Development and Validation of an On-line Hydrogen-Natural Gas Mixing System for Internal Combustion Engine Testing 2008-01-1580

Hydrogen enriched compressed natural gas (HCNG) is thought to be a potential alternative to common hydrocarbon fuels for SI engine applications. Experimental researches focusing on how to use this kind of fuel to its full extent have been conducted for over ten years and are still on their way. From a review of these researches it is found that one of the biggest obstacles of efficiently and economically conducting such experiments is how to mix desired amount of hydrogen with natural gas. Most of the previous experiments use pre-bottled hydrogen/ NG mixtures (by mixing and storing desired amount of hydrogen and NG in high pressure steel cylinders before the tests) which are quite costly and unsafe, due to high pressure operation. More importantly, the blending ratio cannot be varied by that approach. By comparison, this paper presents an on-line hydrogen-natural gas mixing system through which the hydrogen/ NG blending ratio can be easily varied during the tests. This advantage makes it quite suitable for tests aimed at investigating the effects of different hydrogen fraction on engine performance. Furthermore, since the mixing process takes place after both hydrogen and NG passing through the high pressure regulator the gases are actually mixed at low pressure which is good for experiment safety. The actual effects of the system are then examined through measuring the hydrogen fraction in the mixing chamber by spectro-analysis and comparing engine performance, combustion and emissions characteristics using HCNG that comes from both on-line mixing system and well prepared bottled HCNG, which is believed to have a high accuracy of blending ratio.