A Highly Efficient Small Displacement Marine Two Stroke H2DI Engine With Low Emissions

Abstract

A hydrogenfueled twostroke prototype demonstrator based on a 9.9 hp (7.4 kW) production gasoline marine outboard engine is presented, which, while matching the original engine's rated power output on hydrogen, achieves a bestpoint gross indicated thermal efficiency (ITE) of 42.4% at the ICOMIA mode 4 operating point, corresponding to 80% and 71.6% of the rated engine speed and torque, respectively. The brake thermal efficiency (BTE) at the rated power is 32.3%. Preliminary exhaust gas measurements suggest that the engine could also meet the most stringent CARB 5Star marine sparkignition emission standards limiting HC + NOx emissions to 2.5 g/kWh without any aftertreatment. These are realized in a costeffective concept around a proven twostroke base engine and a lowpressure directinjected gaseous hydrogen (LPDI GH2) system, which employs no additional fuel pump and is uniquely adapted from volume production components. Later fuel injection is found to improve thermal efficiency at the expense of increased NOx emissions and, at the extreme, increased cyclic variation. These observations are hypothesized and supported by phenomenological inferences of the observed trends of combustion duration, NOx concentration, and indicated mean effective pressure (IMEP) variance to be due to increasing charge stratification with the later timings. This work outlines the pathway—including investigations of several fuel delivery strategies with limited success—leading to the current status, including design, modeling with GTPOWER, delivery of lube oil, lubrication issues using hydrogen, and calibration sweeps. The experimental results comprising steadystate dynamometer performance, cylinder pressure traces, NOx emission measurements, along with heat release analyses, support the reported numbers and the key finding that late fuel injection timing and charge stratification drive the high efficiencies and the NOx tradeoff; this is discussed and forms the basis for future work.