In-cylinder pressure was measured by a Kistler type 6125B pressure transducer and recorded by a LabVIEW code. The crank angle position was acquired with a BEI XH25D shaft encoder. The intake air system provided compressed, filtered air from the building to the engine. The flow of air from the building supply system was controlled by an electronic regulator which provided precise control (Accuracy: ±0.1 kPa).