Visualization Of Air-Natural Gas Mixing Process In The Intake Manifold For Natural Gas Engine

With the decreasing of petroleum resource and aggravating of air pollution in the world, natural gas engines have been widely developed and applied because of lower exhaust emissions and higher thermal efficiency. The key technology in developing natural gas engines is the CNG supply mode, which has fundamental effects on the dynamic performance, fuel economy, reliability and the exhaust emissions of engines. In this paper the development of natural gas engines and their fuel supply systems were summarized.The visualization of air- natural gas mixing process in a transparent intake manifold has been investigated by means of the Schlieren method. The instantaneous images of the mixing and natural gas jet process were photographed. A new piece of natural gas delivery pipe was designed to improve the mixing quality in the intake manifold.The mixing effects of venture type gas mixer and proportioned adjustment mixer have been compared for the first time. The results indicated that there were several differences in the mixing effects between the two types of mixer. The experiment on the natural gas delivery pipe indicated that the mixing quality would deteriorate greatly when the jet direction and the axis of intake manifold run parallel. The diameter and numbers of the nozzle on the gas delivery pipe and the air flow velocity in the intake manifold were fundamental parameters influencing air -natural gas mixing process. It was found that the mixing effect of the new venture type gas mixer was much more satisfying than the old one and the aliform pipe was better than the columnar pipe.The experiment on the natural gas jet pipe showed that there was stratification of the flow in the intake manifold and the stratification would last for a long distance. The diameter of jet pipe, injection velocity, air flow velocity and the throttle opening had fundamental effects on the diffusion of the natural gas jet.