open access publication

Article, 2024

Widening the operation limits of a SI engine running on neat ammonia

Fuel, ISSN 0016-2361, 1873-7153, Volume 358, Page 130159, 10.1016/j.fuel.2023.130159


Jespersen, Mads Carsten [1] Rasmussen, Thomas Østerby Holst [1] Ivarsson, Anders 0000-0002-9631-6012 (Corresponding author) [1]


  1. [1] Technical University of Denmark
  2. [NORA names: DTU Technical University of Denmark; University; Denmark; Europe, EU; Nordic; OECD]


Present study aims to investigate the lean-burn characteristics of ammonia in a pre-mixed SI (Spark Ignition) engine and the influence of spark energy and discharge characteristics on engine performance and emissions. A wide range of engine operation conditions have been explored with particular focus on emission measurement. Engine parameters have been systematically swept to explore engine control strategies that would be operational in real engine application with a wide range of engine loads and tight emission regulations. Most previous studies required more than 5 % addition of hydrogen to the ammonia in order to achieve stable ignition for wide operation conditions. This has been a major obstacle in the application of ammonia for SI engines due to safety and system complexity issues. In present work, a comprehensive effort was made to understand and optimize the spark ignition system in order to mitigate the need for an ignition improver and all experiments have been performed with 100 % neat ammonia. With present engine modifications, emissions of unburned ammonia was measured to be between 5000 and 10000 ppm and with a combustion efficiency above 95 %. The unburned ammonia is believed to originate from crevices, particularly at the ring-pack. The NOx emission was between 4000 and 8000 ppm even at high excess air ratios. The emission of N2O is critical to minimize, as it is a strong greenhouse gas. It was measured to be between 20 and 80 ppm and appear to be related to post oxidation reactions of ammonia released from crevices during expansion. Advancing the ignition timing has proved to be an efficient handle for balancing the emissions of NH3 and NOx. These emissions will be reduced to H2O and N2 in an SCR catalyst if they are correctly balanced. Fortunately, advancing ignition timing also minimizes the formation of N2O.


H2O, N2, N2O, NH3, NOx, NOx emissions, SCR, SCR catalyst, SI engine, air ratio, ammonia, application of ammonia, applications, catalyst, characteristics, characteristics of ammonia, combustion, combustion efficiency, complex issues, comprehensive effort, conditions, crevice, discharge characteristics, efficiency, efficient handling, efforts, emission, emission measurements, emission regulations, emissions of N2O, emissions of NH3, energy, engine performance, engineering, engineering modifications, engineering parameters, excess air ratio, expansion, experiments, formation, formation of N2O, gas, greenhouse, greenhouse gases, handling, hydrogen, ignition, ignition improver, ignition system, ignition timing, improvement, influence, issues, lean burn characteristics, limitations, load, measurements, modification, operating conditions, operation, operational limits, oxidation reaction, parameters, performance, post-oxidation reaction, present study, ratio, reaction, reduced to H2O, regulation, ring pack, safety, spark energy, spark ignition system, stable ignition, study, system, tight emission regulations, time, unburned ammonia


  • Innovation Fund Denmark
  • European Commission

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