放。In view of high cyclic variation and HC emissions of the lean-burn gasoline engine at idle conditions, an experimental investigation was carried out on a gasoline engine equipped with an electrical controlled hydrogen injection system. The hydrogen volume fraction in the total intake of 3% was adopted through adjusting hydrogen injection duration to study the effect of hydrogen enrichment on combustion and emission characteristics of a lean-burn gasoline engine at idle. The test results demonstrated that the indicated thermal efficiency was improved; flame development period and rapid burning duration were shortened after hydrogen enrichment. When the excess air ratio was 1.3, the coefficient of variation in indicated mean effective pressure was dropped from 33.9% of the original engine to 13.7% of the 3% hydrogen-enriched engine. Under idle and lean conditions, the addition of hydrogen was effective on improving HC, CO and NOx emissions performance of the SI engine.