Abstract
Compressed natural gas (CNG) is being increasingly used as an alternative to conventional fuels such as gasoline for running spark ignition engines. However, even though it is a clean burning fuel, CNG has low energy content per kg when compared to hydrogen. Therefore, hydrogen is blended with CNG in order to improve the fuel characteristics. In the article, the results of experimentation using low hydrogen fraction mixed with CNG, or HCNG are presented. Up to 50% hydrogen and CNG blends (HCNG) were used along with ignition timing for maximum brake torque (ITMBT) and constant ignition timing equal to 25 . A decrease of 14.3%, 28.5%, and 71.4% in CO relative to pure CNG was observed for 5, 10, and 15HCNG. Similarly a reduction of 17.2%, 24.1%, and 51.7% in CO2, and an increase of 25%, 58%, and 66% were observed for 5, 10, and 15HCNG relative to pure CNG. For hydrogen content in the range 10HCNG to 15HCNG, the percentage NOx emission increase was not comparatively large. The results comparing constant ignition timing with ITMBT ignition showed that there was no major reduction in NOx for the engine running on MBT ignition. This can be significant when converting vehicle SI engines to run on HCNG because vehicles engines need not be tuned for MBT ignition for NOx reduction, but constant ignition is enough for the purpose as no significant advantage is observed with MBT in terms of NOx. The application of this study would be useful for SI vehicle manufacturers and owners who would be converting factory/on-road vehicles to run with HCNG. For smaller amounts of hydrogen in HCNG, expensive and complex engine modification to run the engine on maximum brake torque ignition timing could be avoided by both vehicle manufacturers and owners as the effect of maximum brake torque on NOx emissions is negligible. Engine with variable ignition timing is not a necessity for the Purpose of NOx reduction.