Hydrogen marine outboard stepped piston engine to achieve near zero emissions

A novel engine type well suited for operation with hydrogen or gaseous fuels is presented offering a viable two-stroke engine solution for ultra-low emissions. The stepped piston engine presented completely separates the lubrication and air scavenging systems and operates at significantly lower oil consumption levels than conventional two-stroke engines. The unique piston and crossover design provides separation of the hydrogen zones from the critical engine functional areas thereby minimizing or eliminating the corrosion problems observed from conventional hydrogen engines when left standing. Computational fluid dynamics using one dimensional code has confirmed the expectations for ultra-low oxides of nitrogen emission and elimination of other emissions when operating on hydrogen with specific power output of 51.7 kW/l simulated. Hydrogen model predictions indicated a minimum full load SFC of 0.103 kg/kWh at 3500 rpm and full load stoichiometric NOx emissions from 1000 to 5000 rpm of 4–543 ppm. Modelling and experimental performance using standard neat gasoline fuel is also presented and discussed. The experimental gasoline engine produces 55 kW at 5500 rpm and a minimum full load gasoline SFC of 0.304 kg/kWh at 2500 and 5000 rpm compared with 0.263 kg/kWh at 3500 rpm modelled using indolene. The maximum power modelled using indole was 49.4 kW at 5000 rpm.