Review of the addition of hydrogen to the compressed natural Gas Fuel

Abstract

This article presents a collection of studies relating to the development of technologies using hydrogen with compressed natural gas or Hydrogen-enriched Compressed Natural Gas (HCNG). Regarding to the issues of mixing ratio, the data show that the appropriated amount of hydrogen falls between 20%-30% by volume in order to balance any tradeoff between engine performance and emissions. The equivalent ratio can be adjusted to be as low as 0.5-0.6. The ignition timingmust also be retarded (Ignition Delay) by averagely 5 degrees of crankshaft rotation to compensate for the change of burning speed. Theuse of 20%-30% of hydrogen by volume decrease both HC and NOx as compared to the use of CNG alone. In terms of the fuel system design, the individually-stored gas injection system is of interest. It provides flexibility especially for the adjustment of the fuel composition for optimum ration in any operating conditions. But at present, there is no commercial development of such system.