Diesel combustion timing — definition of delay period In Diesel engines, what is the term for the time interval between the start of fuel injection and the start of combustion (auto-ignition)?

Introduction / Context:
The combustion process in a Diesel engine has distinct phases. The initial interval after injection begins determines pressure rise characteristics, noise, and efficiency. Correctly naming this interval is fundamental for diagnostics and timing calibration.

Given Data / Assumptions:

• Compression-ignition engine with mechanical or electronic injection.
• Fuel delivery begins before top dead center near the end of compression.
• Auto-ignition occurs once mixture conditions satisfy temperature and chemistry requirements.

Concept / Approach:
The delay period is the physical and chemical time needed for atomized fuel to heat, vaporize, mix with air, and reach ignition conditions. Excessive delay accumulates more premixed fuel, causing a sharper pressure rise and diesel knock; too little delay can reduce mixing and efficiency.

Step-by-Step Solution:
Mark the start of injection (SOI) as the reference point.Observe in-cylinder pressure and heat release to identify the onset of combustion.Define the time between SOI and start of combustion as the delay period.

Verification / Alternative check:
Combustion analysis with a pressure transducer shows the heat release beginning after a finite delay from SOI; calibration maps adjust injection timing to manage this delay across speed and load.

Why Other Options Are Wrong:
Injection period refers to the duration of fuel delivery, not ignition. Ignition period is a vague term and not the standard. Spill cut-off describes end of delivery in pump systems.

Common Pitfalls:
Confusing delay caused by low temperature with delays from poor atomization or low cetane fuel; multiple causes can overlap.

Final Answer:
delay period