Biomass Fuel Characterization: Ultimate/Proximate Analysis, Dulong's Heating Value Formula & Stoichiometric Air - Renewable Energy Engineering | Agrigyan

• Noise-Induced Hearing Loss (NIHL) in Tractor Operators:
• Assertion (A): Noise Induced Hearing Loss (NIHL) is irreversible. $\implies$ True.
• Chronic occupational exposure to acoustic energy destroys delicate stereocilia of hair cells in the organ of Corti in the inner ear, leading to permanent, irreversible sensorineural hearing loss.
• Reason (R): NIHL is even, being greater in lower frequency than higher frequency. $\implies$ False.
• NIHL is characteristically asymmetric and concentrated at higher frequencies, showing a classic audiometric notch at 4000 Hz (4 kHz), while lower conversational frequencies (500–2000 Hz) are affected much later.
• Conclusion: (A) is true but (R) is false (Option 3).

Correct option: (3) (A) is true but (R) is false

• Internal Combustion Engine Piston Thermal Expansion:
• Statement (I): The top of the piston heats much more than does the lower skirt. $\implies$ Correct.
• The piston crown/top directly absorbs combustion flame temperatures exceeding 1500°C–2000°C, operating at 250°C–300°C, while the lower skirt remains much cooler (100°C–120°C).
• Statement (II): The pistons are made larger at the top to absorb excessive heat released during compression stroke, and are said to have skirt taper. $\implies$ Incorrect.
• Because the piston crown expands significantly more than the skirt, cold pistons are manufactured smaller at the top (tapered) so that at operating temperatures, thermal expansion brings the piston to a uniform cylindrical shape.
• Conclusion: Statement (I) is correct but Statement (II) is incorrect (Option 3).

• Combustion Phases in Compression Ignition (CI) Engines:
• Statement (I): Premixed combustion is smoother and quieter than diffusion combustion. $\implies$ Incorrect.
• Premixed (uncontrolled) combustion is rapid and explosive, producing an extremely steep rate of pressure rise ($dp/d\theta$), which causes diesel knock and combustion roughness. Diffusion (controlled) combustion is smooth and quiet.
• Statement (II): The longer the ignition delay, the higher percentage of the fuel that burns in premixed combustion and lower the percentage that burns in diffusion combustion. $\implies$ Correct.
• prolonged ignition delay allows more injected fuel to vaporize and mix with air before autoignition; when ignition occurs, this large accumulated charge burns simultaneously in rapid premixed combustion.
• Conclusion: Statement (I) is incorrect but Statement (II) is correct (Option 4).

• Peak Combustion Pressure in Diesel Combustion Chambers:
• Precombustion Chambers (Indirect Injection - IDI) divide the combustion space into a small prechamber (20–40% volume) and a main chamber above the piston.
• Fuel injected into the prechamber ignites with limited oxygen, forcing rich, partially burned gases through an orifice into the main chamber, where complete burning occurs progressively.
• This two-stage progressive burning cushions the pressure rise and produces the lowest peak cylinder pressure and lowest rate of pressure rise compared to open (direct injection) chambers.
• Conclusion: Peak pressure is lowest for Precombustion chamber (Option 2).

Correct option: (2) Precombustion chamber