| A series of experiments was completed on a single-cylinder Cooperative Fuel Research engine to determine the effect of H2 addition on the extension of the exhaust gas recirculation (EGR) limit of a natural gas fuelled spark ignition engine. All experiments were conducted at 1200 RPM, wide open throttle and maximum brake torque spark timing. The addition of a 17.4% H2 energy fraction resulted in a doubling of the original EGR mass fraction limit, from 14.8% to 30.0%. Such an extension of the EGR limit had significant, implications on all metrics of engine performance: indicated specific NO emissions decreased by 93%, from 1.5 to 0.1 g/kW h while neither indicated specific CO or indicated specific total hydrocarbon emissions were greatly affected; fuel conversion efficiency (etafc) decreased slightly, from 31.4 to 30.9%, although this change falls within the uncertainty in determining etafc; indicated mean effective pressure decreased by 20%, from 5.21 to 4.17 bar; and "usage" indicated specific CO2 emissions fell by 18%, from 637 to 521 g/kW h. |
