Effect of Hydrogen Addition on Idle Performance of a Spark-Ignited Gasoline Engine at Lean Conditions with a Fixed Spark Advance

摘要

Spark-ignited engines always suffer high specific fuel consumption, emissions, and cyclic variation at idle and lean conditions. An experimental investigation aiming at extending the engine lean burn limits and improving the engine economic and emissions performance with hydrogen addition at idle conditions was carried out on a 4-cylinder spark-ignited (SI) gasoline engine. The engine was modified to permit hydrogen and gasoline to be injected into the intake ports simultaneously to realize a hybrid hydrogen-gasoline engine (HHGE). The hydrogen and gasoline flow rates were governed by a hybrid electronic control unit (HECU). Three hydrogen volumetric fractions of 0, 3, and 6% in the intake were applied to investigate the effects of hydrogen addition on engine thermal efficiency, combustion duration, cyclic variation, and emissions at idle conditions using a fixed spark advance. Under each hydrogen enrichment level, the engine was gradually leaned by reducing the gasoline flow rate until the coefficient of cyclic variation in indicated mean effective pressure (Imep) was above 10%. The test results showed that, with the increase of hydrogen enrichment level, engine-indicated thermal efficiency was improved, and the lean burn limit was extended. The peak in-cylinder temperature and in-cylinder temperature at exhaust valve opening decrease with the increase of excess air ratio and hydrogen blending level. For a specified excess air ratio, HHGEs tend to get high residual gas fraction compared with the original one. The combustion duration was gradually shortened with the increase of hydrogen addition level at diluent conditions. Moreover, CO and NO_x emissions were reduced at lean conditions for the HHGE. HC emissions from the HHGE were also lower than the original one at all excess air ratios.