Effect of Blending Ammonia With Natural Gas Hydrocarbons on the Performance of a Heavy-Duty Spark Ignition Engine

Ammonia (NH₃) is a promising carbon-free fuel candidate to replace conventional petroleum-based fuels. However, NH₃ has low flame speed, low calorific value, narrow flammability limits, and requires high ignition energy. As a result, the use of NH₃ in power applications such as internal combustion (IC) engines may require a secondary fuel to promote and sustain the flame as well as hardware engine modifications such as a higher compression ratio (CR) and a high-energy ignition coil. This work investigated the use of a dual-fuel approach involving NH₃ and natural gas (NG) components (i.e., methane, propane, and ethane) in a single-cylinder four-stroke heavy-duty compression ignition (CI) engine converted to spark ignition (SI), at an engine speed of 1000 rpm, equivalence ratio of 0.8, and an energy substitution ratio (ESR) of the hydrocarbon fuel up to 0.4. Results showed no penalty on efficiency, as the overall combustion phasing was more optimal as ESR increased. In addition, since all the indicated mean effective pressure (IMEP) values were close to each other for different spark timing (ST), it suggests no need for changing the engine control strategy. COV_IMEP showed an increase with ESR, suggesting that the addition of NH₃ led to more cycle-to-cycle variations, with propane having the highest COV_IMEP. This higher cycle-to-cycle variation for propane–ammonia mixtures was probably coming from a competition between its higher reactivity when compared to the other two hydrocarbons and the effect of different fuel properties on the in-cylinder gas motion.