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Experiments has been carried out on a hydraulically actuated rapid compression machine (RCM) under engine like condition using both pure methane and methane with 5 and 30 vol% hydrogen addition with a wide range of excess air ratios (1.0–2.2) for spark ignition (SI) mode. The RCM has a variable compression ratio, charge air preheating and control of cylinder block temperature, allowing both spark ignition and compression ignition without any modifications other than adjustments of the control system. Cylinder pressure and volume recordings were performed. The ignition and early combustion was visualized by a schlieren optical system and a high speed video camera at a rate of 10 000 frames per second. Flame size, and hence the apparent flame propagation velocity is found from the schlieren images, but the images are also used to investigate flame morphology for the different gas mixtures and excess air ratios studied.

The schlieren method is a powerful and widely used technique for studying ignition and combustion. Jointly with high-speed photography, this method is often used in both SI- and CI-engines and combustion bombs, including rapid compression machines (rcm). This paper describes tests carried out on a new hydraulically actuated dynamic combustion rig, using schlieren visualisation in two orthogonal directions. The working principle of the rig is briefly described. Results are presented on ignition properties of low quality gas blends using spark ignition and pilot flame. Methane, ethane and nitrogen were blended at different air-fuel ratios and tested as to ignition and early flame development. For spark ignition tests, the pair of images from the two orthogonal directions enables the use of digital image processing to calculate the flame speed, and to compose a three-dimensional volumetric image of the flame front shape.