kg, then you may not notice much difference when carrying. Here you yourself correlate your forces with the mass of the motor and decide which outboard motor is better just for your collection. If the PLA lives on the transom, then the weight does not matter.
Profitability. Myths and reality.
Let's start with the cost.
Due to the more complex design, the cost of four-stroke motors exceeds two-stroke counterparts. In some cases, this difference is only 10%, and in some cases even 50%. In any case, when calculating per horsepower, two cycles will be cheaper.
Fuel consumption.
At first glance, it may seem that four-stroke outboard motors consume less gasoline, oil and generally have a higher ratio useful action. What is there to hide, the way it is ... One of the main reasons is, of course, the ingress of unspent fuel into the exhaust. The second is provided by the design of a two-stroke engine initially - the oil not only lubricates, but also burns. I don’t know how in your reality, but in my cost good oil for an internal combustion engine outweighs the cost good gasoline several times. And the third more or less significant reason is the combination of the working cycle with the exhaust. In four-stroke engines, the spent mixture begins to be removed only after the cylinder head has dropped to its lowest position, and in two-stroke engines, about halfway through (plus or minus, depending on the specific model).
Now on business. When is it important? After all, for example, at races, no one thinks about economy - the main thing is to come first, and when traveling over long distances ... The truth is that if you go swimming only in July and then once a week, then, quite possibly, your grandchildren will pay off price difference. And if you think about it, which outboard motor is better for you, then fuel consumption will play an insignificant role. And if you earn your living by doing this and the outboard motor rests only when there is ice on the river, then you should seriously think about the cost of feeding your pet ...
Motor resource.
Rumor has it that a four-stroke will last much longer than its two-stroke counterpart. But, as they say, in reality, everything is not as it really is. Real position things is such that all these statements are too theorized. Let's say the declared motor resource of some engine is 2000 hours. In order to test this in practice, you need to ride a boat around the clock for the whole season. Or 3 seasons for 8 hours a day. Every day. No weekends or passes. Regardless weather conditions. And keep in mind that in order to compare, you need to check 2 outboard boat motors. Can you imagine the cost of such a check? And who can afford to spend a year of his life on this? I'm with full confidence I declare that not a single private person has been engaged in such a check and will not be. In practice, if such tests were carried out (which I personally doubt), then they were sponsored by the manufacturers of the PLA and, of course, biased in someone's favor. And if you consider that the engines will be repaired? How then to calculate the motor resource? Everyone knows that some grandpas ride motorcycles from the 70s, just replacing the cylinder head. What can be said about motor resources? In general, here we can say that data on the life of outboard motors are calculated only on paper (or on a computer) and may be far from reality, so it’s hard to say here which outboard motor is better.
Repair and service.
Engines of all makes and for all purposes can experience breakdowns from time to time. And everyone understands that the more expensive the engine, the more expensive the parts for it. For example, instead of fixing a Porsche, you can buy yourself a Zhiguli. It's the same with outboard motors - the cheaper the engine, the cheaper service and repair. If you live in St. Petersburg, then it will be easier for you to make tinctures, repairs, adjustments and other useful things with us and say here which outboard motor is better difficult. Contact our dealers and they will give you necessary information. If you are planning to do an engine overhaul. on your own or by the forces of acquaintances, then most likely you should buy a two-stroke - they are simpler, longer produced and there are more specialists on them. Some craftsmen can fine-tune their two bars right on the water ... But with four, things are more complicated. Although in any case, the initial setup is strongly recommended to be carried out in our workshop or with our master on the road.
Other nuances
Noise. At full speed, two-stroke engines scream louder than their four-stroke competitors. According to many users, at lower speeds, this difference is much less noticeable. And yet, if you are going to troll a shy fish, you should seriously think about extra decibels.
Smoke. Due to the presence of oil in the fuel mixture, two-stroke PLAs smoke noticeably more strongly. If you're using a motor to get from point A to point B, then smoke doesn't matter. And if one day you want to troll with a fair wind, then you will quickly decide for yourself which outboard motor is better. Unless, of course, weight and price play a key role.
Transportation. There is an opinion that outboard motors with a duty cycle of 4 strokes need to be transported only in certain positions, and two-stroke motors can be transported in any way. And this opinion is correct. A certain position of the PLA when transporting four-stroke engines is necessary so that oil does not flow out of the crankcase. Many two-stroke promoters use this as a strong selling point. In fact, I don’t remember that the owners of fours complained about such a trifle. In general, this is a problem in the minds, not in reality.
Oil mixing and non-mixing. Everyone knows that a mixture of gasoline and oil is fed into the combustion chamber of a two-stroke engine, and pure gasoline is fed into a four-stroke engine. And many, when thinking about the topic which outboard motor is better they begin to complain, they say, it is necessary to constantly mix the oil, and even in the right proportions ... The same trifle as transporting on its side from the previous paragraph. Any owner of two cycles knows very well that for running in the majority of LLMs, the proportions are 1 to 25, and when driving 1 to 50 (although some experienced ones recommend 1 to 25 when driving). Who can't divide a liter by 25? Or 50? For whom is it difficult to pour a stack of oil into a canister? Many people pick up a canister of gasoline at a gas station, pour oil in the same place, and by the time they reach the boat, it is mixed. On the waves, mixing continues and is maintained. And even now, most of the oils that are produced for these purposes are self-mixing ... In short, the owners of two-stroke engines do not complain about this.
Exit to planing mode. To enter planing mode, the first thing you need is the presence of an appropriate boat. If the boat was originally designed to sail in a displacement mode, then trying to bring it to gliding is tantamount to trying to bring an aircraft carrier to gliding. If you have a punt, then, depending on its deadrise, you will need about one horse under the hood for every 20-30 kg of total weight. Since the weight of the outboard motor is also included in the total, the lighter the motor, the less horses are needed. On the other hand, the lighter the engine, the less it produces the same horses. According to rough calculations, we can say that if you are the owner of a small vessel and are going to harness your carriage with five horses, then take two-stroke horses - they are lighter. If the question is about fifteen forces, or at least ten, then here the weight of the engine already plays an insignificant role and bother about which outboard motor is better not worth it.
If you have any questions about outboard motors, their selection, operation, maintenance, etc., feel free to contact our dealers. We will be glad to you
2285 ViewsThe era of internal combustion engines spans more than one century. If today the concept of "motor" is more than familiar to the ear, then back in the century before last, this technique was not known to anyone. And no matter how complicated the invention of the internal combustion engine may seem at first, in fact, the engine is quite primitive, and even a person who is far from automotive technology. Today we will consider the principle of operation of a two-stroke engine, study the diagrams of its operation and figure out what the physics of the processes occurring in it is.
Principle of operation
The invention of the simplest 2-stroke internal combustion engine dates back to the end of the 19th century. During the existence of such units, their design has undergone significant changes, has become more perfect and more reliable. However, the scheme of operation itself has not undergone significant changes, and the diagram describing both cycles looks the same as before.
Such a diagram describes the strokes, which are called intake and exhaust.
The intake stroke of a 2-stroke engine involves the supply of fresh fuel mixture from the carburetor to the cylinder. The second is the release of the spent mixture, which immediately enters the muffler, which reduces the noise effect and neutralizes some of the toxic emissions.
The lowest gas pressure in the piston, displayed at the beginning of the diagram, marks the first stroke of the 2-stroke internal combustion engine. During this period of time, the piston tends to its top dead center from the bottom. First, it is worth noting here the state of the piston outlet port, which at this moment is in the open state. The spent mixture is discharged towards the muffler. At this moment, the diagram shows sharp rise pressure, which soon reaches its peak.
It is logical that with a decrease in pressure in the upper chamber of a 2-stroke internal combustion engine, a strong vacuum occurs in the combustion chamber, which is displayed on the operation diagram as a sharp decrease in the initial pressure. The appearance of such a vacuum contributes to the fact that the mixture prepared by the carburetor tends from the area high pressure to the low region, which is a feature of this type.
As a result, the piston reaches its top point and the spark plug starts working. Here, the incoming fresh mixture is ignited, which makes it work to expand and give impetus to the piston, which immediately moves down.
However, on two-stroke motors such a system is not used so often because of its bulkiness and high cost. Most often on a two-stroke engine is installed air system cooling. So, the radiator blows a fan connected to the crankshaft by means of a belt drive. Also, when moving, the hot body is blown with the help of air flows coming through the system of deflectors.
Unfortunately, there are some disadvantages similar system: often the motor overheats, and in the heat you have to resort to certain tricks, which, however, do not completely solve the problem. The lack of indicator equipment does not always allow you to determine the problem by eye.
Summing up
A two-stroke engine is a primitive system that has good properties, and therefore is widely used in technology. Due to the small number of components and relatively simple principle work, self repair such units is not difficult and even a person who is far from technology and does not know all the intricacies of the operation of power units can do it.
On this moment There are two main types of internal combustion engines - two-stroke and four-stroke. In my own way appearance they are practically the same, but two-stroke engines work on a completely different principle. Let's try to figure out what are the main differences between these two ICE types and how a two-stroke engine works.
The principle of operation of the internal combustion engine
In order for your car to perform its direct function - to carry you, it needs to be refueled: gasoline, diesel, propane-butane. Through the fuel line, gasoline enters the engine, the main work in it is performed by pistons and crank mechanism. Gasoline mixes with air, a mixture is formed that explodes and sets the pistons in motion, this moment of movement is transmitted to the crankshaft, and from it to the transmission.
The difference between 2's and 4's stroke engines, as the name implies, consists in the number of cycles, that is, in the engine's duty cycle. The working cycle of any internal combustion engine is a sequence of such processes:
- filling the cylinder with a combustible mixture;
- its inflammation;
- expansion of gases;
- displacement of combustion products.
In a 4-stroke engine, this entire sequence is carried out in 4 cycles, that is, in two revolutions of the crankshaft, in a two-stroke engine, in one revolution. From this we can conclude that 2-stroke engines have more power, and this is true, not in vain because they are used not only for motorcycles, mopeds, various ATVs, snowmobiles and jet skis, but also to propel huge sea ships.
Theoretically, the power should be twice as high. For example, a small motorcycle engine can easily produce a hundred or more horsepower, while a much more massive and large engine of some B or C class car produces 70-100 hp.
Two-stroke engine device
The main advantage of two-stroke engines is the simplicity of their design. Since all processes of the working cycle are completed in one revolution of the crank, there is no need for a complex gas distribution mechanism that controls the movement of the intake and exhaust valves. Inlet valve closes and opens due to the pressure difference, and the exhaust gases exit through the exhaust port to the muffler.
Also, a 2-stroke engine is cooled by fuel, which is mixed with a certain percentage of oil. The oil must be selected exactly two-stroke, since it is adapted to high temperatures and when burned leaves less slag and ash.
The piston moves from bottom dead center to top dead center - BDC and TDC. During the upward movement, the piston compresses the incoming air-fuel mixture. At TDC, the mixture explodes and the piston begins to move down, at which point a new portion of the mixture enters. It turns out that the piston itself pushes out the exhaust gases, and this is the main drawback of two-stroke engines, affecting their efficiency.
Disadvantages of two-stroke engines
Despite the fact that engineers are trying to solve them, there are still drawbacks and they are significant.
The most important of them is the inefficient use of fuel and increased CO2 emissions.
If in four-stroke engines a separate cycle is allocated for the removal of exhaust gases and combustion products, then here this cycle is combined with filling the cylinder with a new portion of the combustible mixture, and no matter how hard the engineers try, it is not possible to avoid mixing it with exhaust gases.
In addition, it is necessary to constantly add oil to gasoline, and it is quite expensive and is consumed faster.
Because of these problems, engine power is also reduced. Theoretically, it should be twice as high as that of 4-stroke internal combustion engines, but in reality this figure does not exceed 50-70 percent. After 2000, many manufacturers abandoned two-stroke internal combustion engines. However, work to improve them is constantly underway.
Video of the principle of operation of this type engines.
