Q1: With increase in __________ Knocking tendency in a spark ignition petrol engine decreases.

ANS:D - engine speed

Engine speed refers to the number of revolutions per minute (RPM) at which the engine's crankshaft rotates. In spark ignition petrol engines, the engine speed plays a significant role in determining the knocking tendency. At higher engine speeds, the piston moves more rapidly within the cylinder, compressing the air-fuel mixture more quickly during the compression stroke. This rapid compression increases the temperature and pressure of the mixture, which can elevate the likelihood of knocking. Additionally, at higher engine speeds, the combustion process must occur more rapidly to maintain engine performance, leaving less time for the fuel to burn smoothly and uniformly, which can further exacerbate the risk of knocking. However, it's important to note that the relationship between engine speed and knocking tendency is not linear and depends on various factors such as engine design, fuel quality, ignition timing, and engine load. In some cases, engine speed may not be the dominant factor influencing knocking tendency, especially if other factors such as compression ratio, air-fuel ratio, or ignition timing are optimized. However, generally speaking, higher engine speeds can contribute to increased knocking tendency in spark ignition petrol engines.