Quantitative governing In this system of governing, the quality of charge (i.e. air-fuel ratio of the mixture) is kept constant. But the quantity of mixture supplied to the engine cylinder is varied by means of a throttle valve which is regulated by the centrifugal governor through rack and pinion arrangement.
The spark ignition engines are governed by Quantitative governing
the part load efficiency of SI engine is poor because air fuel ratio remains constant even if we need low power
Qualitative governing In this system of governing, a control valve is fitted in the fuel delivery pipe, which controls the quantity of fuel to be mixed in the charge. The movement of control valve is regulated by the centrifugal governor through rack and pinion arrangement.
The compression ignition engines are governed by Qualitative governing
part load efficiency of ci engine is good because we can use lean mixture and rich mixtures easily according to our requirement