JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III THERMAL ENGINEERING Previous Question Paper (August - 2022 - R16)

Air standard cycles are theoretical models based on ideal assumptions, whereas actual cycles account for real-world losses and deviations. The primary differences include:

• Working Fluid: Air standard cycles assume air behaves as an ideal gas with constant specific heats throughout the cycle. Actual cycles use a fuel-air mixture that changes composition during combustion and has variable specific heats.
• Combustion Process: In air standard cycles, heat is added via an external source at constant volume or pressure. In actual cycles, combustion is a complex chemical reaction that is time-dependent and occurs over a finite duration.
• Heat Losses: Air standard cycles assume the system is perfectly adiabatic (no heat transfer). Actual cycles experience significant heat transfer to the cylinder walls and cooling system.
• Flow and Friction: Ideal cycles assume instantaneous valve operations and no pressure drops. Actual cycles involve pumping losses, fluid friction, and gradual valve opening/closing timings.
• Efficiency: Air standard efficiency is always higher than actual thermal efficiency due to the absence of these real-world irreversibilities.

The battery ignition system is commonly used in spark-ignition engines to provide the high-voltage current required to create a spark at the spark plug. The system consists of a 6V or 12V battery, an ignition switch, an ignition coil, a contact breaker, a capacitor (condenser), a distributor, and spark plugs.

Working Principle:

1. When the ignition switch is closed, current flows from the battery through the primary winding of the ignition coil.
2. The contact breaker, driven by the engine camshaft, closes the primary circuit, allowing a magnetic field to build up in the coil core.
3. As the engine rotates, the breaker cam opens the contact breaker points, causing a sudden collapse of the magnetic field.
4. This rapid change in flux induces a very high voltage in the secondary winding of the coil (due to the large number of turns).
5. The high voltage is directed to the distributor, which sends the current to the specific spark plug corresponding to the firing order.
6. The capacitor connected in parallel with the contact breaker prevents arcing at the points and helps in faster collapse of the magnetic field to increase the induced voltage.