Effect of a split-injection strategy on the performance of stratified lean combustion for a gasoline direct-injection engine

Abstract

Fuel economy can be significantly improved in a gasoline direct-injection (GDI) engine owing to the stratified mixture formation strategy which guarantees stable combustion under ultra-lean air–fuel mixture conditions. In the GDI engine, it is widely accepted that the spray-guided direct-injection system, which is characterized by a close configuration between the centrally mounted injector and the spark plug, is regarded as a promising technology among the efforts to realize stratified lean combustion. With this configuration, the split injection can be an effective fuel injection scheme because of its potential to modulate the spray characteristics as well as to create a combustible mixture in the proximity of the spark plug. In this study, the split-injection strategy was assessed as a way to achieve ultra-lean operation in a GDI engine and the resulting lean-combustion characteristics were investigated in terms of the engine performance and emissions. The engine was tested at constant operating conditions (an engine speed of 3000 r/min and an indicated mean effective pressure of 0.4 MPa) with a change in the fuel injection pressure ranging from 10 MPa to 20 MPa. The excess air ratio λ varied from stoichiometry to the lean flammability limit, which turned out to be extended in the GDI approach. The engine test results show that the split injection of fuel allowed the formation of an adequately stratified mixture in lean-combustion conditions, and thus stable combustion was guaranteed. These results indicate that an excess air ratio was one of the important factors affecting the thermal efficiency and nitrogen oxide (NO x) emissions and was significantly extended to λ = 2.0 by the split-injection scheme. In addition, several fuel injection parameters such as the injection quantity, the split ratio, and the number of splits were examined with an emphasis on their impact on the fuel economy and emissions. The results demonstrate that there exists a trade-off between the NO x reduction and the efficiency, and therefore it is required to choose an appropriate injection strategy depending on the engine operating conditions in order to satisfy emission regulations.

Combustion and Emission Characteristics According to the Fuel Injection Ratio of an Ultra-Lean LPG Direct Injection Engine

“…The formation of an overly lean mixture can be another reason for increased THC emissions. The CO emission behavior is very similar to that of THC emissions, and is consistent with the results of previous studies on lean mixture combustion [6,7,16,17,20,22,30]. …”

“…However, the optimal fuel injection, spark ignition timing, and ratio of injected fuel amount can differ according to the operating point. As the formation of an appropriate stratified mixture is difficult with a single injection at a certain operating condition, multiple injection strategies were employed in the previous studies [7,16,17,22,25]. In the present study, a two-staged injection strategy is applied and optimized.…”

Optimization and simulation of a voice coil motor for fuel injectors of two-stroke aviation piston engine

“…However, because of mixture scavenging, which leads to fuel short-circuiting and excessive exhaust emissions, 1 people are trying to replace the conventional fuel injection system with gasoline direct injection (GDI) to reduce fuel consumption and CO 2 emission and to improve engine power output. 2 The GDI fuel injection system sprays fuel directly into the combustion chamber with a high injection pressure, resulting in a good atomization and evaporation process, 3,4 which have been widely used in automobiles. However, the normal GDI system has a complex structure which is not good for an aviation piston engine.…”

Effects of split and single injection strategies on particle number emission and combustion of a GDI engine

“…Experimental results from a spray-guided SIDI engine under lean combustion concluded that double injection strategy provides the potential to increase combustion efficiency, to improve combustion stability, and to reduce NO x (oxides of nitrogen) emission as compared to single injection strategy. 17 Park et al 18 indicated that the excess air ratio is one of the important factors affecting the thermal efficiency and nitrogen oxide (NO x ) emission, and it is significantly extended to λ = 2.0 by the split-injection scheme. Two fuel injection strategy with a short delay is a very effective method to ensure combustion stability under lean operation conditions, but it causes a lack of time for fuel evaporation which generates smoke emission.…”