Physics
In a diesel engine the high temperature needed to ignite the fuel is achieved by

The battery
Compressing air in the cylinders
Using heat from exhaust
An electrical spark

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Physics
When a piece of pure silicon is doped with aluminium, then

The doped silicon piece will become p-type
The doped silicon piece will become n-type
The resistivity of the doped silicon piece will increase
The conductivity of the doped silicon piece will remain the same

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