Closed cycle internal combustion engine

A closed cycle apparatus comprising an internal combustion engine having 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, 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 the whole of the exhaust gas is fed by the circuit into driving relationship with turbo charger turbine means and then into compressing relationship with turbo charger impeller means, whereby the whole of the exhaust gas is pre-compressed and means are provided to separate the pre-compressed exhaust gas downstream of the impeller means into a first part which is passed through a first conduit to be further compressed and then treated to remove carbon dioxide and a second part which is passed through a second conduit to be returned to the combustion chamber without being further compressed and treated to remove carbon dioxide.