Emisssions from Hydrogen Enriched CNG Production Engines

In the immediate future the introduction of a wider variety of fuel types will play a significant role in reducing emissions and in solving the energy needs of the transportation industry. Both compressed natural gas, CNG, and hydrogen are expected to play very large roles, and the present paper shows that these fuels, when used together, can offer large benefits in NOx emissions. Significant reductions in NOx emissions will be required for CNG transit buses and heavy duty trucks, if they are to meet the future stringent emissions standards that come into effect in the year 2007. In the present paper a detailed engine model was used to understand and predict the results from engine dynamometer tests from a production automotive engine over a range of hydrogen/CNG gas fuel mixtures. The engine model has the capability to duplicate the testing conditions, such as power, rpm, compression ratio, and inlet conditions, and the model used a finite rate chemical reaction mechanism to predict the NOx emissions. For all the experimental cases considered there is excellent agreement between the experimental data and the predictions of the engine model. Therefore, it appears that the NOx reduction can be well described by the low temperatures caused by low equivalence ratios that are possible with hydrogen enriched CNG.