We have carried out ab initio quantum chemical calculations to discuss the substituent effect of the metal source on the coordination interaction and the reactivity in the gas-phase parasitic reactions in M(t-C 4 H 9 ) 3 /H 2 /NH 3 (M = Al, Ga) systems following the elimination of isobutane. We found that t-butyl groups play two important roles: high ability for electron donation leading to large M -N interaction and high bulkiness leading to large steric repulsion. It is expected that the extension of chain adducts obstructing the growth of AlGaN would be suppressed by the steric hindrance due to bulky substituents lifting up the activation energies in the parasitic reactions.
Recently, ammonia (NH3), which has a higher energy density than hydrogen, has gained attention for zero-carbon emission goals in the transportation sector. However, in a conventional internal combustion engine (ICE), NH3 combustion mechanism is still under investigation. In this paper, to further expand the knowledge on the adoption of NH3 in ICEs, authors conducted NH3/gasoline co-combustion experiments in a modified, 17.7:1 compression ratio, naturally aspirated spark-assisted CI engine with sub-chamber. The sub-chamber was chosen in order to enhance the combustion speed of NH3. In addition, the sub-chamber was equipped with glow and spark plugs to overcome the high auto-ignition temperature of NH3. Engine performance and NOX emissions were studied under three different intake air temperatures. During the experiments, NH3 content was increased gradually where the engine was run under lean conditions. Although higher NH3 content was achieved compared to our previous work, increasing the intake air temperature resulted in decreased charging efficiency. In addition, corrosion was found on the piston ring after 120 h of operation, negatively affecting the engine performance. Furthermore, NH3/gasoline co-combustion duration was shortened drastically with the influence of the sub-chamber, where the longest combustion duration under the present conditions was found to be 17°CA.
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