JNTU B.Tech III PETROLEUM REFINERY ENGINEERING Previous Question Paper (May - 2019 - R16)

Paraffins (alkanes) are saturated hydrocarbons with the general formula C_nH_2n+2; they are characterized by high hydrogen-to-carbon ratios, relatively low octane numbers, and high chemical stability. In contrast, aromatics are unsaturated cyclic compounds containing at least one benzene ring; they possess lower hydrogen-to-carbon ratios, significantly higher octane numbers, and exhibit distinct chemical reactivity due to their delocalized pi-electron systems.

The ASTM distillation test is a critical quality control measure for gasoline that evaluates its volatility characteristics. Its significance lies in ensuring the fuel performs reliably across various engine operating conditions:

• Starting characteristics: The initial boiling point and the percentage evaporated at lower temperatures (e.g., 70°C) indicate the ease of cold starting; higher volatility ensures the engine starts readily in cold weather.
• Warm-up and acceleration: The mid-range distillation temperatures (e.g., 100°C) correlate with engine warm-up performance and smooth acceleration, ensuring sufficient vapor is available to prevent stalling.
• Vapor lock prevention: The distillation curve helps control the concentration of light ends, preventing excessive vaporization in the fuel system that could lead to vapor lock, particularly in hot weather.
• Crankcase dilution: The final boiling point (end point) ensures that heavy, less volatile components are minimized, reducing the risk of fuel accumulation in the engine oil, which can cause lubrication failure.