Why does supercharging increase the likelihood of detonation?

• A. Decrease in intake air density.
• B. Increase in temperature caused by compression of the fuel-air charge before entering cylinders.
• C. Reduction in fuel vaporization.
• D. Lower engine RPM.

Answer: (B)

The key idea is that boosting the intake air raises the pressure and, more importantly, the temperature of the charge as it’s compressed before entering the cylinders. Detonation (auto-ignition of the fuel-air mixture before the spark) becomes more likely when the mixture is hotter and under higher pressure because hot, dense air lowers the octane margin and accelerates ignition. So, the added boost increases the chance that the mixture will ignite prematurely or rapidly, which is detonation.

Why the other options aren’t the mechanism: boosting increases, not decreases, intake air density; the core cause of detonation is the temperature rise from compression and the resulting high-pressure, high-temperature mixture, not a reduced vaporization of fuel; and engine speed alone (lower RPM) doesn’t drive the premature ignition process in the way boost-induced compression and heat do.