Improving cold start, combustion and emission characteristics of a lean burn spark ignition natural gas engine with multi-point hydrogen injection

The cold start, combustion and emission characteristics of a four-cylinder spark ignition (SI) natural gas (CNG) engine were optimized using multi-point hydrogen gas (H2) injection, exhaust gas recirculation (EGR), and an oxidation catalyst (OC). The transient HC emission was also collected with Fast FID measurement within the period of cold start. The results indicate that multi-point H2 injection could improve the cold start performance of CNG SI engine. The peak cylinder pressure and HC emissions maintain stable quickly with hydrogen addition in the stage of cold start. The maximum in-cylinder pressure and the heat release rate increased linearly with the H2 injection duration. Multi-point H2 injection shortens the flame development duration and the combustion duration. The coefficient of variation (COV) of the indicated mean effective pressure (IMEP) increased with the EGR rate and decreased with H2 multi-point injection. Multi-point H2 injection can improve EGR tolerance for CNG engine. The OC could effectively reduce CO emissions for all of the different conditions, but the conversion efficiency for the HC emissions was insufficient. The combination of lean burn combustion, EGR, multi-point H2 injection, and a more effective OC is a potential pathway for CNG engine optimization.