Harley,
Maybe you are mixed up with fuel heating. This is done in these diesel engines. Diesel only ignites at some 600 degr. C.
So it does need cylinder heating by means of glow plugs at cold start.
You must notice the pre-heater indicator for some time at your instrument panel when starting up.
Heated diesel fuel will also help fot better ignition of the fuel.
Furthermore, intake air is even cooled by the intercooler for it's getting hot by the turbo charger. So certainly intake air is not heated for the diesel engine.
Direct injection means injection into the combustion chamber, so at high pressure. Indirect is into the intake air channel, so low pressure, but that is not used so much anymore.
Greets,
Paul