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The liquefied natural gas (LNG)-fueled ships were provisioned to meet the strict emission legislation in the marine application since 2000. However, the scientific approach of burning the low-emission natural gas in lean combustion uncovered that the engine suffers from high methane slip emission. Serious questions are raised about the quantity of methane slip during marine conditions when the load varies in multiple frequencies and amplitudes. Previous studies by these authors explained how methane slip increases during load oscillation. This paper examined several practical methods to reach stable combustion in transient conditions to reduce the methane slip. Employing Proportional-Integral-Derivative (PID) controllers in a closed loop, implementing open-loop lookup tables, model predictive controller (MPC), and an innovated solenoid method are performed in a high-fidelity medium-speed natural gas spark-ignition (SI) engine model.

About 2000 hours of gas engine operation with producer gas from biomass as fuel has been conducted on the gasification combined heat and power (CHP) demonstration and research plant, named “Viking” at the Technical University of Denmark. The plant and engine have been operated continuously and unmanned for five test periods of approximately 400 hours each. Two different control approaches have been applied and investigated: one where the flow rate of the producer gas is fixed and the engine operates with varying excess of air due to variation in gas composition and a second where the excess of air in the exhaust gas is fixed and the flow rate of produced gas from the gasifier is varying. It was seen that the optimal control approach regarding the gasifier operation resulted in engine operation with significant variation of the NOx emissions Producer gas properties and contaminations have been investigated.