Effect of ignition timing retard strategy on NOx reduction in hydrogen-compressed natural gas blend engine with increased compression ratio

To reduce NOx emission, an ignition timing retard strategy was considered for an HCNG engine with an increased CR. The thermal efficiency and emission characteristics at maximum power operation were investigated by retarding the ignition timing from minimum spark advance for best torque (MBT) timing. The results showed that the condition of HCNG30, a CR of 11.5, lambda of 1.8, and retarding the ignition timing by 10 CAD from the MBT timing could produce 2.0% higher thermal efficiency, 61.7% lower NOx emission, and 6.7% higher CH4 emission compared to the base CNG engine condition.