Diploma Thermal Engineering 1 N Scheme important Questions
Dear Friends
We are adding Study Material for Thermal Engineering 1 Important Questions for the Unit 2 – 3 Marks.
THERMODYNAMIC AIR CYCLES AND HEAT TRANSFER
Air cycles – air standard efficiency – reversible and irreversible processes –assumptions in deriving air standard efficiency – Carnot cycle – Otto cycle –Joule cycle – Diesel cycle – comparison of Otto cycle and Diesel cycle -Comparison of ideal and actual p-V diagrams of Otto and Diesel cycles –problems .
- What is a Thermodynamic Air Cycle?
When air is assumed to be the working substance inside the engine cylinder, the cycle is called as an air cycle.
- Define Air Standard efficiency
The thermal efficiency of the engine which uses air as the working medium is know as ‘Air standard Efficiency’. This efficiency is often called as Ideal efficiency
- What is reversible & Irreversible Process?
Reversible and irreversible process: A thermodynamic cycle consists of number of processes. If each process comprising the thermodynamic cycle is reversible, then the cycle is called as reversible cycle. In a reversible cycle there should be no loss of heat due to friction, radiation. The conditions required for reversible cycle are same as that for the reversible process. If those conditions are not satisfied, then it becomes an irreversible cycle. Hence in an irreversible cycle the original conditions are not restored.
- Define otto cycle
The ideal Otto cycle consists of two constant volume and two reversible adiabatic or isentropic processes as show on p-V and T-S diagrams in Fig. (a) and (b)
- Define DIESEL CYCLE
This is an important cycle on which all the diesel engines work. It is also known as constant pressure cycle as heat is received at constant pressure
The ideal diesel cycle consists of two reversible adiabatic or isentropic, a constant pressure and a constant volume processes. These processes are represented on p–v and T-S diagrams as shown in figure.
- Comparison of Otto and Diesel cycle
| Otto Cycle | Diesel Cycle |
| Heat addition takes place at constant volume | Heat addition takes place at constant pressure |
| Petrol engines work on this cycle | Diesel engines work on this cycle. |
| At constant volume, heat rejection takes place. | In diesel cycle also the heat rejection takes place at constant volume. |
| Compression ratio is less. It is 7:1 to 10:1. | Compression ratio is more. It is 11:1 to 22:1 |
| Efficiency is less. | Efficiency is more |
| Adiabatic expansion takes place during the complete backward stroke of the piston. | After the heat addition is cut-off in the backward stroke, the adiabatic expansion takes place during the remaining portion of stroke |
