Experimental study on lean-burn characteristics of an SI engine with hydrogen/gasoline combined injection and EGR

Hydrogen has shown potential for improving the combustion and emission characteristics of the spark ignition (SI) dual-fuel engine. To reduce the additional NO_x emissions caused by hydrogen direct injection, in this research, the cooperative control of the addition of hydrogen with exhaust gas recirculation (EGR) in the hydrogen/gasoline combined injection engine was investigated. The results indicate that both the addition of hydrogen and the use of EGR can increase the brake mean effective pressure (BMEP). As the α_H2 value increases from 0% to 25%, the maximum BMEP increases by 9%, 12.70%, 16.50%, 11.30%, and 8.20%, respectively, compared with the value without EGR at λ = 1.2. The CA0-10 tends to increase with increases in the EGR rate. However, the effect of EGR in increasing the CA0-10 can be offset by the addition of 15% hydrogen at λ = 1.2. Measurements of the coefficient of variation of the indicated mean effective pressure (COV_IMEP) indicate that the addition of hydrogen can effectively extend the EGR limit. Regarding gaseous emissions, NO_x emissions, after the introduction of EGR and the addition of hydrogen, are lower than those of pure gasoline without EGR. An 18% EGR rate yields a significant reduction in NO_x, reaching maximum decreases of about 82.7%, 77.8%, and 60% compared to values without EGR at λ = 1.0, 1.2, and 1.4, respectively. As the EGR rate increases, the hydrocarbon (HC) emissions continuously increase, whereas a blend of 5% hydrogen can significantly reduce the HC emissions at high EGR rates at λ = 1.4. Finally, according to combustion and emissions, the coupling of a 25% addition of hydrogen with 30% EGR at λ = 1.2, and the coupling of a 20% addition of hydrogen with an 18% EGR rate at λ = 1.4 yield the best results.