Effects of Gas Composition on Combustion, Emission and Knocking Characteristics of Marine Lean Burn Gas Engine

The present study has experimentally investigated the effect of fuel gas composition on the combustion, emission and knocking characteristics of a marine lean burn gas engine. The experiments was carried out using the lean burn gas engine, which has the rated power output of 400 kW with spark ignition pre-chamber system. The various compositions of the base fuel gas (Japanese city gas) changed by supplying propane-based LPG (liquefied petroleum gas), butane-based LPG and hydrogen. This paper reports in detail the experimental results on the combustion and emission characteristics of the lean burn gas engine affected by the fuel gas composition. The experimental results showed that the composition of fuel gas mixed with P-LPG and B-LPG has a small effect on the combustion characteristics, and the operation of the engine is hardly affected. However, the addition of hydrogen causes the rise of the maximum combustion pressure and the attention should be paid on the ratio of hydrogen in the fuel gas. With regard to the emission characteristics, the NOx emission increased with increasing the ratio of P-LPG, B-LPG and hydrogen in the base fuel gas. The CO emission increased with increasing the ratio of P-LPG and B-LPG and decreased with increasing the ratio of hydrogen in the base fuel gas. It is expected that such the tendencies depended on the carbon quantity in the fuel gas. In addition, it was found that the knocking characteristics are associated with the methane number of fuel gas.