Automatic pump calorimeter is a laboratory instrument used to measure the calorific value or heating value of a liquid or gaseous fuel. It works by burning a small amount of the fuel in a combustion chamber and transferring the heat generated to a coolant flowing through a heat exchanger. The temperature difference between the inlet and outlet of the coolant is measured, and the calorific value of the fuel is calculated based on the mass flow rate and the heat transfer rate.