Engineering Thermodynamics ME-103 By Prof. S.K.Shukla Department of Mechanical Engineering Indian Institute of Technology (Banaras Hindu University) Varanasi-221005
GAS POWER CYCLE
Internal Combustion Engine I C Engines Spark Ignition Engine Compression Ignition These engines are Petrol Engines and they work on Otto Cycle These engines are Diesel Engines and they work on Diesel Cycle
Basic Components of IC Engine
Basic Definitions The piston inside the cylinder reciprocates between two fixed extreme positions called top – dead centre (TDC) and bottom – dead centre (BDC). Displacement Volume: It is the volume swept by the piston when it moves between TDC and BDC. This is also called as swept volume or stroke volume. Clearance Volume: It is the minimum volume formed in the cylinder when the piston is at the TDC.
Basic Definitions
Indicator Diagram This indicates the power developed due to combustion inside the cylinder. This is nothing but the P-v diagram.
IC Engine Power Cycles The sequence of events in an IC engine power cycle are, Induction of charge. Compression of charge. Ignition of charge. Expansion of the burning gases. Exhaust of the burnt gases.
Petrol Engine Petrol Engine Four – Stroke Two - Stroke
Petrol Engine (Four Stroke)
Petrol Engine (Two Stroke) In two – stroke engine, valves are replaced by ports. There are three ports: Inlet port Exhaust port Transfer port
Petrol Engine (Two Stroke) In two – stroke engine, valves are replaced by ports. There are three ports: Inlet port Exhaust port Transfer port
Events of Petrol Engine (2 Stroke)
Processes in Otto Cycle The processes in Otto cycle are: (1 – 2) Isentropic Compression (2 – 3) Constant volume heat addition. (3 – 4) Isentropic Expansion. (4 – 1) Constant volume heat rejection.
Efficiency of Otto Cycle
Efficiency of Otto Cycle
Diesel Cycle Petrol Engine has a Carburetor and a spark plug whereas, a Diesel engine has fuel injector to spray diesel.
Diesel Cycle
Processes in Diesel Cycle The processes in Diesel cycle are: (1 – 2) Isentropic Compression (2 – 3) Constant pressure heat addition. (3 – 4) Isentropic Expansion. (4 – 1) Constant volume heat rejection.
Efficiency of Diesel Cycle
Dual Cycle
Processes in Dual Cycle The processes in Dual cycle are: (1 – 2) Isentropic Compression (2 – 3) Constant volume heat addition. (3 – 4) Constant Pressure heat addition (4 – 5) Isentropic Expansion. (5 – 1) Constant volume heat rejection.
Efficiency of Diesel Cycle
Efficiency of Diesel Cycle
Mean Effective Pressure of Diesel Cycle
Comparison of Otto, Diesel and Dual Cycles The performance of three cycles are compared on the basis of the following important variables. Compression ratio Maximum pressure Heat addition Net work output
Comparison of Otto, Diesel and Dual Cycles Same Compression ratio and Heat input
Comparison of Otto, Diesel and Dual Cycles Same maximum pressure and Heat input
Comparison of Otto, Diesel and Dual Cycles Same maximum pressure and Temperature
Gas Power Cycles
Assumptions In gas power cycles, the working fluid is gas. The following assumptions are made for convenience: The working fluid is air which continuously circulates in a closed loop. Air behaves as an ideal gas all through. All the processes that make up the cycle are internally reversible. The combustion process is equivalent to the heat addition stage from an external source. The exhaust process is equivalent to the heat rejection process that restores the working fluid to the initial stage.
Simple Gas Turbine
Simple Gas Turbine Gas turbine works on Brayton (Joule) cycle. The various processes are, (1 – 2) Isentropic Compression (2 – 3) Reversible constant pressure heating (3 – 4) Adiabatic Expansion (4 – 1) Reversible constant pressure cooling
Air Standard Brayton Cycle P – v Diagram (for open and closed cycle
Air Standard Brayton Cycle T - s Diagram
Efficiency of Brayton Cycle