Air-standard efficiency of Otto cycle: It is defined as the ratio between work done during Otto cycle to the heat supplied during Otto cycle. Air-Standard Efficiency (thermal efficiency) of Otto cycle, From my previous article,
The Tizard and Pye formula for the efficiency of an ideal four-stroke Otto cycle engine, viz. E = 1 − ( 1 r ) γ − 1 shows that efficiency increases with compression ratio. γ is 1.296 for weaker than theoretical air/fuel mixtures, and 1.2586 for theoretically correct mixtures.
An Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. It is the thermodynamic cycle most commonly found in automobile engines. Thermal efficiency is the quotient of the net work from the system, to the heat added to system.
Otto cycle works on four processes, which are intake stroke, compression stroke, expansion stroke and then exhaust stroke. In Otto cycle the heat addition takes place at constant volume. The overall efficiency is way less than that of diesel cycle. The charge is drawn in by the cylinders during the intake stroke.
Otto Cycle Efficiency We can look again in the Cycle Properties meter window to see that the thermal efficiency of the Otto cycle we have built is about 57.5%. Figure 7: Cycle Properties It turns out that the thermal efficiency of the Otto cycle can be expressed in terms of the volumetric compression ratio.
In order to express the efficiency of the Otto cycle, we need to evaluate the work performed by the gas during one cycle and the heat which the gas received during this cycle. Efficiency is the proportion of the work and the supplied heat. For a cyclic process, the change in the total internal energy of the gas during one cycle is zero.
Thermal efficiency for Otto cycle – κ = 1.4 It is very useful conclusion, because it is desirable to achieve a high compression ratio to extract more mechanical energy from a given mass of air-fuel mixture. A higher compression ratio permit the same combustion temperature to be reached with less fuel, while giving a longer expansion cycle.
Thermal efficiency (air-standard efficiency) of Otto Cycle, The complete derivation of air-standard efficiency of Otto cycle can be found here and the complete derivation of mean effective pressure (m.e.p) of Otto Cycle can be found here. How petrol engine works using Otto Cycle – Animation video
The Otto cycle efficiency increases monotonically with compression ratio. This is because the peak pressure (and peak temperature) increases also. 2. The higher the value of p ˆ / p 1, the higher the maximum efficiency obtained. This reaches a value of about 61% with α = 140 at a compression ratio of 16:1.
Thermal efficiency for Otto cycle – κ = 1.4 It is very useful conclusion, because it is desirable to achieve a high compression ratio to extract more mechanical energy from a given mass of air-fuel mixture. A higher compression ratio permit the same combustion temperature to be reached with less fuel, while giving a longer expansion cycle.wegw