Effect of double-layer hole nozzle with narrow spray angle on combustion and emissions in dual-fuel natural gas engine

Abstract

Diesel injection plays a significant role in the mixing process of dual-fuel engine. The diesel nozzle is an important interaction between the injection system and the combustion chamber that deserves more investigation. To fully assess the effect of a diesel nozzle on combustion and emissions in a dual-fuel engine, and to avoid the diesel impingement on the wall and lubricant dilution with early injection strategy, a diesel nozzle with double-layer hole and a narrow spray angle was designed to enhance the air utilization of the central part of the pre-mixture natural gas, matching combustion with an open chamber shape. Comparison of the high dispersion nozzle with a narrow spray angle and a traditional nozzle on combustion was performed in a six-cylinder dual-fuel engine with a low compression ratio. The results showed that the narrow spray angle nozzle is beneficial at low load with earlier pilot injection, but the original nozzle achieves higher thermal efficiency than that of the narrow spray angle nozzle with the same injection strategy in high load conditions. The main cause remains that the narrow spray angle nozzle has a relatively small hole diameter and short spray penetration due to higher charge density at high load. The flame propagation ignited a natural gas mixture near the cylinder wall, resulting in a slower combustion process and a smoother heat release curve. With a relatively moderate combustion process and considerably earlier injection timing, a narrow spray angle nozzle will reduce rough combustion concerns at high load.