Impact of Pilot Injection on Combustion and Emission Characteristics of a Low-Speed Two-Stroke Marine Diesel Engine

Abstract

Low-speed two-stroke marine diesel engines dominate the modern global long-distance transportation market; with the increasingly stringent regulations, the combustion and emissions of these engines is gaining intense interest. The primary objective of the present study was to understand the effects of air-fuel mixing by pilot injection strategy on the combustion and emission characteristics of the marine diesel engines through a numerical study. Specifically, a computational fluid dynamic (CFD) model was established and validated by experimental data for a typical low-speed two-stroke marine diesel engine. The combustion parameters under different stages were analyzed, including mean in-cylinder temperature and pressure, indicated thermal efficiency (ITE), indicated specific fuel consumption (ISFC), and distribution of fuel-air mixture. Results indicated that, due to the premixing effect, the pilot injection produced unburned soot from the main injection’s ignition as well as decrease the intervals between the middle and final stages of combustion, thus raising the in-cylinder temperature. The interaction between the reduction of soot particles resulted from the increased temperature, and the decrease of the stage intervals led to lower overall boundary heat loss, which improved the effective thermal efficiency. The pilot injection timing and quality, respectively, showed quadratic and linear impact modes on engine performance and emissions.

Evaluation of Control Strategy on Operation Range Expansion of High-Pressure Ammonia Direct Injection Marine Dual-Fuel Engine

“…MAN ES, despite the shortcomings of ammonia’s ignition and combustion characteristics, has a slow speed and large volume in marine engines, so it can afford time for combustion and can be designed with less heat loss, improving the combustion characteristics of ammonia . Previous studies have shown that micropilot fuel injection timing should be optimized to improve efficiency and combustion stability and reduce exhaust emissions. , In particular, Henke et al reported that spray formation due to changes in micropilot fuel injection timing in a dual-fuel engine greatly affects ignition delay and combustion of low-reactivity fuel …”

“…18 Previous studies have shown that micropilot fuel injection timing should be optimized to improve efficiency and combustion stability and reduce exhaust emissions. 19,20 In particular, Henke et al 21 reported that spray formation due to changes in micropilot fuel injection timing in a dual-fuel engine greatly affects ignition delay and combustion of low-reactivity fuel. 22 From previous research results, the authors confirmed that to complement the combustion characteristics of ammonia, it is necessary to control the pilot fuel that helps ignite ammonia and that the injection timing and amount of pilot fuel must be optimized according to operating conditions.…”

Hydraulic Interactions between Injection Events Using Multiple Injection Strategies and a Solenoid Diesel Injector

“…They observed that by adjusting the fuel quantity in both pilot injections, it is possible to reduce the NOx and soot emissions. Liang et al [17], analysed the mixing process and its influence on the combustion and emission characteristics under the pilot injection strategy and utilizing a low-speed two-stroke diesel engine, and they also found that, adjusting the pilot injection's time, it is possible to reduce part of the NOx emissions.…”