12. Which area of the indicator diagram illustrated indicates the ignition delay period in a diesel engine cylinder

Area J indicates the ignition delay period, representing the time between fuel injection and combustion. This period involves atomization, mixing, vaporization, and reaching auto-ignition temperature, and is displayed as a horizontal interval on the indicator diagram between the start of injection and the start of combustion. Regions H, K, and G represent later combustion phases and are therefore incorrect.