Figure. 1. The gas dynamic scheme of the operation of the compression ring of the KAMAZ engine: 1-A CYLINDER 2-A PISTON; 3-A PISTON RING
Breaking through the gap between the piston 2 and the cylinder 1 into the upper piston groove, the working pressure presses the piston ring 3 to the lower shelve of the piston groove with the gas-dynamic force F0, and to the cylinder wall by the radial force Frad and the force of intrinsic elasticity F seal. The calculation of these forces was provided in the authors previous publications.
The most interesting can be seen in this calculation for one of the most popular domestic engines of VAZ-2190, with the following parameters: the maximum pressure of the working gases in the cylinder when the piston is at top dead center, is about Pwork = 80 kg / cm2. The dimensions are in centimetres for convenience of calculations. Diameter of the cylinder is 82 mm = 8.2 cm; the outer radius r1 is 41 mm = 4.1 cm; the inner radius is r238 mm = 3.8 cm; the radial thickness of the ring t = 3.0 mm = 0.3 cm; the height of the upper compression ring h = 1.5 mm = 0.15 cm.
The area of the upper butt is defined by the formula:
S1 = π (r12-r22) = 3.14 (4.123.82) = 3.14 (16.8114.44) = 7.44 cm2.
The area of the inner vertical surface is defined by the formula: S2 = 2 πr2h = 6.28 × 3.8 × 0.15 = 3.58 cm2.
Multiplying the pressure of the working gases by the area values, we get:
Fo = Pwork × S1 = 80 × 7.44 = 595.2 kgf (5.95 kN);
Frad = Pwork × S2 = 80 × 3.58 = 286.4 kgf (2.86 kN).
The conclusion is obvious from the comparison of these two gas-dynamic forces acting on the movable piston ring. Twice the superior axial force reliably pressed the piston ring to the lower flange of the piston groove, depriving the radial force of the working surface of the piston ring from being pressed against the wall of the cylinder.
That is very important to note here. This pattern is observed in all cases where there is an excessive pressure on the piston. About this and not only, we will consider on the different steps of the engine motoring run. But now, running ahead, we can safely predict:
The gas dynamic scheme fundamentally changed the strategy and tactics, the theory and practice of designing internal combustion engines and piston compressors. It optimizes the size, shape and content of the engine and compressor and is reflected in the increase in the efficiency of both with its correct application in calculations.
All justifications are given in the authors work and in this manual. The information were published and patented, brought to the attention of scientists and specialists of the motors. However, producers continue to produce super modern cars equipped with the engines with such significant defects. Lets try again, to spell out in more detail the problem of increasing the efficiency of the internal combustion engines, which is not so difficult to understand, but very important for specialists.
§2. The gas dynamics at the different cycles of the engine operating cycle
The work of (that is most widespread among autotractor internal combustion engines (diameters of cylinders up to 140 mm)), the four-stroke engine consists in effective implementation of all 4 steps of an operating cycle:
admission of a fresh air charge;
compression of the task environment above the piston;
the piston working stroke transforming the huge pressure of working gases to the mechanical work;
release of spent working gases and residues, of the combustion products.
We will consider each of them in the form of a separate project, with its differences and peculiarities. But, as a result, integrated in the integral design of efficient use of the engine.
The working stroke admission (suction) in the cylinder of the engine, or compressor, the estimated amount of fresh air charge.
The task of developers of any constructive element are: define the shape and size of the product, and select the workpiece material based on the conditions in which the element will work. This is a very important stage of the design, from which much will depend on the work of the product. As the initial data, developers only know one size the diameter of the cylinder.
The principal drawback of many domestic designs (including ICE) is that the designers in their calculations take the safety factor not 1.10 or 1.20, as it should be, but 1.50 or 2.0, sometimes more than that. How important this is to the economy are known to most professionals. In the case of mass production, which we are considering, this is simply unacceptable.
Proceeding from the purpose of the working stroke admission, it is necessary to remember, than consolidation between the piston and the cylinder is more reliable, excluding any suction from the crankcase, the extent of discharge of space over the piston is more, the more actively there is a filling of the cylinder with rated quantity of an atmospheric air.
At the beginning of the movement of the piston in the lower position, taking into account the huge speed of displacement of the piston, above it and, accordingly, in the upper piston groove, a certain discharged space is formed. Admission is the only step of an engine motoring run to which influence of the gas dynamic scheme presented on fig. 1 doesnt extend. On this step the gas dynamics is neutral therefore it is possible to approach on other design of pressure rings, proceeding only from the tasks imputed to a step admission.
Making rather difficult calculation of elastic forces of the piston rings, developers shouldnt forget that on all steps of an engine motoring run the sealing (compression) piston ring has to carry out two main task and one compulsory condition:
to condense space between the piston and the cylinder, to provide transfer of heat from a superheated piston crown to the cooled cylinder, at minimum possible mechanical losses on friction.
For the piston ring, which is pressed to the lower flange of the piston groove with the previous stroke, the admission is the relaxation time, one moment. For example, with a piston stroke of 80 mm and a crankshaft rotation speed of 3000 min -1, the piston travel speed is 6 m / s, on the Formula 1 engines the average piston speed is 22.5 m / s. For an extremely short period of time, the piston ring should assume its natural position relative to the piston groove and cylinder wall. The technologists, on this occasion, have the expression: the piston ring shall be installed on the cylinder wall. In the process of moving to the lower dead point by friction of the ring surface of the cylinder, it is shifted to the top flange of the piston groove and is pressed to the cylinder wall with its own elasticity of the ring.
In this case it is worth using the recommendation of the domestic scientist Orlin A.S, therefore, we can take the recommended value of ring pressure on the cylinder walls 0,05 0,3 MPa (0,5 3 kg / cm2) and more [6]. As studies have shown, the expression of the scientist gases are pressed the ring against the wall of the cylinder is not entirely correct with respect to modern piston rings, because they do not correspond to reality. It turns out that they lost their elasticity and were pressed against the lower flange of the piston groove with the superior gas-dynamic force F0.