Preventing diesel knock — which measures are effective? Diesel knock is linked to a long ignition delay and an abrupt pressure rise. Which of the following measures help prevent or reduce knocking in compression-ignition engines?

Introduction / Context:
Diesel knock occurs when a large fraction of fuel auto-ignites almost simultaneously after a prolonged delay, causing a steep pressure rise. Effective countermeasures aim to shorten the delay and smooth the heat release, thereby protecting components and improving NVH (noise, vibration, harshness).

Given Data / Assumptions:

• Conventional compression-ignition engine with direct injection.
• Fuel of appropriate cetane number and normal operating temperatures.
• Mechanical integrity permits reasonable compression ratio and boost levels.

Concept / Approach:
Shorter ignition delay reduces the premixed fuel quantity at the start of combustion and lowers the initial heat-release spike. Higher compression ratio raises end-of-compression temperature and pressure, accelerating pre-flame chemistry and reducing delay. Boosting inlet pressure increases charge density and, often with intercooling, enables better mixture preparation and higher effective compression temperature, again cutting delay.

Step-by-Step Solution:
Identify the root cause: excessive premixed burn due to long delay.Method 1: reduce delay directly by fuel quality (higher cetane) or timing/atomization → option (a).Method 2: raise compression ratio (within design limits) to increase T and p at end of compression → option (b).Method 3: increase inlet pressure (turbo/supercharging) to raise density and temperature, improving ignition and mixing → option (c).Collectively, these justify option (d) All of these.

Verification / Alternative check:
Engine calibration practice uses higher cetane fuels, optimized compression ratios, and boost with suitable injection phasing to minimize knock while achieving emissions targets.

Why Other Options Are Wrong:
Choosing any single measure ignores the multi-factor nature of ignition delay; in practice, several levers are used together.

Common Pitfalls:
Confusing diesel knock with SI knock (detonation); remedies differ because combustion initiation mechanisms are different.

Final Answer:
All of these