Mitigating backfire occurrence in HHO-gasoline plug-in hybrid motorcycle engine

Abstract

HHO-gasoline plug-in hybrid motorcycles present a practical solution for mitigating greenhouse gas emissions, particularly in developing countries. However, backfire poses a major problem to the widespread adoption of HHO-fueled vehicles. Therefore, this work is conducted to evaluate backfire occurrence in HHO-gasoline plug-in hybrid motorcycle engines using both the intake manifold feeding method (MFM) and port injection method (PIM). The results indicate that traditional MFM poses a high risk of backfire occurrence. MFM can supply an HHO flow rate under 2 lpm, corresponding to an average equivalence ratio of hydrogen in the cylinder phi(H_cy) of 0.03 at an engine speed of 2000 rpm, while PIM can supply an equivalence HHO flow rate of 10 lpm under the same conditions. When using PIM, under full loading conditions with an engine speed of 7500 rpm and an injection pressure of 7000 Pa, phi(H_cy) can reach 0.15 without backfire risk. At 2000 rpm, the equivalent ratio of hydrogen upstream of the intake valve phi(H_port) is 0.011 and 0.006 for injection duration angles of 90 degrees CA and 50 degrees CA, respectively. With a fixed injection duration angle of 90 degrees CA, the average phi(H_cy) decreases from 0.44 to 0.15 as engine speed increases from 2000 to 7500 rpm. At loading regimes below 70 %, 4H_port near the intake valve becomes virtually negligible at the commencement of the intake process. The stratified hydrogen equivalence ratio distribution in the combustion chamber exhibits loading-dependent variation, with hydrogen-rich regions concentrated near the spark plug during low-load operation. Across all loading conditions, hydrogenrich regions remain absent from the crevices between the piston crown and cylinder wall, substantially mitigating backfire risk.