DUAL CYCLE, LIMITED PRESSURE CYCLE OR MIXED CYCLE

We were discussing Otto cycle, an ideal cycle for internal combustion spark ignition reciprocating engines or simply petrol engines and also Diesel cycle, the ideal cycle for the operation of internal combustion compression ignition reciprocating engines in our previous posts.

Today we will see here the basic concept of Dual cycle with the help of this post. Dual cycle is also termed as Limited pressure cycle or Mixed cycle.

Dual Cycle or Mixed cycle

Dual cycle will provide us better approximation to a real engine. As we can see from the name of this cycle, we can say that we will secure Dual cycle by considering the concept of Otto cycle and Diesel cycle together. Heat addition process in case of Dual cycle will be combination of heat addition process of Otto cycle and Diesel cycle and therefore this cycle is termed as mixed cycle or Dual cycle.

Heat addition in Dual cycle will be done in two parts i.e. heat energy will be supplied partially at constant volume and partially at constant pressure and hence there will be more time for fuel for combustion which will be injected in to the engine cylinder before end of the compression stroke.

Let us see P-V Diagram, T-S Diagram and various processes of Dual cycle

Process 1-2: Adiabatic compression of the working fluid

Process 2-3: Heat energy addition to the working fluid at constant volume

Process 3-4: Heat energy addition to the working fluid at constant pressure

Process 4-5: Adiabatic expansion of the working fluid or also termed as power stroke

Process 5-1: Rejection of heat energy at constant volume

Thermal efficiency of the Dual cycle

Heat energy supplied

Q₁ = m C_V (T₃-T₂) + m C_P (T₄-T₃)

Heat energy rejected

Q₂ = m C_V (T₅-T₁)

Thermal efficiency of the Dual cycle will be determined as following

Do you have any suggestions? Please write in comment box.

We will see another topic i.e. Brayton cycle: Ideal cycle for gas turbine engines in our next post in the category of thermal engineering.

Reference:

Engineering thermodynamics by P. K. Nag

Engineering thermodynamics by Prof S. K. Som

Image courtesy: Google

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