Rapid or uncontrolled or pre-mixed combustion phase:
Combustion of the fuel which has mixed with air within flammability limits during ignition delay period occurs rapidly in a few crank angle degrees - high heat release characteristics in this phase. If the amount of fuel collected in the combustion chamber during the ignition delay is much - high heat release rate results in a rapid pressure rise which causes the diesel knock.
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For fuels with low cetane number, with long ignition delay, ignition occurs late in the expansion stroke - incomplete combustion, reduced power output, poor fuel conversion efficiency. If the pressure gradient is in the range 0.4 - 0.5 MPa/oCA, engine operation is not smooth and diesels knock starts. This value should be in the range 0.2 to 0.3 MPa/oCA for smooth operation (max allowable value is 1.0 MPa/oCA) of the engine.
Combustion of the fuel which has mixed with air within flammability limits during ignition delay period occurs rapidly in a few crank angle degrees - high heat release characteristics in this phase. If the amount of fuel collected in the combustion chamber during the ignition delay is much - high heat release rate results in a rapid pressure rise which causes the diesel knock.
.
For fuels with low cetane number, with long ignition delay, ignition occurs late in the expansion stroke - incomplete combustion, reduced power output, poor fuel conversion efficiency. If the pressure gradient is in the range 0.4 - 0.5 MPa/oCA, engine operation is not smooth and diesels knock starts. This value should be in the range 0.2 to 0.3 MPa/oCA for smooth operation (max allowable value is 1.0 MPa/oCA) of the engine.
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