Abstract
In opposed-piston, opposed-cylinder (OPOC) two-stroke diesel engines, the relative movement rules of opposed-pistons, combustion chamber components and injector position are different from those of conventional diesel engines. In this study, the combustion and emission characteristics of the OPOC which is equipped with a common-rail injection system are investigated by experimental and numerical simulation. Different split injection strategies involving different pilot injection/fuel mass ratios and injection intervals were compared with a single injection strategy. The numerical simulation was applied to calculate and analyze the effect of split injection strategies on the combustion and emission after validation with the same experimental result (single injection strategy). Results showed that using split injection had a significant beneficial effect on the combustion process, because of the acceleration effect that enhances the air-fuel mixture. Additionally, the temperature of the split injection strategies was higher than that of single strategy, leading to the nitrogen oxides (NOx) increasing and soot decreasing. In addition, it has been found that the split injection condition with a smaller pilot injection/fuel mass ratio and a medium injection interval performed better than the single injection condition in terms of the thermo-atmosphere utilization and space utilization.
Highlights
Facing the energy crisis and environmental pollution, researchers and manufacturers have studied effective energy-saving and emission reduction methods for diesel engines
The combustion pressure curve for the cases with the split injection were higher than single injection
For the in-cylinder pressure, it was observed that the combustion pressure peak increased and the in-cylinder pressure line separated from the compress line earlier with the increase of pilot injection/fuel mass ratio
Summary
Facing the energy crisis and environmental pollution, researchers and manufacturers have studied effective energy-saving and emission reduction methods for diesel engines. The unique engine structure of opposed-piston, opposed-cylinder (OPOC) two-stroke engines gives them the advantages of improved fuel efficiency and power density over conventional diesel engines, and balances performance [4,5]. Owning to nonuniformity and mixing of cylinder charge at the late combustion phase, the combustibles—such as unburnt fuel, and soot fuel-rich combustion products—are burned again [9,10] They are different to conventional diesel engines, in that the OPOC engine uses side injection due to moving pistons on either side. 75% of the total quantity of fuel He found that split injection better utilized the air charge and allowed combustion to continue later into the power stroke compared with a single injection case, without increasing levels of soot production.
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