Ignition and combustion study of premixed ammonia using GDI pilot injection in CI engine
Niels Førby, Thomas B. Thomsen, Rasmus Faurskov Cordtz, Frantz Bræstrup, Jesper Schramm
Abstract
In this study ignition of premixed ammonia was tested using a compression-ignited (CI) pilot fuel. n-heptane (C7H16) was used as pilot fuel, injected with a GDI injector, enabling very small pilot fuel injections. With this setup, the engine was run using up to 98.5 % energy from ammonia – higher than seen in other CI-engine studies with ammonia at the time of writing. The ammonia energy contribution was varied 80–98.5 %, while keeping the total λ-value constant. An important result observed was an increase in combustion efficiency from 81%–90% with higher ammonia energy due to a lower local λ-value of the ammonia–air mixture, indicating that for ammonia-ignition an easily ignitable ammonia–air mixture is preferable compared to a strong pilot injection. Lean ammonia–air mixtures showed a gap in heat release between the pilot and ammonia combustion phases, which lowered the combustion efficiency. Increased ammonia energy led to reduced ammonia-slip and N2O-emissions and increased NO-emissions, and a lower CO-formation showed better pilot fuel oxidation.