a diesel/gas engine works on its basic compression principle which is compression ignition.
Gas is added to the air the engine is taking in to act as "boost" the fire is lit up by the diesel being injected and then the gas makes sure the fire moves very rapidly.
Fuel intake is reduced to save on fuel oil as the gas compensates the defeciency of energy. a diesel/gas vehicle can only be run correctly with an electronic control system that can control the amount of fuel according to engine load, rev count, fuel temperature, air temperature, gas temperature etc..
The systems being made in Pakistan are the worst I have ever seen, they dont even have balanced diesel fuelling - how can you expect they change the spill timing correctly when their test benches are not even calibrated.