Abstract: A closed cycle apparatus comprising a combustion chamber, delivery means to deliver inert carrier gas, combustion supporting gas and fuel into the combustion chamber, means to cause the fuel to burn in the combustion chamber, means to exhaust exhaust gas from the combustion chamber, a circuit through which exhaust gas is ducted from the combustion chamber and returned to the combustion chamber to provide the carrier gas, the circuit including means by which the exhaust gas is treated to remove carbon dioxide from the exhaust gas wherein a part only of the exhaust gas in said circuit is treated to remove carbon dioxide.