Cyclic variation in a hydrogen-enriched spark-ignition gasoline engine under various operating conditions

Abstract

In this paper, the cyclic variation characteristics of a hydrogen-enriched gasoline engine under various operating conditions were experimentally investigated. The test was carried out on a modified four-cylinder gasoline engine equipped with an electronically controlled hydrogen injection system. A hybrid electronic control unit was developed to govern the injection timings and durations of hydrogen and gasoline to accomplish the on-line adjusting of the hydrogen blending level and excess air ratio. The engine was first run at idle condition with an idle speed of 790 rpm and then operated at 1400 rpm to investigate the cyclic variation in a hydrogen-blended gasoline engine at different hydrogen volume fractions in the total intake, excess air ratios, spark timings and manifolds absolute pressures. The test results demonstrated that the coefficient of variation in indicated mean effective pressure was distinctly decreased with the increase of hydrogen blending ratio. At 1400 rpm and a manifolds absolute pressure of 61.5 kPa, the relevant excess air ratio for the engine lean burn limit was extended from 1.45 to 2.55 when the hydrogen volume fraction in the intake was raised from 0% to 4.5%. Besides, for a specified hydrogen addition level, the coefficient of variation in indicated mean effective pressure was continuously increased but the coefficient of variation in the peak cylinder pressure was first raised and then decreased with the increase of excess air ratio. The experimental results also showed that hydrogen addition was more effective on reducing engine cyclic variation at low loads rather than at high loads.