Effect of ammonia and natural gas Co-fueling on combustion and greenhouse gas emissions in a marine diesel engine

This study experimentally investigates the effects of fuel blending strategies on combustion and emission characteristics in a single-cylinder, four-stroke marine diesel engine with natural gas and ammonia. Diesel and ammonia were supplied via direct injection, while natural gas was introduced into the intake port through a solenoid-operated valve, forming a premixed charge with intake air. Experiments were conducted at 900 rpm under 50% load, and mixing ratios were systematically varied by adjusting individual fuel injection durations. Four operating conditions were tested—diesel only; diesel & natural gas; diesel & natural gas & NH 3 ; and diesel & NH 3 —reflecting a progressive transition from carbon-based to low- and zero-carbon fuels. In-cylinder pressure, heat release rate, mass fraction burned, and indicated thermal efficiency were measured, along with emissions of CO 2 , NO x , and N 2 O, to evaluate global warming potential (GWP). show that while blending low-carbon natural gas and carbon-free ammonia significantly reduces CO 2 emissions, increasing the ammonia ratio diminishes combustion stability and increases N 2 O emissions, resulting in a net increase in GWP. These findings indicate that despite ammonia’s promise as a de-carbonization fuel, higher blending levels do not necessarily lead to improved environmental performance.