Diagram shown as a function of crank angle for a 2-stroke engine
The first figure shows a diagram of a typical indicated 2-stroke engine. We need not make a detailed description thereof will suffice to clarify some obscure points, examination of the corresponding path diagram as a function of angular displacement of the crank. This diagram illustrates the second figure.
Nor is there, in this case, correspondence between "time" and "race", for convenience of exposition we have matched the start of the two-stroke points that correspond, respectively, at the beginning of phase COMBUSTION , n at the start of the scanning phase.
A) First Half. Point 3 is performed on power load, and combustion takes place to give birth despuésa expansion. This continues until the piston, corresponding to point 5, opens the exhaust ports. As the cylinder pressure is still high, the exhaust phase begins spontaneously. Immediately thereafter, i.e. when the pressure has fallen to a value approximately equal to that prevailing in the feed line, opens into the inlet port 1 and the air, or the mixture, pushed by the pressure in crankcase or arising from a compressor enters the cylinder.
b) Second time. At this point begins the phase called scanning, which takes place through the PMI, and be open to the exhaust ports and intake takes place simultaneously and the exhaust gas entering the new load. Fresh gases expel combustion gases to take his place.
If the compression of the new charge is performed in the crankcase, the cylinder pressure continues to decrease during the scan, because the cylinder is in communication with the atmosphere and the pressure of power gradually decreases. When, on the contrary, the new load pressure is produced by a compressor, the pressure remains constant in both the intake duct and the cylinder. In some case, exhaust pipe rather long, the inertia of the column produces an exhaust suction of fresh gas in the end of the phase period. For this reason, when in 2 'closes the port admisióny practically ceases introduction of fresh gas, the exhaust can continue with loss of gas that is impossible to replace. Later we will see how in diesel engines this drawback is eliminated slowly taking calls scavenging valves arranged in the intake duct. The cylinder pressure remains almost constant until point 2'' also closes the exhaust port to start the compression phase. In the event that the fresh fluid is compressed in the crankcase, the piston before reaching the top dead center, the inlet check therein and the fluid required for the depression produced during the piston upstroke. The fluid is compressed in the crankcase during the first phase of the next Cerrera.
In the right figure, the rhea striped with purple represents useful work, and marked with blue passive work. We note that here not shown, as in the case of the 4-stroke engine, the intake work, because it forms part of the work expended in compressing the sump or fluid for operation the compressor.
Last review: February 1, 2016