Experimental Study of Fuel Mixture Limitations of Ammonia and Gasoline in a Passive Pre-Chamber Engine

Ammonia as a fuel suffers from a high ignition energy requirement making it hard to ignite in stoichiometric mixtures, especially with normal spark plugs. On the other hand, pre-chambers are proven to provide high ignition energy by producing multiple ignition spots in the main chamber. A pre-chamber is usually categorized as “active” if it has a dedicated fueling system, and as “passive” if it depends solely on the air- fuel mixture being introduced from the main chamber and is therefore simpler than the active type. In this study, an SI light-duty engine was tested with a conventional spark plug with fuel mixtures of gasoline and gaseous ammonia (0%, 25%, 50%, 75%, 90%, and 100% NH₃). The test was then repeated with a passive pre-chamber under the same operating conditions for comparison. Moreover, the engine exhaust was fitted with a fast response analyzer to measure NOX. The use of the conventional spark plug showed stable combustion throughout the fuel mixture sweep. However, the passive pre-chamber showed a fuel mixture limit of 50% NH₃ and increasing the amount of ammonia in the mixture being tended to decrease the combustion stability significantly. NO, and NO₂ emissions were not affected by the choice of the ignition source. However, running the engine on pure ammonia lowered both NO and NO₂ emissions compared to pure gasoline. Moreover, NO₂ emissions were less than 1 ppm for the pure ammonia case.