How a 4 stroke gasoline engine works. Four-stroke engine: the invention of the century

The principle of operation of 2 and 4-stroke engines

Before saying which engine is better, consider the design of engines.

The stroke of the internal combustion engine cycle is the stroke of the piston from one dead center to another. One stroke corresponds to a 180-degree rotation (half-turn) of the crankshaft. With a 4-stroke process, the working cycle is carried out in two revolutions of the shaft, with a 2-stroke process - in one.

The same 4 cycles are present: intake - compression - expansion - release. First, the intake valve opens, the piston goes down, under the action of the resulting vacuum, a fresh air-fuel mixture or air enters the cylinder - this is the intake stroke. Then the valve closes, the piston goes up - compression occurs. The next stroke: the compressed mixture is ignited by a spark, the piston goes down under the influence of this - this is an expansion, or a working stroke of the piston. The engine does useful work during the expansion cycle. Then the piston goes up, the exhaust valve opens, through which the combustion products of the fuel go into the atmosphere - this is the exhaust stroke.

In the case of a two-stroke process, things are no longer so simple. The cycles are conditionally called compression and expansion. As you can see, there was no place for separate intake and exhaust strokes. This is no coincidence. Although there are intake and exhaust processes in a two-stroke engine, for their implementation it is necessary that the pressure at the inlet to the cylinder be above atmospheric. That is, a forced boost is needed. Those who are familiar with two-stroke motorcycle gasoline engines may argue that there are no turbo or mechanical compressors on motorcycles. There really is no separate compressor in a two-stroke motorcycle. The compressor function is assigned to the engine crankcase.

In simple motorcycle engines, there are no valves in the cylinder head, instead there are inlet and outlet ports in the cylinder walls, blocked by the piston body. The inlet windows are connected to the carburetor not directly, but through bypass channels that open into the crankcase. During the upward stroke of the piston, the lower edge opens the window on which the carburetor is located, the working mixture, under the action of the vacuum created by the upward piston, rushes into the crankcase. When the piston goes down, it closes this window, the working mixture begins to compress. The piston goes further down, opening the bypass windows, the working mixture is supplied under pressure to the cylinder, where it displaces the exhaust gases into the exhaust window. The piston goes up again, and the processes under its bottom are repeated, and at this time the working mixture is compressed in the cylinder. The compressed mixture is then ignited by the spark plug and the piston moves down on its expansion stroke, or power stroke.

The 2-stroke motor responds more quickly to the throttle. In 4-stroke cycles, the piston needs to make 2 full revolutions to complete a full cycle, while in 2-stroke cycles, only one.

Push-Pull Drawbacks

1. Greater fuel consumption. Recall that the approximate consumption can be calculated by the formula: for 2 cycles 300 grams per horsepower for 4 cycles 200 grams.

2. Noisy. At maximum speed, 2-stroke engines tend to run a little louder than 4-stroke engines.

3. Comfort. 4-stroke engines do not vibrate as much at low speeds (Only applies to two-cylinder engines. Single-cylinder and 2-stroke and 4-stroke engines vibrate about the same) and do not smoke as much as 2-stroke engines. Smoke is an important point, especially if you like to troll.

4. Durability. Pretty controversial point. There is an opinion that 2-stroke motors 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 4-stroke engines, where the rubbing elements literally float in the oil. But on the other hand, a 4-stroke engine is much more complicated in design than a competitor, it consists of a much larger number of parts, and no one has yet canceled the golden principle of mechanics "The simpler the more reliable".

And again, but in more detail:

What is the difference between 2T and 4T engines?

Let's start with the principle of operation. Any internal combustion engine has a piston that turns the crankshaft (and ultimately the wheels) through the connecting rod, driven by the energy of combustion of fuel vapor mixed with air (combustible mixture).

In a 2T engine, the process of filling the cylinder with a fresh combustible mixture, compressing it, igniting it, power stroke (when the combustion energy forces the piston down, rotating the crankshaft) and exhaust gases is released in two cycles.

First beat. The piston goes up, compressing the fuel mixture. The combustible mixture ignites. Second cycle, working stroke. The expanding gases push the piston down. When it is at the bottom, it opens the exhaust and intake ports in the cylinder walls. Exhaust gases go into the muffler, their place is taken by a fresh fuel mixture and the first cycle is repeated. All this happens in one revolution of the crankshaft.

In a 4T engine, the process of filling the cylinder with a fresh combustible mixture, compressing it, igniting it, running it and exhausting it takes four cycles.

First stroke, inlet. The piston goes down, the intake valve opens, and the fuel mixture enters the cylinder. When the piston reaches the bottom position, the intake valve closes.

Second measure, compression. The piston goes up, both valves are closed, the fuel mixture is compressed. When the piston is at the top, the spark plug ignites the combustible mixture.

Third cycle, working stroke (expansion). The hot gases expand rapidly, pushing the piston down (both valves closed).

Fourth measure, release. By inertia, the crankshaft continues its rotation (for uniform rotation, weights are installed on the crankshaft - crankshaft cheeks), the piston goes up. At the same time, the exhaust valve opens and the exhaust gases exit into the exhaust pipe. In the upper position of the piston, the exhaust valve closes. These 4 cycles occur in two revolutions of the crankshaft.

They say that a two-stroke engine is more powerful and a scooter with it is more dynamic. It's right?

Yes. 2T engine for two turns of the crankshaft manages to use the energy of fuel combustion twice. Many believe that it is twice as powerful as a 4T engine. But pay attention, in a 2T engine, part of the cylinder is occupied by intake and exhaust windows, which means that the amount of fuel that will then burn out is less in volume than in a 4T engine, where the cylinder is one-piece. In the 2T engine, due to the simplicity of the design, the crankshaft is lubricated with oil added to gasoline. Oil in the working mixture reduces the energy released (oil burns worse). Due to the peculiarities of the intake-exhaust of the combustible mixture and exhaust gases in the 2T engine, more of the combustible mixture "flies into the pipe" without burning. In a 4T engine, this process is minimal due to a more complex intake-exhaust mechanism. As a result, 2T engines are indeed more powerful (but not twice as much), but their higher power is achieved in a narrower operating range of crankshaft speeds (that is, you start from a standstill, the scooter barely accelerates, then the so-called “pick up” occurs. ”, the scooter “shoots”, but quickly fades) and you will have to maintain a certain engine speed all the time for a dynamic ride. As you understand, the more powerful the 2T engine, the narrower the rev range, the finer the settings and the more expensive the engine. Either athletes (where it is more important to squeeze everything out now) or owners of chainsaws and lawn mowers (which are simpler and cheaper, the better) can enjoy the full benefits of a 2T engine. If you want to improve the dynamic performance of your scooter, you can install a kit to increase the engine displacement up to 70 cc. After the rework, your scooter will not yield to the 2T model and there will be more riding pleasure.

4T engine is less powerful, so it’s not interesting to ride such a scooter?

It follows from the previous answer that even a slightly less powerful 4T engine has a more favorable characteristic - it is "elastic". Immediately from the start of the movement, it will provide the scooter with “locomotive traction”, that is, you pick up speed smoothly and confidently without “dips” and “pickups”, and a confident set of speed will be available to you throughout the entire range of crankshaft speeds. The lack of power will affect only in the upper operating range of engine speeds, that is, when you "spit" at the limit. Just close to this driving mode, the 2T engine will produce maximum power. Tell me, how long will the equipment operated at the limit of its capabilities last? You do not feel sorry for the money for unscheduled repairs?

Is the 4T engine more reliable?

Undoubtedly.

In a 2T engine, the piston, piston rings and cylinder are actually consumables due to the design features - there are holes in the cylinder. Many scooters roll a 2T engine piston in a season, and a cylinder in two. In a 4T engine, you will forget about it. 4-5 seasons on one piston 4T engine is the norm.

Due to better lubrication (oil is supplied to critical parts not mixed with gasoline, but by spraying or supplying under pressure), a 4T engine is designed for a longer service life. A more complex valve mechanism for the intake and exhaust of gases works more clearly, requires simple and infrequent maintenance.

Is a 4T engine more economical?

Certainly. A 50cc 2T model with decent performance (power 4-5 hp), consumes 3.5 liters of gasoline per 100 km. Plus oil. A 4T engine with a power of 3 hp. "eat" 2.2 liters. gasoline. Oil is not consumed at all.

Not only the speed of emptying your wallet depends on this, but also the mileage at one gas station. Since the scooter tanks are about the same, a 6 liter tank is enough for you to drive 100 km more on a 4T scooter without stopping.

Who would you recommend to buy such a scooter?

First of all, those who will go to the country, to the forest and through the fields for walking and fishing, in the city to work at rush hour. The scooter will give you the opportunity to feel free. For a teenager, this is a toy that is the first step in mastering the world of two-wheeled vehicles and the pleasures that this promises. In any case, it is better to start with reliable, economical and inexpensive equipment, so that the joy of owning a scooter is not overshadowed by a high price, frequent repairs, and high gas costs.

The 4 stroke engine is a reciprocating internal combustion engine. In these units, the working process of all cylinders takes two crankshaft circuits. The two circuits of the crankshaft can also be described as four piston strokes, hence the name four-stroke engine.

Since the middle of the twentieth century, the four-stroke engine has been the most common type of reciprocating internal combustion engine.

Main characteristics of 4 stroke engine

1. The exchange of gases occurs due to the movement of the working piston;
2. 4-stroke engine has a gas distribution mechanism that allows you to switch the cylinder cavity to intake and exhaust;
3. The exchange of gases occurs at the moment of a separate half-turn of the crankshaft;
4. Chain, belt drive and gear reducers allow you to change the timing of ignition, gasoline injection and timing gear relative to the frequency of rotation of the crankshaft.

Story

Approximately 1854-1857, the Italians Eugenio Barsanti and Felicce Matozzi created a device that, according to existing information, looked like a 4-stroke engine. Despite this, the 4-stroke motor was patented only in 1861 by Alfon de Rocher, as the invention of the Italians was lost.

The first workable 4-stroke engine was created by the German engineer Nikolaus Otto, after whom the four-stroke cycle was called the Otto cycle, and the 4-stroke engine using spark plugs was called the Otto engine.

4 stroke engine working principle

In a two-stroke engine, lubrication of the crankshaft, cylinder and piston pins, crankshaft bearing, piston and compression rings occurs by pouring oil into. A 4-stroke engine is distinguished by the fact that in it the crankshaft is located in an oil bath. Due to this feature, there is simply no need to add oil or mix fuel. All the owner of the vehicle needs to do is fill the fuel tank with gasoline, after which you can continue to use the vehicle.

Thus, the car owner does not need to purchase special oil, which is necessary for the operation of two-stroke engines. In addition, the 4-stroke engine is distinguished by a reduced amount of carbon deposits on the muffler walls and piston mirror. Another important difference is that with a two-stroke engine, a combustible mixture splashes into the exhaust pipe - this is due to its design.

Admittedly, four-stroke engines also have some minor drawbacks. For example, such engines have an increased duration of starting the scooter from a standstill. Also, the work on the thermal gap is not particularly high quality. At the same time, it should be noted that the problem with the increased duration of the start of the scooter can be solved by optimizing the centrifugal clutch and transmission options.

Unit design

The device of a 4-stroke engine looks like this: the camshaft is located in the cylinder cover and is driven by a drive wheel mounted on the crankshaft. In a 4-stroke engine, the camshaft is able to open and close the intake and exhaust valves, but only one of them, and which one specifically, depends on the location of the piston. In addition, cams are located on the camshaft, with the help of which the rocker arms are actuated.

After their operation, the rocker arms begin to act on one of the two valves, which leads to its opening. It is worth noting that there should be a narrow gap between the valve and the adjusting screw (it is also called a thermal gap) - during heating, the metal expands, so if there is no or too small a gap, the valves will not be able to completely close the intake and exhaust channels. The clearance at the exhaust valve must be larger than that of the intake valve, since the exhaust gases are hotter than the combustible mixture, and, accordingly, this causes the exhaust valve to heat up more than the intake valve.

That's all the description of the 4-stroke engine device.

4 stroke engine operation

As already mentioned, the operation of a 4-stroke engine consists of two revolutions of the crankshaft, or, one might say, four piston strokes.

The operation of a 4-stroke engine is as follows:

1. (inlet). The piston moves down, which causes the intake valve to open. As a result, the combustible mixture ends up in the cylinder, where it enters from the carburetor. When the piston reaches the bottom position, the intake valve closes.
2. (compression). The piston moves to the top side, which provokes compression of the combustible mixture. After the piston approaches top dead center, the gasoline compressed by the piston ignites.
3. (extension). Gasoline ignites, as a result of which it burns out - this leads to stretching of combustible gases and, accordingly, to the piston moving down (two valves are closed).
4. (release). By inertia, the crankshaft continues to rotate around its axis, and the piston moves up. At the same time, the exhaust valve opens, from where the exhaust gases enter the pipe. When the piston reaches top dead center, the intake valve closes.

At the end 4 stroke engine operation four measures are repeated.

Functioning of a two-stroke unit

Although the article is not about this, it is worth briefly describing the functioning of a two-stroke engine in order to compare them. As the name implies, the operation of such a motor takes place only after two cycles.

1. The piston moves up, which leads to compression of the combustible mixture, after which (without reaching the top dead center) it ignites. When the piston reaches top dead center, the intake windows in the cylinder wall open, due to which the combustible mixture flows into the crank chamber.
2. Under the action of expanding gases, the piston moves downward. Being in the lower position, the piston opens the intake and exhaust windows. Gases enter the exhaust pipe, and in their place is a combustible mixture.

In the 18th century, many inventors worked on the creation of power units that could replace the steam engine. The appearance of devices in which the fuel would burn not in the furnace, but directly in the engine cylinder became possible after the French inventor Philippe Lebon discovered lighting gas in 1799. Two years later, he also designed a gas power unit, where the gas-air mixture was ignited in the cylinder. It had 1 double-acting working cylinder (combustion chambers were located on both sides of the piston, and the working mixture in them was ignited alternately). And only many years later, a more advanced four-stroke engine appeared, which was widely used in many industries.

For the first time such an engine was demonstrated by the German engineer August Otto in 1877. This happened after the Belgian inventor Jean Etienne Lenoir proposed to ignite the combustible mixture with an electric spark. Contributed to its appearance and the invention of a device that allows you to evaporate liquid fuel and ensure the preparation of a working gas-air mixture (carburetor).

Serial production of four-stroke gasoline engines began in 1883. Then the German engineer Gottlieb Daimler proposed to use red-hot tubes inserted inside the cylinders to ignite the gas-air mixture.

Operating procedure

4-stroke internal combustion engine is by far the most common power unit. It functions using the so-called Otto cycle, consisting of four consecutive cycles.

A stroke is one complete piston stroke during which the crankshaft makes two revolutions in the clockwise direction.

The operation of a 4-stroke power unit is easiest to describe by referring to the simplest design, consisting of:

1. the actual cylinder;
2. piston
3. two valves (inlet and outlet);
4. spark plug;
5. crankshaft;
6. connecting rod.

The classic internal combustion engine differs from such a mechanism only in a large number of cylinders, the operation of which is synchronized in a certain way.

In the simplest single-cylinder internal combustion engine, the following are sequentially carried out:

• 1 stroke: intake or suction.

It all starts with the piston at its highest position (top dead center). And the crankshaft makes a half turn (0-180 degrees), pushing the piston to the bottom position (bottom dead center).

Due to this action, a vacuum is created in the upper region of the cylinder and the intake valve opens. It becomes fully open at the time when the piston reaches the bottom level. Due to the resulting rarefaction, a portion of the combustible mixture (air + gasoline vapor) is sucked into the cylinder. When the combustible mixture is mixed with the combustion products from the previous cycle, a working mixture is formed in the cylinder.

Note: in a diesel engine, the combustible mixture is formed directly in the cylinder. First, a portion of air is sucked in, which during the compression process is heated to ignition temperature, and then, before the piston reaches its upper position, a droplet-like liquid fuel is injected. The combustion process occurs only during fuel injection.

• 2nd bar: compression or compression

It starts when the piston moves up from the lower level to the upper one. At this time, the crankshaft again rotates ½ turn (180-360 degrees).

At the same time, the intake and exhaust valves are closed, due to which the working mixture begins to compress.

In this stroke, the pressure and temperature in the cylinder rise to approximately 1.8 MPa and 600 ° C, respectively.

• 3rd cycle: extensions or working stroke

At the moment when the maximum compression value is reached, the spark plug is turned on, from the spark of which the working mixture ignites and burns out. In this stroke, the temperature and pressure in the cylinder reach 2500 ° C and 5 MPa. The increased temperature and pressure cause the piston to move down. And the connecting rod, which connects the piston and the crankshaft, tells the latter a rotational action, and it makes the next ½ turn.

It is in this cycle that thermal energy is converted into mechanical energy, and useful work is carried out. Next, the exhaust valve opens due to the fact that the piston moves down, which ensures that the exhaust gas is removed. When the piston reaches the lowest level, the valve is maximally open. A drop in pressure to 0.65 MPa is accompanied by a decrease in temperature to 1200 C°.

• 4 beat: release

The piston is at the bottom level and under the influence of the rotation of the crankshaft (180-360 degrees) moves up, pushing the exhaust gas through the open exhaust valve.

As a result, the temperature in the cylinder drops to 500 ° C, and the piston is in the upper position. Since it is not possible to get rid of the exhaust gases at all, the residual pressure in the cylinder is kept at the level of 0.1 MPa, and the remaining gas takes part in the next cycle.

The operation of the engine occurs due to the repeated repetition of the 4-stroke cycle.

Design

Today, 4-stroke engines are more complex in design. For example:

• the crankshaft is equipped with a massive flywheel, which ensures smooth movement of the pistons due to inertia;
• the cylinder block is equipped with a gas distribution mechanism;
• the engine is started using a starter;
• the trouble-free functioning of all units is ensured by numerous auxiliary devices (control systems, lubrication, fuel injection, cooling, etc.).

Where applicable

4-stroke motors are used in our daily life very widely. Their power directly depends on the volume and number of cylinders.
They install internal combustion engines in cars and airplanes, tractors and diesel locomotives. They are also used on ships of the sea and river fleet.

Power engineers also paid attention to 4-stroke power units. They are used to power stationary and emergency power generators installed in places where it is impossible or not economically feasible to bring power lines. In addition, such generators are installed at facilities where it is impossible to turn off the power supply (hospitals, banks, military units, etc.).

When buying a new scooter, people often ask questions like " Which is better 2 stroke or 4 stroke". There is no single answer to this question. Each motorist will find both disadvantages and advantages in both types of engines. To figure it out for yourself which scooter is better 2 stroke or 4 stroke, you should first find out What is the difference between 2 stroke and 4 stroke engine.

The difference between a two-stroke and a four-stroke

Main differences between two-stroke and four-stroke engines is due to the difference in their gas exchange devices - the supply of a fuel-air mixture to the cylinder and the removal of exhaust gases. IN 4t engine the processes of cleaning and filling the cylinder are carried out using a special gas distribution mechanism (GRM), which closes and opens the intake and exhaust valves at a specific time in the working cycle. IN engine 2t filling and cleaning of the cylinder are carried out in parallel with the compression and expansion strokes - at a time when the piston is located near BDC (bottom dead center). To do this, there are two holes in the walls of the cylinder - inlet (purge) and outlet, through which the fuel mixture is supplied and the exhaust gases are released. The two-stroke engine does not have a valve timing mechanism, which makes it much lighter and simpler.

Which engine is more powerful 2 stroke or 4 stroke

Unlike a 4 ton engine, in which one stroke occurs for two revolutions of the crankshaft, in a 2 ton engine, a stroke occurs with each revolution of the crankshaft. This means that a two-stroke engine must have (in theory) twice as much liter capacity (the ratio of power to engine volume) as a four-stroke. But in practice, the predominance is only 1.5 - 1.8 times. This happens due to inadequate use of the piston stroke during expansion, the worst mechanism for ridding the cylinder of exhaust gases, the cost of a share of power for scavenging and other phenomena associated with the distinctive features of gas exchange in 2-stroke engines.

Fuel consumption 2t and 4t

Surpassing the four-stroke engine in liter and power density, two stroke engine inferior to him in economy. The expulsion of exhaust gases is carried out in it by a fuel-air mixture arriving in the cylinder from the crank chamber. In this case, part of the fuel mixture ends up in the exhaust channels, being removed together with the exhaust gases and not producing useful work.

Grease 4 t and 2 t

Two-stroke and four-stroke engines have a different design and principle of operation of the engine lubrication system. In 2-stroke scooters, it is carried out by mixing engine oil with fuel in established proportions (usually 1:25 ... 1:50). The fuel-air-oil mixture, circulating in the crank and piston chambers, lubricates the connecting rod and crankshaft bearings, as well as the cylinder mirror. When the fuel mixture ignites, the oil burns together with gasoline. The products of its combustion are removed together with the exhaust gases.

There are 2 methods of mixing oil with gasoline. Conventional mixing before pouring fuel into the tank and a separate supply, in which the fuel-oil mixture is formed in the inlet pipe located between the carburetor and the cylinder.

Separate lubrication system for two-stroke engine

1. oil tank
2. carburetor
3. throttle cable separator
4. throttle stick
5. oil control cable
6. plunger dosing pump
7. oil inlet hose

All modern 2t scooters use separate oil supply(we fill in 2t oil separately from gasoline). IN two stroke scooter the engine has an oil tank, the pipeline of which is connected to an oil pump that supplies oil to the inlet pipe in the amount that is necessary depending on the amount of air-gasoline mixture. The productivity of the pump depends on the position of the "gas" knob. The more fuel is supplied, the more oil is supplied, and vice versa. A separate lubrication system for two-stroke engines is considered more flawless. With it, the ratio of oil to gasoline at light loads can reach 1:200, which leads to a reduction in smoke, a decrease in carbon deposits and oil consumption. This design is used on modern scooters with two-stroke engines.

In a four stroke engine oil does not mix with fuel and served separately. To do this, the engines are equipped with a traditional lubrication system consisting of an oil pump, filter, valves, pipelines. The role of the oil tank can be performed by the engine crankcase (wet sump lubrication system) or a separate tank (dry sump system).

Lubrication system of a four-stroke engine with a wet and dry sump

1. sump
2. oil intake
3. oil pump
4. oil filter
5. safety valve

When lubricating with a “wet” crankcase, pump 3 takes oil from the sump, pumps it into the outlet cavity and then delivers it through the channels to the crankshaft bearings, crankshaft and timing parts. When lubricating with a “dry” sump, oil is poured into the tank, from where it is pumped to the rubbing planes. That part of the oil that flows into the crankcase is pumped out by an auxiliary pump, which gives it back to the reservoir. There is a filter to clean the oil from wear products of engine parts. If necessary, a cooling radiator is also installed, since during operation the oil temperature can rise to high temperatures.

What is the difference between 2-stroke oil and 4-stroke oil?

Since oil burns in 2t engines, but not in 4t engines, the requirements for its properties vary greatly. Oil used in 2-stroke engines must leave a minimum amount of carbon deposits in the form of ash and soot, while oil for 4t engines must guarantee stable performance for as long as possible.

Along with simpler 2-stroke motors, there are 4-stroke outboard motors. This advanced development has brought this class of engines to a qualitatively new level, solving a number of problems and providing the units with the best productivity indicators.

Four stroke outboard motor

The main advantages of the device include:

• The improved design of the new generation, verified to the smallest detail.
• Truly economical consumption of both fuel and oil.
• The silence of work.
• Ability to operate at ultra-low speeds. Boat motor 4-stroke perfect for fishing in places of pike ambush, for example.
• No harmful emissions into the environment (i.e. environmental friendliness).

Our catalog contains high-quality 4-stroke outboard motors with power from 2.5 to 350 l / s, the largest manufacturers in Japan and China. Both simpler models and functional devices with reverse gear, self-diagnosis, intelligent control system, etc. are available.

All goods are certified, have passports and warranty cards. We offer convenient terms of payment and delivery. We provide personalized customer service. Request a callback to get a manager's advice.