Due to the problem with carbon dioxide (CO2) emissions, alternative fuels such as ammonia
(NH3) have been garnering a lot of attention lately. This is due to its carbon-free molecular
structure, ease of transport, and high energy density. Unfortunately, ammonia is not without
flaws since it is considered a difficult fuel to burn in conventional internal combustion engines.
To further investigate the burning characteristics of ammonia, this study is conducted for
ammonia/gasoline co-combustion using a modified engine equipped with a sub-chamber. The
engine ran at 1000 RPM and had a 17.7 compression ratio with two injection timings of -55°
and 10° crank angle (CA) after the top dead center (ATDC), while the ammonia energy ratios
were adjusted across a range from 40% to 70%. The results show that the earlier injection
timing allowed better premixing between the air and fuel mixture, thus enhancing the overall
combustion characteristics. For the later injection timing, the nitrogen oxides (NOx) emissions
decrease at the higher ammonia energy ratio due to the denitrification of nitrogen oxides
(DeNOX) process. Overall, the earlier injection timing appears to be optimal for 40% to 70%
ammonia energy ratio under the present condition.
