Influence of hydrogen addition on the operating range, emissions and efficiency in lean burn natural gas engines at high specific loads

Power to Gas has attracted much attention as a solution to handle the electricity overproduced from renewable energy. This overproduced electricity can be converted into H2H2 and injected into the existing natural gas grid. Therefore, efficient and safe usage of H2H2 enriched natural (HNG) gas is a key issue to spread Power to Gas further. In this paper, the influences of H2H2 addition on the engine combustion process is discussed, focusing on large-bore lean burn gas engines operated at high specific loads. The experimental setup consists of a single cylinder research gas engine with a displacement of 4.77L. The results show a big influence of the addition of H2H2 on the operating range and emissions even with small amounts of H2H2. The misfire limit extends to the leaner side, while knocking must be prevented by a later ignition timing (IGT). Pre-ignition phenomena are limiting the operating range at richer conditions with rising H2H2 amounts. While NOxNOx emissions increase, unburned hydrocarbon (THC) and formaldehyde (HCHO) emissions decrease due to an enhanced combustion. This and the leaner operating conditions, which can overcompensate the actual NOxNOx increase, facilitate a higher efficiency, which is discussed based on a detailed loss analysis.