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The net work produced is also represented by the area enclosed by the cycle on the p–V diagram. The net work is produced per cycle and is also called the useful work, as it can be turned to other useful types of energy and propel a vehicle (kinetic energy) or produce electrical energy. The summation of many such cycles per unit of time is ...
The net work equals the area inside because it is (a) the Riemann sum of work done on the substance due to expansion, minus (b) the work done to re-compress. Because the net variation in state properties during a thermodynamic cycle is zero, it forms a closed loop on a P-V diagram .
The efficiency of the Diesel cycle is dependent on r and γ like the Otto cycle, and also by the cutoff ratio, r c, which is the ratio of the cylinder volume at the beginning and end of the combustion process: [4] = () The Diesel cycle is less efficient than the Otto cycle when using the same compression ratio.
A key feature of the diagram is that the amount of energy expended or received by the system as work can be measured because the net work is represented by the area enclosed by the four lines. In the figure, the processes 1-2-3 produce a work output, but processes from 3-4-1 require a smaller energy input to return to the starting position ...
Expansion of working fluid takes place isentropically and work is done by the system on the piston. The volume ratio / is called the "isentropic expansion ratio". (For the Otto cycle is the same as the compression ratio /). Mechanically this is the expansion of the hot gaseous mixture in the cylinder known as expansion (power) stroke.
2.4 Statistical physics. ... Work done by an expanding gas ... Net work done in cyclic processes = ...
where W n is the net work done by the engine per cycle, q H > 0 is the heat added to the engine from a hot reservoir, and q C = −| q C | < 0 [69] is waste heat given off to a cold reservoir from the engine. Thus the efficiency depends only on the ratio | q C | / | q H |.
where, is the heat absorbed and is the work done. Please note that the term work done relates to the power delivered at the clutch or at the driveshaft. This means the friction and other losses are subtracted from the work done by thermodynamic expansion. Thus an engine not delivering any work to the outside environment has zero efficiency.