On board inert gas generation system with rotary positive displacement compressor

An on board inert gas generation system for use in an aircraft having a source of low pressure air, the inert gas generation system comprising:

• a variable speed rotary positive displacement compressor including an inlet configured to receive a first portion of the low pressure air and an outlet in flow communication with an air separation module;
• a turbine configured to receive a second portion of the low pressure air and to extract therefrom at least a proportion of the energy required for driving the compressor;
• a heat exchanger disposed in a flow path between the compressor and the air separation module, wherein the heat exchanger includes a heating pass and a cooling pass, wherein compressed air from the compressor is passed along the cooling pass to reduce a temperature of the compressed air supplied to the air separation module;
• and
• a first duct configured to supply cool ram air to the heating pass of the heat exchanger,
• wherein the compressor is configured to provide variable air flow to the air separation module.