ABSTRACT
Ammonia (NH3) is emerging as a potential favoured fuel for longer range decarbonised heavy transport, particularly in the marine sector, predominantly due to highly favourable characteristics as an effective hydrogen carrier. This is despite generally unfavourable combustion and toxicity attributes, restricting end use to applications where robust health and safety protocols can always be upheld. In the currently reported work a spark ignited thermodynamic single cylinder research engine equipped with gasoline (E10) direct injection was upgraded to include gaseous ammonia port injection fuelling, with the aim of understanding maximum viable ammonia substitution ratios across the speed-load operating map. The work was conducted under overall stoichiometric conditions with the spark timing re-optimised for maximum brake torque at all stable logged sites. The experiments included industry standard measurements of combustion, performance and engine-out emissions (including NH3 “slip”). With a geometric compression ratio of 12.39:1 it was found possible to run the engine on pure ammonia at low engine speeds (1000–1800rpm) at low to moderate engine loads in a fully warmed up state (e.g. linear low load limit line from 1000rpm/6bar net IMEP to 1800rpm/9bar net IMEP). When progressively dropping down below this threshold load limit, an increasing amount of gasoline co-firing was required to avoid engine misfire. All metrics of combustion, efficiency and emissions tend to improve when moving upwards from the threshold load line. Due to the favourable anti-knock characteristics of NH3, pure ammonia operation was up to 5% more efficient than pure E10 operation under stable operating regions. A maximum net indicated efficiency of 40% was achieved at 1800rpm 16bar IMEPn, with efficiency tending to increase with speed and load. For co-fuelling of E10 and ammonia in a pure ammonia attainable operating region, it was found that addition of E10 improved the combustion, but these improvements were not sufficient to translate into improved thermal efficiency. Emissions of NH3 slip reduced with increased substitution of E10, albeit with increased NOx. However, the reduction in NH3 slip is nearly 10 times the increase in NOx emissions. Comparing pure NH3 and pure E10 operation, NOx reduces by ~60% when switching from pure E10 to pure NH3 (associated with longer and cooler combustion). Future work will be concerned with detailed breakdown of individual NOx species together with measuring the impact of hydrogen enrichment.
