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Push-pull or four-stroke trimmer which is better?
Differences of a two-stroke engine from a four-stroke
The duty cycle of a gasoline engine (ICE) is a series of processes, as a result of which a portion of the force (power) acting on the crankshaft of the engine is made. The work cycle consists of:
- filling the cylinder with fuel consistency;
- its compression;
- ignition consistency;
- expansion of gases and cleaning of their cylinder.
The cycle in the internal combustion engine is the movement of the piston in one direction (up or down). For one revolution of the crankshaft two steps are performed. The one in which the expansion of the burnt gases occurs and the necessary work is performed is called the piston stroke.
Engines in which the duty cycle takes 2 cycles (one revolution of the crankshaft) are called two-stroke. Engines in which the duty cycle takes 4 cycles (two crankshaft revolutions) are called four-stroke. Two- and four-stroke engines can be both gasoline (carburetor) and diesel. What are the main operational and design features of gasoline two-stroke and four-stroke engines? What is the difference between push-pull and four-stroke? To better understand this, you need to familiarize yourself with the principle of their work.
The principle of operation of a two-stroke gasoline engine
During compression, the piston moves from bottom dead center to top. Push-pull or four-stroke? Which outboard motor is better what is two or. After the purge window (2) first closes, through which the fuel mixture enters the cylinder, and then the exhaust (3), through which the exhaust gases exit, compression of the air-gas mixture begins. At the same time, a vacuum is created in the crank chamber (1), which sucks the next portion of fuel from the carburetor. When the piston approaches the top dead center, the mixture ignites from the spark of the candle, and the resulting gases push the piston down, rotating the crankshaft and doing useful work.
In the crank chamber during operation, the pressure increases, compressing the fuel mixture that got there in the previous cycle. Upon reaching the upper surface of the piston (its sealing ring) of the exhaust window, the latter opens, releasing exhaust gases into the muffler. With further movement, the piston opens the purge window, and the fuel mixture under pressure in the crank chamber enters the cylinder, displacing the remaining exhaust gases (by purging) and filling the over-piston space. Which electric trimmer is best for a summer residence? that cut, push-pull or. When the piston moves to the bottom dead center, the duty cycle repeats.
>Operational and design differences of two-stroke and four-stroke gasoline engines >2T or 4T? Advantages and disadvantages.
Lecture on 2-and 4-stroke engines from the point of view of the consumer. Have questions? go to the forum
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In a two-stroke engine, the filling and cleaning of the cylinder is performed simultaneously with the compression and expansion strokes. while the piston is near bottom dead center. For this, there are two openings in the cylinder walls. an inlet or a purge and an outlet, through which the fuel mixture is inlet and exhaust gas is released. There is no gas distribution mechanism with valves in a two-stroke engine, which makes it much simpler and easier.
Video: Which Trimmer is Better Push-Pull or Four-Pull
Liter capacity. In contrast to the four-stroke engine, in which one stroke is accounted for two revolutions of the crankshaft, in the two-stroke stroke the stroke is made at each revolution of the crankshaft. This means that a 2-stroke engine should have (theoretically) twice as much liter capacity (the ratio of power to engine displacement) than a 4-stroke one. In practice, however, the excess is only 1.5-1.8 times. This is due to the incomplete use of the piston stroke during expansion, the worst mechanism for releasing the cylinder from exhaust gases, the waste of part of the power for purging, and other phenomena associated with the gas exchange features of 2-stroke engines.
Fuel consumption. Surpassing the four-stroke engine in liter and specific power, the two-stroke engine is inferior to it in efficiency. The exhaust gas is displaced in it by an air-fuel mixture entering the cylinder from the crank chamber. In this case, part of the fuel mixture enters the exhaust channels, moving away with the exhaust gases and not doing useful work.
Two methods of mixing oil with gasoline are used. Simple 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.
In the latter case, the engine has an oil tank, the pipeline of which is connected to a plunger pump, which supplies oil to the inlet pipe in exactly the amount required depending on the amount of air-gasoline mixture. Pump performance depends on the position of the "gas" supply knob. The more fuel is supplied, the more oil is supplied, and vice versa. Separate lubrication system of two-stroke engines is more advanced. With it, the ratio of oil to gasoline at low loads can reach 1: 200, which leads to a decrease in smoke, a decrease in the formation of soot and oil consumption. This system is used, for example, on modern scooters with two-stroke engines.
In a four-stroke engine, oil does not mix with gasoline, but is supplied separately. For this, the engines are equipped with a classic lubrication system consisting of an oil pump, a filter, valves, a pipe line. The role of the oil tank can be performed by the engine crankcase (lubrication system with a wet sump) or a separate tank (system with a dry sump).
When lubricating with a wet sump, pump 3 draws oil from the sump, pumps it into the outlet cavity and then feeds it through the channels to the crankshaft bearings, parts of the crank group and the gas distribution mechanism.
When lubricating with a “dry” sump, oil is poured into the tank, from where it is pumped to rubbing surfaces. That part of the oil that flows into the crankcase is pumped out by an additional pump, which returns it to the tank.
There is a filter for cleaning oil from products of wear of engine parts. If necessary, a cooling radiator is also installed, since during operation the oil temperature can rise to high temperatures.
Since oil burns out in two-stroke engines, but not in four-stroke engines, the requirements for its properties vary greatly. The oil used in two-stroke engines should leave a minimum of soot in the form of ash and soot, while the oil for four-stroke engines should ensure the stability of performance for as long as possible.
Comparison of the main parameters of two-stroke and four-stroke engines:
- Liter capacity. 2-stroke engines are 1.5-1.8 times higher than 4-stroke engines.
- Specific power (the ratio of power to engine mass). Also higher in 2-stroke.
- Fuel supply and cylinder cleaning. 4-stroke engines are equipped with a gas distribution mechanism, which is absent in 2-stroke engines.
- Profitability. Higher in 4-stroke, fuel consumption of which is about 20-30% lower than in 2-stroke.