Full load performance and emission characteristics of hydrogen-compressed natural gas engines with valve overlap changes

Natural gas vehicle engines are preferred over diesel engines because they release significantly lower amounts of nitrogen oxides (NOx) and carbon dioxide emissions. Hydrogen-compressed natural gas (HCNG) technology is a promising alternative to that used in conventional compressed natural gas engines because hydrogen possesses stable lean combustion characteristics. Although the NOx emissions requirements are satisfied, methane emissions must be filtered using an oxidation catalyst. An alternative is required for methane reduction because improving the conversion efficiency of methane is expensive. In this study, the strategy of varying the valve overlap was employed to reduce methane emissions. Although a torque valve cannot meet engine emission specifications, the hydrocarbon and methane emissions were reduced by approximately 41% by decreasing the valve overlap duration while using HCNG fuel. The level of NOx emissions was approximately equivalent to or slightly higher than that of a conventional camshaft.