Internal combustion (IC) engines fueled by hydrogen are among the most efficient means of converting chemical energy to mechanical work. The exhaust has near-zero carbon-based emissions, and the engines can be operated in a manner in which pollutants are minimal. In addition, in automotive applications, hydrogen engines have the potential for efficiencies higher than fuel cells.[1] In addition, hydrogen engines are likely to have a small increase in engine costs compared to conventionally fueled engines. However, there are challenges to using hydrogen in IC engines. In particular, efficient combustion of hydrogen in engines produces nitrogen oxides (NOx) that generally cannot be treated with conventional three-way catalysts.
This work presents the results of experiments which consider changes in direct injection hydrogen engine design to improve engine performance, consisting primarily of engine efficiency and NOx emissions. Two cylinder head configurations and two fuel injector designs were considered. One cylinder head used central spark ignition and the other used dual side spark ignition. One fuel injector used a symmetric geometry of five holes (5H, a central hole with 4 holes arranged at cardinal compass points around the central hole), and the other used a six hole geometry with three holes on each side of the nozzle (3+3H) aimed towards the spark plug locations of the dual side ignition cylinder head (β=0°) and aimed perpendicular to the axis between the two ignition locations (β=90°). Two engine speeds were tested, 1500 and 3000 rpm, with constant equivalence ratio of φ = 0.4. The new dual side ignition cylinder head design, when coupled with the 3+3H β=0° injector, produced 47.7% net indicated thermal efficiency (ITE) while producing only 51 ppm of NOx. The results are discussed in terms of fuel/air mixing times, fuel/air stratification and heat transfer losses.
