Internal Combustion Engines
Pre-ignition is caused by the spontaneous combustion of the mixture before the end of the compression stroke, and is due to

Overheated spark plug points
Cylinder walls being too hot
Red hot carbon deposits on cylinder walls
Any one of the listed here

ANSWER DOWNLOAD EXAMIANS APP

Internal Combustion Engines
Fuel consumption of diesel engines is not guaranteed at one quarter load because at such low loads

The friction is unpredictable
The friction is high
The small difference in cooling water temperature or in internal friction has a disproportionate effect
The engine is rarely operated

ANSWER DOWNLOAD EXAMIANS APP