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Examoogle • User • info@examoogle.com • EE-2024-8821
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In a diesel engine, the duration between the time of injection and ignition is known as?
Delay period
Period of ignition
Burning period
Pre-ignition period
Delay period
Quick Summary: The delay period in a diesel engine, also known as ignition delay, is the time interval between the start of fuel injection and the actual commencement of combustion. It represents the physical and chemical preparation time required for the air-fuel mixture to reach self-ignition temperature.
The delay period in a diesel engine, also known as ignition delay, is the time interval between the start of fuel injection and the actual commencement of combustion. It represents the physical and chemical preparation time required for the air-fuel mixture to reach self-ignition temperature.
tdelay=tignition−tinjection — Defining the duration of the delay period as the difference in crank angles or time.
During the delay period, physical processes (atomization, vaporization, and mixing of fuel with air) and chemical processes (pre-flame reactions and chain initiation) occur. Once these processes conclude and the local mixture reaches its auto-ignition temperature, the ignition delay ends and uncontrolled combustion begins.
The delay period consists of a physical delay and a chemical delay.
Physical delay involves droplet atomization and vapor mixing.
Chemical delay involves pre-flame reactions leading to auto-ignition.
High cetane number fuels reduce the ignition delay period.
Excessive delay leads to 'Diesel Knock' due to rapid pressure rise.
Enables precise control of combustion start
Provides data to optimize engine timing
Excessive duration causes high thermal stress
Causes combustion noise (diesel knock)
Compression Ignition (CI) engine design
Fuel quality testing for diesel engines
Short ignition delay is preferred to minimize peak pressure and combustion noise.
Option B (Period of ignition) is inaccurate as it usually refers to the entire burning phase.
Option C (Burning period) follows the delay period.
Option D (Pre-ignition period) is generally associated with abnormal combustion in SI engines.
A is correct — The delay period is the time interval starting from fuel injection until the initiation of chemical combustion.
Always remember that in CI engines, the cetane number is inversely proportional to the ignition delay; higher cetane fuels ignite faster.