Which of the following is NOT listed as a measure to help avoid diesel knock?

• A. Electronically controlled fuel injection
• B. Designs aimed at better mixing of fuel and air
• C. Appropriate compression ratio in engine design
• D. Use of turbocharging to boost power

Answer: (D)

Diesel knock comes from the combustion process happening too rapidly or unevenly, causing sharp pressure rises that produce a knocking sound. To avoid this, engineers focus on controlling when and how the fuel burns and how the air and fuel mix, as well as keeping peak cylinder temperatures in check.

Electronically controlled fuel injection helps by precisely timing and metering the fuel and shaping the spray, which smooths the combustion rate and prevents sudden, premature ignition. Designing for better mixing of fuel and air reduces local pockets of rich fuel that can ignite too early, leading to knock. Choosing an appropriate compression ratio keeps peak temperatures and pressures at levels that avoid spontaneous ignition before the intended combustion event.

Turbocharging, while it increases engine power by forcing more air into the cylinder, is not a measure used to prevent diesel knock. It changes the engine’s breathing and can affect knock risk, but its primary purpose isn’t to avoid knock; it’s to boost power and efficiency, so it’s not considered a measure for knock prevention.