Page 52 - 4461
P. 52
across the boundary.
Otto cycle is the ideal cycle for spark-ignition reciprocating engines. It is named after
Nikolaus A. Otto, who built a successful four-stroke engine in 1876 in Germany using
the cycle proposed by Frenchman Beau de Rochas in 1862. The ideal Otto cycle, which
closely resembles the actual operating conditions, utilizes the air-standard
assumptions.
It consists of four internally reversible processes:
1-2 isentropic compression;
2-3 constant volume heat addition;
3-4 isentropic expansion;
4-1 constant volume heat rejection.
2
Pascal (Pa) is the unit of pressure defined as newtons per square meter (N/m ).
Polytropic process is a process in which pressure and volume are often related by
n
PV = C, where n and C are constants, during expansion and compression processes of
real gases.
Potential energy (PE) is the energy that a system possesses as a result of its elevation in
a gravitational field and is expressed as P E = mgh.
Power is the work done per unit time is called and has the unit kJ/s, or kW.
Pressure is defined as the force exerted by a fluid per unit area.
Pressure ratio is the ratio of final to initial pressures during a compression process.
Process is any change that a system undergoes from one equilibrium state to another. To
describe a process completely, one should specify the initial and final states of the
process, as well as the path it follows, and the interactions with the surroundings.
Pump is a steady flow device used to increase the pressure of a liquid while
compressors increase the pressure of gases.
Pure substance is a substance that has a fixed chemical composition throughout.
Radiation is the transfer of energy due to the emission of electromagnetic waves (or
photons).
Rankine cycle is the ideal cycle for vapor power plants. The ideal Rankine cycle does
not involve any internal irreversibility and consists of the following four processes:
1-2 isentropic compression in a pump;
2-3 constant pressure heat addition in a boiler;
3-4 isentropic expansion in a turbine;
52
