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.