A Diesel Genset is combination of Diesel Engine and an Alternator. Mainly Alternator is generator and Engine is used to rotate the alternator. Engine can be run by Gas (in case of Gas generator) or Gasoline (other fuel) as well.
Diesel generator sets are generally used as emergency power-supply in Industries, As a backup power supply if the grid fails.
Alternator generates the power when it is rotating. Engine is used for rotating purpose.
Diesel Engine commonly works in four cycle. 1st cycle is Intake, then 2nd is Compression, next 3rd is Combustion and finaly 4th is Exhaust.
Diesel Genset works according to the law of Energy conversion. We know from law that Energy cannot be created but only be converted into other forms of energy from existing energy. Diesel have chemical energy, during combustion chemical energy converted into heat and force. that force works as a mechanical energy to rotate the Alternator. Alternator converts the mechanical energy into Electrical Energy that means Electrical power supply. In the process, some energy losses as heat which goes to atmosphere by the help of radiator. Radiator is an genset cooling system. Now a days Modern diesel engine can convert energy with the efficiency of 43% to 44% that means 56% to 57% energy is losses as heat.
So, we can divide Genset into main three section 1. Engine 2. Alternator & 3. Radiator. These three parts have other sub parts or helping spare parts as well. Such as Exhaust, turbo charger, water separator, fuel filter, lube oil filter, air filter , control panel, battery, battery charger, breather filter, oil chamber, After cooler, starter motor and few others spare parts as well.
Now we can sense that genset is more complex thing that we expect when question comes about quality and efficiency, though it have a simple but excellent working principle.