Internal Combustion Engines
By higher octane number of spark ignition fuel, it is meant that the fuel has

Lower volatility
Longer ignition delay
Higher flash point
Higher heating value

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Internal Combustion Engines
In a typical medium speed 4-stroke cycle diesel engines

Exhaust valve opens at bottom dead center and closes at top dead center
Exhaust valve opens just after bottom dead center and closes just before top dead center
Exhaust valve opens at 35° before bottom dead center and closes at 20° after top dead center
May open and close anywhere

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