Ammonia's fuel properties present significant challenges when it is used in internal combustion engines. Firstly, it has a relatively low calorific value, meaning a larger volume of fuel is required to produce the same amount of energy as conventional fuels.On top of that, unfavorable combustion characteristics, such as a low cetane number and slow flame speed, complicate its direct application. The low cetane number makes compression ignition difficult, while the slow flame speed can lead to inefficient or incomplete combustion. These properties often necessitate specific engine modifications or dual-fuel strategies to ensure stable and efficient operation.

Table 1 provides a comparison of fuel properties for liquefued ammonia (respectively cooled and compressed), liquefied hydrogen (respectively cooled and compressed), diesel, gasoline, methanol, and ethanol. Note that this table is for comparison purposes only; not all values were obtained from experimental studies. An important takeaway from Table 1 is ammonia's low gravimetric energy content (18.6 MJ/kg). This value is less than half that of gasoline and only about one-sixth that of hydrogen (120 MJ/kg), highlighting a significant disadvantage in energy per unit of mass. However, it is important to note that ammonia's volumetric energy density as a liquid (11.65–12.69 MJ/L) is significantly higher than that of either compressed or liquefied hydrogen. This means that ammonia can be stored as a liquid at moderate pressures and temperatures, whereas hydrogen requires either extremely high pressures or cryogenic temperatures, making ammonia's storage simpler and more practical.