Combustion and emission characteristics of a spark ignition engine fueled with ammonia/gasoline and pure ammonia.

The decarbonization movement has sparked interests in ammonia (NH 3) as a fuel for internal combustion engines in the transportation sector. Despite its promise, the poor combustion and emission performance are the main obstacles to widespread application. The purpose of this paper is to investigate the combustion and emission performance of a single-cylinder spark ignition engine fueled with NH 3 /gasoline blends under different operating conditions. The effects of NH 3 blending ratio, engine load, EGR ratio, engine speed, intake variable valve timing (VVT) phase and the composition and octane of the fuel were examined. The results indicated that blending NH 3 could effectively suppress knock, optimize combustion phase and improve thermal efficiency. Blending NH 3 had minimal impact on flame propagation in the main combustion duration (denoted by CA50 - CA10 and CA90 - CA50) under knock-free conditions but negative effects were exhibited on the development of initial flame kernel. The combustion stability under high NH 3 blending ratios were improved by increasing engine load, decreasing EGR ratio, etc. Furthermore, stable and efficient combustion of pure NH 3 with COV of 1.3% and indicated thermal efficiency of 41% was realized with a commercial ignition coil and without intake-charge heating. The fuel-type NO x exhibited a positive temperature correlation and negative pressure correlation. Accordingly, NO x emissions were decreased with spark timing (ST) advancing within a specific range of NH 3 blending ratios. However, it remained essentially unchanged or showed a slight increase with advanced ST at high NH 3 blending ratio. NH 3 emission was simultaneously affected by both the "crevice mechanism" and the "flame quenching mechanism". Particularly, the influence of the "flame quenching mechanism" intensified under higher NH 3 blending ratio and lower engine load conditions. N 2 O emission was regulated by the low-temperature oxidation path of NH 3. Increasing the combustion temperature could effectively decrease N 2 O emission. • Performance of SI engine fueled with NH 3 /gasoline was systematically investigated. • The fuel economy was improved through NH 3 addition under high load conditions. • Stable and efficient combustion of pure NH 3 with COV = 1.3% and ITE = 41.0% was achieved. • Factors influencing NO x , NH 3 and N 2 O emissions were identified. [ABSTRACT FROM AUTHOR]