Diesel Engine Operation Using Ammonia as a Carbon-Free Fuel

Ammonia combustion does not produce carbon dioxide and thus can be regarded as a carbon-free fuel. Ammonia was used as a fuel in a compression-ignition engine in this study. Vapor ammonia was introduced into the engine intake port, and diesel fuel was injected directly into the cylinder to initiate combustion. This dual-fuel approach was chosen because ammonia has a high resistance to autoignition. A liquid ammonia tank was used for fuel storage and a high pressure relief valve regulated the ammonia flow rate, and ignition was controlled by diesel fuel injection. Ammonia was used as an energy replacement for diesel fuel. The results showed that the peak engine torque could be achieved by using different combinations of diesel fuel and ammonia. During testing, a maximum energy replacement of 95% was measured. It should be noted that, if more ammonia is added, a higher than rated power can be achieved depending on engine load conditions. It was also shown that CO₂ emissions were reduced monotonically for the same engine torque output as the amount of the ammonia in the fuel mixture increased. Additionally, burning ammonia in engines does not necessarily increase NOx emissions despite the fuel-bound nitrogen. Lower levels of NOx emissions were obtained as long as energy substitution by ammonia did not exceed 60%. This is thought to occur because of the lower combustion temperature of ammonia.