The Glow plug generates heat through resistivity dissipating the power supplied from a Voltage source. The Glow Plug is much simpler to operate than the spark plug. All It needs is 12 volts and an appropriate position to ignite the air/fuel mixture.
The relay is needed for the microcontroller to be able to switch on the power from the 12-volt battery to the glow plug.
The glow plug mount can withstand the pressures generated by the combustion chamber.
The fittings for the glow plug could be simplified.
The Glow Plug has yet to ignite the air propane mixture due to the health of the available 12-volt battery.