Indicated Work Per Cycle

Pressure data for the gas in the cylinder over the operating cycle of the engine can be used to calculate
the work transfer from the gas to the piston .

The cylinder pressure and corresponding cylinder
volume throughtout the engine cycle can be plotted
on P-V diagram .

The indicated work per cycle /Cylinder is obtained
by integrating around the curve to obtain the area
enclosed on the diagram .

Note

The term indicated is used because such P-V
diagram used to be generated directly with advice
called an engine indicator.

With two-stroke cycle in the figure below , the enclosed integration is straightforward .

With addition of inlet and exhaust strokes for the four stroke cycle,some unknowns are introduced as two definintions of indicated output are in common use.these will be defined as :

Gross indicated work per cycle : Work delivered to the piston over the compresssion and expansion
                                                 strokes only .

Net indicated work per cycle :   Work delivered to the piston over the entire four-stroke cycle .

In the following fig the sum of areas A and C i.e ( A+C ) is the Gross indicated work per cycle.

The indicated work per cycle is the sum of areas ( A+C ) -- ( B+C ) = A -- B

Where A and B regarded as positive quantity.

The pumping Losses work:   Area ( B + C ) is the work transfer between the piston and the cylinder gases
                                                       during inlet and exhaust srtrokes .

The power per cylinder is related to the indicated work per cycle by :

                                                             W * N
                                              P = --------------------------
                                                        n

Where n is the number of crank revolution for each power stroke per cylinder.

For four stroke cycles n equal 2 , and for two stroke cycles n equal 1 .This power is the indicated
power ; the rate of work transfer from the gas within the cylinder to the piston .