engine cycle


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engine cycle

[′en·jən ‚sī·kəl]
(thermodynamics)
Any series of thermodynamic phases constituting a cycle for the conversion of heat into work; examples are the Otto cycle, Stirling cycle, and Diesel cycle.

Cycle, Engine

 

a sequence of processes that regularly recur in an internal or external combustion engine and form the basis of the engine’s operation. A distinction is made between thermo-dynamic and actual cycles. In an actual cycle, as opposed to a thermodynamic cycle, allowances are made for heat losses, hydrodynamic losses, and so forth.

An engine cycle may be plotted as a closed curve in coordinates of the volume and pressure (V, p) or the entropy and temperature (S, T) of the working fluid. The area bounded by the contour is proportional to the work done. Figure 1 gives examples of thermodynamic cycles that are prototypes of the actual cycles of a carburetor engine (Figure 1,a) and a diesel engine (Figure l,b and l,c). The cycle of the carburetor engine consists of compression of the working fluid (adiabatic curve ac), addition of the heat Q1 (isochor cz), incomplete expansion (adiabatic curve zb), and rejection of the heat Q2 (isochor ba). The diesel cycle comprises compression of the working medium (adiabatic curve ac), addition of the heat Q1 (isobar cz), incomplete expansion of the working fluid (adiabatic curve zb), and rejection of the heat Q2 (isochor ba); or it may consist of compression (isotherm ac), addition of the heat Q1 (isochor cz’) and Q” (isobar zz’), incomplete expansion (adiabatic curve zb), and rejection of the heat Q2 (isochor ba).

The gas-turbine cycle (Figure 1, d) with constant-pressure heat addition and complete expansion involves compression of the

Figure 1. Thermodynamic engine cycles: (a) carburetor engine, (b) and (c) diesel engine, and (d) gas-turbine engine

working fluid (adiabatic curve ac), addition of the heat Q1 (isobar cz), expansion of the working medium (adiabatic curve zb), and release of the heat Q2 (isobar ba). A cycle with constant-volume addition of the heat Q1 is also possible.

Steam engines and turbines operate on the Rankine cycle. (See alsoCARNOT CYCLE and CYCLE.)

engine cycle

engine cycleclick for a larger image
Otto cycle.
engine cycleclick for a larger image
Brayton cycle.
i. The cycle of events that must be accomplished in the transformation of chemical energy into mechanical energy. The two most common cycles are the Otto cycle, which describes the events of a reciprocating engine, and the Brayton cycle, which describes the transformation taking place in a gas turbine engine. See also Otto cycle and Brayton cycle.
ii. A specific activity in an engine such as from one start to the switch-off of the engine, one advance and retard of the engine, etc. For ease of record keeping within airlines, cycles are recorded as one takeoff and landing. The recording of cycles such as the times the engine has been started and switched off and the times the throttle has been advanced and retarded require special recording procedures for maintenance runs.
References in periodicals archive ?
Embedded technologies within the GP200E allow for the rasterization of incoming print jobs while a current one is in progress, providing continuous engine cycle timing for maximum document throughput.
The Time Between Overhaul (TBO) can also be extended up to 8,000 hours or 12 years depending on the operation and it is independent of engine cycles.
Over the next three years, these engines will accumulate approximately 40,000 engine cycles leading up to entry into service.
The new version has raced on other engine cycles and hopefully that's what we'll have for Brazil.
Rolls-Royce said that Trent 900-powered A380s have now been in service for one year and have flown 56,000 in-service hours with more than 8,000 engine cycles.
The papers are organized into sections on engine cycles with variable valve actuation, cam phasing systems, profile switching and lost motion systems, cylinder deactivation, mechanical variable valvetrain systems, and camless valve actuation.
Completely clean, the various engine cycles occur in three separate chambers--an intake/compression chamber, a chamber for the injection of additional compressed air/expansion, and an expansion/exhaust chamber.
Completely clean, the various engine cycles occur in three separate chambers -- an intake/compression chamber, a chamber for the injection of additional compressed air/expansion, and an expansion/exhaust chamber.
Under these conditions, a preignition event leads to very heavy knock, which can cause catastrophic damage in only a few engine cycles.
The GP7200 engine draws from the success of the GE90 and PW4000 programs, which together total more than 67 million engine hours and more than 12 million engine cycles in service.
Rolls-Royce future engine technologies are aimed at progressing advanced engine cycles that meet or exceed CLEEN goals for fuel burn reduction, while improving engine weight and noise.
The GP7200 engine draws from the success of the GE90 and PW4000 programs, which together total above 67 million engine hours and above 12 million engine cycles in service.